Linux-2.6.12-rc2

[GitHub/mt8127/android_kernel_alcatel_ttab.git] / fs / xfs / linux-2.6 / xfs_buf.c

/*
 * Copyright (c) 2000-2004 Silicon Graphics, Inc.  All Rights Reserved.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of version 2 of the GNU General Public License as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it would be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 *
 * Further, this software is distributed without any warranty that it is
 * free of the rightful claim of any third person regarding infringement
 * or the like.  Any license provided herein, whether implied or
 * otherwise, applies only to this software file.  Patent licenses, if
 * any, provided herein do not apply to combinations of this program with
 * other software, or any other product whatsoever.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write the Free Software Foundation, Inc., 59
 * Temple Place - Suite 330, Boston MA 02111-1307, USA.
 *
 * Contact information: Silicon Graphics, Inc., 1600 Amphitheatre Pkwy,
 * Mountain View, CA  94043, or:
 *
 * http://www.sgi.com
 *
 * For further information regarding this notice, see:
 *
 * http://oss.sgi.com/projects/GenInfo/SGIGPLNoticeExplan/
 */

/*
 *      The xfs_buf.c code provides an abstract buffer cache model on top
 *      of the Linux page cache.  Cached metadata blocks for a file system
 *      are hashed to the inode for the block device.  xfs_buf.c assembles
 *      buffers (xfs_buf_t) on demand to aggregate such cached pages for I/O.
 *
 *      Written by Steve Lord, Jim Mostek, Russell Cattelan
 *                  and Rajagopal Ananthanarayanan ("ananth") at SGI.
 *
 */

#include <linux/stddef.h>
#include <linux/errno.h>
#include <linux/slab.h>
#include <linux/pagemap.h>
#include <linux/init.h>
#include <linux/vmalloc.h>
#include <linux/bio.h>
#include <linux/sysctl.h>
#include <linux/proc_fs.h>
#include <linux/workqueue.h>
#include <linux/percpu.h>
#include <linux/blkdev.h>
#include <linux/hash.h>

#include "xfs_linux.h"

/*
 * File wide globals
 */

STATIC kmem_cache_t *pagebuf_cache;
STATIC kmem_shaker_t pagebuf_shake;
STATIC int pagebuf_daemon_wakeup(int, unsigned int);
STATIC void pagebuf_delwri_queue(xfs_buf_t *, int);
STATIC struct workqueue_struct *pagebuf_logio_workqueue;
STATIC struct workqueue_struct *pagebuf_dataio_workqueue;

/*
 * Pagebuf debugging
 */

#ifdef PAGEBUF_TRACE
void
pagebuf_trace(
        xfs_buf_t       *pb,
        char            *id,
        void            *data,
        void            *ra)
{
        ktrace_enter(pagebuf_trace_buf,
                pb, id,
                (void *)(unsigned long)pb->pb_flags,
                (void *)(unsigned long)pb->pb_hold.counter,
                (void *)(unsigned long)pb->pb_sema.count.counter,
                (void *)current,
                data, ra,
                (void *)(unsigned long)((pb->pb_file_offset>>32) & 0xffffffff),
                (void *)(unsigned long)(pb->pb_file_offset & 0xffffffff),
                (void *)(unsigned long)pb->pb_buffer_length,
                NULL, NULL, NULL, NULL, NULL);
}
ktrace_t *pagebuf_trace_buf;
#define PAGEBUF_TRACE_SIZE      4096
#define PB_TRACE(pb, id, data)  \
        pagebuf_trace(pb, id, (void *)data, (void *)__builtin_return_address(0))
#else
#define PB_TRACE(pb, id, data)  do { } while (0)
#endif

#ifdef PAGEBUF_LOCK_TRACKING
# define PB_SET_OWNER(pb)       ((pb)->pb_last_holder = current->pid)
# define PB_CLEAR_OWNER(pb)     ((pb)->pb_last_holder = -1)
# define PB_GET_OWNER(pb)       ((pb)->pb_last_holder)
#else
# define PB_SET_OWNER(pb)       do { } while (0)
# define PB_CLEAR_OWNER(pb)     do { } while (0)
# define PB_GET_OWNER(pb)       do { } while (0)
#endif

/*
 * Pagebuf allocation / freeing.
 */

#define pb_to_gfp(flags) \
        ((((flags) & PBF_READ_AHEAD) ? __GFP_NORETRY : \
          ((flags) & PBF_DONT_BLOCK) ? GFP_NOFS : GFP_KERNEL) | __GFP_NOWARN)

#define pb_to_km(flags) \
         (((flags) & PBF_DONT_BLOCK) ? KM_NOFS : KM_SLEEP)


#define pagebuf_allocate(flags) \
        kmem_zone_alloc(pagebuf_cache, pb_to_km(flags))
#define pagebuf_deallocate(pb) \
        kmem_zone_free(pagebuf_cache, (pb));

/*
 * Page Region interfaces.
 *
 * For pages in filesystems where the blocksize is smaller than the
 * pagesize, we use the page->private field (long) to hold a bitmap
 * of uptodate regions within the page.
 *
 * Each such region is "bytes per page / bits per long" bytes long.
 *
 * NBPPR == number-of-bytes-per-page-region
 * BTOPR == bytes-to-page-region (rounded up)
 * BTOPRT == bytes-to-page-region-truncated (rounded down)
 */
#if (BITS_PER_LONG == 32)
#define PRSHIFT         (PAGE_CACHE_SHIFT - 5)  /* (32 == 1<<5) */
#elif (BITS_PER_LONG == 64)
#define PRSHIFT         (PAGE_CACHE_SHIFT - 6)  /* (64 == 1<<6) */
#else
#error BITS_PER_LONG must be 32 or 64
#endif
#define NBPPR           (PAGE_CACHE_SIZE/BITS_PER_LONG)
#define BTOPR(b)        (((unsigned int)(b) + (NBPPR - 1)) >> PRSHIFT)
#define BTOPRT(b)       (((unsigned int)(b) >> PRSHIFT))

STATIC unsigned long
page_region_mask(
        size_t          offset,
        size_t          length)
{
        unsigned long   mask;
        int             first, final;

        first = BTOPR(offset);
        final = BTOPRT(offset + length - 1);
        first = min(first, final);

        mask = ~0UL;
        mask <<= BITS_PER_LONG - (final - first);
        mask >>= BITS_PER_LONG - (final);

        ASSERT(offset + length <= PAGE_CACHE_SIZE);
        ASSERT((final - first) < BITS_PER_LONG && (final - first) >= 0);

        return mask;
}

STATIC inline void
set_page_region(
        struct page     *page,
        size_t          offset,
        size_t          length)
{
        page->private |= page_region_mask(offset, length);
        if (page->private == ~0UL)
                SetPageUptodate(page);
}

STATIC inline int
test_page_region(
        struct page     *page,
        size_t          offset,
        size_t          length)
{
        unsigned long   mask = page_region_mask(offset, length);

        return (mask && (page->private & mask) == mask);
}

/*
 * Mapping of multi-page buffers into contiguous virtual space
 */

typedef struct a_list {
        void            *vm_addr;
        struct a_list   *next;
} a_list_t;

