Merge branch 'block-dir' of git://brick.kernel.dk/data/git/linux-2.6-block
authorLinus Torvalds <torvalds@g5.osdl.org>
Mon, 7 Nov 2005 16:32:39 +0000 (08:32 -0800)
committerLinus Torvalds <torvalds@g5.osdl.org>
Mon, 7 Nov 2005 16:32:39 +0000 (08:32 -0800)
1  2 
Makefile
block/as-iosched.c
block/ll_rw_blk.c

diff --cc Makefile
Simple merge
index 0000000000000000000000000000000000000000,c6744ff382944a590767cef1827e627c1915c7ad..a78e160b59a3545b8a06b78e2c78e503f1494d24
mode 000000,100644..100644
--- /dev/null
@@@ -1,0 -1,1985 +1,2005 @@@
 - *                     Nick Piggin <piggin@cyberone.com.au>
+ /*
+  *  linux/drivers/block/as-iosched.c
+  *
+  *  Anticipatory & deadline i/o scheduler.
+  *
+  *  Copyright (C) 2002 Jens Axboe <axboe@suse.de>
 -      AS_TASK_RUNNING=0,      /* Process has not exitted */
++ *                     Nick Piggin <nickpiggin@yahoo.com.au>
+  *
+  */
+ #include <linux/kernel.h>
+ #include <linux/fs.h>
+ #include <linux/blkdev.h>
+ #include <linux/elevator.h>
+ #include <linux/bio.h>
+ #include <linux/config.h>
+ #include <linux/module.h>
+ #include <linux/slab.h>
+ #include <linux/init.h>
+ #include <linux/compiler.h>
+ #include <linux/hash.h>
+ #include <linux/rbtree.h>
+ #include <linux/interrupt.h>
+ #define REQ_SYNC      1
+ #define REQ_ASYNC     0
+ /*
+  * See Documentation/block/as-iosched.txt
+  */
+ /*
+  * max time before a read is submitted.
+  */
+ #define default_read_expire (HZ / 8)
+ /*
+  * ditto for writes, these limits are not hard, even
+  * if the disk is capable of satisfying them.
+  */
+ #define default_write_expire (HZ / 4)
+ /*
+  * read_batch_expire describes how long we will allow a stream of reads to
+  * persist before looking to see whether it is time to switch over to writes.
+  */
+ #define default_read_batch_expire (HZ / 2)
+ /*
+  * write_batch_expire describes how long we want a stream of writes to run for.
+  * This is not a hard limit, but a target we set for the auto-tuning thingy.
+  * See, the problem is: we can send a lot of writes to disk cache / TCQ in
+  * a short amount of time...
+  */
+ #define default_write_batch_expire (HZ / 8)
+ /*
+  * max time we may wait to anticipate a read (default around 6ms)
+  */
+ #define default_antic_expire ((HZ / 150) ? HZ / 150 : 1)
+ /*
+  * Keep track of up to 20ms thinktimes. We can go as big as we like here,
+  * however huge values tend to interfere and not decay fast enough. A program
+  * might be in a non-io phase of operation. Waiting on user input for example,
+  * or doing a lengthy computation. A small penalty can be justified there, and
+  * will still catch out those processes that constantly have large thinktimes.
+  */
+ #define MAX_THINKTIME (HZ/50UL)
+ /* Bits in as_io_context.state */
+ enum as_io_states {
 -                      /* process anticipated on has exitted or timed out*/
++      AS_TASK_RUNNING=0,      /* Process has not exited */
+       AS_TASK_IOSTARTED,      /* Process has started some IO */
+       AS_TASK_IORUNNING,      /* Process has completed some IO */
+ };
+ enum anticipation_status {
+       ANTIC_OFF=0,            /* Not anticipating (normal operation)  */
+       ANTIC_WAIT_REQ,         /* The last read has not yet completed  */
+       ANTIC_WAIT_NEXT,        /* Currently anticipating a request vs
+                                  last read (which has completed) */
+       ANTIC_FINISHED,         /* Anticipating but have found a candidate
+                                * or timed out */
+ };
+ struct as_data {
+       /*
+        * run time data
+        */
+       struct request_queue *q;        /* the "owner" queue */
+       /*
+        * requests (as_rq s) are present on both sort_list and fifo_list
+        */
+       struct rb_root sort_list[2];
+       struct list_head fifo_list[2];
+       struct as_rq *next_arq[2];      /* next in sort order */
+       sector_t last_sector[2];        /* last REQ_SYNC & REQ_ASYNC sectors */
+       struct list_head *hash;         /* request hash */
+       unsigned long exit_prob;        /* probability a task will exit while
+                                          being waited on */
++      unsigned long exit_no_coop;     /* probablility an exited task will
++                                         not be part of a later cooperating
++                                         request */
+       unsigned long new_ttime_total;  /* mean thinktime on new proc */
+       unsigned long new_ttime_mean;
+       u64 new_seek_total;             /* mean seek on new proc */
+       sector_t new_seek_mean;
+       unsigned long current_batch_expires;
+       unsigned long last_check_fifo[2];
+       int changed_batch;              /* 1: waiting for old batch to end */
+       int new_batch;                  /* 1: waiting on first read complete */
+       int batch_data_dir;             /* current batch REQ_SYNC / REQ_ASYNC */
+       int write_batch_count;          /* max # of reqs in a write batch */
+       int current_write_count;        /* how many requests left this batch */
+       int write_batch_idled;          /* has the write batch gone idle? */
+       mempool_t *arq_pool;
+       enum anticipation_status antic_status;
+       unsigned long antic_start;      /* jiffies: when it started */
+       struct timer_list antic_timer;  /* anticipatory scheduling timer */
+       struct work_struct antic_work;  /* Deferred unplugging */
+       struct io_context *io_context;  /* Identify the expected process */
+       int ioc_finished; /* IO associated with io_context is finished */
+       int nr_dispatched;
+       /*
+        * settings that change how the i/o scheduler behaves
+        */
+       unsigned long fifo_expire[2];
+       unsigned long batch_expire[2];
+       unsigned long antic_expire;
+ };
+ #define list_entry_fifo(ptr)  list_entry((ptr), struct as_rq, fifo)
+ /*
+  * per-request data.
+  */
+ enum arq_state {
+       AS_RQ_NEW=0,            /* New - not referenced and not on any lists */
+       AS_RQ_QUEUED,           /* In the request queue. It belongs to the
+                                  scheduler */
+       AS_RQ_DISPATCHED,       /* On the dispatch list. It belongs to the
+                                  driver now */
+       AS_RQ_PRESCHED,         /* Debug poisoning for requests being used */
+       AS_RQ_REMOVED,
+       AS_RQ_MERGED,
+       AS_RQ_POSTSCHED,        /* when they shouldn't be */
+ };
+ struct as_rq {
+       /*
+        * rbtree index, key is the starting offset
+        */
+       struct rb_node rb_node;
+       sector_t rb_key;
+       struct request *request;
+       struct io_context *io_context;  /* The submitting task */
+       /*
+        * request hash, key is the ending offset (for back merge lookup)
+        */
+       struct list_head hash;
+       unsigned int on_hash;
+       /*
+        * expire fifo
+        */
+       struct list_head fifo;
+       unsigned long expires;
+       unsigned int is_sync;
+       enum arq_state state;
+ };
+ #define RQ_DATA(rq)   ((struct as_rq *) (rq)->elevator_private)
+ static kmem_cache_t *arq_pool;
+ /*
+  * IO Context helper functions
+  */
+ /* Called to deallocate the as_io_context */
+ static void free_as_io_context(struct as_io_context *aic)
+ {
+       kfree(aic);
+ }
+ /* Called when the task exits */
+ static void exit_as_io_context(struct as_io_context *aic)
+ {
+       WARN_ON(!test_bit(AS_TASK_RUNNING, &aic->state));
+       clear_bit(AS_TASK_RUNNING, &aic->state);
+ }
+ static struct as_io_context *alloc_as_io_context(void)
+ {
+       struct as_io_context *ret;
+       ret = kmalloc(sizeof(*ret), GFP_ATOMIC);
+       if (ret) {
+               ret->dtor = free_as_io_context;
+               ret->exit = exit_as_io_context;
+               ret->state = 1 << AS_TASK_RUNNING;
+               atomic_set(&ret->nr_queued, 0);
+               atomic_set(&ret->nr_dispatched, 0);
+               spin_lock_init(&ret->lock);
+               ret->ttime_total = 0;
+               ret->ttime_samples = 0;
+               ret->ttime_mean = 0;
+               ret->seek_total = 0;
+               ret->seek_samples = 0;
+               ret->seek_mean = 0;
+       }
+       return ret;
+ }
+ /*
+  * If the current task has no AS IO context then create one and initialise it.
+  * Then take a ref on the task's io context and return it.
+  */
+ static struct io_context *as_get_io_context(void)
+ {
+       struct io_context *ioc = get_io_context(GFP_ATOMIC);
+       if (ioc && !ioc->aic) {
+               ioc->aic = alloc_as_io_context();
+               if (!ioc->aic) {
+                       put_io_context(ioc);
+                       ioc = NULL;
+               }
+       }
+       return ioc;
+ }
+ static void as_put_io_context(struct as_rq *arq)
+ {
+       struct as_io_context *aic;
+       if (unlikely(!arq->io_context))
+               return;
+       aic = arq->io_context->aic;
+       if (arq->is_sync == REQ_SYNC && aic) {
+               spin_lock(&aic->lock);
+               set_bit(AS_TASK_IORUNNING, &aic->state);
+               aic->last_end_request = jiffies;
+               spin_unlock(&aic->lock);
+       }
+       put_io_context(arq->io_context);
+ }
+ /*
+  * the back merge hash support functions
+  */
+ static const int as_hash_shift = 6;
+ #define AS_HASH_BLOCK(sec)    ((sec) >> 3)
+ #define AS_HASH_FN(sec)               (hash_long(AS_HASH_BLOCK((sec)), as_hash_shift))
+ #define AS_HASH_ENTRIES               (1 << as_hash_shift)
+ #define rq_hash_key(rq)               ((rq)->sector + (rq)->nr_sectors)
+ #define list_entry_hash(ptr)  list_entry((ptr), struct as_rq, hash)
+ static inline void __as_del_arq_hash(struct as_rq *arq)
+ {
+       arq->on_hash = 0;
+       list_del_init(&arq->hash);
+ }
+ static inline void as_del_arq_hash(struct as_rq *arq)
+ {
+       if (arq->on_hash)
+               __as_del_arq_hash(arq);
+ }
+ static void as_add_arq_hash(struct as_data *ad, struct as_rq *arq)
+ {
+       struct request *rq = arq->request;
+       BUG_ON(arq->on_hash);
+       arq->on_hash = 1;
+       list_add(&arq->hash, &ad->hash[AS_HASH_FN(rq_hash_key(rq))]);
+ }
+ /*
+  * move hot entry to front of chain
+  */
+ static inline void as_hot_arq_hash(struct as_data *ad, struct as_rq *arq)
+ {
+       struct request *rq = arq->request;
+       struct list_head *head = &ad->hash[AS_HASH_FN(rq_hash_key(rq))];
+       if (!arq->on_hash) {
+               WARN_ON(1);
+               return;
+       }
+       if (arq->hash.prev != head) {
+               list_del(&arq->hash);
+               list_add(&arq->hash, head);
+       }
+ }
+ static struct request *as_find_arq_hash(struct as_data *ad, sector_t offset)
+ {
+       struct list_head *hash_list = &ad->hash[AS_HASH_FN(offset)];
+       struct list_head *entry, *next = hash_list->next;
+       while ((entry = next) != hash_list) {
+               struct as_rq *arq = list_entry_hash(entry);
+               struct request *__rq = arq->request;
+               next = entry->next;
+               BUG_ON(!arq->on_hash);
+               if (!rq_mergeable(__rq)) {
+                       as_del_arq_hash(arq);
+                       continue;
+               }
+               if (rq_hash_key(__rq) == offset)
+                       return __rq;
+       }
+       return NULL;
+ }
+ /*
+  * rb tree support functions
+  */
+ #define RB_NONE               (2)
+ #define RB_EMPTY(root)        ((root)->rb_node == NULL)
+ #define ON_RB(node)   ((node)->rb_color != RB_NONE)
+ #define RB_CLEAR(node)        ((node)->rb_color = RB_NONE)
+ #define rb_entry_arq(node)    rb_entry((node), struct as_rq, rb_node)
+ #define ARQ_RB_ROOT(ad, arq)  (&(ad)->sort_list[(arq)->is_sync])
+ #define rq_rb_key(rq)         (rq)->sector
+ /*
+  * as_find_first_arq finds the first (lowest sector numbered) request
+  * for the specified data_dir. Used to sweep back to the start of the disk
+  * (1-way elevator) after we process the last (highest sector) request.
+  */
+ static struct as_rq *as_find_first_arq(struct as_data *ad, int data_dir)
+ {
+       struct rb_node *n = ad->sort_list[data_dir].rb_node;
+       if (n == NULL)
+               return NULL;
+       for (;;) {
+               if (n->rb_left == NULL)
+                       return rb_entry_arq(n);
+               n = n->rb_left;
+       }
+ }
+ /*
+  * Add the request to the rb tree if it is unique.  If there is an alias (an
+  * existing request against the same sector), which can happen when using
+  * direct IO, then return the alias.
+  */
+ static struct as_rq *as_add_arq_rb(struct as_data *ad, struct as_rq *arq)
+ {
+       struct rb_node **p = &ARQ_RB_ROOT(ad, arq)->rb_node;
+       struct rb_node *parent = NULL;
+       struct as_rq *__arq;
+       struct request *rq = arq->request;
+       arq->rb_key = rq_rb_key(rq);
+       while (*p) {
+               parent = *p;
+               __arq = rb_entry_arq(parent);
+               if (arq->rb_key < __arq->rb_key)
+                       p = &(*p)->rb_left;
+               else if (arq->rb_key > __arq->rb_key)
+                       p = &(*p)->rb_right;
+               else
+                       return __arq;
+       }
+       rb_link_node(&arq->rb_node, parent, p);
+       rb_insert_color(&arq->rb_node, ARQ_RB_ROOT(ad, arq));
+       return NULL;
+ }
+ static inline void as_del_arq_rb(struct as_data *ad, struct as_rq *arq)
+ {
+       if (!ON_RB(&arq->rb_node)) {
+               WARN_ON(1);
+               return;
+       }
+       rb_erase(&arq->rb_node, ARQ_RB_ROOT(ad, arq));
+       RB_CLEAR(&arq->rb_node);
+ }
+ static struct request *
+ as_find_arq_rb(struct as_data *ad, sector_t sector, int data_dir)
+ {
+       struct rb_node *n = ad->sort_list[data_dir].rb_node;
+       struct as_rq *arq;
+       while (n) {
+               arq = rb_entry_arq(n);
+               if (sector < arq->rb_key)
+                       n = n->rb_left;
+               else if (sector > arq->rb_key)
+                       n = n->rb_right;
+               else
+                       return arq->request;
+       }
+       return NULL;
+ }
+ /*
+  * IO Scheduler proper
+  */
+ #define MAXBACK (1024 * 1024) /*
+                                * Maximum distance the disk will go backward
+                                * for a request.
+                                */
+ #define BACK_PENALTY  2
+ /*
+  * as_choose_req selects the preferred one of two requests of the same data_dir
+  * ignoring time - eg. timeouts, which is the job of as_dispatch_request
+  */
+ static struct as_rq *
+ as_choose_req(struct as_data *ad, struct as_rq *arq1, struct as_rq *arq2)
+ {
+       int data_dir;
+       sector_t last, s1, s2, d1, d2;
+       int r1_wrap=0, r2_wrap=0;       /* requests are behind the disk head */
+       const sector_t maxback = MAXBACK;
+       if (arq1 == NULL || arq1 == arq2)
+               return arq2;
+       if (arq2 == NULL)
+               return arq1;
+       data_dir = arq1->is_sync;
+       last = ad->last_sector[data_dir];
+       s1 = arq1->request->sector;
+       s2 = arq2->request->sector;
+       BUG_ON(data_dir != arq2->is_sync);
+       /*
+        * Strict one way elevator _except_ in the case where we allow
+        * short backward seeks which are biased as twice the cost of a
+        * similar forward seek.
+        */
+       if (s1 >= last)
+               d1 = s1 - last;
+       else if (s1+maxback >= last)
+               d1 = (last - s1)*BACK_PENALTY;
+       else {
+               r1_wrap = 1;
+               d1 = 0; /* shut up, gcc */
+       }
+       if (s2 >= last)
+               d2 = s2 - last;
+       else if (s2+maxback >= last)
+               d2 = (last - s2)*BACK_PENALTY;
+       else {
+               r2_wrap = 1;
+               d2 = 0;
+       }
+       /* Found required data */
+       if (!r1_wrap && r2_wrap)
+               return arq1;
+       else if (!r2_wrap && r1_wrap)
+               return arq2;
+       else if (r1_wrap && r2_wrap) {
+               /* both behind the head */
+               if (s1 <= s2)
+                       return arq1;
+               else
+                       return arq2;
+       }
+       /* Both requests in front of the head */
+       if (d1 < d2)
+               return arq1;
+       else if (d2 < d1)
+               return arq2;
+       else {
+               if (s1 >= s2)
+                       return arq1;
+               else
+                       return arq2;
+       }
+ }
+ /*
+  * as_find_next_arq finds the next request after @prev in elevator order.
+  * this with as_choose_req form the basis for how the scheduler chooses
+  * what request to process next. Anticipation works on top of this.
+  */
+ static struct as_rq *as_find_next_arq(struct as_data *ad, struct as_rq *last)
+ {
+       const int data_dir = last->is_sync;
+       struct as_rq *ret;
+       struct rb_node *rbnext = rb_next(&last->rb_node);
+       struct rb_node *rbprev = rb_prev(&last->rb_node);
+       struct as_rq *arq_next, *arq_prev;
+       BUG_ON(!ON_RB(&last->rb_node));
+       if (rbprev)
+               arq_prev = rb_entry_arq(rbprev);
+       else
+               arq_prev = NULL;
+       if (rbnext)
+               arq_next = rb_entry_arq(rbnext);
+       else {
+               arq_next = as_find_first_arq(ad, data_dir);
+               if (arq_next == last)
+                       arq_next = NULL;
+       }
+       ret = as_choose_req(ad, arq_next, arq_prev);
+       return ret;
+ }
+ /*
+  * anticipatory scheduling functions follow
+  */
+ /*
+  * as_antic_expired tells us when we have anticipated too long.
+  * The funny "absolute difference" math on the elapsed time is to handle
+  * jiffy wraps, and disks which have been idle for 0x80000000 jiffies.
+  */
+ static int as_antic_expired(struct as_data *ad)
+ {
+       long delta_jif;
+       delta_jif = jiffies - ad->antic_start;
+       if (unlikely(delta_jif < 0))
+               delta_jif = -delta_jif;
+       if (delta_jif < ad->antic_expire)
+               return 0;
+       return 1;
+ }
+ /*
+  * as_antic_waitnext starts anticipating that a nice request will soon be
+  * submitted. See also as_antic_waitreq
+  */
+ static void as_antic_waitnext(struct as_data *ad)
+ {
+       unsigned long timeout;
+       BUG_ON(ad->antic_status != ANTIC_OFF
+                       && ad->antic_status != ANTIC_WAIT_REQ);
+       timeout = ad->antic_start + ad->antic_expire;
+       mod_timer(&ad->antic_timer, timeout);
+       ad->antic_status = ANTIC_WAIT_NEXT;
+ }
+ /*
+  * as_antic_waitreq starts anticipating. We don't start timing the anticipation
+  * until the request that we're anticipating on has finished. This means we
+  * are timing from when the candidate process wakes up hopefully.
+  */
+ static void as_antic_waitreq(struct as_data *ad)
+ {
+       BUG_ON(ad->antic_status == ANTIC_FINISHED);
+       if (ad->antic_status == ANTIC_OFF) {
+               if (!ad->io_context || ad->ioc_finished)
+                       as_antic_waitnext(ad);
+               else
+                       ad->antic_status = ANTIC_WAIT_REQ;
+       }
+ }
+ /*
+  * This is called directly by the functions in this file to stop anticipation.
+  * We kill the timer and schedule a call to the request_fn asap.
+  */
+ static void as_antic_stop(struct as_data *ad)
+ {
+       int status = ad->antic_status;
+       if (status == ANTIC_WAIT_REQ || status == ANTIC_WAIT_NEXT) {
+               if (status == ANTIC_WAIT_NEXT)
+                       del_timer(&ad->antic_timer);
+               ad->antic_status = ANTIC_FINISHED;
+               /* see as_work_handler */
+               kblockd_schedule_work(&ad->antic_work);
+       }
+ }
+ /*
+  * as_antic_timeout is the timer function set by as_antic_waitnext.
+  */
+ static void as_antic_timeout(unsigned long data)
+ {
+       struct request_queue *q = (struct request_queue *)data;
+       struct as_data *ad = q->elevator->elevator_data;
+       unsigned long flags;
+       spin_lock_irqsave(q->queue_lock, flags);
+       if (ad->antic_status == ANTIC_WAIT_REQ
+                       || ad->antic_status == ANTIC_WAIT_NEXT) {
+               struct as_io_context *aic = ad->io_context->aic;
+               ad->antic_status = ANTIC_FINISHED;
+               kblockd_schedule_work(&ad->antic_work);
+               if (aic->ttime_samples == 0) {
 -static int as_close_req(struct as_data *ad, struct as_rq *arq)
++                      /* process anticipated on has exited or timed out*/
+                       ad->exit_prob = (7*ad->exit_prob + 256)/8;
+               }
++              if (!test_bit(AS_TASK_RUNNING, &aic->state)) {
++                      /* process not "saved" by a cooperating request */
++                      ad->exit_no_coop = (7*ad->exit_no_coop + 256)/8;
++              }
+       }
+       spin_unlock_irqrestore(q->queue_lock, flags);
+ }
++static void as_update_thinktime(struct as_data *ad, struct as_io_context *aic,
++                              unsigned long ttime)
++{
++      /* fixed point: 1.0 == 1<<8 */
++      if (aic->ttime_samples == 0) {
++              ad->new_ttime_total = (7*ad->new_ttime_total + 256*ttime) / 8;
++              ad->new_ttime_mean = ad->new_ttime_total / 256;
++
++              ad->exit_prob = (7*ad->exit_prob)/8;
++      }
++      aic->ttime_samples = (7*aic->ttime_samples + 256) / 8;
++      aic->ttime_total = (7*aic->ttime_total + 256*ttime) / 8;
++      aic->ttime_mean = (aic->ttime_total + 128) / aic->ttime_samples;
++}
++
++static void as_update_seekdist(struct as_data *ad, struct as_io_context *aic,
++                              sector_t sdist)
++{
++      u64 total;
++
++      if (aic->seek_samples == 0) {
++              ad->new_seek_total = (7*ad->new_seek_total + 256*(u64)sdist)/8;
++              ad->new_seek_mean = ad->new_seek_total / 256;
++      }
++
++      /*
++       * Don't allow the seek distance to get too large from the
++       * odd fragment, pagein, etc
++       */
++      if (aic->seek_samples <= 60) /* second&third seek */
++              sdist = min(sdist, (aic->seek_mean * 4) + 2*1024*1024);
++      else
++              sdist = min(sdist, (aic->seek_mean * 4) + 2*1024*64);
++
++      aic->seek_samples = (7*aic->seek_samples + 256) / 8;
++      aic->seek_total = (7*aic->seek_total + (u64)256*sdist) / 8;
++      total = aic->seek_total + (aic->seek_samples/2);
++      do_div(total, aic->seek_samples);
++      aic->seek_mean = (sector_t)total;
++}
++
++/*
++ * as_update_iohist keeps a decaying histogram of IO thinktimes, and
++ * updates @aic->ttime_mean based on that. It is called when a new
++ * request is queued.