STATIC a_list_t         *as_free_head;
STATIC int              as_list_len;
STATIC DEFINE_SPINLOCK(as_lock);

/*
 * Try to batch vunmaps because they are costly.
 */
STATIC void
free_address(
        void            *addr)
{
        a_list_t        *aentry;

        aentry = kmalloc(sizeof(a_list_t), GFP_ATOMIC & ~__GFP_HIGH);
        if (likely(aentry)) {
                spin_lock(&as_lock);
                aentry->next = as_free_head;
                aentry->vm_addr = addr;
                as_free_head = aentry;
                as_list_len++;
                spin_unlock(&as_lock);
        } else {
                vunmap(addr);
        }
}

STATIC void
purge_addresses(void)
{
        a_list_t        *aentry, *old;

        if (as_free_head == NULL)
                return;

        spin_lock(&as_lock);
        aentry = as_free_head;
        as_free_head = NULL;
        as_list_len = 0;
        spin_unlock(&as_lock);

        while ((old = aentry) != NULL) {
                vunmap(aentry->vm_addr);
                aentry = aentry->next;
                kfree(old);
        }
}

/*
 *      Internal pagebuf object manipulation
 */

STATIC void
_pagebuf_initialize(
        xfs_buf_t               *pb,
        xfs_buftarg_t           *target,
        loff_t                  range_base,
        size_t                  range_length,
        page_buf_flags_t        flags)
{
        /*
         * We don't want certain flags to appear in pb->pb_flags.
         */
        flags &= ~(PBF_LOCK|PBF_MAPPED|PBF_DONT_BLOCK|PBF_READ_AHEAD);

        memset(pb, 0, sizeof(xfs_buf_t));
        atomic_set(&pb->pb_hold, 1);
        init_MUTEX_LOCKED(&pb->pb_iodonesema);
        INIT_LIST_HEAD(&pb->pb_list);
        INIT_LIST_HEAD(&pb->pb_hash_list);
        init_MUTEX_LOCKED(&pb->pb_sema); /* held, no waiters */
        PB_SET_OWNER(pb);
        pb->pb_target = target;
        pb->pb_file_offset = range_base;
        /*
         * Set buffer_length and count_desired to the same value initially.
         * I/O routines should use count_desired, which will be the same in
         * most cases but may be reset (e.g. XFS recovery).
         */
        pb->pb_buffer_length = pb->pb_count_desired = range_length;
        pb->pb_flags = flags | PBF_NONE;
        pb->pb_bn = XFS_BUF_DADDR_NULL;
        atomic_set(&pb->pb_pin_count, 0);
        init_waitqueue_head(&pb->pb_waiters);

        XFS_STATS_INC(pb_create);
        PB_TRACE(pb, "initialize", target);
}

/*
 * Allocate a page array capable of holding a specified number
 * of pages, and point the page buf at it.
 */
STATIC int
_pagebuf_get_pages(
        xfs_buf_t               *pb,
        int                     page_count,
        page_buf_flags_t        flags)
{
        /* Make sure that we have a page list */
        if (pb->pb_pages == NULL) {
                pb->pb_offset = page_buf_poff(pb->pb_file_offset);
                pb->pb_page_count = page_count;
                if (page_count <= PB_PAGES) {
                        pb->pb_pages = pb->pb_page_array;
                } else {
                        pb->pb_pages = kmem_alloc(sizeof(struct page *) *
                                        page_count, pb_to_km(flags));
                        if (pb->pb_pages == NULL)
                                return -ENOMEM;
                }
                memset(pb->pb_pages, 0, sizeof(struct page *) * page_count);
        }
        return 0;
}

/*
 *      Frees pb_pages if it was malloced.
 */
STATIC void
_pagebuf_free_pages(
        xfs_buf_t       *bp)
{
        if (bp->pb_pages != bp->pb_page_array) {
                kmem_free(bp->pb_pages,
                          bp->pb_page_count * sizeof(struct page *));
        }
}

/*
 *      Releases the specified buffer.
 *
 *      The modification state of any associated pages is left unchanged.
 *      The buffer most not be on any hash - use pagebuf_rele instead for
 *      hashed and refcounted buffers
 */
void
pagebuf_free(
        xfs_buf_t               *bp)
{
        PB_TRACE(bp, "free", 0);

        ASSERT(list_empty(&bp->pb_hash_list));

        if (bp->pb_flags & _PBF_PAGE_CACHE) {
                uint            i;

                if ((bp->pb_flags & PBF_MAPPED) && (bp->pb_page_count > 1))
                        free_address(bp->pb_addr - bp->pb_offset);

                for (i = 0; i < bp->pb_page_count; i++)
                        page_cache_release(bp->pb_pages[i]);
                _pagebuf_free_pages(bp);
        } else if (bp->pb_flags & _PBF_KMEM_ALLOC) {
                 /*
                  * XXX(hch): bp->pb_count_desired might be incorrect (see
                  * pagebuf_associate_memory for details), but fortunately
                  * the Linux version of kmem_free ignores the len argument..
                  */
                kmem_free(bp->pb_addr, bp->pb_count_desired);
                _pagebuf_free_pages(bp);
        }

        pagebuf_deallocate(bp);
}

/*
 *      Finds all pages for buffer in question and builds it's page list.
 */
STATIC int
_pagebuf_lookup_pages(
        xfs_buf_t               *bp,
        uint                    flags)
{
        struct address_space    *mapping = bp->pb_target->pbr_mapping;
        size_t                  blocksize = bp->pb_target->pbr_bsize;
        size_t                  size = bp->pb_count_desired;
        size_t                  nbytes, offset;
        int                     gfp_mask = pb_to_gfp(flags);
        unsigned short          page_count, i;
        pgoff_t                 first;
        loff_t                  end;
        int                     error;

        end = bp->pb_file_offset + bp->pb_buffer_length;
        page_count = page_buf_btoc(end) - page_buf_btoct(bp->pb_file_offset);

        error = _pagebuf_get_pages(bp, page_count, flags);
        if (unlikely(error))
                return error;
        bp->pb_flags |= _PBF_PAGE_CACHE;

        offset = bp->pb_offset;
        first = bp->pb_file_offset >> PAGE_CACHE_SHIFT;

        for (i = 0; i < bp->pb_page_count; i++) {
                struct page     *page;
                uint            retries = 0;

              retry:
                page = find_or_create_page(mapping, first + i, gfp_mask);
                if (unlikely(page == NULL)) {
                        if (flags & PBF_READ_AHEAD) {
                                bp->pb_page_count = i;
                                for (i = 0; i < bp->pb_page_count; i++)
                                        unlock_page(bp->pb_pages[i]);
                                return -ENOMEM;
                        }

                        /*
                         * This could deadlock.
                         *
                         * But until all the XFS lowlevel code is revamped to
                         * handle buffer allocation failures we can't do much.
                         */
                        if (!(++retries % 100))
                                printk(KERN_ERR
                                        "XFS: possible memory allocation "
                                        "deadlock in %s (mode:0x%x)\n",
                                        __FUNCTION__, gfp_mask);

                        XFS_STATS_INC(pb_page_retries);
                        pagebuf_daemon_wakeup(0, gfp_mask);
                        blk_congestion_wait(WRITE, HZ/50);
                        goto retry;
                }