++ */
++static void as_update_iohist(struct as_data *ad, struct as_io_context *aic,
++                              struct request *rq)
++{
++      struct as_rq *arq = RQ_DATA(rq);
++      int data_dir = arq->is_sync;
++      unsigned long thinktime = 0;
++      sector_t seek_dist;
++
++      if (aic == NULL)
++              return;
++
++      if (data_dir == REQ_SYNC) {
++              unsigned long in_flight = atomic_read(&aic->nr_queued)
++                                      + atomic_read(&aic->nr_dispatched);
++              spin_lock(&aic->lock);
++              if (test_bit(AS_TASK_IORUNNING, &aic->state) ||
++                      test_bit(AS_TASK_IOSTARTED, &aic->state)) {
++                      /* Calculate read -> read thinktime */
++                      if (test_bit(AS_TASK_IORUNNING, &aic->state)
++                                                      && in_flight == 0) {
++                              thinktime = jiffies - aic->last_end_request;
++                              thinktime = min(thinktime, MAX_THINKTIME-1);
++                      }
++                      as_update_thinktime(ad, aic, thinktime);
++
++                      /* Calculate read -> read seek distance */
++                      if (aic->last_request_pos < rq->sector)
++                              seek_dist = rq->sector - aic->last_request_pos;
++                      else
++                              seek_dist = aic->last_request_pos - rq->sector;
++                      as_update_seekdist(ad, aic, seek_dist);
++              }
++              aic->last_request_pos = rq->sector + rq->nr_sectors;
++              set_bit(AS_TASK_IOSTARTED, &aic->state);
++              spin_unlock(&aic->lock);
++      }
++}
++
+ /*
+  * as_close_req decides if one request is considered "close" to the
+  * previous one issued.
+  */
 -      if (delay <= 1)
 -              delta = 64;
++static int as_close_req(struct as_data *ad, struct as_io_context *aic,
++                              struct as_rq *arq)
+ {
+       unsigned long delay;    /* milliseconds */
+       sector_t last = ad->last_sector[ad->batch_data_dir];
+       sector_t next = arq->request->sector;
+       sector_t delta; /* acceptable close offset (in sectors) */
++      sector_t s;
+       if (ad->antic_status == ANTIC_OFF || !ad->ioc_finished)
+               delay = 0;
+       else
+               delay = ((jiffies - ad->antic_start) * 1000) / HZ;
 -              delta = 64 << (delay-1);
++      if (delay == 0)
++              delta = 8192;
+       else if (delay <= 20 && delay <= ad->antic_expire)
 -      return (last - (delta>>1) <= next) && (next <= last + delta);
++              delta = 8192 << delay;
+       else
+               return 1;
 - * If the task which has submitted the request has exitted, break anticipation.
++      if ((last <= next + (delta>>1)) && (next <= last + delta))
++              return 1;
++
++      if (last < next)
++              s = next - last;
++      else
++              s = last - next;
++
++      if (aic->seek_samples == 0) {
++              /*
++               * Process has just started IO. Use past statistics to
++               * gauge success possibility
++               */
++              if (ad->new_seek_mean > s) {
++                      /* this request is better than what we're expecting */
++                      return 1;
++              }
++
++      } else {
++              if (aic->seek_mean > s) {
++                      /* this request is better than what we're expecting */
++                      return 1;
++              }
++      }
++
++      return 0;
+ }
+ /*
+  * as_can_break_anticipation returns true if we have been anticipating this
+  * request.
+  *
+  * It also returns true if the process against which we are anticipating
+  * submits a write - that's presumably an fsync, O_SYNC write, etc. We want to
+  * dispatch it ASAP, because we know that application will not be submitting
+  * any new reads.
+  *
 -      sector_t s;
++ * If the task which has submitted the request has exited, break anticipation.
+  *
+  * If this task has queued some other IO, do not enter enticipation.
+  */
+ static int as_can_break_anticipation(struct as_data *ad, struct as_rq *arq)
+ {
+       struct io_context *ioc;
+       struct as_io_context *aic;
 -      if (!test_bit(AS_TASK_RUNNING, &aic->state)) {
 -              /* process anticipated on has exitted */
 -              if (aic->ttime_samples == 0)
 -                      ad->exit_prob = (7*ad->exit_prob + 256)/8;
 -              return 1;
 -      }
 -
+       ioc = ad->io_context;
+       BUG_ON(!ioc);
+       if (arq && ioc == arq->io_context) {
+               /* request from same process */
+               return 1;
+       }
+       if (ad->ioc_finished && as_antic_expired(ad)) {
+               /*
+                * In this situation status should really be FINISHED,
+                * however the timer hasn't had the chance to run yet.
+                */
+               return 1;
+       }
+       aic = ioc->aic;
+       if (!aic)
+               return 0;
 -      if (arq && arq->is_sync == REQ_SYNC && as_close_req(ad, arq)) {
+       if (atomic_read(&aic->nr_queued) > 0) {
+               /* process has more requests queued */
+               return 1;
+       }
+       if (atomic_read(&aic->nr_dispatched) > 0) {
+               /* process has more requests dispatched */
+               return 1;
+       }
 -               * This makes close requests from another process reset
 -               * our thinktime delay. Is generally useful when there are
++      if (arq && arq->is_sync == REQ_SYNC && as_close_req(ad, aic, arq)) {
+               /*
+                * Found a close request that is not one of ours.
+                *
 -              spin_lock(&aic->lock);
 -              aic->last_end_request = jiffies;
 -              spin_unlock(&aic->lock);
++               * This makes close requests from another process update
++               * our IO history. Is generally useful when there are
+                * two or more cooperating processes working in the same
+                * area.
+                */
 -              if (ad->exit_prob > 128)
++              if (!test_bit(AS_TASK_RUNNING, &aic->state)) {
++                      if (aic->ttime_samples == 0)
++                              ad->exit_prob = (7*ad->exit_prob + 256)/8;
++
++                      ad->exit_no_coop = (7*ad->exit_no_coop)/8;
++              }
++
++              as_update_iohist(ad, aic, arq->request);
+               return 1;
+       }
++      if (!test_bit(AS_TASK_RUNNING, &aic->state)) {
++              /* process anticipated on has exited */
++              if (aic->ttime_samples == 0)
++                      ad->exit_prob = (7*ad->exit_prob + 256)/8;
++
++              if (ad->exit_no_coop > 128)
++                      return 1;
++      }
+       if (aic->ttime_samples == 0) {
+               if (ad->new_ttime_mean > ad->antic_expire)
+                       return 1;
 -      if (!arq)
 -              return 0;
 -
 -      if (ad->last_sector[REQ_SYNC] < arq->request->sector)
 -              s = arq->request->sector - ad->last_sector[REQ_SYNC];
 -      else
 -              s = ad->last_sector[REQ_SYNC] - arq->request->sector;
 -
 -      if (aic->seek_samples == 0) {
 -              /*
 -               * Process has just started IO. Use past statistics to
 -               * guage success possibility
 -               */
 -              if (ad->new_seek_mean > s) {
 -                      /* this request is better than what we're expecting */
 -                      return 1;
 -              }
 -
 -      } else {
 -              if (aic->seek_mean > s) {
 -                      /* this request is better than what we're expecting */
 -                      return 1;
 -              }
 -      }
 -
++              if (ad->exit_prob * ad->exit_no_coop > 128*256)
+                       return 1;
+       } else if (aic->ttime_mean > ad->antic_expire) {
+               /* the process thinks too much between requests */
+               return 1;
+       }
 -       *
+       return 0;
+ }
+ /*
+  * as_can_anticipate indicates weather we should either run arq
+  * or keep anticipating a better request.
+  */
+ static int as_can_anticipate(struct as_data *ad, struct as_rq *arq)
+ {
+       if (!ad->io_context)
+               /*
+                * Last request submitted was a write
+                */
+               return 0;
+       if (ad->antic_status == ANTIC_FINISHED)
+               /*
+                * Don't restart if we have just finished. Run the next request
+                */
+               return 0;
+       if (as_can_break_anticipation(ad, arq))
+               /*
+                * This request is a good candidate. Don't keep anticipating,
+                * run it.
+                */
+               return 0;
+       /*
+        * OK from here, we haven't finished, and don't have a decent request!
+        * Status is either ANTIC_OFF so start waiting,
+        * ANTIC_WAIT_REQ so continue waiting for request to finish
+        * or ANTIC_WAIT_NEXT so continue waiting for an acceptable request.
 -static void as_update_thinktime(struct as_data *ad, struct as_io_context *aic, unsigned long ttime)
 -{
 -      /* fixed point: 1.0 == 1<<8 */
 -      if (aic->ttime_samples == 0) {
 -              ad->new_ttime_total = (7*ad->new_ttime_total + 256*ttime) / 8;
 -              ad->new_ttime_mean = ad->new_ttime_total / 256;
 -
 -              ad->exit_prob = (7*ad->exit_prob)/8;
 -      }
 -      aic->ttime_samples = (7*aic->ttime_samples + 256) / 8;
 -      aic->ttime_total = (7*aic->ttime_total + 256*ttime) / 8;
 -      aic->ttime_mean = (aic->ttime_total + 128) / aic->ttime_samples;
 -}
 -
 -static void as_update_seekdist(struct as_data *ad, struct as_io_context *aic, sector_t sdist)
 -{
 -      u64 total;
 -
 -      if (aic->seek_samples == 0) {
 -              ad->new_seek_total = (7*ad->new_seek_total + 256*(u64)sdist)/8;
 -              ad->new_seek_mean = ad->new_seek_total / 256;
 -      }
 -
 -      /*
 -       * Don't allow the seek distance to get too large from the
 -       * odd fragment, pagein, etc
 -       */
 -      if (aic->seek_samples <= 60) /* second&third seek */
 -              sdist = min(sdist, (aic->seek_mean * 4) + 2*1024*1024);
 -      else
 -              sdist = min(sdist, (aic->seek_mean * 4) + 2*1024*64);
 -
 -      aic->seek_samples = (7*aic->seek_samples + 256) / 8;
 -      aic->seek_total = (7*aic->seek_total + (u64)256*sdist) / 8;
 -      total = aic->seek_total + (aic->seek_samples/2);
 -      do_div(total, aic->seek_samples);
 -      aic->seek_mean = (sector_t)total;
 -}
 -
 -/*
 - * as_update_iohist keeps a decaying histogram of IO thinktimes, and
 - * updates @aic->ttime_mean based on that. It is called when a new
 - * request is queued.
 - */
 -static void as_update_iohist(struct as_data *ad, struct as_io_context *aic, struct request *rq)
 -{
 -      struct as_rq *arq = RQ_DATA(rq);
 -      int data_dir = arq->is_sync;
 -      unsigned long thinktime;
 -      sector_t seek_dist;
 -
 -      if (aic == NULL)
 -              return;
 -
 -      if (data_dir == REQ_SYNC) {
 -              unsigned long in_flight = atomic_read(&aic->nr_queued)
 -                                      + atomic_read(&aic->nr_dispatched);
 -              spin_lock(&aic->lock);
 -              if (test_bit(AS_TASK_IORUNNING, &aic->state) ||
 -                      test_bit(AS_TASK_IOSTARTED, &aic->state)) {
 -                      /* Calculate read -> read thinktime */
 -                      if (test_bit(AS_TASK_IORUNNING, &aic->state)
 -                                                      && in_flight == 0) {
 -                              thinktime = jiffies - aic->last_end_request;
 -                              thinktime = min(thinktime, MAX_THINKTIME-1);
 -                      } else
 -                              thinktime = 0;
 -                      as_update_thinktime(ad, aic, thinktime);
 -
 -                      /* Calculate read -> read seek distance */
 -                      if (aic->last_request_pos < rq->sector)
 -                              seek_dist = rq->sector - aic->last_request_pos;
 -                      else
 -                              seek_dist = aic->last_request_pos - rq->sector;
 -                      as_update_seekdist(ad, aic, seek_dist);
 -              }
 -              aic->last_request_pos = rq->sector + rq->nr_sectors;
 -              set_bit(AS_TASK_IOSTARTED, &aic->state);
 -              spin_unlock(&aic->lock);
 -      }
 -}
 -
+        */
+       return 1;
+ }
 -      if (!(reads && writes && as_batch_expired(ad)) ) {
+ /*
+  * as_update_arq must be called whenever a request (arq) is added to
+  * the sort_list. This function keeps caches up to date, and checks if the
+  * request might be one we are "anticipating"
+  */
+ static void as_update_arq(struct as_data *ad, struct as_rq *arq)
+ {
+       const int data_dir = arq->is_sync;
+       /* keep the next_arq cache up to date */
+       ad->next_arq[data_dir] = as_choose_req(ad, arq, ad->next_arq[data_dir]);
+       /*
+        * have we been anticipating this request?
+        * or does it come from the same process as the one we are anticipating
+        * for?
+        */
+       if (ad->antic_status == ANTIC_WAIT_REQ
+                       || ad->antic_status == ANTIC_WAIT_NEXT) {
+               if (as_can_break_anticipation(ad, arq))
+                       as_antic_stop(ad);
+       }
+ }
+ /*
+  * Gathers timings and resizes the write batch automatically
+  */
+ static void update_write_batch(struct as_data *ad)
+ {
+       unsigned long batch = ad->batch_expire[REQ_ASYNC];
+       long write_time;
+       write_time = (jiffies - ad->current_batch_expires) + batch;
+       if (write_time < 0)
+               write_time = 0;
+       if (write_time > batch && !ad->write_batch_idled) {
+               if (write_time > batch * 3)
+                       ad->write_batch_count /= 2;
+               else
+                       ad->write_batch_count--;
+       } else if (write_time < batch && ad->current_write_count == 0) {
+               if (batch > write_time * 3)
+                       ad->write_batch_count *= 2;
+               else
+                       ad->write_batch_count++;
+       }
+       if (ad->write_batch_count < 1)
+               ad->write_batch_count = 1;
+ }
+ /*
+  * as_completed_request is to be called when a request has completed and
+  * returned something to the requesting process, be it an error or data.
+  */
+ static void as_completed_request(request_queue_t *q, struct request *rq)
+ {
+       struct as_data *ad = q->elevator->elevator_data;
+       struct as_rq *arq = RQ_DATA(rq);
+       WARN_ON(!list_empty(&rq->queuelist));
+       if (arq->state != AS_RQ_REMOVED) {
+               printk("arq->state %d\n", arq->state);
+               WARN_ON(1);
+               goto out;
+       }
+       if (ad->changed_batch && ad->nr_dispatched == 1) {
+               kblockd_schedule_work(&ad->antic_work);
+               ad->changed_batch = 0;
+               if (ad->batch_data_dir == REQ_SYNC)
+                       ad->new_batch = 1;
+       }
+       WARN_ON(ad->nr_dispatched == 0);
+       ad->nr_dispatched--;
+       /*
+        * Start counting the batch from when a request of that direction is
+        * actually serviced. This should help devices with big TCQ windows
+        * and writeback caches
+        */
+       if (ad->new_batch && ad->batch_data_dir == arq->is_sync) {
+               update_write_batch(ad);
+               ad->current_batch_expires = jiffies +
+                               ad->batch_expire[REQ_SYNC];
+               ad->new_batch = 0;
+       }
+       if (ad->io_context == arq->io_context && ad->io_context) {
+               ad->antic_start = jiffies;
+               ad->ioc_finished = 1;
+               if (ad->antic_status == ANTIC_WAIT_REQ) {
+                       /*
+                        * We were waiting on this request, now anticipate
+                        * the next one
+                        */
+                       as_antic_waitnext(ad);
+               }
+       }
+       as_put_io_context(arq);
+ out:
+       arq->state = AS_RQ_POSTSCHED;
+ }
+ /*
+  * as_remove_queued_request removes a request from the pre dispatch queue
+  * without updating refcounts. It is expected the caller will drop the
+  * reference unless it replaces the request at somepart of the elevator
+  * (ie. the dispatch queue)
+  */
+ static void as_remove_queued_request(request_queue_t *q, struct request *rq)
+ {
+       struct as_rq *arq = RQ_DATA(rq);
+       const int data_dir = arq->is_sync;
+       struct as_data *ad = q->elevator->elevator_data;
+       WARN_ON(arq->state != AS_RQ_QUEUED);
+       if (arq->io_context && arq->io_context->aic) {
+               BUG_ON(!atomic_read(&arq->io_context->aic->nr_queued));
+               atomic_dec(&arq->io_context->aic->nr_queued);
+       }
+       /*
+        * Update the "next_arq" cache if we are about to remove its
+        * entry
+        */
+       if (ad->next_arq[data_dir] == arq)
+               ad->next_arq[data_dir] = as_find_next_arq(ad, arq);
+       list_del_init(&arq->fifo);
+       as_del_arq_hash(arq);
+       as_del_arq_rb(ad, arq);
+ }
+ /*
+  * as_fifo_expired returns 0 if there are no expired reads on the fifo,
+  * 1 otherwise.  It is ratelimited so that we only perform the check once per
+  * `fifo_expire' interval.  Otherwise a large number of expired requests
+  * would create a hopeless seekstorm.
+  *
+  * See as_antic_expired comment.
+  */
+ static int as_fifo_expired(struct as_data *ad, int adir)
+ {
+       struct as_rq *arq;
+       long delta_jif;
+       delta_jif = jiffies - ad->last_check_fifo[adir];
+       if (unlikely(delta_jif < 0))
+               delta_jif = -delta_jif;
+       if (delta_jif < ad->fifo_expire[adir])
+               return 0;
+       ad->last_check_fifo[adir] = jiffies;
+       if (list_empty(&ad->fifo_list[adir]))
+               return 0;
+       arq = list_entry_fifo(ad->fifo_list[adir].next);
+       return time_after(jiffies, arq->expires);
+ }
+ /*
+  * as_batch_expired returns true if the current batch has expired. A batch
+  * is a set of reads or a set of writes.
+  */
+ static inline int as_batch_expired(struct as_data *ad)
+ {
+       if (ad->changed_batch || ad->new_batch)
+               return 0;
+       if (ad->batch_data_dir == REQ_SYNC)
+               /* TODO! add a check so a complete fifo gets written? */
+               return time_after(jiffies, ad->current_batch_expires);
+       return time_after(jiffies, ad->current_batch_expires)
+               || ad->current_write_count == 0;
+ }
+ /*
+  * move an entry to dispatch queue
+  */
+ static void as_move_to_dispatch(struct as_data *ad, struct as_rq *arq)
+ {
+       struct request *rq = arq->request;
+       const int data_dir = arq->is_sync;
+       BUG_ON(!ON_RB(&arq->rb_node));
+       as_antic_stop(ad);
+       ad->antic_status = ANTIC_OFF;
+       /*
+        * This has to be set in order to be correctly updated by
+        * as_find_next_arq
+        */
+       ad->last_sector[data_dir] = rq->sector + rq->nr_sectors;
+       if (data_dir == REQ_SYNC) {
+               /* In case we have to anticipate after this */
+               copy_io_context(&ad->io_context, &arq->io_context);
+       } else {
+               if (ad->io_context) {
+                       put_io_context(ad->io_context);
+                       ad->io_context = NULL;
+               }
+               if (ad->current_write_count != 0)
+                       ad->current_write_count--;
+       }
+       ad->ioc_finished = 0;
+       ad->next_arq[data_dir] = as_find_next_arq(ad, arq);
+       /*
+        * take it off the sort and fifo list, add to dispatch queue
+        */
+       while (!list_empty(&rq->queuelist)) {
+               struct request *__rq = list_entry_rq(rq->queuelist.next);
+               struct as_rq *__arq = RQ_DATA(__rq);
+               list_del(&__rq->queuelist);
+               elv_dispatch_add_tail(ad->q, __rq);
+               if (__arq->io_context && __arq->io_context->aic)
+                       atomic_inc(&__arq->io_context->aic->nr_dispatched);
+               WARN_ON(__arq->state != AS_RQ_QUEUED);
+               __arq->state = AS_RQ_DISPATCHED;
+               ad->nr_dispatched++;
+       }
+       as_remove_queued_request(ad->q, rq);
+       WARN_ON(arq->state != AS_RQ_QUEUED);
+       elv_dispatch_sort(ad->q, rq);
+       arq->state = AS_RQ_DISPATCHED;
+       if (arq->io_context && arq->io_context->aic)
+               atomic_inc(&arq->io_context->aic->nr_dispatched);
+       ad->nr_dispatched++;
+ }
+ /*
+  * as_dispatch_request selects the best request according to
+  * read/write expire, batch expire, etc, and moves it to the dispatch
+  * queue. Returns 1 if a request was found, 0 otherwise.
+  */
+ static int as_dispatch_request(request_queue_t *q, int force)
+ {
+       struct as_data *ad = q->elevator->elevator_data;
+       struct as_rq *arq;
+       const int reads = !list_empty(&ad->fifo_list[REQ_SYNC]);
+       const int writes = !list_empty(&ad->fifo_list[REQ_ASYNC]);
+       if (unlikely(force)) {
+               /*
+                * Forced dispatch, accounting is useless.  Reset
+                * accounting states and dump fifo_lists.  Note that
+                * batch_data_dir is reset to REQ_SYNC to avoid
+                * screwing write batch accounting as write batch
+                * accounting occurs on W->R transition.
+                */
+               int dispatched = 0;
+               ad->batch_data_dir = REQ_SYNC;
+               ad->changed_batch = 0;
+               ad->new_batch = 0;
+               while (ad->next_arq[REQ_SYNC]) {
+                       as_move_to_dispatch(ad, ad->next_arq[REQ_SYNC]);
+                       dispatched++;
+               }
+               ad->last_check_fifo[REQ_SYNC] = jiffies;
+               while (ad->next_arq[REQ_ASYNC]) {
+                       as_move_to_dispatch(ad, ad->next_arq[REQ_ASYNC]);
+                       dispatched++;
+               }
+               ad->last_check_fifo[REQ_ASYNC] = jiffies;
+               return dispatched;
+       }
+       /* Signal that the write batch was uncontended, so we can't time it */
+       if (ad->batch_data_dir == REQ_ASYNC && !reads) {
+               if (ad->current_write_count == 0 || !writes)
+                       ad->write_batch_idled = 1;
+       }
+       if (!(reads || writes)
+               || ad->antic_status == ANTIC_WAIT_REQ
+               || ad->antic_status == ANTIC_WAIT_NEXT
+               || ad->changed_batch)
+               return 0;
 -as_add_aliased_request(struct as_data *ad, struct as_rq *arq, struct as_rq *alias)
++      if (!(reads && writes && as_batch_expired(ad))) {
+               /*
+                * batch is still running or no reads or no writes
+                */
+               arq = ad->next_arq[ad->batch_data_dir];
+               if (ad->batch_data_dir == REQ_SYNC && ad->antic_expire) {
+                       if (as_fifo_expired(ad, REQ_SYNC))
+                               goto fifo_expired;
+                       if (as_can_anticipate(ad, arq)) {
+                               as_antic_waitreq(ad);
+                               return 0;
+                       }
+               }
+               if (arq) {
+                       /* we have a "next request" */
+                       if (reads && !writes)
+                               ad->current_batch_expires =
+                                       jiffies + ad->batch_expire[REQ_SYNC];
+                       goto dispatch_request;
+               }
+       }
+       /*
+        * at this point we are not running a batch. select the appropriate
+        * data direction (read / write)
+        */
+       if (reads) {
+               BUG_ON(RB_EMPTY(&ad->sort_list[REQ_SYNC]));
+               if (writes && ad->batch_data_dir == REQ_SYNC)
+                       /*
+                        * Last batch was a read, switch to writes
+                        */
+                       goto dispatch_writes;
+               if (ad->batch_data_dir == REQ_ASYNC) {
+                       WARN_ON(ad->new_batch);
+                       ad->changed_batch = 1;
+               }
+               ad->batch_data_dir = REQ_SYNC;
+               arq = list_entry_fifo(ad->fifo_list[ad->batch_data_dir].next);
+               ad->last_check_fifo[ad->batch_data_dir] = jiffies;
+               goto dispatch_request;
+       }
+       /*
+        * the last batch was a read
+        */
+       if (writes) {
+ dispatch_writes:
+               BUG_ON(RB_EMPTY(&ad->sort_list[REQ_ASYNC]));
+               if (ad->batch_data_dir == REQ_SYNC) {
+                       ad->changed_batch = 1;
+                       /*
+                        * new_batch might be 1 when the queue runs out of
+                        * reads. A subsequent submission of a write might
+                        * cause a change of batch before the read is finished.
+                        */
+                       ad->new_batch = 0;
+               }
+               ad->batch_data_dir = REQ_ASYNC;
+               ad->current_write_count = ad->write_batch_count;
+               ad->write_batch_idled = 0;
+               arq = ad->next_arq[ad->batch_data_dir];
+               goto dispatch_request;
+       }
+       BUG();
+       return 0;
+ dispatch_request:
+       /*
+        * If a request has expired, service it.
+        */
+       if (as_fifo_expired(ad, ad->batch_data_dir)) {
+ fifo_expired:
+               arq = list_entry_fifo(ad->fifo_list[ad->batch_data_dir].next);
+               BUG_ON(arq == NULL);
+       }
+       if (ad->changed_batch) {
+               WARN_ON(ad->new_batch);
+               if (ad->nr_dispatched)
+                       return 0;
+               if (ad->batch_data_dir == REQ_ASYNC)
+                       ad->current_batch_expires = jiffies +
+                                       ad->batch_expire[REQ_ASYNC];
+               else
+                       ad->new_batch = 1;
+               ad->changed_batch = 0;
+       }
+       /*
+        * arq is the selected appropriate request.
+        */
+       as_move_to_dispatch(ad, arq);
+       return 1;
+ }
+ /*
+  * Add arq to a list behind alias
+  */
+ static inline void
 -static struct request *
 -as_former_request(request_queue_t *q, struct request *rq)
++as_add_aliased_request(struct as_data *ad, struct as_rq *arq,
++                              struct as_rq *alias)
+ {
+       struct request  *req = arq->request;
+       struct list_head *insert = alias->request->queuelist.prev;
+       /*
+        * Transfer list of aliases
+        */
+       while (!list_empty(&req->queuelist)) {
+               struct request *__rq = list_entry_rq(req->queuelist.next);
+               struct as_rq *__arq = RQ_DATA(__rq);
+               list_move_tail(&__rq->queuelist, &alias->request->queuelist);
+               WARN_ON(__arq->state != AS_RQ_QUEUED);
+       }
+       /*
+        * Another request with the same start sector on the rbtree.
+        * Link this request to that sector. They are untangled in
+        * as_move_to_dispatch
+        */
+       list_add(&arq->request->queuelist, insert);
+       /*
+        * Don't want to have to handle merges.
+        */
+       as_del_arq_hash(arq);
+       arq->request->flags |= REQ_NOMERGE;
+ }
+ /*
+  * add arq to rbtree and fifo
+  */
+ static void as_add_request(request_queue_t *q, struct request *rq)
+ {
+       struct as_data *ad = q->elevator->elevator_data;
+       struct as_rq *arq = RQ_DATA(rq);
+       struct as_rq *alias;
+       int data_dir;
+       if (arq->state != AS_RQ_PRESCHED) {
+               printk("arq->state: %d\n", arq->state);
+               WARN_ON(1);
+       }
+       arq->state = AS_RQ_NEW;
+       if (rq_data_dir(arq->request) == READ
+                       || current->flags&PF_SYNCWRITE)
+               arq->is_sync = 1;
+       else
+               arq->is_sync = 0;
+       data_dir = arq->is_sync;
+       arq->io_context = as_get_io_context();
+       if (arq->io_context) {
+               as_update_iohist(ad, arq->io_context->aic, arq->request);
+               atomic_inc(&arq->io_context->aic->nr_queued);
+       }
+       alias = as_add_arq_rb(ad, arq);
+       if (!alias) {
+               /*
+                * set expire time (only used for reads) and add to fifo list
+                */
+               arq->expires = jiffies + ad->fifo_expire[data_dir];
+               list_add_tail(&arq->fifo, &ad->fifo_list[data_dir]);
+               if (rq_mergeable(arq->request))
+                       as_add_arq_hash(ad, arq);
+               as_update_arq(ad, arq); /* keep state machine up to date */
+       } else {
+               as_add_aliased_request(ad, arq, alias);
+               /*
+                * have we been anticipating this request?
+                * or does it come from the same process as the one we are
+                * anticipating for?
+                */
+               if (ad->antic_status == ANTIC_WAIT_REQ
+                               || ad->antic_status == ANTIC_WAIT_NEXT) {
+                       if (as_can_break_anticipation(ad, arq))
+                               as_antic_stop(ad);
+               }
+       }
+       arq->state = AS_RQ_QUEUED;
+ }
+ static void as_activate_request(request_queue_t *q, struct request *rq)
+ {
+       struct as_rq *arq = RQ_DATA(rq);
+       WARN_ON(arq->state != AS_RQ_DISPATCHED);
+       arq->state = AS_RQ_REMOVED;
+       if (arq->io_context && arq->io_context->aic)
+               atomic_dec(&arq->io_context->aic->nr_dispatched);
+ }
+ static void as_deactivate_request(request_queue_t *q, struct request *rq)
+ {
+       struct as_rq *arq = RQ_DATA(rq);
+       WARN_ON(arq->state != AS_RQ_REMOVED);
+       arq->state = AS_RQ_DISPATCHED;
+       if (arq->io_context && arq->io_context->aic)
+               atomic_inc(&arq->io_context->aic->nr_dispatched);
+ }
+ /*
+  * as_queue_empty tells us if there are requests left in the device. It may
+  * not be the case that a driver can get the next request even if the queue
+  * is not empty - it is used in the block layer to check for plugging and
+  * merging opportunities
+  */
+ static int as_queue_empty(request_queue_t *q)
+ {
+       struct as_data *ad = q->elevator->elevator_data;
+       return list_empty(&ad->fifo_list[REQ_ASYNC])
+               && list_empty(&ad->fifo_list[REQ_SYNC]);
+ }
 -static struct request *
 -as_latter_request(request_queue_t *q, struct request *rq)
++static struct request *as_former_request(request_queue_t *q,
++                                      struct request *rq)
+ {
+       struct as_rq *arq = RQ_DATA(rq);
+       struct rb_node *rbprev = rb_prev(&arq->rb_node);
+       struct request *ret = NULL;
+       if (rbprev)
+               ret = rb_entry_arq(rbprev)->request;
+       return ret;
+ }
 -              if ((alias = as_add_arq_rb(ad, arq)) ) {
++static struct request *as_latter_request(request_queue_t *q,
++                                      struct request *rq)
+ {
+       struct as_rq *arq = RQ_DATA(rq);
+       struct rb_node *rbnext = rb_next(&arq->rb_node);
+       struct request *ret = NULL;
+       if (rbnext)
+               ret = rb_entry_arq(rbnext)->request;
+       return ret;
+ }
+ static int
+ as_merge(request_queue_t *q, struct request **req, struct bio *bio)
+ {
+       struct as_data *ad = q->elevator->elevator_data;
+       sector_t rb_key = bio->bi_sector + bio_sectors(bio);
+       struct request *__rq;
+       int ret;
+       /*
+        * see if the merge hash can satisfy a back merge
+        */
+       __rq = as_find_arq_hash(ad, bio->bi_sector);
+       if (__rq) {
+               BUG_ON(__rq->sector + __rq->nr_sectors != bio->bi_sector);
+               if (elv_rq_merge_ok(__rq, bio)) {
+                       ret = ELEVATOR_BACK_MERGE;
+                       goto out;
+               }
+       }
+       /*
+        * check for front merge
+        */
+       __rq = as_find_arq_rb(ad, rb_key, bio_data_dir(bio));
+       if (__rq) {
+               BUG_ON(rb_key != rq_rb_key(__rq));
+               if (elv_rq_merge_ok(__rq, bio)) {
+                       ret = ELEVATOR_FRONT_MERGE;
+                       goto out;
+               }
+       }
+       return ELEVATOR_NO_MERGE;
+ out:
+       if (ret) {
+               if (rq_mergeable(__rq))
+                       as_hot_arq_hash(ad, RQ_DATA(__rq));
+       }
+       *req = __rq;
+       return ret;
+ }
+ static void as_merged_request(request_queue_t *q, struct request *req)
+ {
+       struct as_data *ad = q->elevator->elevator_data;
+       struct as_rq *arq = RQ_DATA(req);
+       /*
+        * hash always needs to be repositioned, key is end sector
+        */
+       as_del_arq_hash(arq);
+       as_add_arq_hash(ad, arq);
+       /*
+        * if the merge was a front merge, we need to reposition request
+        */
+       if (rq_rb_key(req) != arq->rb_key) {
+               struct as_rq *alias, *next_arq = NULL;
+               if (ad->next_arq[arq->is_sync] == arq)
+                       next_arq = as_find_next_arq(ad, arq);
+               /*
+                * Note! We should really be moving any old aliased requests
+                * off this request and try to insert them into the rbtree. We
+                * currently don't bother. Ditto the next function.
+                */
+               as_del_arq_rb(ad, arq);
 -static void
 -as_merged_requests(request_queue_t *q, struct request *req,
 -                       struct request *next)
++              if ((alias = as_add_arq_rb(ad, arq))) {
+                       list_del_init(&arq->fifo);
+                       as_add_aliased_request(ad, arq, alias);
+                       if (next_arq)
+                               ad->next_arq[arq->is_sync] = next_arq;
+               }
+               /*
+                * Note! At this stage of this and the next function, our next
+                * request may not be optimal - eg the request may have "grown"
+                * behind the disk head. We currently don't bother adjusting.
+                */
+       }
+ }
 -              if ((alias = as_add_arq_rb(ad, arq)) ) {
++static void as_merged_requests(request_queue_t *q, struct request *req,
++                              struct request *next)
+ {
+       struct as_data *ad = q->elevator->elevator_data;
+       struct as_rq *arq = RQ_DATA(req);
+       struct as_rq *anext = RQ_DATA(next);
+       BUG_ON(!arq);
+       BUG_ON(!anext);
+       /*
+        * reposition arq (this is the merged request) in hash, and in rbtree
+        * in case of a front merge
+        */
+       as_del_arq_hash(arq);
+       as_add_arq_hash(ad, arq);
+       if (rq_rb_key(req) != arq->rb_key) {
+               struct as_rq *alias, *next_arq = NULL;
+               if (ad->next_arq[arq->is_sync] == arq)
+                       next_arq = as_find_next_arq(ad, arq);
+               as_del_arq_rb(ad, arq);
 -      pos += sprintf(page+pos, "%lu %% exit probability\n", 100*ad->exit_prob/256);
++              if ((alias = as_add_arq_rb(ad, arq))) {
+                       list_del_init(&arq->fifo);
+                       as_add_aliased_request(ad, arq, alias);
+                       if (next_arq)
+                               ad->next_arq[arq->is_sync] = next_arq;
+               }
+       }
+       /*
+        * if anext expires before arq, assign its expire time to arq
+        * and move into anext position (anext will be deleted) in fifo
+        */
+       if (!list_empty(&arq->fifo) && !list_empty(&anext->fifo)) {
+               if (time_before(anext->expires, arq->expires)) {
+                       list_move(&arq->fifo, &anext->fifo);
+                       arq->expires = anext->expires;
+                       /*
+                        * Don't copy here but swap, because when anext is
+                        * removed below, it must contain the unused context
+                        */
+                       swap_io_context(&arq->io_context, &anext->io_context);
+               }
+       }
+       /*
+        * Transfer list of aliases
+        */
+       while (!list_empty(&next->queuelist)) {
+               struct request *__rq = list_entry_rq(next->queuelist.next);
+               struct as_rq *__arq = RQ_DATA(__rq);
+               list_move_tail(&__rq->queuelist, &req->queuelist);
+               WARN_ON(__arq->state != AS_RQ_QUEUED);
+       }
+       /*
+        * kill knowledge of next, this one is a goner
+        */
+       as_remove_queued_request(q, next);
+       as_put_io_context(anext);
+       anext->state = AS_RQ_MERGED;
+ }
+ /*
+  * This is executed in a "deferred" process context, by kblockd. It calls the
+  * driver's request_fn so the driver can submit that request.
+  *
+  * IMPORTANT! This guy will reenter the elevator, so set up all queue global
+  * state before calling, and don't rely on any state over calls.
+  *
+  * FIXME! dispatch queue is not a queue at all!
+  */
+ static void as_work_handler(void *data)
+ {
+       struct request_queue *q = data;
+       unsigned long flags;
+       spin_lock_irqsave(q->queue_lock, flags);
+       if (!as_queue_empty(q))
+               q->request_fn(q);
+       spin_unlock_irqrestore(q->queue_lock, flags);
+ }
+ static void as_put_request(request_queue_t *q, struct request *rq)
+ {
+       struct as_data *ad = q->elevator->elevator_data;
+       struct as_rq *arq = RQ_DATA(rq);
+       if (!arq) {
+               WARN_ON(1);
+               return;
+       }
+       if (unlikely(arq->state != AS_RQ_POSTSCHED &&
+                    arq->state != AS_RQ_PRESCHED &&
+                    arq->state != AS_RQ_MERGED)) {
+               printk("arq->state %d\n", arq->state);
+               WARN_ON(1);
+       }
+       mempool_free(arq, ad->arq_pool);
+       rq->elevator_private = NULL;
+ }
+ static int as_set_request(request_queue_t *q, struct request *rq,
+                         struct bio *bio, gfp_t gfp_mask)
+ {
+       struct as_data *ad = q->elevator->elevator_data;
+       struct as_rq *arq = mempool_alloc(ad->arq_pool, gfp_mask);
+       if (arq) {
+               memset(arq, 0, sizeof(*arq));
+               RB_CLEAR(&arq->rb_node);
+               arq->request = rq;
+               arq->state = AS_RQ_PRESCHED;
+               arq->io_context = NULL;
+               INIT_LIST_HEAD(&arq->hash);
+               arq->on_hash = 0;
+               INIT_LIST_HEAD(&arq->fifo);
+               rq->elevator_private = arq;
+               return 0;
+       }
+       return 1;
+ }
+ static int as_may_queue(request_queue_t *q, int rw, struct bio *bio)
+ {
+       int ret = ELV_MQUEUE_MAY;
+       struct as_data *ad = q->elevator->elevator_data;
+       struct io_context *ioc;
+       if (ad->antic_status == ANTIC_WAIT_REQ ||
+                       ad->antic_status == ANTIC_WAIT_NEXT) {
+               ioc = as_get_io_context();
+               if (ad->io_context == ioc)
+                       ret = ELV_MQUEUE_MUST;
+               put_io_context(ioc);
+       }
+       return ret;
+ }
+ static void as_exit_queue(elevator_t *e)
+ {
+       struct as_data *ad = e->elevator_data;
+       del_timer_sync(&ad->antic_timer);
+       kblockd_flush();
+       BUG_ON(!list_empty(&ad->fifo_list[REQ_SYNC]));
+       BUG_ON(!list_empty(&ad->fifo_list[REQ_ASYNC]));
+       mempool_destroy(ad->arq_pool);
+       put_io_context(ad->io_context);
+       kfree(ad->hash);
+       kfree(ad);
+ }
+ /*
+  * initialize elevator private data (as_data), and alloc a arq for
+  * each request on the free lists
+  */
+ static int as_init_queue(request_queue_t *q, elevator_t *e)
+ {
+       struct as_data *ad;
+       int i;
+       if (!arq_pool)
+               return -ENOMEM;
+       ad = kmalloc_node(sizeof(*ad), GFP_KERNEL, q->node);
+       if (!ad)
+               return -ENOMEM;
+       memset(ad, 0, sizeof(*ad));
+       ad->q = q; /* Identify what queue the data belongs to */
+       ad->hash = kmalloc_node(sizeof(struct list_head)*AS_HASH_ENTRIES,
+                               GFP_KERNEL, q->node);
+       if (!ad->hash) {
+               kfree(ad);
+               return -ENOMEM;
+       }
+       ad->arq_pool = mempool_create_node(BLKDEV_MIN_RQ, mempool_alloc_slab,
+                               mempool_free_slab, arq_pool, q->node);
+       if (!ad->arq_pool) {
+               kfree(ad->hash);
+               kfree(ad);
+               return -ENOMEM;
+       }
+       /* anticipatory scheduling helpers */
+       ad->antic_timer.function = as_antic_timeout;
+       ad->antic_timer.data = (unsigned long)q;
+       init_timer(&ad->antic_timer);
+       INIT_WORK(&ad->antic_work, as_work_handler, q);
+       for (i = 0; i < AS_HASH_ENTRIES; i++)
+               INIT_LIST_HEAD(&ad->hash[i]);
+       INIT_LIST_HEAD(&ad->fifo_list[REQ_SYNC]);
+       INIT_LIST_HEAD(&ad->fifo_list[REQ_ASYNC]);
+       ad->sort_list[REQ_SYNC] = RB_ROOT;
+       ad->sort_list[REQ_ASYNC] = RB_ROOT;
+       ad->fifo_expire[REQ_SYNC] = default_read_expire;
+       ad->fifo_expire[REQ_ASYNC] = default_write_expire;
+       ad->antic_expire = default_antic_expire;
+       ad->batch_expire[REQ_SYNC] = default_read_batch_expire;
+       ad->batch_expire[REQ_ASYNC] = default_write_batch_expire;
+       e->elevator_data = ad;
+       ad->current_batch_expires = jiffies + ad->batch_expire[REQ_SYNC];
+       ad->write_batch_count = ad->batch_expire[REQ_ASYNC] / 10;
+       if (ad->write_batch_count < 2)
+               ad->write_batch_count = 2;
+       return 0;
+ }
+ /*
+  * sysfs parts below
+  */
+ struct as_fs_entry {
+       struct attribute attr;
+       ssize_t (*show)(struct as_data *, char *);
+       ssize_t (*store)(struct as_data *, const char *, size_t);
+ };
+ static ssize_t
+ as_var_show(unsigned int var, char *page)
+ {
+       return sprintf(page, "%d\n", var);
+ }
+ static ssize_t
+ as_var_store(unsigned long *var, const char *page, size_t count)
+ {
+       char *p = (char *) page;
+       *var = simple_strtoul(p, &p, 10);
+       return count;
+ }
+ static ssize_t as_est_show(struct as_data *ad, char *page)
+ {
+       int pos = 0;
 -      pos += sprintf(page+pos, "%llu sectors new seek distance\n", (unsigned long long)ad->new_seek_mean);
++      pos += sprintf(page+pos, "%lu %% exit probability\n",
++                              100*ad->exit_prob/256);
++      pos += sprintf(page+pos, "%lu %% probability of exiting without a "
++                              "cooperating process submitting IO\n",
++                              100*ad->exit_no_coop/256);
+       pos += sprintf(page+pos, "%lu ms new thinktime\n", ad->new_ttime_mean);
++      pos += sprintf(page+pos, "%llu sectors new seek distance\n",
++                              (unsigned long long)ad->new_seek_mean);
+       return pos;
+ }
+ #define SHOW_FUNCTION(__FUNC, __VAR)                          \
+ static ssize_t __FUNC(struct as_data *ad, char *page)         \
+ {                                                             \
+       return as_var_show(jiffies_to_msecs((__VAR)), (page));  \
+ }
+ SHOW_FUNCTION(as_readexpire_show, ad->fifo_expire[REQ_SYNC]);
+ SHOW_FUNCTION(as_writeexpire_show, ad->fifo_expire[REQ_ASYNC]);
+ SHOW_FUNCTION(as_anticexpire_show, ad->antic_expire);
+ SHOW_FUNCTION(as_read_batchexpire_show, ad->batch_expire[REQ_SYNC]);
+ SHOW_FUNCTION(as_write_batchexpire_show, ad->batch_expire[REQ_ASYNC]);
+ #undef SHOW_FUNCTION
+ #define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX)                               \
+ static ssize_t __FUNC(struct as_data *ad, const char *page, size_t count)     \
+ {                                                                     \
+       int ret = as_var_store(__PTR, (page), count);           \
+       if (*(__PTR) < (MIN))                                           \
+               *(__PTR) = (MIN);                                       \
+       else if (*(__PTR) > (MAX))                                      \
+               *(__PTR) = (MAX);                                       \
+       *(__PTR) = msecs_to_jiffies(*(__PTR));                          \
+       return ret;                                                     \
+ }
+ STORE_FUNCTION(as_readexpire_store, &ad->fifo_expire[REQ_SYNC], 0, INT_MAX);
+ STORE_FUNCTION(as_writeexpire_store, &ad->fifo_expire[REQ_ASYNC], 0, INT_MAX);
+ STORE_FUNCTION(as_anticexpire_store, &ad->antic_expire, 0, INT_MAX);
+ STORE_FUNCTION(as_read_batchexpire_store,
+                       &ad->batch_expire[REQ_SYNC], 0, INT_MAX);
+ STORE_FUNCTION(as_write_batchexpire_store,
+                       &ad->batch_expire[REQ_ASYNC], 0, INT_MAX);
+ #undef STORE_FUNCTION
+ static struct as_fs_entry as_est_entry = {
+       .attr = {.name = "est_time", .mode = S_IRUGO },
+       .show = as_est_show,
+ };
+ static struct as_fs_entry as_readexpire_entry = {
+       .attr = {.name = "read_expire", .mode = S_IRUGO | S_IWUSR },
+       .show = as_readexpire_show,
+       .store = as_readexpire_store,
+ };
+ static struct as_fs_entry as_writeexpire_entry = {
+       .attr = {.name = "write_expire", .mode = S_IRUGO | S_IWUSR },
+       .show = as_writeexpire_show,
+       .store = as_writeexpire_store,
+ };
+ static struct as_fs_entry as_anticexpire_entry = {
+       .attr = {.name = "antic_expire", .mode = S_IRUGO | S_IWUSR },
+       .show = as_anticexpire_show,
+       .store = as_anticexpire_store,
+ };
+ static struct as_fs_entry as_read_batchexpire_entry = {
+       .attr = {.name = "read_batch_expire", .mode = S_IRUGO | S_IWUSR },
+       .show = as_read_batchexpire_show,
+       .store = as_read_batchexpire_store,
+ };
+ static struct as_fs_entry as_write_batchexpire_entry = {
+       .attr = {.name = "write_batch_expire", .mode = S_IRUGO | S_IWUSR },
+       .show = as_write_batchexpire_show,
+       .store = as_write_batchexpire_store,
+ };
+ static struct attribute *default_attrs[] = {
+       &as_est_entry.attr,
+       &as_readexpire_entry.attr,
+       &as_writeexpire_entry.attr,
+       &as_anticexpire_entry.attr,
+       &as_read_batchexpire_entry.attr,
+       &as_write_batchexpire_entry.attr,
+       NULL,
+ };
+ #define to_as(atr) container_of((atr), struct as_fs_entry, attr)
+ static ssize_t
+ as_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
+ {
+       elevator_t *e = container_of(kobj, elevator_t, kobj);
+       struct as_fs_entry *entry = to_as(attr);
+       if (!entry->show)
+               return -EIO;
+       return entry->show(e->elevator_data, page);
+ }
+ static ssize_t
+ as_attr_store(struct kobject *kobj, struct attribute *attr,
+                   const char *page, size_t length)
+ {
+       elevator_t *e = container_of(kobj, elevator_t, kobj);
+       struct as_fs_entry *entry = to_as(attr);
+       if (!entry->store)
+               return -EIO;
+       return entry->store(e->elevator_data, page, length);
+ }
+ static struct sysfs_ops as_sysfs_ops = {
+       .show   = as_attr_show,
+       .store  = as_attr_store,
+ };
+ static struct kobj_type as_ktype = {
+       .sysfs_ops      = &as_sysfs_ops,
+       .default_attrs  = default_attrs,
+ };
+ static struct elevator_type iosched_as = {
+       .ops = {
+               .elevator_merge_fn =            as_merge,
+               .elevator_merged_fn =           as_merged_request,
+               .elevator_merge_req_fn =        as_merged_requests,
+               .elevator_dispatch_fn =         as_dispatch_request,
+               .elevator_add_req_fn =          as_add_request,
+               .elevator_activate_req_fn =     as_activate_request,
+               .elevator_deactivate_req_fn =   as_deactivate_request,
+               .elevator_queue_empty_fn =      as_queue_empty,
+               .elevator_completed_req_fn =    as_completed_request,
+               .elevator_former_req_fn =       as_former_request,
+               .elevator_latter_req_fn =       as_latter_request,
+               .elevator_set_req_fn =          as_set_request,
+               .elevator_put_req_fn =          as_put_request,
+               .elevator_may_queue_fn =        as_may_queue,
+               .elevator_init_fn =             as_init_queue,
+               .elevator_exit_fn =             as_exit_queue,
+       },
+       .elevator_ktype = &as_ktype,
+       .elevator_name = "anticipatory",
+       .elevator_owner = THIS_MODULE,
+ };
+ static int __init as_init(void)
+ {
+       int ret;
+       arq_pool = kmem_cache_create("as_arq", sizeof(struct as_rq),
+                                    0, 0, NULL, NULL);
+       if (!arq_pool)
+               return -ENOMEM;
+       ret = elv_register(&iosched_as);
+       if (!ret) {
+               /*
+                * don't allow AS to get unregistered, since we would have
+                * to browse all tasks in the system and release their
+                * as_io_context first
+                */
+               __module_get(THIS_MODULE);
+               return 0;
+       }
+       kmem_cache_destroy(arq_pool);
+       return ret;
+ }
+ static void __exit as_exit(void)
+ {
+       elv_unregister(&iosched_as);
+       kmem_cache_destroy(arq_pool);
+ }
+ module_init(as_init);
+ module_exit(as_exit);
+ MODULE_AUTHOR("Nick Piggin");
+ MODULE_LICENSE("GPL");
+ MODULE_DESCRIPTION("anticipatory IO scheduler");
index 0000000000000000000000000000000000000000,2747741677fb0d92c10dc76c272763eb6f2b1a96..5f52e30b43f812c75cef8289571e9a1a35bd2808
mode 000000,100644..100644
--- /dev/null
@@@ -1,0 -1,3613 +1,3612 @@@
 - *
+ /*
+  *  linux/drivers/block/ll_rw_blk.c
+  *
+  * Copyright (C) 1991, 1992 Linus Torvalds
+  * Copyright (C) 1994,      Karl Keyte: Added support for disk statistics
+  * Elevator latency, (C) 2000  Andrea Arcangeli <andrea@suse.de> SuSE
+  * Queue request tables / lock, selectable elevator, Jens Axboe <axboe@suse.de>
+  * kernel-doc documentation started by NeilBrown <neilb@cse.unsw.edu.au> -  July2000
+  * bio rewrite, highmem i/o, etc, Jens Axboe <axboe@suse.de> - may 2001
+  */
+ /*
+  * This handles all read/write requests to block devices
+  */
+ #include <linux/config.h>
+ #include <linux/kernel.h>
+ #include <linux/module.h>
+ #include <linux/backing-dev.h>
+ #include <linux/bio.h>
+ #include <linux/blkdev.h>
+ #include <linux/highmem.h>
+ #include <linux/mm.h>
+ #include <linux/kernel_stat.h>
+ #include <linux/string.h>
+ #include <linux/init.h>
+ #include <linux/bootmem.h>    /* for max_pfn/max_low_pfn */
+ #include <linux/completion.h>
+ #include <linux/slab.h>
+ #include <linux/swap.h>
+ #include <linux/writeback.h>
+ #include <linux/blkdev.h>
+ /*
+  * for max sense size
+  */
+ #include <scsi/scsi_cmnd.h>
+ static void blk_unplug_work(void *data);
+ static void blk_unplug_timeout(unsigned long data);
+ static void drive_stat_acct(struct request *rq, int nr_sectors, int new_io);
+ /*
+  * For the allocated request tables
+  */
+ static kmem_cache_t *request_cachep;
+ /*
+  * For queue allocation
+  */
+ static kmem_cache_t *requestq_cachep;
+ /*
+  * For io context allocations
+  */
+ static kmem_cache_t *iocontext_cachep;
+ static wait_queue_head_t congestion_wqh[2] = {
+               __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[0]),
+               __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[1])
+       };
+ /*
+  * Controlling structure to kblockd
+  */
+ static struct workqueue_struct *kblockd_workqueue; 
+ unsigned long blk_max_low_pfn, blk_max_pfn;
+ EXPORT_SYMBOL(blk_max_low_pfn);
+ EXPORT_SYMBOL(blk_max_pfn);
+ /* Amount of time in which a process may batch requests */
+ #define BLK_BATCH_TIME        (HZ/50UL)
+ /* Number of requests a "batching" process may submit */
+ #define BLK_BATCH_REQ 32
+ /*
+  * Return the threshold (number of used requests) at which the queue is
+  * considered to be congested.  It include a little hysteresis to keep the
+  * context switch rate down.