                XFS_STATS_INC(pb_page_found);

                nbytes = min_t(size_t, size, PAGE_CACHE_SIZE - offset);
                size -= nbytes;

                if (!PageUptodate(page)) {
                        page_count--;
                        if (blocksize >= PAGE_CACHE_SIZE) {
                                if (flags & PBF_READ)
                                        bp->pb_locked = 1;
                        } else if (!PagePrivate(page)) {
                                if (test_page_region(page, offset, nbytes))
                                        page_count++;
                        }
                }

                bp->pb_pages[i] = page;
                offset = 0;
        }

        if (!bp->pb_locked) {
                for (i = 0; i < bp->pb_page_count; i++)
                        unlock_page(bp->pb_pages[i]);
        }

        if (page_count) {
                /* if we have any uptodate pages, mark that in the buffer */
                bp->pb_flags &= ~PBF_NONE;

                /* if some pages aren't uptodate, mark that in the buffer */
                if (page_count != bp->pb_page_count)
                        bp->pb_flags |= PBF_PARTIAL;
        }

        PB_TRACE(bp, "lookup_pages", (long)page_count);
        return error;
}

/*
 *      Map buffer into kernel address-space if nessecary.
 */
STATIC int
_pagebuf_map_pages(
        xfs_buf_t               *bp,
        uint                    flags)
{
        /* A single page buffer is always mappable */
        if (bp->pb_page_count == 1) {
                bp->pb_addr = page_address(bp->pb_pages[0]) + bp->pb_offset;
                bp->pb_flags |= PBF_MAPPED;
        } else if (flags & PBF_MAPPED) {
                if (as_list_len > 64)
                        purge_addresses();
                bp->pb_addr = vmap(bp->pb_pages, bp->pb_page_count,
                                VM_MAP, PAGE_KERNEL);
                if (unlikely(bp->pb_addr == NULL))
                        return -ENOMEM;
                bp->pb_addr += bp->pb_offset;
                bp->pb_flags |= PBF_MAPPED;
        }

        return 0;
}

/*
 *      Finding and Reading Buffers
 */

/*
 *      _pagebuf_find
 *
 *      Looks up, and creates if absent, a lockable buffer for
 *      a given range of an inode.  The buffer is returned
 *      locked.  If other overlapping buffers exist, they are
 *      released before the new buffer is created and locked,
 *      which may imply that this call will block until those buffers
 *      are unlocked.  No I/O is implied by this call.
 */
xfs_buf_t *
_pagebuf_find(
        xfs_buftarg_t           *btp,   /* block device target          */
        loff_t                  ioff,   /* starting offset of range     */
        size_t                  isize,  /* length of range              */
        page_buf_flags_t        flags,  /* PBF_TRYLOCK                  */
        xfs_buf_t               *new_pb)/* newly allocated buffer       */
{
        loff_t                  range_base;
        size_t                  range_length;
        xfs_bufhash_t           *hash;
        xfs_buf_t               *pb, *n;

        range_base = (ioff << BBSHIFT);
        range_length = (isize << BBSHIFT);

        /* Check for IOs smaller than the sector size / not sector aligned */
        ASSERT(!(range_length < (1 << btp->pbr_sshift)));
        ASSERT(!(range_base & (loff_t)btp->pbr_smask));

        hash = &btp->bt_hash[hash_long((unsigned long)ioff, btp->bt_hashshift)];

        spin_lock(&hash->bh_lock);

        list_for_each_entry_safe(pb, n, &hash->bh_list, pb_hash_list) {
                ASSERT(btp == pb->pb_target);
                if (pb->pb_file_offset == range_base &&
                    pb->pb_buffer_length == range_length) {
                        /*
                         * If we look at something bring it to the
                         * front of the list for next time.
                         */
                        atomic_inc(&pb->pb_hold);
                        list_move(&pb->pb_hash_list, &hash->bh_list);
                        goto found;
                }
        }

        /* No match found */
        if (new_pb) {
                _pagebuf_initialize(new_pb, btp, range_base,
                                range_length, flags);
                new_pb->pb_hash = hash;
                list_add(&new_pb->pb_hash_list, &hash->bh_list);
        } else {
                XFS_STATS_INC(pb_miss_locked);
        }

        spin_unlock(&hash->bh_lock);
        return new_pb;

found:
        spin_unlock(&hash->bh_lock);

        /* Attempt to get the semaphore without sleeping,
         * if this does not work then we need to drop the
         * spinlock and do a hard attempt on the semaphore.
         */
        if (down_trylock(&pb->pb_sema)) {
                if (!(flags & PBF_TRYLOCK)) {
                        /* wait for buffer ownership */
                        PB_TRACE(pb, "get_lock", 0);
                        pagebuf_lock(pb);
                        XFS_STATS_INC(pb_get_locked_waited);
                } else {
                        /* We asked for a trylock and failed, no need
                         * to look at file offset and length here, we
                         * know that this pagebuf at least overlaps our
                         * pagebuf and is locked, therefore our buffer
                         * either does not exist, or is this buffer
                         */

                        pagebuf_rele(pb);
                        XFS_STATS_INC(pb_busy_locked);
                        return (NULL);
                }
        } else {
                /* trylock worked */
                PB_SET_OWNER(pb);
        }

        if (pb->pb_flags & PBF_STALE)
                pb->pb_flags &= PBF_MAPPED;
        PB_TRACE(pb, "got_lock", 0);
        XFS_STATS_INC(pb_get_locked);
        return (pb);
}

/*
 *      xfs_buf_get_flags assembles a buffer covering the specified range.
 *
 *      Storage in memory for all portions of the buffer will be allocated,
 *      although backing storage may not be.
 */
xfs_buf_t *
xfs_buf_get_flags(                      /* allocate a buffer            */
        xfs_buftarg_t           *target,/* target for buffer            */
        loff_t                  ioff,   /* starting offset of range     */
        size_t                  isize,  /* length of range              */
        page_buf_flags_t        flags)  /* PBF_TRYLOCK                  */
{
        xfs_buf_t               *pb, *new_pb;
        int                     error = 0, i;

        new_pb = pagebuf_allocate(flags);
        if (unlikely(!new_pb))
                return NULL;

        pb = _pagebuf_find(target, ioff, isize, flags, new_pb);
        if (pb == new_pb) {
                error = _pagebuf_lookup_pages(pb, flags);
                if (error)
                        goto no_buffer;
        } else {
                pagebuf_deallocate(new_pb);
                if (unlikely(pb == NULL))
                        return NULL;
        }

        for (i = 0; i < pb->pb_page_count; i++)
                mark_page_accessed(pb->pb_pages[i]);

        if (!(pb->pb_flags & PBF_MAPPED)) {
                error = _pagebuf_map_pages(pb, flags);
                if (unlikely(error)) {
                        printk(KERN_WARNING "%s: failed to map pages\n",
                                        __FUNCTION__);
                        goto no_buffer;
                }
        }

        XFS_STATS_INC(pb_get);

        /*
         * Always fill in the block number now, the mapped cases can do
         * their own overlay of this later.
         */
        pb->pb_bn = ioff;
        pb->pb_count_desired = pb->pb_buffer_length;