+  */
+ static inline int queue_congestion_on_threshold(struct request_queue *q)
+ {
+       return q->nr_congestion_on;
+ }
+ /*
+  * The threshold at which a queue is considered to be uncongested
+  */
+ static inline int queue_congestion_off_threshold(struct request_queue *q)
+ {
+       return q->nr_congestion_off;
+ }
+ static void blk_queue_congestion_threshold(struct request_queue *q)
+ {
+       int nr;
+       nr = q->nr_requests - (q->nr_requests / 8) + 1;
+       if (nr > q->nr_requests)
+               nr = q->nr_requests;
+       q->nr_congestion_on = nr;
+       nr = q->nr_requests - (q->nr_requests / 8) - (q->nr_requests / 16) - 1;
+       if (nr < 1)
+               nr = 1;
+       q->nr_congestion_off = nr;
+ }
+ /*
+  * A queue has just exitted congestion.  Note this in the global counter of
+  * congested queues, and wake up anyone who was waiting for requests to be
+  * put back.
+  */
+ static void clear_queue_congested(request_queue_t *q, int rw)
+ {
+       enum bdi_state bit;
+       wait_queue_head_t *wqh = &congestion_wqh[rw];
+       bit = (rw == WRITE) ? BDI_write_congested : BDI_read_congested;
+       clear_bit(bit, &q->backing_dev_info.state);
+       smp_mb__after_clear_bit();
+       if (waitqueue_active(wqh))
+               wake_up(wqh);
+ }
+ /*
+  * A queue has just entered congestion.  Flag that in the queue's VM-visible
+  * state flags and increment the global gounter of congested queues.
+  */
+ static void set_queue_congested(request_queue_t *q, int rw)
+ {
+       enum bdi_state bit;
+       bit = (rw == WRITE) ? BDI_write_congested : BDI_read_congested;
+       set_bit(bit, &q->backing_dev_info.state);
+ }
+ /**
+  * blk_get_backing_dev_info - get the address of a queue's backing_dev_info
+  * @bdev:     device
+  *
+  * Locates the passed device's request queue and returns the address of its
+  * backing_dev_info
+  *
+  * Will return NULL if the request queue cannot be located.
+  */
+ struct backing_dev_info *blk_get_backing_dev_info(struct block_device *bdev)
+ {
+       struct backing_dev_info *ret = NULL;
+       request_queue_t *q = bdev_get_queue(bdev);
+       if (q)
+               ret = &q->backing_dev_info;
+       return ret;
+ }
+ EXPORT_SYMBOL(blk_get_backing_dev_info);
+ void blk_queue_activity_fn(request_queue_t *q, activity_fn *fn, void *data)
+ {
+       q->activity_fn = fn;
+       q->activity_data = data;
+ }
+ EXPORT_SYMBOL(blk_queue_activity_fn);
+ /**
+  * blk_queue_prep_rq - set a prepare_request function for queue
+  * @q:                queue
+  * @pfn:      prepare_request function
+  *
+  * It's possible for a queue to register a prepare_request callback which
+  * is invoked before the request is handed to the request_fn. The goal of
+  * the function is to prepare a request for I/O, it can be used to build a
+  * cdb from the request data for instance.
+  *
+  */
+ void blk_queue_prep_rq(request_queue_t *q, prep_rq_fn *pfn)
+ {
+       q->prep_rq_fn = pfn;
+ }
+ EXPORT_SYMBOL(blk_queue_prep_rq);
+ /**
+  * blk_queue_merge_bvec - set a merge_bvec function for queue
+  * @q:                queue
+  * @mbfn:     merge_bvec_fn
+  *
+  * Usually queues have static limitations on the max sectors or segments that
+  * we can put in a request. Stacking drivers may have some settings that
+  * are dynamic, and thus we have to query the queue whether it is ok to
+  * add a new bio_vec to a bio at a given offset or not. If the block device
+  * has such limitations, it needs to register a merge_bvec_fn to control
+  * the size of bio's sent to it. Note that a block device *must* allow a
+  * single page to be added to an empty bio. The block device driver may want
+  * to use the bio_split() function to deal with these bio's. By default
+  * no merge_bvec_fn is defined for a queue, and only the fixed limits are
+  * honored.
+  */
+ void blk_queue_merge_bvec(request_queue_t *q, merge_bvec_fn *mbfn)
+ {
+       q->merge_bvec_fn = mbfn;
+ }
+ EXPORT_SYMBOL(blk_queue_merge_bvec);
+ /**
+  * blk_queue_make_request - define an alternate make_request function for a device
+  * @q:  the request queue for the device to be affected
+  * @mfn: the alternate make_request function
+  *
+  * Description:
+  *    The normal way for &struct bios to be passed to a device
+  *    driver is for them to be collected into requests on a request
+  *    queue, and then to allow the device driver to select requests
+  *    off that queue when it is ready.  This works well for many block
+  *    devices. However some block devices (typically virtual devices
+  *    such as md or lvm) do not benefit from the processing on the
+  *    request queue, and are served best by having the requests passed
+  *    directly to them.  This can be achieved by providing a function
+  *    to blk_queue_make_request().
+  *
+  * Caveat:
+  *    The driver that does this *must* be able to deal appropriately
+  *    with buffers in "highmemory". This can be accomplished by either calling
+  *    __bio_kmap_atomic() to get a temporary kernel mapping, or by calling
+  *    blk_queue_bounce() to create a buffer in normal memory.
+  **/
+ void blk_queue_make_request(request_queue_t * q, make_request_fn * mfn)
+ {
+       /*
+        * set defaults
+        */
+       q->nr_requests = BLKDEV_MAX_RQ;
+       blk_queue_max_phys_segments(q, MAX_PHYS_SEGMENTS);
+       blk_queue_max_hw_segments(q, MAX_HW_SEGMENTS);
+       q->make_request_fn = mfn;
+       q->backing_dev_info.ra_pages = (VM_MAX_READAHEAD * 1024) / PAGE_CACHE_SIZE;
+       q->backing_dev_info.state = 0;
+       q->backing_dev_info.capabilities = BDI_CAP_MAP_COPY;
+       blk_queue_max_sectors(q, MAX_SECTORS);
+       blk_queue_hardsect_size(q, 512);
+       blk_queue_dma_alignment(q, 511);
+       blk_queue_congestion_threshold(q);
+       q->nr_batching = BLK_BATCH_REQ;
+       q->unplug_thresh = 4;           /* hmm */
+       q->unplug_delay = (3 * HZ) / 1000;      /* 3 milliseconds */
+       if (q->unplug_delay == 0)
+               q->unplug_delay = 1;
+       INIT_WORK(&q->unplug_work, blk_unplug_work, q);
+       q->unplug_timer.function = blk_unplug_timeout;
+       q->unplug_timer.data = (unsigned long)q;
+       /*
+        * by default assume old behaviour and bounce for any highmem page
+        */
+       blk_queue_bounce_limit(q, BLK_BOUNCE_HIGH);
+       blk_queue_activity_fn(q, NULL, NULL);
+ }
+ EXPORT_SYMBOL(blk_queue_make_request);
+ static inline void rq_init(request_queue_t *q, struct request *rq)
+ {
+       INIT_LIST_HEAD(&rq->queuelist);
+       rq->errors = 0;
+       rq->rq_status = RQ_ACTIVE;
+       rq->bio = rq->biotail = NULL;
+       rq->ioprio = 0;
+       rq->buffer = NULL;
+       rq->ref_count = 1;
+       rq->q = q;
+       rq->waiting = NULL;
+       rq->special = NULL;
+       rq->data_len = 0;
+       rq->data = NULL;
+       rq->nr_phys_segments = 0;
+       rq->sense = NULL;
+       rq->end_io = NULL;
+       rq->end_io_data = NULL;
+ }
+ /**
+  * blk_queue_ordered - does this queue support ordered writes
+  * @q:     the request queue
+  * @flag:  see below
+  *
+  * Description:
+  *   For journalled file systems, doing ordered writes on a commit
+  *   block instead of explicitly doing wait_on_buffer (which is bad
+  *   for performance) can be a big win. Block drivers supporting this
+  *   feature should call this function and indicate so.
+  *
+  **/
+ void blk_queue_ordered(request_queue_t *q, int flag)
+ {
+       switch (flag) {
+               case QUEUE_ORDERED_NONE:
+                       if (q->flush_rq)
+                               kmem_cache_free(request_cachep, q->flush_rq);
+                       q->flush_rq = NULL;
+                       q->ordered = flag;
+                       break;
+               case QUEUE_ORDERED_TAG:
+                       q->ordered = flag;
+                       break;
+               case QUEUE_ORDERED_FLUSH:
+                       q->ordered = flag;
+                       if (!q->flush_rq)
+                               q->flush_rq = kmem_cache_alloc(request_cachep,
+                                                               GFP_KERNEL);
+                       break;
+               default:
+                       printk("blk_queue_ordered: bad value %d\n", flag);
+                       break;
+       }
+ }
+ EXPORT_SYMBOL(blk_queue_ordered);
+ /**
+  * blk_queue_issue_flush_fn - set function for issuing a flush
+  * @q:     the request queue
+  * @iff:   the function to be called issuing the flush
+  *
+  * Description:
+  *   If a driver supports issuing a flush command, the support is notified
+  *   to the block layer by defining it through this call.
+  *
+  **/
+ void blk_queue_issue_flush_fn(request_queue_t *q, issue_flush_fn *iff)
+ {
+       q->issue_flush_fn = iff;
+ }
+ EXPORT_SYMBOL(blk_queue_issue_flush_fn);
+ /*
+  * Cache flushing for ordered writes handling
+  */
+ static void blk_pre_flush_end_io(struct request *flush_rq)
+ {
+       struct request *rq = flush_rq->end_io_data;
+       request_queue_t *q = rq->q;
+       elv_completed_request(q, flush_rq);
+       rq->flags |= REQ_BAR_PREFLUSH;
+       if (!flush_rq->errors)
+               elv_requeue_request(q, rq);
+       else {
+               q->end_flush_fn(q, flush_rq);
+               clear_bit(QUEUE_FLAG_FLUSH, &q->queue_flags);
+               q->request_fn(q);
+       }
+ }
+ static void blk_post_flush_end_io(struct request *flush_rq)
+ {
+       struct request *rq = flush_rq->end_io_data;
+       request_queue_t *q = rq->q;
+       elv_completed_request(q, flush_rq);
+       rq->flags |= REQ_BAR_POSTFLUSH;
+       q->end_flush_fn(q, flush_rq);
+       clear_bit(QUEUE_FLAG_FLUSH, &q->queue_flags);
+       q->request_fn(q);
+ }
+ struct request *blk_start_pre_flush(request_queue_t *q, struct request *rq)
+ {
+       struct request *flush_rq = q->flush_rq;
+       BUG_ON(!blk_barrier_rq(rq));
+       if (test_and_set_bit(QUEUE_FLAG_FLUSH, &q->queue_flags))
+               return NULL;
+       rq_init(q, flush_rq);
+       flush_rq->elevator_private = NULL;
+       flush_rq->flags = REQ_BAR_FLUSH;
+       flush_rq->rq_disk = rq->rq_disk;
+       flush_rq->rl = NULL;
+       /*
+        * prepare_flush returns 0 if no flush is needed, just mark both
+        * pre and post flush as done in that case
+        */
+       if (!q->prepare_flush_fn(q, flush_rq)) {
+               rq->flags |= REQ_BAR_PREFLUSH | REQ_BAR_POSTFLUSH;
+               clear_bit(QUEUE_FLAG_FLUSH, &q->queue_flags);
+               return rq;
+       }
+       /*
+        * some drivers dequeue requests right away, some only after io
+        * completion. make sure the request is dequeued.
+        */
+       if (!list_empty(&rq->queuelist))
+               blkdev_dequeue_request(rq);
+       flush_rq->end_io_data = rq;
+       flush_rq->end_io = blk_pre_flush_end_io;
+       __elv_add_request(q, flush_rq, ELEVATOR_INSERT_FRONT, 0);
+       return flush_rq;
+ }
+ static void blk_start_post_flush(request_queue_t *q, struct request *rq)
+ {
+       struct request *flush_rq = q->flush_rq;
+       BUG_ON(!blk_barrier_rq(rq));
+       rq_init(q, flush_rq);
+       flush_rq->elevator_private = NULL;
+       flush_rq->flags = REQ_BAR_FLUSH;
+       flush_rq->rq_disk = rq->rq_disk;
+       flush_rq->rl = NULL;
+       if (q->prepare_flush_fn(q, flush_rq)) {
+               flush_rq->end_io_data = rq;
+               flush_rq->end_io = blk_post_flush_end_io;
+               __elv_add_request(q, flush_rq, ELEVATOR_INSERT_FRONT, 0);
+               q->request_fn(q);
+       }
+ }
+ static inline int blk_check_end_barrier(request_queue_t *q, struct request *rq,
+                                       int sectors)
+ {
+       if (sectors > rq->nr_sectors)
+               sectors = rq->nr_sectors;
+       rq->nr_sectors -= sectors;
+       return rq->nr_sectors;
+ }
+ static int __blk_complete_barrier_rq(request_queue_t *q, struct request *rq,
+                                    int sectors, int queue_locked)
+ {
+       if (q->ordered != QUEUE_ORDERED_FLUSH)
+               return 0;
+       if (!blk_fs_request(rq) || !blk_barrier_rq(rq))
+               return 0;
+       if (blk_barrier_postflush(rq))
+               return 0;
+       if (!blk_check_end_barrier(q, rq, sectors)) {
+               unsigned long flags = 0;
+               if (!queue_locked)
+                       spin_lock_irqsave(q->queue_lock, flags);
+               blk_start_post_flush(q, rq);
+               if (!queue_locked)
+                       spin_unlock_irqrestore(q->queue_lock, flags);
+       }
+       return 1;
+ }
+ /**
+  * blk_complete_barrier_rq - complete possible barrier request
+  * @q:  the request queue for the device
+  * @rq:  the request
+  * @sectors:  number of sectors to complete
+  *
+  * Description:
+  *   Used in driver end_io handling to determine whether to postpone
+  *   completion of a barrier request until a post flush has been done. This
+  *   is the unlocked variant, used if the caller doesn't already hold the
+  *   queue lock.
+  **/
+ int blk_complete_barrier_rq(request_queue_t *q, struct request *rq, int sectors)
+ {
+       return __blk_complete_barrier_rq(q, rq, sectors, 0);
+ }
+ EXPORT_SYMBOL(blk_complete_barrier_rq);
+ /**
+  * blk_complete_barrier_rq_locked - complete possible barrier request
+  * @q:  the request queue for the device
+  * @rq:  the request
+  * @sectors:  number of sectors to complete
+  *
+  * Description:
+  *   See blk_complete_barrier_rq(). This variant must be used if the caller
+  *   holds the queue lock.
+  **/
+ int blk_complete_barrier_rq_locked(request_queue_t *q, struct request *rq,
+                                  int sectors)
+ {
+       return __blk_complete_barrier_rq(q, rq, sectors, 1);
+ }
+ EXPORT_SYMBOL(blk_complete_barrier_rq_locked);
+ /**
+  * blk_queue_bounce_limit - set bounce buffer limit for queue
+  * @q:  the request queue for the device
+  * @dma_addr:   bus address limit
+  *
+  * Description:
+  *    Different hardware can have different requirements as to what pages
+  *    it can do I/O directly to. A low level driver can call
+  *    blk_queue_bounce_limit to have lower memory pages allocated as bounce
+  *    buffers for doing I/O to pages residing above @page. By default
+  *    the block layer sets this to the highest numbered "low" memory page.
+  **/
+ void blk_queue_bounce_limit(request_queue_t *q, u64 dma_addr)
+ {
+       unsigned long bounce_pfn = dma_addr >> PAGE_SHIFT;
+       /*
+        * set appropriate bounce gfp mask -- unfortunately we don't have a
+        * full 4GB zone, so we have to resort to low memory for any bounces.
+        * ISA has its own < 16MB zone.
+        */
+       if (bounce_pfn < blk_max_low_pfn) {
+               BUG_ON(dma_addr < BLK_BOUNCE_ISA);
+               init_emergency_isa_pool();
+               q->bounce_gfp = GFP_NOIO | GFP_DMA;
+       } else
+               q->bounce_gfp = GFP_NOIO;
+       q->bounce_pfn = bounce_pfn;
+ }
+ EXPORT_SYMBOL(blk_queue_bounce_limit);
+ /**
+  * blk_queue_max_sectors - set max sectors for a request for this queue
+  * @q:  the request queue for the device
+  * @max_sectors:  max sectors in the usual 512b unit
+  *
+  * Description:
+  *    Enables a low level driver to set an upper limit on the size of
+  *    received requests.
+  **/
+ void blk_queue_max_sectors(request_queue_t *q, unsigned short max_sectors)
+ {
+       if ((max_sectors << 9) < PAGE_CACHE_SIZE) {
+               max_sectors = 1 << (PAGE_CACHE_SHIFT - 9);
+               printk("%s: set to minimum %d\n", __FUNCTION__, max_sectors);
+       }
+       q->max_sectors = q->max_hw_sectors = max_sectors;
+ }
+ EXPORT_SYMBOL(blk_queue_max_sectors);
+ /**
+  * blk_queue_max_phys_segments - set max phys segments for a request for this queue
+  * @q:  the request queue for the device
+  * @max_segments:  max number of segments
+  *
+  * Description:
+  *    Enables a low level driver to set an upper limit on the number of
+  *    physical data segments in a request.  This would be the largest sized
+  *    scatter list the driver could handle.
+  **/
+ void blk_queue_max_phys_segments(request_queue_t *q, unsigned short max_segments)
+ {
+       if (!max_segments) {
+               max_segments = 1;
+               printk("%s: set to minimum %d\n", __FUNCTION__, max_segments);
+       }
+       q->max_phys_segments = max_segments;
+ }
+ EXPORT_SYMBOL(blk_queue_max_phys_segments);
+ /**
+  * blk_queue_max_hw_segments - set max hw segments for a request for this queue
+  * @q:  the request queue for the device
+  * @max_segments:  max number of segments
+  *
+  * Description:
+  *    Enables a low level driver to set an upper limit on the number of
+  *    hw data segments in a request.  This would be the largest number of
+  *    address/length pairs the host adapter can actually give as once
+  *    to the device.
+  **/
+ void blk_queue_max_hw_segments(request_queue_t *q, unsigned short max_segments)
+ {
+       if (!max_segments) {
+               max_segments = 1;
+               printk("%s: set to minimum %d\n", __FUNCTION__, max_segments);
+       }
+       q->max_hw_segments = max_segments;
+ }
+ EXPORT_SYMBOL(blk_queue_max_hw_segments);
+ /**
+  * blk_queue_max_segment_size - set max segment size for blk_rq_map_sg
+  * @q:  the request queue for the device
+  * @max_size:  max size of segment in bytes
+  *
+  * Description:
+  *    Enables a low level driver to set an upper limit on the size of a
+  *    coalesced segment
+  **/
+ void blk_queue_max_segment_size(request_queue_t *q, unsigned int max_size)
+ {
+       if (max_size < PAGE_CACHE_SIZE) {
+               max_size = PAGE_CACHE_SIZE;
+               printk("%s: set to minimum %d\n", __FUNCTION__, max_size);
+       }
+       q->max_segment_size = max_size;
+ }
+ EXPORT_SYMBOL(blk_queue_max_segment_size);
+ /**
+  * blk_queue_hardsect_size - set hardware sector size for the queue
+  * @q:  the request queue for the device
+  * @size:  the hardware sector size, in bytes
+  *
+  * Description:
+  *   This should typically be set to the lowest possible sector size
+  *   that the hardware can operate on (possible without reverting to
+  *   even internal read-modify-write operations). Usually the default
+  *   of 512 covers most hardware.
+  **/
+ void blk_queue_hardsect_size(request_queue_t *q, unsigned short size)
+ {
+       q->hardsect_size = size;
+ }
+ EXPORT_SYMBOL(blk_queue_hardsect_size);
+ /*
+  * Returns the minimum that is _not_ zero, unless both are zero.
+  */
+ #define min_not_zero(l, r) (l == 0) ? r : ((r == 0) ? l : min(l, r))
+ /**
+  * blk_queue_stack_limits - inherit underlying queue limits for stacked drivers
+  * @t:        the stacking driver (top)
+  * @b:  the underlying device (bottom)
+  **/
+ void blk_queue_stack_limits(request_queue_t *t, request_queue_t *b)
+ {
+       /* zero is "infinity" */
+       t->max_sectors = t->max_hw_sectors =
+               min_not_zero(t->max_sectors,b->max_sectors);
+       t->max_phys_segments = min(t->max_phys_segments,b->max_phys_segments);
+       t->max_hw_segments = min(t->max_hw_segments,b->max_hw_segments);
+       t->max_segment_size = min(t->max_segment_size,b->max_segment_size);
+       t->hardsect_size = max(t->hardsect_size,b->hardsect_size);
+ }
+ EXPORT_SYMBOL(blk_queue_stack_limits);
+ /**
+  * blk_queue_segment_boundary - set boundary rules for segment merging
+  * @q:  the request queue for the device
+  * @mask:  the memory boundary mask
+  **/
+ void blk_queue_segment_boundary(request_queue_t *q, unsigned long mask)
+ {
+       if (mask < PAGE_CACHE_SIZE - 1) {
+               mask = PAGE_CACHE_SIZE - 1;
+               printk("%s: set to minimum %lx\n", __FUNCTION__, mask);
+       }
+       q->seg_boundary_mask = mask;
+ }
+ EXPORT_SYMBOL(blk_queue_segment_boundary);
+ /**
+  * blk_queue_dma_alignment - set dma length and memory alignment
+  * @q:     the request queue for the device
+  * @mask:  alignment mask
+  *
+  * description:
+  *    set required memory and length aligment for direct dma transactions.
+  *    this is used when buiding direct io requests for the queue.
+  *
+  **/
+ void blk_queue_dma_alignment(request_queue_t *q, int mask)
+ {
+       q->dma_alignment = mask;
+ }
+ EXPORT_SYMBOL(blk_queue_dma_alignment);
+ /**
+  * blk_queue_find_tag - find a request by its tag and queue
+  * @q:         The request queue for the device
+  * @tag: The tag of the request
+  *
+  * Notes:
+  *    Should be used when a device returns a tag and you want to match
+  *    it with a request.
+  *
+  *    no locks need be held.
+  **/
+ struct request *blk_queue_find_tag(request_queue_t *q, int tag)
+ {
+       struct blk_queue_tag *bqt = q->queue_tags;
+       if (unlikely(bqt == NULL || tag >= bqt->real_max_depth))
+               return NULL;
+       return bqt->tag_index[tag];
+ }
+ EXPORT_SYMBOL(blk_queue_find_tag);
+ /**
+  * __blk_queue_free_tags - release tag maintenance info
+  * @q:  the request queue for the device
+  *
+  *  Notes:
+  *    blk_cleanup_queue() will take care of calling this function, if tagging
+  *    has been used. So there's no need to call this directly.
+  **/
+ static void __blk_queue_free_tags(request_queue_t *q)
+ {
+       struct blk_queue_tag *bqt = q->queue_tags;
+       if (!bqt)
+               return;
+       if (atomic_dec_and_test(&bqt->refcnt)) {
+               BUG_ON(bqt->busy);
+               BUG_ON(!list_empty(&bqt->busy_list));
+               kfree(bqt->tag_index);
+               bqt->tag_index = NULL;
+               kfree(bqt->tag_map);
+               bqt->tag_map = NULL;
+               kfree(bqt);
+       }
+       q->queue_tags = NULL;
+       q->queue_flags &= ~(1 << QUEUE_FLAG_QUEUED);
+ }
+ /**
+  * blk_queue_free_tags - release tag maintenance info
+  * @q:  the request queue for the device
+  *
+  *  Notes:
+  *    This is used to disabled tagged queuing to a device, yet leave
+  *    queue in function.
+  **/
+ void blk_queue_free_tags(request_queue_t *q)
+ {
+       clear_bit(QUEUE_FLAG_QUEUED, &q->queue_flags);
+ }
+ EXPORT_SYMBOL(blk_queue_free_tags);
+ static int
+ init_tag_map(request_queue_t *q, struct blk_queue_tag *tags, int depth)
+ {
+       struct request **tag_index;
+       unsigned long *tag_map;
+       int nr_ulongs;
+       if (depth > q->nr_requests * 2) {
+               depth = q->nr_requests * 2;
+               printk(KERN_ERR "%s: adjusted depth to %d\n",
+                               __FUNCTION__, depth);
+       }
+       tag_index = kmalloc(depth * sizeof(struct request *), GFP_ATOMIC);
+       if (!tag_index)
+               goto fail;
+       nr_ulongs = ALIGN(depth, BITS_PER_LONG) / BITS_PER_LONG;
+       tag_map = kmalloc(nr_ulongs * sizeof(unsigned long), GFP_ATOMIC);
+       if (!tag_map)
+               goto fail;
+       memset(tag_index, 0, depth * sizeof(struct request *));
+       memset(tag_map, 0, nr_ulongs * sizeof(unsigned long));
+       tags->real_max_depth = depth;
+       tags->max_depth = depth;
+       tags->tag_index = tag_index;
+       tags->tag_map = tag_map;
+       return 0;
+ fail:
+       kfree(tag_index);
+       return -ENOMEM;
+ }
+ /**
+  * blk_queue_init_tags - initialize the queue tag info
+  * @q:  the request queue for the device
+  * @depth:  the maximum queue depth supported
+  * @tags: the tag to use
+  **/
+ int blk_queue_init_tags(request_queue_t *q, int depth,
+                       struct blk_queue_tag *tags)
+ {
+       int rc;
+       BUG_ON(tags && q->queue_tags && tags != q->queue_tags);
+       if (!tags && !q->queue_tags) {
+               tags = kmalloc(sizeof(struct blk_queue_tag), GFP_ATOMIC);
+               if (!tags)
+                       goto fail;
+               if (init_tag_map(q, tags, depth))
+                       goto fail;
+               INIT_LIST_HEAD(&tags->busy_list);
+               tags->busy = 0;
+               atomic_set(&tags->refcnt, 1);
+       } else if (q->queue_tags) {
+               if ((rc = blk_queue_resize_tags(q, depth)))
+                       return rc;
+               set_bit(QUEUE_FLAG_QUEUED, &q->queue_flags);
+               return 0;
+       } else
+               atomic_inc(&tags->refcnt);
+       /*
+        * assign it, all done
+        */
+       q->queue_tags = tags;
+       q->queue_flags |= (1 << QUEUE_FLAG_QUEUED);
+       return 0;
+ fail:
+       kfree(tags);
+       return -ENOMEM;
+ }
+ EXPORT_SYMBOL(blk_queue_init_tags);
+ /**
+  * blk_queue_resize_tags - change the queueing depth
+  * @q:  the request queue for the device
+  * @new_depth: the new max command queueing depth
+  *
+  *  Notes:
+  *    Must be called with the queue lock held.
+  **/
+ int blk_queue_resize_tags(request_queue_t *q, int new_depth)
+ {
+       struct blk_queue_tag *bqt = q->queue_tags;
+       struct request **tag_index;
+       unsigned long *tag_map;
+       int max_depth, nr_ulongs;
+       if (!bqt)
+               return -ENXIO;
+       /*
+        * if we already have large enough real_max_depth.  just
+        * adjust max_depth.  *NOTE* as requests with tag value
+        * between new_depth and real_max_depth can be in-flight, tag
+        * map can not be shrunk blindly here.
+        */
+       if (new_depth <= bqt->real_max_depth) {
+               bqt->max_depth = new_depth;
+               return 0;
+       }
+       /*
+        * save the old state info, so we can copy it back
+        */
+       tag_index = bqt->tag_index;
+       tag_map = bqt->tag_map;
+       max_depth = bqt->real_max_depth;
+       if (init_tag_map(q, bqt, new_depth))
+               return -ENOMEM;
+       memcpy(bqt->tag_index, tag_index, max_depth * sizeof(struct request *));
+       nr_ulongs = ALIGN(max_depth, BITS_PER_LONG) / BITS_PER_LONG;
+       memcpy(bqt->tag_map, tag_map, nr_ulongs * sizeof(unsigned long));
+       kfree(tag_index);
+       kfree(tag_map);
+       return 0;
+ }
+ EXPORT_SYMBOL(blk_queue_resize_tags);
+ /**
+  * blk_queue_end_tag - end tag operations for a request
+  * @q:  the request queue for the device
+  * @rq: the request that has completed
+  *
+  *  Description:
+  *    Typically called when end_that_request_first() returns 0, meaning
+  *    all transfers have been done for a request. It's important to call
+  *    this function before end_that_request_last(), as that will put the
+  *    request back on the free list thus corrupting the internal tag list.
+  *
+  *  Notes:
+  *   queue lock must be held.
+  **/
+ void blk_queue_end_tag(request_queue_t *q, struct request *rq)
+ {
+       struct blk_queue_tag *bqt = q->queue_tags;
+       int tag = rq->tag;
+       BUG_ON(tag == -1);
+       if (unlikely(tag >= bqt->real_max_depth))
+               /*
+                * This can happen after tag depth has been reduced.
+                * FIXME: how about a warning or info message here?
+                */
+               return;
+       if (unlikely(!__test_and_clear_bit(tag, bqt->tag_map))) {
+               printk(KERN_ERR "%s: attempt to clear non-busy tag (%d)\n",
+                      __FUNCTION__, tag);
+               return;
+       }
+       list_del_init(&rq->queuelist);
+       rq->flags &= ~REQ_QUEUED;
+       rq->tag = -1;
+       if (unlikely(bqt->tag_index[tag] == NULL))
+               printk(KERN_ERR "%s: tag %d is missing\n",
+                      __FUNCTION__, tag);
+       bqt->tag_index[tag] = NULL;
+       bqt->busy--;
+ }
+ EXPORT_SYMBOL(blk_queue_end_tag);
+ /**
+  * blk_queue_start_tag - find a free tag and assign it
+  * @q:  the request queue for the device
+  * @rq:  the block request that needs tagging
+  *
+  *  Description:
+  *    This can either be used as a stand-alone helper, or possibly be
+  *    assigned as the queue &prep_rq_fn (in which case &struct request
+  *    automagically gets a tag assigned). Note that this function
+  *    assumes that any type of request can be queued! if this is not
+  *    true for your device, you must check the request type before
+  *    calling this function.  The request will also be removed from
+  *    the request queue, so it's the drivers responsibility to readd
+  *    it if it should need to be restarted for some reason.
+  *
+  *  Notes:
+  *   queue lock must be held.
+  **/
+ int blk_queue_start_tag(request_queue_t *q, struct request *rq)
+ {
+       struct blk_queue_tag *bqt = q->queue_tags;
+       int tag;
+       if (unlikely((rq->flags & REQ_QUEUED))) {
+               printk(KERN_ERR 
+                      "%s: request %p for device [%s] already tagged %d",
+                      __FUNCTION__, rq,
+                      rq->rq_disk ? rq->rq_disk->disk_name : "?", rq->tag);
+               BUG();
+       }
+       tag = find_first_zero_bit(bqt->tag_map, bqt->max_depth);
+       if (tag >= bqt->max_depth)
+               return 1;
+       __set_bit(tag, bqt->tag_map);
+       rq->flags |= REQ_QUEUED;
+       rq->tag = tag;
+       bqt->tag_index[tag] = rq;
+       blkdev_dequeue_request(rq);
+       list_add(&rq->queuelist, &bqt->busy_list);
+       bqt->busy++;
+       return 0;
+ }
+ EXPORT_SYMBOL(blk_queue_start_tag);
+ /**
+  * blk_queue_invalidate_tags - invalidate all pending tags
+  * @q:  the request queue for the device
+  *
+  *  Description:
+  *   Hardware conditions may dictate a need to stop all pending requests.
+  *   In this case, we will safely clear the block side of the tag queue and
+  *   readd all requests to the request queue in the right order.
+  *
+  *  Notes:
+  *   queue lock must be held.
+  **/
+ void blk_queue_invalidate_tags(request_queue_t *q)
+ {
+       struct blk_queue_tag *bqt = q->queue_tags;
+       struct list_head *tmp, *n;
+       struct request *rq;
+       list_for_each_safe(tmp, n, &bqt->busy_list) {
+               rq = list_entry_rq(tmp);
+               if (rq->tag == -1) {
+                       printk(KERN_ERR
+                              "%s: bad tag found on list\n", __FUNCTION__);
+                       list_del_init(&rq->queuelist);
+                       rq->flags &= ~REQ_QUEUED;
+               } else
+                       blk_queue_end_tag(q, rq);
+               rq->flags &= ~REQ_STARTED;
+               __elv_add_request(q, rq, ELEVATOR_INSERT_BACK, 0);
+       }
+ }
+ EXPORT_SYMBOL(blk_queue_invalidate_tags);
+ static char *rq_flags[] = {
+       "REQ_RW",
+       "REQ_FAILFAST",
+       "REQ_SORTED",
+       "REQ_SOFTBARRIER",
+       "REQ_HARDBARRIER",
+       "REQ_CMD",
+       "REQ_NOMERGE",
+       "REQ_STARTED",
+       "REQ_DONTPREP",
+       "REQ_QUEUED",
+       "REQ_ELVPRIV",
+       "REQ_PC",
+       "REQ_BLOCK_PC",
+       "REQ_SENSE",
+       "REQ_FAILED",
+       "REQ_QUIET",
+       "REQ_SPECIAL",
+       "REQ_DRIVE_CMD",
+       "REQ_DRIVE_TASK",
+       "REQ_DRIVE_TASKFILE",
+       "REQ_PREEMPT",
+       "REQ_PM_SUSPEND",
+       "REQ_PM_RESUME",
+       "REQ_PM_SHUTDOWN",
+ };
+ void blk_dump_rq_flags(struct request *rq, char *msg)
+ {
+       int bit;
+       printk("%s: dev %s: flags = ", msg,
+               rq->rq_disk ? rq->rq_disk->disk_name : "?");
+       bit = 0;
+       do {
+               if (rq->flags & (1 << bit))
+                       printk("%s ", rq_flags[bit]);
+               bit++;
+       } while (bit < __REQ_NR_BITS);
+       printk("\nsector %llu, nr/cnr %lu/%u\n", (unsigned long long)rq->sector,
+                                                      rq->nr_sectors,
+                                                      rq->current_nr_sectors);
+       printk("bio %p, biotail %p, buffer %p, data %p, len %u\n", rq->bio, rq->biotail, rq->buffer, rq->data, rq->data_len);
+       if (rq->flags & (REQ_BLOCK_PC | REQ_PC)) {
+               printk("cdb: ");
+               for (bit = 0; bit < sizeof(rq->cmd); bit++)
+                       printk("%02x ", rq->cmd[bit]);
+               printk("\n");
+       }
+ }
+ EXPORT_SYMBOL(blk_dump_rq_flags);
+ void blk_recount_segments(request_queue_t *q, struct bio *bio)
+ {
+       struct bio_vec *bv, *bvprv = NULL;
+       int i, nr_phys_segs, nr_hw_segs, seg_size, hw_seg_size, cluster;
+       int high, highprv = 1;
+       if (unlikely(!bio->bi_io_vec))
+               return;
+       cluster = q->queue_flags & (1 << QUEUE_FLAG_CLUSTER);
+       hw_seg_size = seg_size = nr_phys_segs = nr_hw_segs = 0;
+       bio_for_each_segment(bv, bio, i) {
+               /*
+                * the trick here is making sure that a high page is never
+                * considered part of another segment, since that might
+                * change with the bounce page.
+                */
+               high = page_to_pfn(bv->bv_page) >= q->bounce_pfn;
+               if (high || highprv)
+                       goto new_hw_segment;
+               if (cluster) {
+                       if (seg_size + bv->bv_len > q->max_segment_size)
+                               goto new_segment;
+                       if (!BIOVEC_PHYS_MERGEABLE(bvprv, bv))
+                               goto new_segment;
+                       if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bv))
+                               goto new_segment;
+                       if (BIOVEC_VIRT_OVERSIZE(hw_seg_size + bv->bv_len))
+                               goto new_hw_segment;
+                       seg_size += bv->bv_len;
+                       hw_seg_size += bv->bv_len;
+                       bvprv = bv;
+                       continue;
+               }
+ new_segment:
+               if (BIOVEC_VIRT_MERGEABLE(bvprv, bv) &&
+                   !BIOVEC_VIRT_OVERSIZE(hw_seg_size + bv->bv_len)) {
+                       hw_seg_size += bv->bv_len;
+               } else {
+ new_hw_segment:
+                       if (hw_seg_size > bio->bi_hw_front_size)
+                               bio->bi_hw_front_size = hw_seg_size;
+                       hw_seg_size = BIOVEC_VIRT_START_SIZE(bv) + bv->bv_len;
+                       nr_hw_segs++;
+               }
+               nr_phys_segs++;
+               bvprv = bv;
+               seg_size = bv->bv_len;
+               highprv = high;
+       }
+       if (hw_seg_size > bio->bi_hw_back_size)
+               bio->bi_hw_back_size = hw_seg_size;
+       if (nr_hw_segs == 1 && hw_seg_size > bio->bi_hw_front_size)
+               bio->bi_hw_front_size = hw_seg_size;
+       bio->bi_phys_segments = nr_phys_segs;
+       bio->bi_hw_segments = nr_hw_segs;
+       bio->bi_flags |= (1 << BIO_SEG_VALID);
+ }
+ static int blk_phys_contig_segment(request_queue_t *q, struct bio *bio,
+                                  struct bio *nxt)
+ {
+       if (!(q->queue_flags & (1 << QUEUE_FLAG_CLUSTER)))
+               return 0;
+       if (!BIOVEC_PHYS_MERGEABLE(__BVEC_END(bio), __BVEC_START(nxt)))
+               return 0;
+       if (bio->bi_size + nxt->bi_size > q->max_segment_size)
+               return 0;
+       /*
+        * bio and nxt are contigous in memory, check if the queue allows
+        * these two to be merged into one
+        */
+       if (BIO_SEG_BOUNDARY(q, bio, nxt))
+               return 1;
+       return 0;
+ }
+ static int blk_hw_contig_segment(request_queue_t *q, struct bio *bio,
+                                struct bio *nxt)
+ {
+       if (unlikely(!bio_flagged(bio, BIO_SEG_VALID)))
+               blk_recount_segments(q, bio);
+       if (unlikely(!bio_flagged(nxt, BIO_SEG_VALID)))
+               blk_recount_segments(q, nxt);
+       if (!BIOVEC_VIRT_MERGEABLE(__BVEC_END(bio), __BVEC_START(nxt)) ||
+           BIOVEC_VIRT_OVERSIZE(bio->bi_hw_front_size + bio->bi_hw_back_size))
+               return 0;
+       if (bio->bi_size + nxt->bi_size > q->max_segment_size)
+               return 0;
+       return 1;
+ }
+ /*
+  * map a request to scatterlist, return number of sg entries setup. Caller
+  * must make sure sg can hold rq->nr_phys_segments entries
+  */
+ int blk_rq_map_sg(request_queue_t *q, struct request *rq, struct scatterlist *sg)
+ {
+       struct bio_vec *bvec, *bvprv;
+       struct bio *bio;
+       int nsegs, i, cluster;
+       nsegs = 0;
+       cluster = q->queue_flags & (1 << QUEUE_FLAG_CLUSTER);
+       /*
+        * for each bio in rq
+        */
+       bvprv = NULL;
+       rq_for_each_bio(bio, rq) {
+               /*
+                * for each segment in bio
+                */
+               bio_for_each_segment(bvec, bio, i) {
+                       int nbytes = bvec->bv_len;
+                       if (bvprv && cluster) {
+                               if (sg[nsegs - 1].length + nbytes > q->max_segment_size)
+                                       goto new_segment;
+                               if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec))
+                                       goto new_segment;
+                               if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec))
+                                       goto new_segment;
+                               sg[nsegs - 1].length += nbytes;
+                       } else {
+ new_segment:
+                               memset(&sg[nsegs],0,sizeof(struct scatterlist));
+                               sg[nsegs].page = bvec->bv_page;
+                               sg[nsegs].length = nbytes;
+                               sg[nsegs].offset = bvec->bv_offset;
+                               nsegs++;
+                       }
+                       bvprv = bvec;
+               } /* segments in bio */
+       } /* bios in rq */
+       return nsegs;
+ }
+ EXPORT_SYMBOL(blk_rq_map_sg);
+ /*
+  * the standard queue merge functions, can be overridden with device
+  * specific ones if so desired
+  */
+ static inline int ll_new_mergeable(request_queue_t *q,
+                                  struct request *req,
+                                  struct bio *bio)
+ {
+       int nr_phys_segs = bio_phys_segments(q, bio);
+       if (req->nr_phys_segments + nr_phys_segs > q->max_phys_segments) {
+               req->flags |= REQ_NOMERGE;
+               if (req == q->last_merge)
+                       q->last_merge = NULL;
+               return 0;
+       }
+       /*
+        * A hw segment is just getting larger, bump just the phys
+        * counter.
+        */
+       req->nr_phys_segments += nr_phys_segs;
+       return 1;
+ }
+ static inline int ll_new_hw_segment(request_queue_t *q,
+                                   struct request *req,
+                                   struct bio *bio)
+ {
+       int nr_hw_segs = bio_hw_segments(q, bio);
+       int nr_phys_segs = bio_phys_segments(q, bio);
+       if (req->nr_hw_segments + nr_hw_segs > q->max_hw_segments
+           || req->nr_phys_segments + nr_phys_segs > q->max_phys_segments) {
+               req->flags |= REQ_NOMERGE;
+               if (req == q->last_merge)
+                       q->last_merge = NULL;
+               return 0;
+       }
+       /*
+        * This will form the start of a new hw segment.  Bump both
+        * counters.
+        */
+       req->nr_hw_segments += nr_hw_segs;
+       req->nr_phys_segments += nr_phys_segs;
+       return 1;
+ }
+ static int ll_back_merge_fn(request_queue_t *q, struct request *req, 
+                           struct bio *bio)
+ {
+       int len;
+       if (req->nr_sectors + bio_sectors(bio) > q->max_sectors) {
+               req->flags |= REQ_NOMERGE;
+               if (req == q->last_merge)
+                       q->last_merge = NULL;
+               return 0;
+       }
+       if (unlikely(!bio_flagged(req->biotail, BIO_SEG_VALID)))
+               blk_recount_segments(q, req->biotail);
+       if (unlikely(!bio_flagged(bio, BIO_SEG_VALID)))
+               blk_recount_segments(q, bio);
+       len = req->biotail->bi_hw_back_size + bio->bi_hw_front_size;
+       if (BIOVEC_VIRT_MERGEABLE(__BVEC_END(req->biotail), __BVEC_START(bio)) &&
+           !BIOVEC_VIRT_OVERSIZE(len)) {
+               int mergeable =  ll_new_mergeable(q, req, bio);
+               if (mergeable) {
+                       if (req->nr_hw_segments == 1)
+                               req->bio->bi_hw_front_size = len;
+                       if (bio->bi_hw_segments == 1)
+                               bio->bi_hw_back_size = len;
+               }
+               return mergeable;
+       }
+       return ll_new_hw_segment(q, req, bio);
+ }
+ static int ll_front_merge_fn(request_queue_t *q, struct request *req, 
+                            struct bio *bio)
+ {
+       int len;
+       if (req->nr_sectors + bio_sectors(bio) > q->max_sectors) {
+               req->flags |= REQ_NOMERGE;
+               if (req == q->last_merge)
+                       q->last_merge = NULL;
+               return 0;
+       }
+       len = bio->bi_hw_back_size + req->bio->bi_hw_front_size;
+       if (unlikely(!bio_flagged(bio, BIO_SEG_VALID)))
+               blk_recount_segments(q, bio);
+       if (unlikely(!bio_flagged(req->bio, BIO_SEG_VALID)))
+               blk_recount_segments(q, req->bio);
+       if (BIOVEC_VIRT_MERGEABLE(__BVEC_END(bio), __BVEC_START(req->bio)) &&
+           !BIOVEC_VIRT_OVERSIZE(len)) {
+               int mergeable =  ll_new_mergeable(q, req, bio);
+               if (mergeable) {
+                       if (bio->bi_hw_segments == 1)
+                               bio->bi_hw_front_size = len;
+                       if (req->nr_hw_segments == 1)
+                               req->biotail->bi_hw_back_size = len;
+               }
+               return mergeable;
+       }
+       return ll_new_hw_segment(q, req, bio);
+ }
+ static int ll_merge_requests_fn(request_queue_t *q, struct request *req,
+                               struct request *next)
+ {
+       int total_phys_segments;
+       int total_hw_segments;
+       /*
+        * First check if the either of the requests are re-queued
+        * requests.  Can't merge them if they are.