        PB_TRACE(pb, "get", (unsigned long)flags);
        return pb;

 no_buffer:
        if (flags & (PBF_LOCK | PBF_TRYLOCK))
                pagebuf_unlock(pb);
        pagebuf_rele(pb);
        return NULL;
}

xfs_buf_t *
xfs_buf_read_flags(
        xfs_buftarg_t           *target,
        loff_t                  ioff,
        size_t                  isize,
        page_buf_flags_t        flags)
{
        xfs_buf_t               *pb;

        flags |= PBF_READ;

        pb = xfs_buf_get_flags(target, ioff, isize, flags);
        if (pb) {
                if (PBF_NOT_DONE(pb)) {
                        PB_TRACE(pb, "read", (unsigned long)flags);
                        XFS_STATS_INC(pb_get_read);
                        pagebuf_iostart(pb, flags);
                } else if (flags & PBF_ASYNC) {
                        PB_TRACE(pb, "read_async", (unsigned long)flags);
                        /*
                         * Read ahead call which is already satisfied,
                         * drop the buffer
                         */
                        goto no_buffer;
                } else {
                        PB_TRACE(pb, "read_done", (unsigned long)flags);
                        /* We do not want read in the flags */
                        pb->pb_flags &= ~PBF_READ;
                }
        }

        return pb;

 no_buffer:
        if (flags & (PBF_LOCK | PBF_TRYLOCK))
                pagebuf_unlock(pb);
        pagebuf_rele(pb);
        return NULL;
}

/*
 * Create a skeletal pagebuf (no pages associated with it).
 */
xfs_buf_t *
pagebuf_lookup(
        xfs_buftarg_t           *target,
        loff_t                  ioff,
        size_t                  isize,
        page_buf_flags_t        flags)
{
        xfs_buf_t               *pb;

        pb = pagebuf_allocate(flags);
        if (pb) {
                _pagebuf_initialize(pb, target, ioff, isize, flags);
        }
        return pb;
}

/*
 * If we are not low on memory then do the readahead in a deadlock
 * safe manner.
 */
void
pagebuf_readahead(
        xfs_buftarg_t           *target,
        loff_t                  ioff,
        size_t                  isize,
        page_buf_flags_t        flags)
{
        struct backing_dev_info *bdi;

        bdi = target->pbr_mapping->backing_dev_info;
        if (bdi_read_congested(bdi))
                return;

        flags |= (PBF_TRYLOCK|PBF_ASYNC|PBF_READ_AHEAD);
        xfs_buf_read_flags(target, ioff, isize, flags);
}

xfs_buf_t *
pagebuf_get_empty(
        size_t                  len,
        xfs_buftarg_t           *target)
{
        xfs_buf_t               *pb;

        pb = pagebuf_allocate(0);
        if (pb)
                _pagebuf_initialize(pb, target, 0, len, 0);
        return pb;
}

static inline struct page *
mem_to_page(
        void                    *addr)
{
        if (((unsigned long)addr < VMALLOC_START) ||
            ((unsigned long)addr >= VMALLOC_END)) {
                return virt_to_page(addr);
        } else {
                return vmalloc_to_page(addr);
        }
}

int
pagebuf_associate_memory(
        xfs_buf_t               *pb,
        void                    *mem,
        size_t                  len)
{
        int                     rval;
        int                     i = 0;
        size_t                  ptr;
        size_t                  end, end_cur;
        off_t                   offset;
        int                     page_count;

        page_count = PAGE_CACHE_ALIGN(len) >> PAGE_CACHE_SHIFT;
        offset = (off_t) mem - ((off_t)mem & PAGE_CACHE_MASK);
        if (offset && (len > PAGE_CACHE_SIZE))
                page_count++;

        /* Free any previous set of page pointers */
        if (pb->pb_pages)
                _pagebuf_free_pages(pb);

        pb->pb_pages = NULL;
        pb->pb_addr = mem;

        rval = _pagebuf_get_pages(pb, page_count, 0);
        if (rval)
                return rval;

        pb->pb_offset = offset;
        ptr = (size_t) mem & PAGE_CACHE_MASK;
        end = PAGE_CACHE_ALIGN((size_t) mem + len);
        end_cur = end;
        /* set up first page */
        pb->pb_pages[0] = mem_to_page(mem);

        ptr += PAGE_CACHE_SIZE;
        pb->pb_page_count = ++i;
        while (ptr < end) {
                pb->pb_pages[i] = mem_to_page((void *)ptr);
                pb->pb_page_count = ++i;
                ptr += PAGE_CACHE_SIZE;
        }
        pb->pb_locked = 0;

        pb->pb_count_desired = pb->pb_buffer_length = len;
        pb->pb_flags |= PBF_MAPPED;

        return 0;
}

xfs_buf_t *
pagebuf_get_no_daddr(
        size_t                  len,
        xfs_buftarg_t           *target)
{
        size_t                  malloc_len = len;
        xfs_buf_t               *bp;
        void                    *data;
        int                     error;

        bp = pagebuf_allocate(0);
        if (unlikely(bp == NULL))
                goto fail;
        _pagebuf_initialize(bp, target, 0, len, PBF_FORCEIO);

 try_again:
        data = kmem_alloc(malloc_len, KM_SLEEP | KM_MAYFAIL);
        if (unlikely(data == NULL))
                goto fail_free_buf;

        /* check whether alignment matches.. */
        if ((__psunsigned_t)data !=
            ((__psunsigned_t)data & ~target->pbr_smask)) {
                /* .. else double the size and try again */
                kmem_free(data, malloc_len);
                malloc_len <<= 1;
                goto try_again;
        }

        error = pagebuf_associate_memory(bp, data, len);
        if (error)
                goto fail_free_mem;
        bp->pb_flags |= _PBF_KMEM_ALLOC;

        pagebuf_unlock(bp);

        PB_TRACE(bp, "no_daddr", data);
        return bp;
 fail_free_mem:
        kmem_free(data, malloc_len);
 fail_free_buf:
        pagebuf_free(bp);
 fail:
        return NULL;
}

/*
 *      pagebuf_hold
 *
 *      Increment reference count on buffer, to hold the buffer concurrently
 *      with another thread which may release (free) the buffer asynchronously.
 *
 *      Must hold the buffer already to call this function.
 */
void
pagebuf_hold(
        xfs_buf_t               *pb)
{
        atomic_inc(&pb->pb_hold);
        PB_TRACE(pb, "hold", 0);
}

/*
 *      pagebuf_rele
 *
 *      pagebuf_rele releases a hold on the specified buffer.  If the
 *      the hold count is 1, pagebuf_rele calls pagebuf_free.
 */
void
pagebuf_rele(
        xfs_buf_t               *pb)
{
        xfs_bufhash_t           *hash = pb->pb_hash;

        PB_TRACE(pb, "rele", pb->pb_relse);

        /*
         * pagebuf_lookup buffers are not hashed, not delayed write,
         * and don't have their own release routines.  Special case.
         */
        if (unlikely(!hash)) {
                ASSERT(!pb->pb_relse);
                if (atomic_dec_and_test(&pb->pb_hold))
                        xfs_buf_free(pb);
                return;
        }

        if (atomic_dec_and_lock(&pb->pb_hold, &hash->bh_lock)) {
                int             do_free = 1;

                if (pb->pb_relse) {
                        atomic_inc(&pb->pb_hold);
                        spin_unlock(&hash->bh_lock);
                        (*(pb->pb_relse)) (pb);
                        spin_lock(&hash->bh_lock);
                        do_free = 0;
                }

                if (pb->pb_flags & PBF_DELWRI) {
                        pb->pb_flags |= PBF_ASYNC;
                        atomic_inc(&pb->pb_hold);
                        pagebuf_delwri_queue(pb, 0);
                        do_free = 0;
                } else if (pb->pb_flags & PBF_FS_MANAGED) {
                        do_free = 0;
                }

                if (do_free) {
                        list_del_init(&pb->pb_hash_list);
                        spin_unlock(&hash->bh_lock);
                        pagebuf_free(pb);
                } else {
                        spin_unlock(&hash->bh_lock);
                }
        }
}


/*
 *      Mutual exclusion on buffers.  Locking model:
 *
 *      Buffers associated with inodes for which buffer locking
 *      is not enabled are not protected by semaphores, and are
 *      assumed to be exclusively owned by the caller.  There is a
 *      spinlock in the buffer, used by the caller when concurrent
 *      access is possible.
 */

/*
 *      pagebuf_cond_lock
 *
 *      pagebuf_cond_lock locks a buffer object, if it is not already locked.
 *      Note that this in no way
 *      locks the underlying pages, so it is only useful for synchronizing
 *      concurrent use of page buffer objects, not for synchronizing independent
 *      access to the underlying pages.
 */
int
pagebuf_cond_lock(                      /* lock buffer, if not locked   */
                                        /* returns -EBUSY if locked)    */
        xfs_buf_t               *pb)
{
        int                     locked;

        locked = down_trylock(&pb->pb_sema) == 0;
        if (locked) {
                PB_SET_OWNER(pb);
        }
        PB_TRACE(pb, "cond_lock", (long)locked);
        return(locked ? 0 : -EBUSY);
}

#if defined(DEBUG) || defined(XFS_BLI_TRACE)
/*
 *      pagebuf_lock_value
 *
 *      Return lock value for a pagebuf
 */
int
pagebuf_lock_value(
        xfs_buf_t               *pb)
{
        return(atomic_read(&pb->pb_sema.count));
}
#endif

/*
 *      pagebuf_lock
 *
 *      pagebuf_lock locks a buffer object.  Note that this in no way
 *      locks the underlying pages, so it is only useful for synchronizing
 *      concurrent use of page buffer objects, not for synchronizing independent
 *      access to the underlying pages.
 */
int
pagebuf_lock(
        xfs_buf_t               *pb)
{
        PB_TRACE(pb, "lock", 0);
        if (atomic_read(&pb->pb_io_remaining))
                blk_run_address_space(pb->pb_target->pbr_mapping);
        down(&pb->pb_sema);
        PB_SET_OWNER(pb);
        PB_TRACE(pb, "locked", 0);
        return 0;
}

/*
 *      pagebuf_unlock
 *
 *      pagebuf_unlock releases the lock on the buffer object created by
 *      pagebuf_lock or pagebuf_cond_lock (not any
 *      pinning of underlying pages created by pagebuf_pin).
 */
void
pagebuf_unlock(                         /* unlock buffer                */
        xfs_buf_t               *pb)    /* buffer to unlock             */
{
        PB_CLEAR_OWNER(pb);
        up(&pb->pb_sema);
        PB_TRACE(pb, "unlock", 0);
}


/*
 *      Pinning Buffer Storage in Memory
 */

/*
 *      pagebuf_pin
 *
 *      pagebuf_pin locks all of the memory represented by a buffer in
 *      memory.  Multiple calls to pagebuf_pin and pagebuf_unpin, for
 *      the same or different buffers affecting a given page, will
 *      properly count the number of outstanding "pin" requests.  The
 *      buffer may be released after the pagebuf_pin and a different
 *      buffer used when calling pagebuf_unpin, if desired.
 *      pagebuf_pin should be used by the file system when it wants be
 *      assured that no attempt will be made to force the affected
 *      memory to disk.  It does not assure that a given logical page
 *      will not be moved to a different physical page.
 */
void
pagebuf_pin(
        xfs_buf_t               *pb)
{
        atomic_inc(&pb->pb_pin_count);
        PB_TRACE(pb, "pin", (long)pb->pb_pin_count.counter);
}

/*
 *      pagebuf_unpin
 *
 *      pagebuf_unpin reverses the locking of memory performed by
 *      pagebuf_pin.  Note that both functions affected the logical
 *      pages associated with the buffer, not the buffer itself.
 */
void
pagebuf_unpin(
        xfs_buf_t               *pb)
{
        if (atomic_dec_and_test(&pb->pb_pin_count)) {
                wake_up_all(&pb->pb_waiters);
        }
        PB_TRACE(pb, "unpin", (long)pb->pb_pin_count.counter);
}

int
pagebuf_ispin(
        xfs_buf_t               *pb)
{
        return atomic_read(&pb->pb_pin_count);
}

/*
 *      pagebuf_wait_unpin
 *
 *      pagebuf_wait_unpin waits until all of the memory associated
 *      with the buffer is not longer locked in memory.  It returns
 *      immediately if none of the affected pages are locked.
 */
static inline void
_pagebuf_wait_unpin(
        xfs_buf_t               *pb)
{
        DECLARE_WAITQUEUE       (wait, current);

        if (atomic_read(&pb->pb_pin_count) == 0)
                return;

        add_wait_queue(&pb->pb_waiters, &wait);
        for (;;) {
                set_current_state(TASK_UNINTERRUPTIBLE);
                if (atomic_read(&pb->pb_pin_count) == 0)
                        break;
                if (atomic_read(&pb->pb_io_remaining))
                        blk_run_address_space(pb->pb_target->pbr_mapping);
                schedule();
        }
        remove_wait_queue(&pb->pb_waiters, &wait);
        set_current_state(TASK_RUNNING);
}

/*
 *      Buffer Utility Routines
 */

/*
 *      pagebuf_iodone
 *
 *      pagebuf_iodone marks a buffer for which I/O is in progress
 *      done with respect to that I/O.  The pb_iodone routine, if
 *      present, will be called as a side-effect.
 */
STATIC void
pagebuf_iodone_work(
        void                    *v)
{
        xfs_buf_t               *bp = (xfs_buf_t *)v;

        if (bp->pb_iodone)
                (*(bp->pb_iodone))(bp);
        else if (bp->pb_flags & PBF_ASYNC)
                xfs_buf_relse(bp);
}

void
pagebuf_iodone(
        xfs_buf_t               *pb,
        int                     dataio,
        int                     schedule)
{
        pb->pb_flags &= ~(PBF_READ | PBF_WRITE);
        if (pb->pb_error == 0) {
                pb->pb_flags &= ~(PBF_PARTIAL | PBF_NONE);
        }