+        */
+       if (req->special || next->special)
+               return 0;
+       /*
+        * Will it become too large?
+        */
+       if ((req->nr_sectors + next->nr_sectors) > q->max_sectors)
+               return 0;
+       total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
+       if (blk_phys_contig_segment(q, req->biotail, next->bio))
+               total_phys_segments--;
+       if (total_phys_segments > q->max_phys_segments)
+               return 0;
+       total_hw_segments = req->nr_hw_segments + next->nr_hw_segments;
+       if (blk_hw_contig_segment(q, req->biotail, next->bio)) {
+               int len = req->biotail->bi_hw_back_size + next->bio->bi_hw_front_size;
+               /*
+                * propagate the combined length to the end of the requests
+                */
+               if (req->nr_hw_segments == 1)
+                       req->bio->bi_hw_front_size = len;
+               if (next->nr_hw_segments == 1)
+                       next->biotail->bi_hw_back_size = len;
+               total_hw_segments--;
+       }
+       if (total_hw_segments > q->max_hw_segments)
+               return 0;
+       /* Merge is OK... */
+       req->nr_phys_segments = total_phys_segments;
+       req->nr_hw_segments = total_hw_segments;
+       return 1;
+ }
+ /*
+  * "plug" the device if there are no outstanding requests: this will
+  * force the transfer to start only after we have put all the requests
+  * on the list.
+  *
+  * This is called with interrupts off and no requests on the queue and
+  * with the queue lock held.
+  */
+ void blk_plug_device(request_queue_t *q)
+ {
+       WARN_ON(!irqs_disabled());
+       /*
+        * don't plug a stopped queue, it must be paired with blk_start_queue()
+        * which will restart the queueing
+        */
+       if (test_bit(QUEUE_FLAG_STOPPED, &q->queue_flags))
+               return;
+       if (!test_and_set_bit(QUEUE_FLAG_PLUGGED, &q->queue_flags))
+               mod_timer(&q->unplug_timer, jiffies + q->unplug_delay);
+ }
+ EXPORT_SYMBOL(blk_plug_device);
+ /*
+  * remove the queue from the plugged list, if present. called with
+  * queue lock held and interrupts disabled.
+  */
+ int blk_remove_plug(request_queue_t *q)
+ {
+       WARN_ON(!irqs_disabled());
+       if (!test_and_clear_bit(QUEUE_FLAG_PLUGGED, &q->queue_flags))
+               return 0;
+       del_timer(&q->unplug_timer);
+       return 1;
+ }
+ EXPORT_SYMBOL(blk_remove_plug);
+ /*
+  * remove the plug and let it rip..
+  */
+ void __generic_unplug_device(request_queue_t *q)
+ {
+       if (unlikely(test_bit(QUEUE_FLAG_STOPPED, &q->queue_flags)))
+               return;
+       if (!blk_remove_plug(q))
+               return;
+       q->request_fn(q);
+ }
+ EXPORT_SYMBOL(__generic_unplug_device);
+ /**
+  * generic_unplug_device - fire a request queue
+  * @q:    The &request_queue_t in question
+  *
+  * Description:
+  *   Linux uses plugging to build bigger requests queues before letting
+  *   the device have at them. If a queue is plugged, the I/O scheduler
+  *   is still adding and merging requests on the queue. Once the queue
+  *   gets unplugged, the request_fn defined for the queue is invoked and
+  *   transfers started.
+  **/
+ void generic_unplug_device(request_queue_t *q)
+ {
+       spin_lock_irq(q->queue_lock);
+       __generic_unplug_device(q);
+       spin_unlock_irq(q->queue_lock);
+ }
+ EXPORT_SYMBOL(generic_unplug_device);
+ static void blk_backing_dev_unplug(struct backing_dev_info *bdi,
+                                  struct page *page)
+ {
+       request_queue_t *q = bdi->unplug_io_data;
+       /*
+        * devices don't necessarily have an ->unplug_fn defined
+        */
+       if (q->unplug_fn)
+               q->unplug_fn(q);
+ }
+ static void blk_unplug_work(void *data)
+ {
+       request_queue_t *q = data;
+       q->unplug_fn(q);
+ }
+ static void blk_unplug_timeout(unsigned long data)
+ {
+       request_queue_t *q = (request_queue_t *)data;
+       kblockd_schedule_work(&q->unplug_work);
+ }
+ /**
+  * blk_start_queue - restart a previously stopped queue
+  * @q:    The &request_queue_t in question
+  *
+  * Description:
+  *   blk_start_queue() will clear the stop flag on the queue, and call
+  *   the request_fn for the queue if it was in a stopped state when
+  *   entered. Also see blk_stop_queue(). Queue lock must be held.
+  **/
+ void blk_start_queue(request_queue_t *q)
+ {
+       clear_bit(QUEUE_FLAG_STOPPED, &q->queue_flags);
+       /*
+        * one level of recursion is ok and is much faster than kicking
+        * the unplug handling
+        */
+       if (!test_and_set_bit(QUEUE_FLAG_REENTER, &q->queue_flags)) {
+               q->request_fn(q);
+               clear_bit(QUEUE_FLAG_REENTER, &q->queue_flags);
+       } else {
+               blk_plug_device(q);
+               kblockd_schedule_work(&q->unplug_work);
+       }
+ }
+ EXPORT_SYMBOL(blk_start_queue);
+ /**
+  * blk_stop_queue - stop a queue
+  * @q:    The &request_queue_t in question
+  *
+  * Description:
+  *   The Linux block layer assumes that a block driver will consume all
+  *   entries on the request queue when the request_fn strategy is called.
+  *   Often this will not happen, because of hardware limitations (queue
+  *   depth settings). If a device driver gets a 'queue full' response,
+  *   or if it simply chooses not to queue more I/O at one point, it can
+  *   call this function to prevent the request_fn from being called until
+  *   the driver has signalled it's ready to go again. This happens by calling
+  *   blk_start_queue() to restart queue operations. Queue lock must be held.
+  **/
+ void blk_stop_queue(request_queue_t *q)
+ {
+       blk_remove_plug(q);
+       set_bit(QUEUE_FLAG_STOPPED, &q->queue_flags);
+ }
+ EXPORT_SYMBOL(blk_stop_queue);
+ /**
+  * blk_sync_queue - cancel any pending callbacks on a queue
+  * @q: the queue
+  *
+  * Description:
+  *     The block layer may perform asynchronous callback activity
+  *     on a queue, such as calling the unplug function after a timeout.
+  *     A block device may call blk_sync_queue to ensure that any
+  *     such activity is cancelled, thus allowing it to release resources
+  *     the the callbacks might use. The caller must already have made sure
+  *     that its ->make_request_fn will not re-add plugging prior to calling
+  *     this function.
+  *
+  */
+ void blk_sync_queue(struct request_queue *q)
+ {
+       del_timer_sync(&q->unplug_timer);
+       kblockd_flush();
+ }
+ EXPORT_SYMBOL(blk_sync_queue);
+ /**
+  * blk_run_queue - run a single device queue
+  * @q:        The queue to run
+  */
+ void blk_run_queue(struct request_queue *q)
+ {
+       unsigned long flags;
+       spin_lock_irqsave(q->queue_lock, flags);
+       blk_remove_plug(q);
+       if (!elv_queue_empty(q))
+               q->request_fn(q);
+       spin_unlock_irqrestore(q->queue_lock, flags);
+ }
+ EXPORT_SYMBOL(blk_run_queue);
+ /**
+  * blk_cleanup_queue: - release a &request_queue_t when it is no longer needed
+  * @q:    the request queue to be released
+  *
+  * Description:
+  *     blk_cleanup_queue is the pair to blk_init_queue() or
+  *     blk_queue_make_request().  It should be called when a request queue is
+  *     being released; typically when a block device is being de-registered.
+  *     Currently, its primary task it to free all the &struct request
+  *     structures that were allocated to the queue and the queue itself.
+  *
+  * Caveat:
+  *     Hopefully the low level driver will have finished any
+  *     outstanding requests first...
+  **/
+ void blk_cleanup_queue(request_queue_t * q)
+ {
+       struct request_list *rl = &q->rq;
+       if (!atomic_dec_and_test(&q->refcnt))
+               return;
+       if (q->elevator)
+               elevator_exit(q->elevator);
+       blk_sync_queue(q);
+       if (rl->rq_pool)
+               mempool_destroy(rl->rq_pool);
+       if (q->queue_tags)
+               __blk_queue_free_tags(q);
+       blk_queue_ordered(q, QUEUE_ORDERED_NONE);
+       kmem_cache_free(requestq_cachep, q);
+ }
+ EXPORT_SYMBOL(blk_cleanup_queue);
+ static int blk_init_free_list(request_queue_t *q)
+ {
+       struct request_list *rl = &q->rq;
+       rl->count[READ] = rl->count[WRITE] = 0;
+       rl->starved[READ] = rl->starved[WRITE] = 0;
+       rl->elvpriv = 0;
+       init_waitqueue_head(&rl->wait[READ]);
+       init_waitqueue_head(&rl->wait[WRITE]);
+       rl->rq_pool = mempool_create_node(BLKDEV_MIN_RQ, mempool_alloc_slab,
+                               mempool_free_slab, request_cachep, q->node);
+       if (!rl->rq_pool)
+               return -ENOMEM;
+       return 0;
+ }
+ static int __make_request(request_queue_t *, struct bio *);
+ request_queue_t *blk_alloc_queue(gfp_t gfp_mask)
+ {
+       return blk_alloc_queue_node(gfp_mask, -1);
+ }
+ EXPORT_SYMBOL(blk_alloc_queue);
+ request_queue_t *blk_alloc_queue_node(gfp_t gfp_mask, int node_id)
+ {
+       request_queue_t *q;
+       q = kmem_cache_alloc_node(requestq_cachep, gfp_mask, node_id);
+       if (!q)
+               return NULL;
+       memset(q, 0, sizeof(*q));
+       init_timer(&q->unplug_timer);
+       atomic_set(&q->refcnt, 1);
+       q->backing_dev_info.unplug_io_fn = blk_backing_dev_unplug;
+       q->backing_dev_info.unplug_io_data = q;
+       return q;
+ }
+ EXPORT_SYMBOL(blk_alloc_queue_node);
+ /**
+  * blk_init_queue  - prepare a request queue for use with a block device
+  * @rfn:  The function to be called to process requests that have been
+  *        placed on the queue.
+  * @lock: Request queue spin lock
+  *
+  * Description:
+  *    If a block device wishes to use the standard request handling procedures,
+  *    which sorts requests and coalesces adjacent requests, then it must
+  *    call blk_init_queue().  The function @rfn will be called when there
+  *    are requests on the queue that need to be processed.  If the device
+  *    supports plugging, then @rfn may not be called immediately when requests
+  *    are available on the queue, but may be called at some time later instead.
+  *    Plugged queues are generally unplugged when a buffer belonging to one
+  *    of the requests on the queue is needed, or due to memory pressure.
+  *
+  *    @rfn is not required, or even expected, to remove all requests off the
+  *    queue, but only as many as it can handle at a time.  If it does leave
+  *    requests on the queue, it is responsible for arranging that the requests
+  *    get dealt with eventually.
+  *
+  *    The queue spin lock must be held while manipulating the requests on the
+  *    request queue.
+  *
+  *    Function returns a pointer to the initialized request queue, or NULL if
+  *    it didn't succeed.
+  *
+  * Note:
+  *    blk_init_queue() must be paired with a blk_cleanup_queue() call
+  *    when the block device is deactivated (such as at module unload).
+  **/
+ request_queue_t *blk_init_queue(request_fn_proc *rfn, spinlock_t *lock)
+ {
+       return blk_init_queue_node(rfn, lock, -1);
+ }
+ EXPORT_SYMBOL(blk_init_queue);
+ request_queue_t *
+ blk_init_queue_node(request_fn_proc *rfn, spinlock_t *lock, int node_id)
+ {
+       request_queue_t *q = blk_alloc_queue_node(GFP_KERNEL, node_id);
+       if (!q)
+               return NULL;
+       q->node = node_id;
+       if (blk_init_free_list(q))
+               goto out_init;
+       /*
+        * if caller didn't supply a lock, they get per-queue locking with
+        * our embedded lock
+        */
+       if (!lock) {
+               spin_lock_init(&q->__queue_lock);
+               lock = &q->__queue_lock;
+       }
+       q->request_fn           = rfn;
+       q->back_merge_fn        = ll_back_merge_fn;
+       q->front_merge_fn       = ll_front_merge_fn;
+       q->merge_requests_fn    = ll_merge_requests_fn;
+       q->prep_rq_fn           = NULL;
+       q->unplug_fn            = generic_unplug_device;
+       q->queue_flags          = (1 << QUEUE_FLAG_CLUSTER);
+       q->queue_lock           = lock;
+       blk_queue_segment_boundary(q, 0xffffffff);
+       blk_queue_make_request(q, __make_request);
+       blk_queue_max_segment_size(q, MAX_SEGMENT_SIZE);
+       blk_queue_max_hw_segments(q, MAX_HW_SEGMENTS);
+       blk_queue_max_phys_segments(q, MAX_PHYS_SEGMENTS);
+       /*
+        * all done
+        */
+       if (!elevator_init(q, NULL)) {
+               blk_queue_congestion_threshold(q);
+               return q;
+       }
+       blk_cleanup_queue(q);
+ out_init:
+       kmem_cache_free(requestq_cachep, q);
+       return NULL;
+ }
+ EXPORT_SYMBOL(blk_init_queue_node);
+ int blk_get_queue(request_queue_t *q)
+ {
+       if (likely(!test_bit(QUEUE_FLAG_DEAD, &q->queue_flags))) {
+               atomic_inc(&q->refcnt);
+               return 0;
+       }
+       return 1;
+ }
+ EXPORT_SYMBOL(blk_get_queue);
+ static inline void blk_free_request(request_queue_t *q, struct request *rq)
+ {
+       if (rq->flags & REQ_ELVPRIV)
+               elv_put_request(q, rq);
+       mempool_free(rq, q->rq.rq_pool);
+ }
+ static inline struct request *
+ blk_alloc_request(request_queue_t *q, int rw, struct bio *bio,
+                 int priv, gfp_t gfp_mask)
+ {
+       struct request *rq = mempool_alloc(q->rq.rq_pool, gfp_mask);
+       if (!rq)
+               return NULL;
+       /*
+        * first three bits are identical in rq->flags and bio->bi_rw,
+        * see bio.h and blkdev.h
+        */
+       rq->flags = rw;
+       if (priv) {
+               if (unlikely(elv_set_request(q, rq, bio, gfp_mask))) {
+                       mempool_free(rq, q->rq.rq_pool);
+                       return NULL;
+               }
+               rq->flags |= REQ_ELVPRIV;
+       }
+       return rq;
+ }
+ /*
+  * ioc_batching returns true if the ioc is a valid batching request and
+  * should be given priority access to a request.
+  */
+ static inline int ioc_batching(request_queue_t *q, struct io_context *ioc)
+ {
+       if (!ioc)
+               return 0;
+       /*
+        * Make sure the process is able to allocate at least 1 request
+        * even if the batch times out, otherwise we could theoretically
+        * lose wakeups.
+        */
+       return ioc->nr_batch_requests == q->nr_batching ||
+               (ioc->nr_batch_requests > 0
+               && time_before(jiffies, ioc->last_waited + BLK_BATCH_TIME));
+ }
+ /*
+  * ioc_set_batching sets ioc to be a new "batcher" if it is not one. This
+  * will cause the process to be a "batcher" on all queues in the system. This
+  * is the behaviour we want though - once it gets a wakeup it should be given
+  * a nice run.
+  */
+ static void ioc_set_batching(request_queue_t *q, struct io_context *ioc)
+ {
+       if (!ioc || ioc_batching(q, ioc))
+               return;
+       ioc->nr_batch_requests = q->nr_batching;
+       ioc->last_waited = jiffies;
+ }
+ static void __freed_request(request_queue_t *q, int rw)
+ {
+       struct request_list *rl = &q->rq;
+       if (rl->count[rw] < queue_congestion_off_threshold(q))
+               clear_queue_congested(q, rw);
+       if (rl->count[rw] + 1 <= q->nr_requests) {
+               if (waitqueue_active(&rl->wait[rw]))
+                       wake_up(&rl->wait[rw]);
+               blk_clear_queue_full(q, rw);
+       }
+ }
+ /*
+  * A request has just been released.  Account for it, update the full and
+  * congestion status, wake up any waiters.   Called under q->queue_lock.
+  */
+ static void freed_request(request_queue_t *q, int rw, int priv)
+ {
+       struct request_list *rl = &q->rq;
+       rl->count[rw]--;
+       if (priv)
+               rl->elvpriv--;
+       __freed_request(q, rw);
+       if (unlikely(rl->starved[rw ^ 1]))
+               __freed_request(q, rw ^ 1);
+ }
+ #define blkdev_free_rq(list) list_entry((list)->next, struct request, queuelist)
+ /*
+  * Get a free request, queue_lock must be held.
+  * Returns NULL on failure, with queue_lock held.
+  * Returns !NULL on success, with queue_lock *not held*.
+  */
+ static struct request *get_request(request_queue_t *q, int rw, struct bio *bio,
+                                  gfp_t gfp_mask)
+ {
+       struct request *rq = NULL;
+       struct request_list *rl = &q->rq;
+       struct io_context *ioc = current_io_context(GFP_ATOMIC);
+       int priv;
+       if (rl->count[rw]+1 >= q->nr_requests) {
+               /*
+                * The queue will fill after this allocation, so set it as
+                * full, and mark this process as "batching". This process
+                * will be allowed to complete a batch of requests, others
+                * will be blocked.
+                */
+               if (!blk_queue_full(q, rw)) {
+                       ioc_set_batching(q, ioc);
+                       blk_set_queue_full(q, rw);
+               }
+       }
+       switch (elv_may_queue(q, rw, bio)) {
+               case ELV_MQUEUE_NO:
+                       goto rq_starved;
+               case ELV_MQUEUE_MAY:
+                       break;
+               case ELV_MQUEUE_MUST:
+                       goto get_rq;
+       }
+       if (blk_queue_full(q, rw) && !ioc_batching(q, ioc)) {
+               /*
+                * The queue is full and the allocating process is not a
+                * "batcher", and not exempted by the IO scheduler
+                */
+               goto out;
+       }
+ get_rq:
+       /*
+        * Only allow batching queuers to allocate up to 50% over the defined
+        * limit of requests, otherwise we could have thousands of requests
+        * allocated with any setting of ->nr_requests
+        */
+       if (rl->count[rw] >= (3 * q->nr_requests / 2))
+               goto out;
+       rl->count[rw]++;
+       rl->starved[rw] = 0;
+       if (rl->count[rw] >= queue_congestion_on_threshold(q))
+               set_queue_congested(q, rw);
+       priv = !test_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
+       if (priv)
+               rl->elvpriv++;
+       spin_unlock_irq(q->queue_lock);
+       rq = blk_alloc_request(q, rw, bio, priv, gfp_mask);
+       if (!rq) {
+               /*
+                * Allocation failed presumably due to memory. Undo anything
+                * we might have messed up.
+                *
+                * Allocating task should really be put onto the front of the
+                * wait queue, but this is pretty rare.
+                */
+               spin_lock_irq(q->queue_lock);
+               freed_request(q, rw, priv);
+               /*
+                * in the very unlikely event that allocation failed and no
+                * requests for this direction was pending, mark us starved
+                * so that freeing of a request in the other direction will
+                * notice us. another possible fix would be to split the
+                * rq mempool into READ and WRITE
+                */
+ rq_starved:
+               if (unlikely(rl->count[rw] == 0))
+                       rl->starved[rw] = 1;
+               goto out;
+       }
+       if (ioc_batching(q, ioc))
+               ioc->nr_batch_requests--;
+       
+       rq_init(q, rq);
+       rq->rl = rl;
+ out:
+       return rq;
+ }
+ /*
+  * No available requests for this queue, unplug the device and wait for some
+  * requests to become available.
+  *
+  * Called with q->queue_lock held, and returns with it unlocked.
+  */
+ static struct request *get_request_wait(request_queue_t *q, int rw,
+                                       struct bio *bio)
+ {
+       struct request *rq;
+       rq = get_request(q, rw, bio, GFP_NOIO);
+       while (!rq) {
+               DEFINE_WAIT(wait);
+               struct request_list *rl = &q->rq;
+               prepare_to_wait_exclusive(&rl->wait[rw], &wait,
+                               TASK_UNINTERRUPTIBLE);
+               rq = get_request(q, rw, bio, GFP_NOIO);
+               if (!rq) {
+                       struct io_context *ioc;
+                       __generic_unplug_device(q);
+                       spin_unlock_irq(q->queue_lock);
+                       io_schedule();
+                       /*
+                        * After sleeping, we become a "batching" process and
+                        * will be able to allocate at least one request, and
+                        * up to a big batch of them for a small period time.
+                        * See ioc_batching, ioc_set_batching
+                        */
+                       ioc = current_io_context(GFP_NOIO);
+                       ioc_set_batching(q, ioc);
+                       spin_lock_irq(q->queue_lock);
+               }
+               finish_wait(&rl->wait[rw], &wait);
+       }
+       return rq;
+ }
+ struct request *blk_get_request(request_queue_t *q, int rw, gfp_t gfp_mask)
+ {
+       struct request *rq;
+       BUG_ON(rw != READ && rw != WRITE);
+       spin_lock_irq(q->queue_lock);
+       if (gfp_mask & __GFP_WAIT) {
+               rq = get_request_wait(q, rw, NULL);
+       } else {
+               rq = get_request(q, rw, NULL, gfp_mask);
+               if (!rq)
+                       spin_unlock_irq(q->queue_lock);
+       }
+       /* q->queue_lock is unlocked at this point */
+       return rq;
+ }
+ EXPORT_SYMBOL(blk_get_request);
+ /**
+  * blk_requeue_request - put a request back on queue
+  * @q:                request queue where request should be inserted
+  * @rq:               request to be inserted
+  *
+  * Description:
+  *    Drivers often keep queueing requests until the hardware cannot accept
+  *    more, when that condition happens we need to put the request back
+  *    on the queue. Must be called with queue lock held.
+  */
+ void blk_requeue_request(request_queue_t *q, struct request *rq)
+ {
+       if (blk_rq_tagged(rq))
+               blk_queue_end_tag(q, rq);
+       elv_requeue_request(q, rq);
+ }
+ EXPORT_SYMBOL(blk_requeue_request);
+ /**
+  * blk_insert_request - insert a special request in to a request queue
+  * @q:                request queue where request should be inserted
+  * @rq:               request to be inserted
+  * @at_head:  insert request at head or tail of queue
+  * @data:     private data
+  *
+  * Description:
+  *    Many block devices need to execute commands asynchronously, so they don't
+  *    block the whole kernel from preemption during request execution.  This is
+  *    accomplished normally by inserting aritficial requests tagged as
+  *    REQ_SPECIAL in to the corresponding request queue, and letting them be
+  *    scheduled for actual execution by the request queue.
+  *
+  *    We have the option of inserting the head or the tail of the queue.
+  *    Typically we use the tail for new ioctls and so forth.  We use the head
+  *    of the queue for things like a QUEUE_FULL message from a device, or a
+  *    host that is unable to accept a particular command.
+  */
+ void blk_insert_request(request_queue_t *q, struct request *rq,
+                       int at_head, void *data)
+ {
+       int where = at_head ? ELEVATOR_INSERT_FRONT : ELEVATOR_INSERT_BACK;
+       unsigned long flags;
+       /*
+        * tell I/O scheduler that this isn't a regular read/write (ie it
+        * must not attempt merges on this) and that it acts as a soft
+        * barrier
+        */
+       rq->flags |= REQ_SPECIAL | REQ_SOFTBARRIER;
+       rq->special = data;
+       spin_lock_irqsave(q->queue_lock, flags);
+       /*
+        * If command is tagged, release the tag
+        */
+       if (blk_rq_tagged(rq))
+               blk_queue_end_tag(q, rq);
+       drive_stat_acct(rq, rq->nr_sectors, 1);
+       __elv_add_request(q, rq, where, 0);
+       if (blk_queue_plugged(q))
+               __generic_unplug_device(q);
+       else
+               q->request_fn(q);
+       spin_unlock_irqrestore(q->queue_lock, flags);
+ }
+ EXPORT_SYMBOL(blk_insert_request);
+ /**
+  * blk_rq_map_user - map user data to a request, for REQ_BLOCK_PC usage
+  * @q:                request queue where request should be inserted
+  * @rq:               request structure to fill
+  * @ubuf:     the user buffer
+  * @len:      length of user data
+  *
+  * Description:
+  *    Data will be mapped directly for zero copy io, if possible. Otherwise
+  *    a kernel bounce buffer is used.