        PB_TRACE(pb, "iodone", pb->pb_iodone);

        if ((pb->pb_iodone) || (pb->pb_flags & PBF_ASYNC)) {
                if (schedule) {
                        INIT_WORK(&pb->pb_iodone_work, pagebuf_iodone_work, pb);
                        queue_work(dataio ? pagebuf_dataio_workqueue :
                                pagebuf_logio_workqueue, &pb->pb_iodone_work);
                } else {
                        pagebuf_iodone_work(pb);
                }
        } else {
                up(&pb->pb_iodonesema);
        }
}

/*
 *      pagebuf_ioerror
 *
 *      pagebuf_ioerror sets the error code for a buffer.
 */
void
pagebuf_ioerror(                        /* mark/clear buffer error flag */
        xfs_buf_t               *pb,    /* buffer to mark               */
        int                     error)  /* error to store (0 if none)   */
{
        ASSERT(error >= 0 && error <= 0xffff);
        pb->pb_error = (unsigned short)error;
        PB_TRACE(pb, "ioerror", (unsigned long)error);
}

/*
 *      pagebuf_iostart
 *
 *      pagebuf_iostart initiates I/O on a buffer, based on the flags supplied.
 *      If necessary, it will arrange for any disk space allocation required,
 *      and it will break up the request if the block mappings require it.
 *      The pb_iodone routine in the buffer supplied will only be called
 *      when all of the subsidiary I/O requests, if any, have been completed.
 *      pagebuf_iostart calls the pagebuf_ioinitiate routine or
 *      pagebuf_iorequest, if the former routine is not defined, to start
 *      the I/O on a given low-level request.
 */
int
pagebuf_iostart(                        /* start I/O on a buffer          */
        xfs_buf_t               *pb,    /* buffer to start                */
        page_buf_flags_t        flags)  /* PBF_LOCK, PBF_ASYNC, PBF_READ, */
                                        /* PBF_WRITE, PBF_DELWRI,         */
                                        /* PBF_DONT_BLOCK                 */
{
        int                     status = 0;

        PB_TRACE(pb, "iostart", (unsigned long)flags);

        if (flags & PBF_DELWRI) {
                pb->pb_flags &= ~(PBF_READ | PBF_WRITE | PBF_ASYNC);
                pb->pb_flags |= flags & (PBF_DELWRI | PBF_ASYNC);
                pagebuf_delwri_queue(pb, 1);
                return status;
        }

        pb->pb_flags &= ~(PBF_READ | PBF_WRITE | PBF_ASYNC | PBF_DELWRI | \
                        PBF_READ_AHEAD | _PBF_RUN_QUEUES);
        pb->pb_flags |= flags & (PBF_READ | PBF_WRITE | PBF_ASYNC | \
                        PBF_READ_AHEAD | _PBF_RUN_QUEUES);

        BUG_ON(pb->pb_bn == XFS_BUF_DADDR_NULL);

        /* For writes allow an alternate strategy routine to precede
         * the actual I/O request (which may not be issued at all in
         * a shutdown situation, for example).
         */
        status = (flags & PBF_WRITE) ?
                pagebuf_iostrategy(pb) : pagebuf_iorequest(pb);

        /* Wait for I/O if we are not an async request.
         * Note: async I/O request completion will release the buffer,
         * and that can already be done by this point.  So using the
         * buffer pointer from here on, after async I/O, is invalid.
         */
        if (!status && !(flags & PBF_ASYNC))
                status = pagebuf_iowait(pb);

        return status;
}

/*
 * Helper routine for pagebuf_iorequest
 */

STATIC __inline__ int
_pagebuf_iolocked(
        xfs_buf_t               *pb)
{
        ASSERT(pb->pb_flags & (PBF_READ|PBF_WRITE));
        if (pb->pb_flags & PBF_READ)
                return pb->pb_locked;
        return 0;
}

STATIC __inline__ void
_pagebuf_iodone(
        xfs_buf_t               *pb,
        int                     schedule)
{
        if (atomic_dec_and_test(&pb->pb_io_remaining) == 1) {
                pb->pb_locked = 0;
                pagebuf_iodone(pb, (pb->pb_flags & PBF_FS_DATAIOD), schedule);
        }
}

STATIC int
bio_end_io_pagebuf(
        struct bio              *bio,
        unsigned int            bytes_done,
        int                     error)
{
        xfs_buf_t               *pb = (xfs_buf_t *)bio->bi_private;
        unsigned int            i, blocksize = pb->pb_target->pbr_bsize;
        struct bio_vec          *bvec = bio->bi_io_vec;

        if (bio->bi_size)
                return 1;

        if (!test_bit(BIO_UPTODATE, &bio->bi_flags))
                pb->pb_error = EIO;

        for (i = 0; i < bio->bi_vcnt; i++, bvec++) {
                struct page     *page = bvec->bv_page;

                if (pb->pb_error) {
                        SetPageError(page);
                } else if (blocksize == PAGE_CACHE_SIZE) {
                        SetPageUptodate(page);
                } else if (!PagePrivate(page) &&
                                (pb->pb_flags & _PBF_PAGE_CACHE)) {
                        set_page_region(page, bvec->bv_offset, bvec->bv_len);
                }

                if (_pagebuf_iolocked(pb)) {
                        unlock_page(page);
                }
        }

        _pagebuf_iodone(pb, 1);
        bio_put(bio);
        return 0;
}

STATIC void
_pagebuf_ioapply(
        xfs_buf_t               *pb)
{
        int                     i, rw, map_i, total_nr_pages, nr_pages;
        struct bio              *bio;
        int                     offset = pb->pb_offset;
        int                     size = pb->pb_count_desired;
        sector_t                sector = pb->pb_bn;
        unsigned int            blocksize = pb->pb_target->pbr_bsize;
        int                     locking = _pagebuf_iolocked(pb);

        total_nr_pages = pb->pb_page_count;
        map_i = 0;

        if (pb->pb_flags & _PBF_RUN_QUEUES) {
                pb->pb_flags &= ~_PBF_RUN_QUEUES;
                rw = (pb->pb_flags & PBF_READ) ? READ_SYNC : WRITE_SYNC;
        } else {
                rw = (pb->pb_flags & PBF_READ) ? READ : WRITE;
        }

        /* Special code path for reading a sub page size pagebuf in --
         * we populate up the whole page, and hence the other metadata
         * in the same page.  This optimization is only valid when the
         * filesystem block size and the page size are equal.
         */
        if ((pb->pb_buffer_length < PAGE_CACHE_SIZE) &&
            (pb->pb_flags & PBF_READ) && locking &&
            (blocksize == PAGE_CACHE_SIZE)) {
                bio = bio_alloc(GFP_NOIO, 1);

                bio->bi_bdev = pb->pb_target->pbr_bdev;
                bio->bi_sector = sector - (offset >> BBSHIFT);
                bio->bi_end_io = bio_end_io_pagebuf;
                bio->bi_private = pb;

                bio_add_page(bio, pb->pb_pages[0], PAGE_CACHE_SIZE, 0);
                size = 0;

                atomic_inc(&pb->pb_io_remaining);

                goto submit_io;
        }

        /* Lock down the pages which we need to for the request */
        if (locking && (pb->pb_flags & PBF_WRITE) && (pb->pb_locked == 0)) {
                for (i = 0; size; i++) {
                        int             nbytes = PAGE_CACHE_SIZE - offset;
                        struct page     *page = pb->pb_pages[i];