+  *
+  *    A matching blk_rq_unmap_user() must be issued at the end of io, while
+  *    still in process context.
+  *
+  *    Note: The mapped bio may need to be bounced through blk_queue_bounce()
+  *    before being submitted to the device, as pages mapped may be out of
+  *    reach. It's the callers responsibility to make sure this happens. The
+  *    original bio must be passed back in to blk_rq_unmap_user() for proper
+  *    unmapping.
+  */
+ int blk_rq_map_user(request_queue_t *q, struct request *rq, void __user *ubuf,
+                   unsigned int len)
+ {
+       unsigned long uaddr;
+       struct bio *bio;
+       int reading;
+       if (len > (q->max_sectors << 9))
+               return -EINVAL;
+       if (!len || !ubuf)
+               return -EINVAL;
+       reading = rq_data_dir(rq) == READ;
+       /*
+        * if alignment requirement is satisfied, map in user pages for
+        * direct dma. else, set up kernel bounce buffers
+        */
+       uaddr = (unsigned long) ubuf;
+       if (!(uaddr & queue_dma_alignment(q)) && !(len & queue_dma_alignment(q)))
+               bio = bio_map_user(q, NULL, uaddr, len, reading);
+       else
+               bio = bio_copy_user(q, uaddr, len, reading);
+       if (!IS_ERR(bio)) {
+               rq->bio = rq->biotail = bio;
+               blk_rq_bio_prep(q, rq, bio);
+               rq->buffer = rq->data = NULL;
+               rq->data_len = len;
+               return 0;
+       }
+       /*
+        * bio is the err-ptr
+        */
+       return PTR_ERR(bio);
+ }
+ EXPORT_SYMBOL(blk_rq_map_user);
+ /**
+  * blk_rq_map_user_iov - map user data to a request, for REQ_BLOCK_PC usage
+  * @q:                request queue where request should be inserted
+  * @rq:               request to map data to
+  * @iov:      pointer to the iovec
+  * @iov_count:        number of elements in the iovec
+  *
+  * Description:
+  *    Data will be mapped directly for zero copy io, if possible. Otherwise
+  *    a kernel bounce buffer is used.
+  *
+  *    A matching blk_rq_unmap_user() must be issued at the end of io, while
+  *    still in process context.
+  *
+  *    Note: The mapped bio may need to be bounced through blk_queue_bounce()
+  *    before being submitted to the device, as pages mapped may be out of
+  *    reach. It's the callers responsibility to make sure this happens. The
+  *    original bio must be passed back in to blk_rq_unmap_user() for proper
+  *    unmapping.
+  */
+ int blk_rq_map_user_iov(request_queue_t *q, struct request *rq,
+                       struct sg_iovec *iov, int iov_count)
+ {
+       struct bio *bio;
+       if (!iov || iov_count <= 0)
+               return -EINVAL;
+       /* we don't allow misaligned data like bio_map_user() does.  If the
+        * user is using sg, they're expected to know the alignment constraints
+        * and respect them accordingly */
+       bio = bio_map_user_iov(q, NULL, iov, iov_count, rq_data_dir(rq)== READ);
+       if (IS_ERR(bio))
+               return PTR_ERR(bio);
+       rq->bio = rq->biotail = bio;
+       blk_rq_bio_prep(q, rq, bio);
+       rq->buffer = rq->data = NULL;
+       rq->data_len = bio->bi_size;
+       return 0;
+ }
+ EXPORT_SYMBOL(blk_rq_map_user_iov);
+ /**
+  * blk_rq_unmap_user - unmap a request with user data
+  * @bio:      bio to be unmapped
+  * @ulen:     length of user buffer
+  *
+  * Description:
+  *    Unmap a bio previously mapped by blk_rq_map_user().
+  */
+ int blk_rq_unmap_user(struct bio *bio, unsigned int ulen)
+ {
+       int ret = 0;
+       if (bio) {
+               if (bio_flagged(bio, BIO_USER_MAPPED))
+                       bio_unmap_user(bio);
+               else
+                       ret = bio_uncopy_user(bio);
+       }
+       return 0;
+ }
+ EXPORT_SYMBOL(blk_rq_unmap_user);
+ /**
+  * blk_rq_map_kern - map kernel data to a request, for REQ_BLOCK_PC usage
+  * @q:                request queue where request should be inserted
+  * @rq:               request to fill
+  * @kbuf:     the kernel buffer
+  * @len:      length of user data
+  * @gfp_mask: memory allocation flags
+  */
+ int blk_rq_map_kern(request_queue_t *q, struct request *rq, void *kbuf,
+                   unsigned int len, gfp_t gfp_mask)
+ {
+       struct bio *bio;
+       if (len > (q->max_sectors << 9))
+               return -EINVAL;
+       if (!len || !kbuf)
+               return -EINVAL;
+       bio = bio_map_kern(q, kbuf, len, gfp_mask);
+       if (IS_ERR(bio))
+               return PTR_ERR(bio);
+       if (rq_data_dir(rq) == WRITE)
+               bio->bi_rw |= (1 << BIO_RW);
+       rq->bio = rq->biotail = bio;
+       blk_rq_bio_prep(q, rq, bio);
+       rq->buffer = rq->data = NULL;
+       rq->data_len = len;
+       return 0;
+ }
+ EXPORT_SYMBOL(blk_rq_map_kern);
+ /**
+  * blk_execute_rq_nowait - insert a request into queue for execution
+  * @q:                queue to insert the request in
+  * @bd_disk:  matching gendisk
+  * @rq:               request to insert
+  * @at_head:    insert request at head or tail of queue
+  * @done:     I/O completion handler
+  *
+  * Description:
+  *    Insert a fully prepared request at the back of the io scheduler queue
+  *    for execution.  Don't wait for completion.
+  */
+ void blk_execute_rq_nowait(request_queue_t *q, struct gendisk *bd_disk,
+                          struct request *rq, int at_head,
+                          void (*done)(struct request *))
+ {
+       int where = at_head ? ELEVATOR_INSERT_FRONT : ELEVATOR_INSERT_BACK;
+       rq->rq_disk = bd_disk;
+       rq->flags |= REQ_NOMERGE;
+       rq->end_io = done;
+       elv_add_request(q, rq, where, 1);
+       generic_unplug_device(q);
+ }
+ /**
+  * blk_execute_rq - insert a request into queue for execution
+  * @q:                queue to insert the request in
+  * @bd_disk:  matching gendisk
+  * @rq:               request to insert
+  * @at_head:    insert request at head or tail of queue
+  *
+  * Description:
+  *    Insert a fully prepared request at the back of the io scheduler queue
+  *    for execution and wait for completion.
+  */
+ int blk_execute_rq(request_queue_t *q, struct gendisk *bd_disk,
+                  struct request *rq, int at_head)
+ {
+       DECLARE_COMPLETION(wait);
+       char sense[SCSI_SENSE_BUFFERSIZE];
+       int err = 0;
+       /*
+        * we need an extra reference to the request, so we can look at
+        * it after io completion
+        */
+       rq->ref_count++;
+       if (!rq->sense) {
+               memset(sense, 0, sizeof(sense));
+               rq->sense = sense;
+               rq->sense_len = 0;
+       }
+       rq->waiting = &wait;
+       blk_execute_rq_nowait(q, bd_disk, rq, at_head, blk_end_sync_rq);
+       wait_for_completion(&wait);
+       rq->waiting = NULL;
+       if (rq->errors)
+               err = -EIO;
+       return err;
+ }
+ EXPORT_SYMBOL(blk_execute_rq);
+ /**
+  * blkdev_issue_flush - queue a flush
+  * @bdev:     blockdev to issue flush for
+  * @error_sector:     error sector
+  *
+  * Description:
+  *    Issue a flush for the block device in question. Caller can supply
+  *    room for storing the error offset in case of a flush error, if they
+  *    wish to.  Caller must run wait_for_completion() on its own.
+  */
+ int blkdev_issue_flush(struct block_device *bdev, sector_t *error_sector)
+ {
+       request_queue_t *q;
+       if (bdev->bd_disk == NULL)
+               return -ENXIO;
+       q = bdev_get_queue(bdev);
+       if (!q)
+               return -ENXIO;
+       if (!q->issue_flush_fn)
+               return -EOPNOTSUPP;
+       return q->issue_flush_fn(q, bdev->bd_disk, error_sector);
+ }
+ EXPORT_SYMBOL(blkdev_issue_flush);
+ static void drive_stat_acct(struct request *rq, int nr_sectors, int new_io)
+ {
+       int rw = rq_data_dir(rq);
+       if (!blk_fs_request(rq) || !rq->rq_disk)
+               return;
+       if (!new_io) {
+               __disk_stat_inc(rq->rq_disk, merges[rw]);
+       } else {
+               disk_round_stats(rq->rq_disk);
+               rq->rq_disk->in_flight++;
+       }
+ }
+ /*
+  * add-request adds a request to the linked list.
+  * queue lock is held and interrupts disabled, as we muck with the
+  * request queue list.
+  */
+ static inline void add_request(request_queue_t * q, struct request * req)
+ {
+       drive_stat_acct(req, req->nr_sectors, 1);
+       if (q->activity_fn)
+               q->activity_fn(q->activity_data, rq_data_dir(req));
+       /*
+        * elevator indicated where it wants this request to be
+        * inserted at elevator_merge time
+        */
+       __elv_add_request(q, req, ELEVATOR_INSERT_SORT, 0);
+ }
+  
+ /*
+  * disk_round_stats() - Round off the performance stats on a struct
+  * disk_stats.
+  *
+  * The average IO queue length and utilisation statistics are maintained
+  * by observing the current state of the queue length and the amount of
+  * time it has been in this state for.
+  *
+  * Normally, that accounting is done on IO completion, but that can result
+  * in more than a second's worth of IO being accounted for within any one
+  * second, leading to >100% utilisation.  To deal with that, we call this
+  * function to do a round-off before returning the results when reading
+  * /proc/diskstats.  This accounts immediately for all queue usage up to
+  * the current jiffies and restarts the counters again.
+  */
+ void disk_round_stats(struct gendisk *disk)
+ {
+       unsigned long now = jiffies;
+       if (now == disk->stamp)
+               return;
+       if (disk->in_flight) {
+               __disk_stat_add(disk, time_in_queue,
+                               disk->in_flight * (now - disk->stamp));
+               __disk_stat_add(disk, io_ticks, (now - disk->stamp));
+       }
+       disk->stamp = now;
+ }
+ /*
+  * queue lock must be held
+  */
+ static void __blk_put_request(request_queue_t *q, struct request *req)
+ {
+       struct request_list *rl = req->rl;
+       if (unlikely(!q))
+               return;
+       if (unlikely(--req->ref_count))
+               return;
+       elv_completed_request(q, req);
+       req->rq_status = RQ_INACTIVE;
+       req->rl = NULL;
+       /*
+        * Request may not have originated from ll_rw_blk. if not,
+        * it didn't come out of our reserved rq pools
+        */
+       if (rl) {
+               int rw = rq_data_dir(req);
+               int priv = req->flags & REQ_ELVPRIV;
+               BUG_ON(!list_empty(&req->queuelist));
+               blk_free_request(q, req);
+               freed_request(q, rw, priv);
+       }
+ }
+ void blk_put_request(struct request *req)
+ {
+       unsigned long flags;
+       request_queue_t *q = req->q;
+       /*
+        * Gee, IDE calls in w/ NULL q.  Fix IDE and remove the
+        * following if (q) test.
+        */
+       if (q) {
+               spin_lock_irqsave(q->queue_lock, flags);
+               __blk_put_request(q, req);
+               spin_unlock_irqrestore(q->queue_lock, flags);
+       }
+ }
+ EXPORT_SYMBOL(blk_put_request);
+ /**
+  * blk_end_sync_rq - executes a completion event on a request
+  * @rq: request to complete
+  */
+ void blk_end_sync_rq(struct request *rq)
+ {
+       struct completion *waiting = rq->waiting;
+       rq->waiting = NULL;
+       __blk_put_request(rq->q, rq);
+       /*
+        * complete last, if this is a stack request the process (and thus
+        * the rq pointer) could be invalid right after this complete()
+        */
+       complete(waiting);
+ }
+ EXPORT_SYMBOL(blk_end_sync_rq);
+ /**
+  * blk_congestion_wait - wait for a queue to become uncongested
+  * @rw: READ or WRITE
+  * @timeout: timeout in jiffies
+  *
+  * Waits for up to @timeout jiffies for a queue (any queue) to exit congestion.
+  * If no queues are congested then just wait for the next request to be
+  * returned.
+  */
+ long blk_congestion_wait(int rw, long timeout)
+ {
+       long ret;
+       DEFINE_WAIT(wait);
+       wait_queue_head_t *wqh = &congestion_wqh[rw];
+       prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
+       ret = io_schedule_timeout(timeout);
+       finish_wait(wqh, &wait);
+       return ret;
+ }
+ EXPORT_SYMBOL(blk_congestion_wait);
+ /*
+  * Has to be called with the request spinlock acquired
+  */
+ static int attempt_merge(request_queue_t *q, struct request *req,
+                         struct request *next)
+ {
+       if (!rq_mergeable(req) || !rq_mergeable(next))
+               return 0;
+       /*
+        * not contigious
+        */
+       if (req->sector + req->nr_sectors != next->sector)
+               return 0;
+       if (rq_data_dir(req) != rq_data_dir(next)
+           || req->rq_disk != next->rq_disk
+           || next->waiting || next->special)
+               return 0;
+       /*
+        * If we are allowed to merge, then append bio list
+        * from next to rq and release next. merge_requests_fn
+        * will have updated segment counts, update sector
+        * counts here.
+        */
+       if (!q->merge_requests_fn(q, req, next))
+               return 0;
+       /*
+        * At this point we have either done a back merge
+        * or front merge. We need the smaller start_time of
+        * the merged requests to be the current request
+        * for accounting purposes.
+        */
+       if (time_after(req->start_time, next->start_time))
+               req->start_time = next->start_time;
+       req->biotail->bi_next = next->bio;
+       req->biotail = next->biotail;
+       req->nr_sectors = req->hard_nr_sectors += next->hard_nr_sectors;
+       elv_merge_requests(q, req, next);
+       if (req->rq_disk) {
+               disk_round_stats(req->rq_disk);
+               req->rq_disk->in_flight--;
+       }
+       req->ioprio = ioprio_best(req->ioprio, next->ioprio);
+       __blk_put_request(q, next);
+       return 1;
+ }
+ static inline int attempt_back_merge(request_queue_t *q, struct request *rq)
+ {
+       struct request *next = elv_latter_request(q, rq);
+       if (next)
+               return attempt_merge(q, rq, next);
+       return 0;
+ }
+ static inline int attempt_front_merge(request_queue_t *q, struct request *rq)
+ {
+       struct request *prev = elv_former_request(q, rq);
+       if (prev)
+               return attempt_merge(q, prev, rq);
+       return 0;
+ }
+ /**
+  * blk_attempt_remerge  - attempt to remerge active head with next request
+  * @q:    The &request_queue_t belonging to the device
+  * @rq:   The head request (usually)
+  *
+  * Description:
+  *    For head-active devices, the queue can easily be unplugged so quickly
+  *    that proper merging is not done on the front request. This may hurt
+  *    performance greatly for some devices. The block layer cannot safely
+  *    do merging on that first request for these queues, but the driver can
+  *    call this function and make it happen any way. Only the driver knows
+  *    when it is safe to do so.
+  **/
+ void blk_attempt_remerge(request_queue_t *q, struct request *rq)
+ {
+       unsigned long flags;
+       spin_lock_irqsave(q->queue_lock, flags);
+       attempt_back_merge(q, rq);
+       spin_unlock_irqrestore(q->queue_lock, flags);
+ }
+ EXPORT_SYMBOL(blk_attempt_remerge);
+ static int __make_request(request_queue_t *q, struct bio *bio)
+ {
+       struct request *req;
+       int el_ret, rw, nr_sectors, cur_nr_sectors, barrier, err, sync;
+       unsigned short prio;
+       sector_t sector;
+       sector = bio->bi_sector;
+       nr_sectors = bio_sectors(bio);
+       cur_nr_sectors = bio_cur_sectors(bio);
+       prio = bio_prio(bio);
+       rw = bio_data_dir(bio);
+       sync = bio_sync(bio);
+       /*
+        * low level driver can indicate that it wants pages above a
+        * certain limit bounced to low memory (ie for highmem, or even
+        * ISA dma in theory)
+        */
+       blk_queue_bounce(q, &bio);
+       spin_lock_prefetch(q->queue_lock);
+       barrier = bio_barrier(bio);
+       if (unlikely(barrier) && (q->ordered == QUEUE_ORDERED_NONE)) {
+               err = -EOPNOTSUPP;
+               goto end_io;
+       }
+       spin_lock_irq(q->queue_lock);
+       if (unlikely(barrier) || elv_queue_empty(q))
+               goto get_rq;
+       el_ret = elv_merge(q, &req, bio);
+       switch (el_ret) {
+               case ELEVATOR_BACK_MERGE:
+                       BUG_ON(!rq_mergeable(req));
+                       if (!q->back_merge_fn(q, req, bio))
+                               break;
+                       req->biotail->bi_next = bio;
+                       req->biotail = bio;
+                       req->nr_sectors = req->hard_nr_sectors += nr_sectors;
+                       req->ioprio = ioprio_best(req->ioprio, prio);
+                       drive_stat_acct(req, nr_sectors, 0);
+                       if (!attempt_back_merge(q, req))
+                               elv_merged_request(q, req);
+                       goto out;
+               case ELEVATOR_FRONT_MERGE:
+                       BUG_ON(!rq_mergeable(req));
+                       if (!q->front_merge_fn(q, req, bio))
+                               break;
+                       bio->bi_next = req->bio;
+                       req->bio = bio;
+                       /*
+                        * may not be valid. if the low level driver said
+                        * it didn't need a bounce buffer then it better
+                        * not touch req->buffer either...
+                        */
+                       req->buffer = bio_data(bio);
+                       req->current_nr_sectors = cur_nr_sectors;
+                       req->hard_cur_sectors = cur_nr_sectors;
+                       req->sector = req->hard_sector = sector;
+                       req->nr_sectors = req->hard_nr_sectors += nr_sectors;
+                       req->ioprio = ioprio_best(req->ioprio, prio);
+                       drive_stat_acct(req, nr_sectors, 0);
+                       if (!attempt_front_merge(q, req))
+                               elv_merged_request(q, req);
+                       goto out;
+               /* ELV_NO_MERGE: elevator says don't/can't merge. */
+               default:
+                       ;
+       }
+ get_rq:
+       /*
+        * Grab a free request. This is might sleep but can not fail.
+        * Returns with the queue unlocked.
+        */
+       req = get_request_wait(q, rw, bio);
+       /*
+        * After dropping the lock and possibly sleeping here, our request
+        * may now be mergeable after it had proven unmergeable (above).
+        * We don't worry about that case for efficiency. It won't happen
+        * often, and the elevators are able to handle it.
+        */
+       req->flags |= REQ_CMD;
+       /*
+        * inherit FAILFAST from bio (for read-ahead, and explicit FAILFAST)
+        */
+       if (bio_rw_ahead(bio) || bio_failfast(bio))
+               req->flags |= REQ_FAILFAST;
+       /*
+        * REQ_BARRIER implies no merging, but lets make it explicit
+        */
+       if (unlikely(barrier))
+               req->flags |= (REQ_HARDBARRIER | REQ_NOMERGE);
+       req->errors = 0;
+       req->hard_sector = req->sector = sector;
+       req->hard_nr_sectors = req->nr_sectors = nr_sectors;
+       req->current_nr_sectors = req->hard_cur_sectors = cur_nr_sectors;
+       req->nr_phys_segments = bio_phys_segments(q, bio);
+       req->nr_hw_segments = bio_hw_segments(q, bio);
+       req->buffer = bio_data(bio);    /* see ->buffer comment above */
+       req->waiting = NULL;
+       req->bio = req->biotail = bio;
+       req->ioprio = prio;
+       req->rq_disk = bio->bi_bdev->bd_disk;
+       req->start_time = jiffies;
+       spin_lock_irq(q->queue_lock);
+       if (elv_queue_empty(q))
+               blk_plug_device(q);
+       add_request(q, req);
+ out:
+       if (sync)
+               __generic_unplug_device(q);
+       spin_unlock_irq(q->queue_lock);
+       return 0;
+ end_io:
+       bio_endio(bio, nr_sectors << 9, err);
+       return 0;
+ }
+ /*
+  * If bio->bi_dev is a partition, remap the location
+  */
+ static inline void blk_partition_remap(struct bio *bio)
+ {
+       struct block_device *bdev = bio->bi_bdev;
+       if (bdev != bdev->bd_contains) {
+               struct hd_struct *p = bdev->bd_part;
+               const int rw = bio_data_dir(bio);
+               p->sectors[rw] += bio_sectors(bio);
+               p->ios[rw]++;
+               bio->bi_sector += p->start_sect;
+               bio->bi_bdev = bdev->bd_contains;
+       }
+ }
+ static void handle_bad_sector(struct bio *bio)
+ {
+       char b[BDEVNAME_SIZE];
+       printk(KERN_INFO "attempt to access beyond end of device\n");
+       printk(KERN_INFO "%s: rw=%ld, want=%Lu, limit=%Lu\n",
+                       bdevname(bio->bi_bdev, b),
+                       bio->bi_rw,
+                       (unsigned long long)bio->bi_sector + bio_sectors(bio),
+                       (long long)(bio->bi_bdev->bd_inode->i_size >> 9));
+       set_bit(BIO_EOF, &bio->bi_flags);
+ }
+ /**
+  * generic_make_request: hand a buffer to its device driver for I/O
+  * @bio:  The bio describing the location in memory and on the device.
+  *
+  * generic_make_request() is used to make I/O requests of block
+  * devices. It is passed a &struct bio, which describes the I/O that needs
+  * to be done.
+  *
+  * generic_make_request() does not return any status.  The
+  * success/failure status of the request, along with notification of
+  * completion, is delivered asynchronously through the bio->bi_end_io
+  * function described (one day) else where.
+  *
+  * The caller of generic_make_request must make sure that bi_io_vec
+  * are set to describe the memory buffer, and that bi_dev and bi_sector are
+  * set to describe the device address, and the
+  * bi_end_io and optionally bi_private are set to describe how
+  * completion notification should be signaled.
+  *
+  * generic_make_request and the drivers it calls may use bi_next if this
+  * bio happens to be merged with someone else, and may change bi_dev and
+  * bi_sector for remaps as it sees fit.  So the values of these fields
+  * should NOT be depended on after the call to generic_make_request.
+  */
+ void generic_make_request(struct bio *bio)
+ {
+       request_queue_t *q;
+       sector_t maxsector;
+       int ret, nr_sectors = bio_sectors(bio);
+       might_sleep();
+       /* Test device or partition size, when known. */
+       maxsector = bio->bi_bdev->bd_inode->i_size >> 9;
+       if (maxsector) {
+               sector_t sector = bio->bi_sector;
+               if (maxsector < nr_sectors || maxsector - nr_sectors < sector) {
+                       /*
+                        * This may well happen - the kernel calls bread()
+                        * without checking the size of the device, e.g., when
+                        * mounting a device.
+                        */
+                       handle_bad_sector(bio);
+                       goto end_io;
+               }
+       }
+       /*
+        * Resolve the mapping until finished. (drivers are
+        * still free to implement/resolve their own stacking
+        * by explicitly returning 0)
+        *
+        * NOTE: we don't repeat the blk_size check for each new device.
+        * Stacking drivers are expected to know what they are doing.