                        if (nbytes > size)
                                nbytes = size;

                        lock_page(page);

                        size -= nbytes;
                        offset = 0;
                }
                offset = pb->pb_offset;
                size = pb->pb_count_desired;
        }

next_chunk:
        atomic_inc(&pb->pb_io_remaining);
        nr_pages = BIO_MAX_SECTORS >> (PAGE_SHIFT - BBSHIFT);
        if (nr_pages > total_nr_pages)
                nr_pages = total_nr_pages;

        bio = bio_alloc(GFP_NOIO, nr_pages);
        bio->bi_bdev = pb->pb_target->pbr_bdev;
        bio->bi_sector = sector;
        bio->bi_end_io = bio_end_io_pagebuf;
        bio->bi_private = pb;

        for (; size && nr_pages; nr_pages--, map_i++) {
                int     nbytes = PAGE_CACHE_SIZE - offset;

                if (nbytes > size)
                        nbytes = size;

                if (bio_add_page(bio, pb->pb_pages[map_i],
                                        nbytes, offset) < nbytes)
                        break;

                offset = 0;
                sector += nbytes >> BBSHIFT;
                size -= nbytes;
                total_nr_pages--;
        }

submit_io:
        if (likely(bio->bi_size)) {
                submit_bio(rw, bio);
                if (size)
                        goto next_chunk;
        } else {
                bio_put(bio);
                pagebuf_ioerror(pb, EIO);
        }
}

/*
 *      pagebuf_iorequest -- the core I/O request routine.
 */
int
pagebuf_iorequest(                      /* start real I/O               */
        xfs_buf_t               *pb)    /* buffer to convey to device   */
{
        PB_TRACE(pb, "iorequest", 0);

        if (pb->pb_flags & PBF_DELWRI) {
                pagebuf_delwri_queue(pb, 1);
                return 0;
        }

        if (pb->pb_flags & PBF_WRITE) {
                _pagebuf_wait_unpin(pb);
        }

        pagebuf_hold(pb);

        /* Set the count to 1 initially, this will stop an I/O
         * completion callout which happens before we have started
         * all the I/O from calling pagebuf_iodone too early.
         */
        atomic_set(&pb->pb_io_remaining, 1);
        _pagebuf_ioapply(pb);
        _pagebuf_iodone(pb, 0);

        pagebuf_rele(pb);
        return 0;
}

/*
 *      pagebuf_iowait
 *
 *      pagebuf_iowait waits for I/O to complete on the buffer supplied.
 *      It returns immediately if no I/O is pending.  In any case, it returns
 *      the error code, if any, or 0 if there is no error.
 */
int
pagebuf_iowait(
        xfs_buf_t               *pb)
{
        PB_TRACE(pb, "iowait", 0);
        if (atomic_read(&pb->pb_io_remaining))
                blk_run_address_space(pb->pb_target->pbr_mapping);
        down(&pb->pb_iodonesema);
        PB_TRACE(pb, "iowaited", (long)pb->pb_error);
        return pb->pb_error;
}

caddr_t
pagebuf_offset(
        xfs_buf_t               *pb,
        size_t                  offset)
{
        struct page             *page;

        offset += pb->pb_offset;

        page = pb->pb_pages[offset >> PAGE_CACHE_SHIFT];
        return (caddr_t) page_address(page) + (offset & (PAGE_CACHE_SIZE - 1));
}

/*
 *      pagebuf_iomove
 *
 *      Move data into or out of a buffer.
 */
void
pagebuf_iomove(
        xfs_buf_t               *pb,    /* buffer to process            */
        size_t                  boff,   /* starting buffer offset       */
        size_t                  bsize,  /* length to copy               */
        caddr_t                 data,   /* data address                 */
        page_buf_rw_t           mode)   /* read/write flag              */
{
        size_t                  bend, cpoff, csize;
        struct page             *page;

        bend = boff + bsize;
        while (boff < bend) {
                page = pb->pb_pages[page_buf_btoct(boff + pb->pb_offset)];
                cpoff = page_buf_poff(boff + pb->pb_offset);
                csize = min_t(size_t,
                              PAGE_CACHE_SIZE-cpoff, pb->pb_count_desired-boff);

                ASSERT(((csize + cpoff) <= PAGE_CACHE_SIZE));

                switch (mode) {
                case PBRW_ZERO:
                        memset(page_address(page) + cpoff, 0, csize);
                        break;
                case PBRW_READ:
                        memcpy(data, page_address(page) + cpoff, csize);
                        break;
                case PBRW_WRITE:
                        memcpy(page_address(page) + cpoff, data, csize);
                }

                boff += csize;
                data += csize;
        }
}

/*
 *      Handling of buftargs.
 */

/*
 * Wait for any bufs with callbacks that have been submitted but
 * have not yet returned... walk the hash list for the target.
 */
void
xfs_wait_buftarg(
        xfs_buftarg_t   *btp)
{
        xfs_buf_t       *bp, *n;
        xfs_bufhash_t   *hash;
        uint            i;

        for (i = 0; i < (1 << btp->bt_hashshift); i++) {
                hash = &btp->bt_hash[i];
again:
                spin_lock(&hash->bh_lock);
                list_for_each_entry_safe(bp, n, &hash->bh_list, pb_hash_list) {
                        ASSERT(btp == bp->pb_target);
                        if (!(bp->pb_flags & PBF_FS_MANAGED)) {
                                spin_unlock(&hash->bh_lock);
                                delay(100);
                                goto again;
                        }
                }
                spin_unlock(&hash->bh_lock);
        }
}

/*
 * Allocate buffer hash table for a given target.
 * For devices containing metadata (i.e. not the log/realtime devices)
 * we need to allocate a much larger hash table.
 */
STATIC void
xfs_alloc_bufhash(
        xfs_buftarg_t           *btp,
        int                     external)
{
        unsigned int            i;

        btp->bt_hashshift = external ? 3 : 8;   /* 8 or 256 buckets */
        btp->bt_hashmask = (1 << btp->bt_hashshift) - 1;
        btp->bt_hash = kmem_zalloc((1 << btp->bt_hashshift) *
                                        sizeof(xfs_bufhash_t), KM_SLEEP);
        for (i = 0; i < (1 << btp->bt_hashshift); i++) {
                spin_lock_init(&btp->bt_hash[i].bh_lock);
                INIT_LIST_HEAD(&btp->bt_hash[i].bh_list);
        }
}

STATIC void
xfs_free_bufhash(
        xfs_buftarg_t           *btp)
{
        kmem_free(btp->bt_hash,
                        (1 << btp->bt_hashshift) * sizeof(xfs_bufhash_t));
        btp->bt_hash = NULL;
}

void
xfs_free_buftarg(
        xfs_buftarg_t           *btp,
        int                     external)
{
        xfs_flush_buftarg(btp, 1);
        if (external)
                xfs_blkdev_put(btp->pbr_bdev);
        xfs_free_bufhash(btp);
        iput(btp->pbr_mapping->host);
        kmem_free(btp, sizeof(*btp));
}

void
xfs_incore_relse(
        xfs_buftarg_t           *btp,
        int                     delwri_only,
        int                     wait)
{
        invalidate_bdev(btp->pbr_bdev, 1);
        truncate_inode_pages(btp->pbr_mapping, 0LL);
}