+        */
+       do {
+               char b[BDEVNAME_SIZE];
+               q = bdev_get_queue(bio->bi_bdev);
+               if (!q) {
+                       printk(KERN_ERR
+                              "generic_make_request: Trying to access "
+                               "nonexistent block-device %s (%Lu)\n",
+                               bdevname(bio->bi_bdev, b),
+                               (long long) bio->bi_sector);
+ end_io:
+                       bio_endio(bio, bio->bi_size, -EIO);
+                       break;
+               }
+               if (unlikely(bio_sectors(bio) > q->max_hw_sectors)) {
+                       printk("bio too big device %s (%u > %u)\n", 
+                               bdevname(bio->bi_bdev, b),
+                               bio_sectors(bio),
+                               q->max_hw_sectors);
+                       goto end_io;
+               }
+               if (unlikely(test_bit(QUEUE_FLAG_DEAD, &q->queue_flags)))
+                       goto end_io;
+               /*
+                * If this device has partitions, remap block n
+                * of partition p to block n+start(p) of the disk.
+                */
+               blk_partition_remap(bio);
+               ret = q->make_request_fn(q, bio);
+       } while (ret);
+ }
+ EXPORT_SYMBOL(generic_make_request);
+ /**
+  * submit_bio: submit a bio to the block device layer for I/O
+  * @rw: whether to %READ or %WRITE, or maybe to %READA (read ahead)
+  * @bio: The &struct bio which describes the I/O
+  *
+  * submit_bio() is very similar in purpose to generic_make_request(), and
+  * uses that function to do most of the work. Both are fairly rough
+  * interfaces, @bio must be presetup and ready for I/O.
+  *
+  */
+ void submit_bio(int rw, struct bio *bio)
+ {
+       int count = bio_sectors(bio);
+       BIO_BUG_ON(!bio->bi_size);
+       BIO_BUG_ON(!bio->bi_io_vec);
+       bio->bi_rw |= rw;
+       if (rw & WRITE)
+               mod_page_state(pgpgout, count);
+       else
+               mod_page_state(pgpgin, count);
+       if (unlikely(block_dump)) {
+               char b[BDEVNAME_SIZE];
+               printk(KERN_DEBUG "%s(%d): %s block %Lu on %s\n",
+                       current->comm, current->pid,
+                       (rw & WRITE) ? "WRITE" : "READ",
+                       (unsigned long long)bio->bi_sector,
+                       bdevname(bio->bi_bdev,b));
+       }
+       generic_make_request(bio);
+ }
+ EXPORT_SYMBOL(submit_bio);
+ static void blk_recalc_rq_segments(struct request *rq)
+ {
+       struct bio *bio, *prevbio = NULL;
+       int nr_phys_segs, nr_hw_segs;
+       unsigned int phys_size, hw_size;
+       request_queue_t *q = rq->q;
+       if (!rq->bio)
+               return;
+       phys_size = hw_size = nr_phys_segs = nr_hw_segs = 0;
+       rq_for_each_bio(bio, rq) {
+               /* Force bio hw/phys segs to be recalculated. */
+               bio->bi_flags &= ~(1 << BIO_SEG_VALID);
+               nr_phys_segs += bio_phys_segments(q, bio);
+               nr_hw_segs += bio_hw_segments(q, bio);
+               if (prevbio) {
+                       int pseg = phys_size + prevbio->bi_size + bio->bi_size;
+                       int hseg = hw_size + prevbio->bi_size + bio->bi_size;
+                       if (blk_phys_contig_segment(q, prevbio, bio) &&
+                           pseg <= q->max_segment_size) {
+                               nr_phys_segs--;
+                               phys_size += prevbio->bi_size + bio->bi_size;
+                       } else
+                               phys_size = 0;
+                       if (blk_hw_contig_segment(q, prevbio, bio) &&
+                           hseg <= q->max_segment_size) {
+                               nr_hw_segs--;
+                               hw_size += prevbio->bi_size + bio->bi_size;
+                       } else
+                               hw_size = 0;
+               }
+               prevbio = bio;
+       }
+       rq->nr_phys_segments = nr_phys_segs;
+       rq->nr_hw_segments = nr_hw_segs;
+ }
+ static void blk_recalc_rq_sectors(struct request *rq, int nsect)
+ {
+       if (blk_fs_request(rq)) {
+               rq->hard_sector += nsect;
+               rq->hard_nr_sectors -= nsect;
+               /*
+                * Move the I/O submission pointers ahead if required.
+                */
+               if ((rq->nr_sectors >= rq->hard_nr_sectors) &&
+                   (rq->sector <= rq->hard_sector)) {
+                       rq->sector = rq->hard_sector;
+                       rq->nr_sectors = rq->hard_nr_sectors;
+                       rq->hard_cur_sectors = bio_cur_sectors(rq->bio);
+                       rq->current_nr_sectors = rq->hard_cur_sectors;
+                       rq->buffer = bio_data(rq->bio);
+               }
+               /*
+                * if total number of sectors is less than the first segment
+                * size, something has gone terribly wrong
+                */
+               if (rq->nr_sectors < rq->current_nr_sectors) {
+                       printk("blk: request botched\n");
+                       rq->nr_sectors = rq->current_nr_sectors;
+               }
+       }
+ }
+ static int __end_that_request_first(struct request *req, int uptodate,
+                                   int nr_bytes)
+ {
+       int total_bytes, bio_nbytes, error, next_idx = 0;
+       struct bio *bio;
+       /*
+        * extend uptodate bool to allow < 0 value to be direct io error
+        */
+       error = 0;
+       if (end_io_error(uptodate))
+               error = !uptodate ? -EIO : uptodate;
+       /*
+        * for a REQ_BLOCK_PC request, we want to carry any eventual
+        * sense key with us all the way through
+        */
+       if (!blk_pc_request(req))
+               req->errors = 0;
+       if (!uptodate) {
+               if (blk_fs_request(req) && !(req->flags & REQ_QUIET))
+                       printk("end_request: I/O error, dev %s, sector %llu\n",
+                               req->rq_disk ? req->rq_disk->disk_name : "?",
+                               (unsigned long long)req->sector);
+       }
+       if (blk_fs_request(req) && req->rq_disk) {
+               const int rw = rq_data_dir(req);
+               __disk_stat_add(req->rq_disk, sectors[rw], nr_bytes >> 9);
+       }
+       total_bytes = bio_nbytes = 0;
+       while ((bio = req->bio) != NULL) {
+               int nbytes;
+               if (nr_bytes >= bio->bi_size) {
+                       req->bio = bio->bi_next;
+                       nbytes = bio->bi_size;
+                       bio_endio(bio, nbytes, error);
+                       next_idx = 0;
+                       bio_nbytes = 0;
+               } else {
+                       int idx = bio->bi_idx + next_idx;
+                       if (unlikely(bio->bi_idx >= bio->bi_vcnt)) {
+                               blk_dump_rq_flags(req, "__end_that");
+                               printk("%s: bio idx %d >= vcnt %d\n",
+                                               __FUNCTION__,
+                                               bio->bi_idx, bio->bi_vcnt);
+                               break;
+                       }
+                       nbytes = bio_iovec_idx(bio, idx)->bv_len;
+                       BIO_BUG_ON(nbytes > bio->bi_size);
+                       /*
+                        * not a complete bvec done
+                        */
+                       if (unlikely(nbytes > nr_bytes)) {
+                               bio_nbytes += nr_bytes;
+                               total_bytes += nr_bytes;
+                               break;
+                       }
+                       /*
+                        * advance to the next vector
+                        */
+                       next_idx++;
+                       bio_nbytes += nbytes;
+               }
+               total_bytes += nbytes;
+               nr_bytes -= nbytes;
+               if ((bio = req->bio)) {
+                       /*
+                        * end more in this run, or just return 'not-done'
+                        */
+                       if (unlikely(nr_bytes <= 0))
+                               break;
+               }
+       }
+       /*
+        * completely done
+        */
+       if (!req->bio)
+               return 0;
+       /*
+        * if the request wasn't completed, update state
+        */
+       if (bio_nbytes) {
+               bio_endio(bio, bio_nbytes, error);
+               bio->bi_idx += next_idx;
+               bio_iovec(bio)->bv_offset += nr_bytes;
+               bio_iovec(bio)->bv_len -= nr_bytes;
+       }
+       blk_recalc_rq_sectors(req, total_bytes >> 9);
+       blk_recalc_rq_segments(req);
+       return 1;
+ }
+ /**
+  * end_that_request_first - end I/O on a request
+  * @req:      the request being processed
+  * @uptodate: 1 for success, 0 for I/O error, < 0 for specific error
+  * @nr_sectors: number of sectors to end I/O on
+  *
+  * Description:
+  *     Ends I/O on a number of sectors attached to @req, and sets it up
+  *     for the next range of segments (if any) in the cluster.
+  *
+  * Return:
+  *     0 - we are done with this request, call end_that_request_last()
+  *     1 - still buffers pending for this request
+  **/
+ int end_that_request_first(struct request *req, int uptodate, int nr_sectors)
+ {
+       return __end_that_request_first(req, uptodate, nr_sectors << 9);
+ }
+ EXPORT_SYMBOL(end_that_request_first);
+ /**
+  * end_that_request_chunk - end I/O on a request
+  * @req:      the request being processed
+  * @uptodate: 1 for success, 0 for I/O error, < 0 for specific error
+  * @nr_bytes: number of bytes to complete
+  *
+  * Description:
+  *     Ends I/O on a number of bytes attached to @req, and sets it up
+  *     for the next range of segments (if any). Like end_that_request_first(),
+  *     but deals with bytes instead of sectors.
+  *
+  * Return:
+  *     0 - we are done with this request, call end_that_request_last()
+  *     1 - still buffers pending for this request
+  **/
+ int end_that_request_chunk(struct request *req, int uptodate, int nr_bytes)
+ {
+       return __end_that_request_first(req, uptodate, nr_bytes);
+ }
+ EXPORT_SYMBOL(end_that_request_chunk);
+ /*
+  * queue lock must be held
+  */
+ void end_that_request_last(struct request *req)
+ {
+       struct gendisk *disk = req->rq_disk;
+       if (unlikely(laptop_mode) && blk_fs_request(req))
+               laptop_io_completion();
+       if (disk && blk_fs_request(req)) {
+               unsigned long duration = jiffies - req->start_time;
+               const int rw = rq_data_dir(req);
+               __disk_stat_inc(disk, ios[rw]);
+               __disk_stat_add(disk, ticks[rw], duration);
+               disk_round_stats(disk);
+               disk->in_flight--;
+       }
+       if (req->end_io)
+               req->end_io(req);
+       else
+               __blk_put_request(req->q, req);
+ }
+ EXPORT_SYMBOL(end_that_request_last);
+ void end_request(struct request *req, int uptodate)
+ {
+       if (!end_that_request_first(req, uptodate, req->hard_cur_sectors)) {
+               add_disk_randomness(req->rq_disk);
+               blkdev_dequeue_request(req);
+               end_that_request_last(req);
+       }
+ }
+ EXPORT_SYMBOL(end_request);
+ void blk_rq_bio_prep(request_queue_t *q, struct request *rq, struct bio *bio)
+ {
+       /* first three bits are identical in rq->flags and bio->bi_rw */
+       rq->flags |= (bio->bi_rw & 7);
+       rq->nr_phys_segments = bio_phys_segments(q, bio);
+       rq->nr_hw_segments = bio_hw_segments(q, bio);
+       rq->current_nr_sectors = bio_cur_sectors(bio);
+       rq->hard_cur_sectors = rq->current_nr_sectors;
+       rq->hard_nr_sectors = rq->nr_sectors = bio_sectors(bio);
+       rq->buffer = bio_data(bio);
+       rq->bio = rq->biotail = bio;
+ }
+ EXPORT_SYMBOL(blk_rq_bio_prep);
+ int kblockd_schedule_work(struct work_struct *work)
+ {
+       return queue_work(kblockd_workqueue, work);
+ }
+ EXPORT_SYMBOL(kblockd_schedule_work);
+ void kblockd_flush(void)
+ {
+       flush_workqueue(kblockd_workqueue);
+ }
+ EXPORT_SYMBOL(kblockd_flush);
+ int __init blk_dev_init(void)
+ {
+       kblockd_workqueue = create_workqueue("kblockd");
+       if (!kblockd_workqueue)
+               panic("Failed to create kblockd\n");
+       request_cachep = kmem_cache_create("blkdev_requests",
+                       sizeof(struct request), 0, SLAB_PANIC, NULL, NULL);
+       requestq_cachep = kmem_cache_create("blkdev_queue",
+                       sizeof(request_queue_t), 0, SLAB_PANIC, NULL, NULL);
+       iocontext_cachep = kmem_cache_create("blkdev_ioc",
+                       sizeof(struct io_context), 0, SLAB_PANIC, NULL, NULL);
+       blk_max_low_pfn = max_low_pfn;
+       blk_max_pfn = max_pfn;
+       return 0;
+ }
+ /*
+  * IO Context helper functions
+  */
+ void put_io_context(struct io_context *ioc)
+ {
+       if (ioc == NULL)
+               return;
+       BUG_ON(atomic_read(&ioc->refcount) == 0);
+       if (atomic_dec_and_test(&ioc->refcount)) {
+               if (ioc->aic && ioc->aic->dtor)
+                       ioc->aic->dtor(ioc->aic);
+               if (ioc->cic && ioc->cic->dtor)
+                       ioc->cic->dtor(ioc->cic);
+               kmem_cache_free(iocontext_cachep, ioc);
+       }
+ }
+ EXPORT_SYMBOL(put_io_context);
+ /* Called by the exitting task */
+ void exit_io_context(void)
+ {
+       unsigned long flags;
+       struct io_context *ioc;
+       local_irq_save(flags);
+       task_lock(current);
+       ioc = current->io_context;
+       current->io_context = NULL;
+       ioc->task = NULL;
+       task_unlock(current);
+       local_irq_restore(flags);
+       if (ioc->aic && ioc->aic->exit)
+               ioc->aic->exit(ioc->aic);
+       if (ioc->cic && ioc->cic->exit)
+               ioc->cic->exit(ioc->cic);
+       put_io_context(ioc);
+ }
+ /*
+  * If the current task has no IO context then create one and initialise it.
+  * Otherwise, return its existing IO context.
+  *
+  * This returned IO context doesn't have a specifically elevated refcount,
+  * but since the current task itself holds a reference, the context can be
+  * used in general code, so long as it stays within `current` context.
+  */
+ struct io_context *current_io_context(gfp_t gfp_flags)
+ {
+       struct task_struct *tsk = current;
+       struct io_context *ret;
+       ret = tsk->io_context;
+       if (likely(ret))
+               return ret;
+       ret = kmem_cache_alloc(iocontext_cachep, gfp_flags);
+       if (ret) {
+               atomic_set(&ret->refcount, 1);
+               ret->task = current;
+               ret->set_ioprio = NULL;
+               ret->last_waited = jiffies; /* doesn't matter... */
+               ret->nr_batch_requests = 0; /* because this is 0 */
+               ret->aic = NULL;
+               ret->cic = NULL;
+               tsk->io_context = ret;
+       }
+       return ret;
+ }
+ EXPORT_SYMBOL(current_io_context);
+ /*
+  * If the current task has no IO context then create one and initialise it.
+  * If it does have a context, take a ref on it.
+  *
+  * This is always called in the context of the task which submitted the I/O.
+  */
+ struct io_context *get_io_context(gfp_t gfp_flags)
+ {
+       struct io_context *ret;
+       ret = current_io_context(gfp_flags);
+       if (likely(ret))
+               atomic_inc(&ret->refcount);
+       return ret;
+ }
+ EXPORT_SYMBOL(get_io_context);
+ void copy_io_context(struct io_context **pdst, struct io_context **psrc)
+ {
+       struct io_context *src = *psrc;
+       struct io_context *dst = *pdst;
+       if (src) {
+               BUG_ON(atomic_read(&src->refcount) == 0);
+               atomic_inc(&src->refcount);
+               put_io_context(dst);
+               *pdst = src;
+       }
+ }
+ EXPORT_SYMBOL(copy_io_context);
+ void swap_io_context(struct io_context **ioc1, struct io_context **ioc2)
+ {
+       struct io_context *temp;
+       temp = *ioc1;
+       *ioc1 = *ioc2;
+       *ioc2 = temp;
+ }
+ EXPORT_SYMBOL(swap_io_context);
+ /*
+  * sysfs parts below
+  */
+ struct queue_sysfs_entry {
+       struct attribute attr;
+       ssize_t (*show)(struct request_queue *, char *);
+       ssize_t (*store)(struct request_queue *, const char *, size_t);
+ };
+ static ssize_t
+ queue_var_show(unsigned int var, char *page)
+ {
+       return sprintf(page, "%d\n", var);
+ }
+ static ssize_t
+ queue_var_store(unsigned long *var, const char *page, size_t count)
+ {
+       char *p = (char *) page;
+       *var = simple_strtoul(p, &p, 10);
+       return count;
+ }
+ static ssize_t queue_requests_show(struct request_queue *q, char *page)
+ {
+       return queue_var_show(q->nr_requests, (page));
+ }
+ static ssize_t
+ queue_requests_store(struct request_queue *q, const char *page, size_t count)
+ {
+       struct request_list *rl = &q->rq;
+       int ret = queue_var_store(&q->nr_requests, page, count);
+       if (q->nr_requests < BLKDEV_MIN_RQ)
+               q->nr_requests = BLKDEV_MIN_RQ;
+       blk_queue_congestion_threshold(q);
+       if (rl->count[READ] >= queue_congestion_on_threshold(q))
+               set_queue_congested(q, READ);
+       else if (rl->count[READ] < queue_congestion_off_threshold(q))
+               clear_queue_congested(q, READ);
+       if (rl->count[WRITE] >= queue_congestion_on_threshold(q))
+               set_queue_congested(q, WRITE);
+       else if (rl->count[WRITE] < queue_congestion_off_threshold(q))
+               clear_queue_congested(q, WRITE);
+       if (rl->count[READ] >= q->nr_requests) {
+               blk_set_queue_full(q, READ);
+       } else if (rl->count[READ]+1 <= q->nr_requests) {
+               blk_clear_queue_full(q, READ);
+               wake_up(&rl->wait[READ]);
+       }
+       if (rl->count[WRITE] >= q->nr_requests) {
+               blk_set_queue_full(q, WRITE);
+       } else if (rl->count[WRITE]+1 <= q->nr_requests) {
+               blk_clear_queue_full(q, WRITE);
+               wake_up(&rl->wait[WRITE]);
+       }
+       return ret;
+ }
+ static ssize_t queue_ra_show(struct request_queue *q, char *page)
+ {
+       int ra_kb = q->backing_dev_info.ra_pages << (PAGE_CACHE_SHIFT - 10);
+       return queue_var_show(ra_kb, (page));
+ }
+ static ssize_t
+ queue_ra_store(struct request_queue *q, const char *page, size_t count)
+ {
+       unsigned long ra_kb;
+       ssize_t ret = queue_var_store(&ra_kb, page, count);
+       spin_lock_irq(q->queue_lock);
+       if (ra_kb > (q->max_sectors >> 1))
+               ra_kb = (q->max_sectors >> 1);
+       q->backing_dev_info.ra_pages = ra_kb >> (PAGE_CACHE_SHIFT - 10);
+       spin_unlock_irq(q->queue_lock);
+       return ret;
+ }
+ static ssize_t queue_max_sectors_show(struct request_queue *q, char *page)
+ {
+       int max_sectors_kb = q->max_sectors >> 1;
+       return queue_var_show(max_sectors_kb, (page));
+ }
+ static ssize_t
+ queue_max_sectors_store(struct request_queue *q, const char *page, size_t count)
+ {
+       unsigned long max_sectors_kb,
+                       max_hw_sectors_kb = q->max_hw_sectors >> 1,
+                       page_kb = 1 << (PAGE_CACHE_SHIFT - 10);
+       ssize_t ret = queue_var_store(&max_sectors_kb, page, count);
+       int ra_kb;
+       if (max_sectors_kb > max_hw_sectors_kb || max_sectors_kb < page_kb)
+               return -EINVAL;
+       /*
+        * Take the queue lock to update the readahead and max_sectors
+        * values synchronously:
+        */
+       spin_lock_irq(q->queue_lock);
+       /*
+        * Trim readahead window as well, if necessary:
+        */
+       ra_kb = q->backing_dev_info.ra_pages << (PAGE_CACHE_SHIFT - 10);
+       if (ra_kb > max_sectors_kb)
+               q->backing_dev_info.ra_pages =
+                               max_sectors_kb >> (PAGE_CACHE_SHIFT - 10);
+       q->max_sectors = max_sectors_kb << 1;
+       spin_unlock_irq(q->queue_lock);
+       return ret;
+ }
+ static ssize_t queue_max_hw_sectors_show(struct request_queue *q, char *page)
+ {
+       int max_hw_sectors_kb = q->max_hw_sectors >> 1;
+       return queue_var_show(max_hw_sectors_kb, (page));
+ }
+ static struct queue_sysfs_entry queue_requests_entry = {
+       .attr = {.name = "nr_requests", .mode = S_IRUGO | S_IWUSR },
+       .show = queue_requests_show,
+       .store = queue_requests_store,
+ };
+ static struct queue_sysfs_entry queue_ra_entry = {
+       .attr = {.name = "read_ahead_kb", .mode = S_IRUGO | S_IWUSR },
+       .show = queue_ra_show,
+       .store = queue_ra_store,
+ };
+ static struct queue_sysfs_entry queue_max_sectors_entry = {
+       .attr = {.name = "max_sectors_kb", .mode = S_IRUGO | S_IWUSR },
+       .show = queue_max_sectors_show,
+       .store = queue_max_sectors_store,
+ };
+ static struct queue_sysfs_entry queue_max_hw_sectors_entry = {
+       .attr = {.name = "max_hw_sectors_kb", .mode = S_IRUGO },
+       .show = queue_max_hw_sectors_show,
+ };
+ static struct queue_sysfs_entry queue_iosched_entry = {
+       .attr = {.name = "scheduler", .mode = S_IRUGO | S_IWUSR },
+       .show = elv_iosched_show,
+       .store = elv_iosched_store,
+ };
+ static struct attribute *default_attrs[] = {
+       &queue_requests_entry.attr,
+       &queue_ra_entry.attr,
+       &queue_max_hw_sectors_entry.attr,
+       &queue_max_sectors_entry.attr,
+       &queue_iosched_entry.attr,
+       NULL,
+ };
+ #define to_queue(atr) container_of((atr), struct queue_sysfs_entry, attr)
+ static ssize_t
+ queue_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
+ {
+       struct queue_sysfs_entry *entry = to_queue(attr);
+       struct request_queue *q;
+       q = container_of(kobj, struct request_queue, kobj);
+       if (!entry->show)
+               return -EIO;
+       return entry->show(q, page);
+ }
+ static ssize_t
+ queue_attr_store(struct kobject *kobj, struct attribute *attr,
+                   const char *page, size_t length)
+ {
+       struct queue_sysfs_entry *entry = to_queue(attr);
+       struct request_queue *q;
+       q = container_of(kobj, struct request_queue, kobj);
+       if (!entry->store)
+               return -EIO;
+       return entry->store(q, page, length);
+ }
+ static struct sysfs_ops queue_sysfs_ops = {
+       .show   = queue_attr_show,
+       .store  = queue_attr_store,
+ };
+ static struct kobj_type queue_ktype = {
+       .sysfs_ops      = &queue_sysfs_ops,
+       .default_attrs  = default_attrs,
+ };
+ int blk_register_queue(struct gendisk *disk)
+ {
+       int ret;
+       request_queue_t *q = disk->queue;
+       if (!q || !q->request_fn)
+               return -ENXIO;
+       q->kobj.parent = kobject_get(&disk->kobj);
+       if (!q->kobj.parent)
+               return -EBUSY;
+       snprintf(q->kobj.name, KOBJ_NAME_LEN, "%s", "queue");
+       q->kobj.ktype = &queue_ktype;
+       ret = kobject_register(&q->kobj);
+       if (ret < 0)
+               return ret;
+       ret = elv_register_queue(q);
+       if (ret) {
+               kobject_unregister(&q->kobj);
+               return ret;
+       }
+       return 0;
+ }
+ void blk_unregister_queue(struct gendisk *disk)
+ {
+       request_queue_t *q = disk->queue;
+       if (q && q->request_fn) {
+               elv_unregister_queue(q);
+               kobject_unregister(&q->kobj);
+               kobject_put(&disk->kobj);
+       }
+ }