STATIC int
xfs_setsize_buftarg_flags(
        xfs_buftarg_t           *btp,
        unsigned int            blocksize,
        unsigned int            sectorsize,
        int                     verbose)
{
        btp->pbr_bsize = blocksize;
        btp->pbr_sshift = ffs(sectorsize) - 1;
        btp->pbr_smask = sectorsize - 1;

        if (set_blocksize(btp->pbr_bdev, sectorsize)) {
                printk(KERN_WARNING
                        "XFS: Cannot set_blocksize to %u on device %s\n",
                        sectorsize, XFS_BUFTARG_NAME(btp));
                return EINVAL;
        }

        if (verbose &&
            (PAGE_CACHE_SIZE / BITS_PER_LONG) > sectorsize) {
                printk(KERN_WARNING
                        "XFS: %u byte sectors in use on device %s.  "
                        "This is suboptimal; %u or greater is ideal.\n",
                        sectorsize, XFS_BUFTARG_NAME(btp),
                        (unsigned int)PAGE_CACHE_SIZE / BITS_PER_LONG);
        }

        return 0;
}

/*
* When allocating the initial buffer target we have not yet
* read in the superblock, so don't know what sized sectors
* are being used is at this early stage.  Play safe.
*/
STATIC int
xfs_setsize_buftarg_early(
        xfs_buftarg_t           *btp,
        struct block_device     *bdev)
{
        return xfs_setsize_buftarg_flags(btp,
                        PAGE_CACHE_SIZE, bdev_hardsect_size(bdev), 0);
}

int
xfs_setsize_buftarg(
        xfs_buftarg_t           *btp,
        unsigned int            blocksize,
        unsigned int            sectorsize)
{
        return xfs_setsize_buftarg_flags(btp, blocksize, sectorsize, 1);
}

STATIC int
xfs_mapping_buftarg(
        xfs_buftarg_t           *btp,
        struct block_device     *bdev)
{
        struct backing_dev_info *bdi;
        struct inode            *inode;
        struct address_space    *mapping;
        static struct address_space_operations mapping_aops = {
                .sync_page = block_sync_page,
        };

        inode = new_inode(bdev->bd_inode->i_sb);
        if (!inode) {
                printk(KERN_WARNING
                        "XFS: Cannot allocate mapping inode for device %s\n",
                        XFS_BUFTARG_NAME(btp));
                return ENOMEM;
        }
        inode->i_mode = S_IFBLK;
        inode->i_bdev = bdev;
        inode->i_rdev = bdev->bd_dev;
        bdi = blk_get_backing_dev_info(bdev);
        if (!bdi)
                bdi = &default_backing_dev_info;
        mapping = &inode->i_data;
        mapping->a_ops = &mapping_aops;
        mapping->backing_dev_info = bdi;
        mapping_set_gfp_mask(mapping, GFP_NOFS);
        btp->pbr_mapping = mapping;
        return 0;
}

xfs_buftarg_t *
xfs_alloc_buftarg(
        struct block_device     *bdev,
        int                     external)
{
        xfs_buftarg_t           *btp;

        btp = kmem_zalloc(sizeof(*btp), KM_SLEEP);

        btp->pbr_dev =  bdev->bd_dev;
        btp->pbr_bdev = bdev;
        if (xfs_setsize_buftarg_early(btp, bdev))
                goto error;
        if (xfs_mapping_buftarg(btp, bdev))
                goto error;
        xfs_alloc_bufhash(btp, external);
        return btp;

error:
        kmem_free(btp, sizeof(*btp));
        return NULL;
}


/*
 * Pagebuf delayed write buffer handling
 */

STATIC LIST_HEAD(pbd_delwrite_queue);
STATIC DEFINE_SPINLOCK(pbd_delwrite_lock);

STATIC void
pagebuf_delwri_queue(
        xfs_buf_t               *pb,
        int                     unlock)
{
        PB_TRACE(pb, "delwri_q", (long)unlock);
        ASSERT(pb->pb_flags & PBF_DELWRI);

        spin_lock(&pbd_delwrite_lock);
        /* If already in the queue, dequeue and place at tail */
        if (!list_empty(&pb->pb_list)) {
                if (unlock) {
                        atomic_dec(&pb->pb_hold);
                }
                list_del(&pb->pb_list);
        }

        list_add_tail(&pb->pb_list, &pbd_delwrite_queue);
        pb->pb_queuetime = jiffies;
        spin_unlock(&pbd_delwrite_lock);

        if (unlock)
                pagebuf_unlock(pb);
}

void
pagebuf_delwri_dequeue(
        xfs_buf_t               *pb)
{
        int                     dequeued = 0;

        spin_lock(&pbd_delwrite_lock);
        if ((pb->pb_flags & PBF_DELWRI) && !list_empty(&pb->pb_list)) {
                list_del_init(&pb->pb_list);
                dequeued = 1;
        }
        pb->pb_flags &= ~PBF_DELWRI;
        spin_unlock(&pbd_delwrite_lock);

        if (dequeued)
                pagebuf_rele(pb);

        PB_TRACE(pb, "delwri_dq", (long)dequeued);
}

STATIC void
pagebuf_runall_queues(
        struct workqueue_struct *queue)
{
        flush_workqueue(queue);
}

/* Defines for pagebuf daemon */
STATIC DECLARE_COMPLETION(pagebuf_daemon_done);
STATIC struct task_struct *pagebuf_daemon_task;
STATIC int pagebuf_daemon_active;
STATIC int force_flush;


STATIC int
pagebuf_daemon_wakeup(
        int                     priority,
        unsigned int            mask)
{
        force_flush = 1;
        barrier();
        wake_up_process(pagebuf_daemon_task);
        return 0;
}

STATIC int
pagebuf_daemon(
        void                    *data)
{
        struct list_head        tmp;
        unsigned long           age;
        xfs_buftarg_t           *target;
        xfs_buf_t               *pb, *n;

        /*  Set up the thread  */
        daemonize("xfsbufd");
        current->flags |= PF_MEMALLOC;

        pagebuf_daemon_task = current;
        pagebuf_daemon_active = 1;
        barrier();

        INIT_LIST_HEAD(&tmp);
        do {
                try_to_freeze(PF_FREEZE);

                set_current_state(TASK_INTERRUPTIBLE);
                schedule_timeout((xfs_buf_timer_centisecs * HZ) / 100);

                age = (xfs_buf_age_centisecs * HZ) / 100;
                spin_lock(&pbd_delwrite_lock);
                list_for_each_entry_safe(pb, n, &pbd_delwrite_queue, pb_list) {
                        PB_TRACE(pb, "walkq1", (long)pagebuf_ispin(pb));
                        ASSERT(pb->pb_flags & PBF_DELWRI);

                        if (!pagebuf_ispin(pb) && !pagebuf_cond_lock(pb)) {
                                if (!force_flush &&
                                    time_before(jiffies,
                                                pb->pb_queuetime + age)) {
                                        pagebuf_unlock(pb);
                                        break;
                                }

                                pb->pb_flags &= ~PBF_DELWRI;
                                pb->pb_flags |= PBF_WRITE;
                                list_move(&pb->pb_list, &tmp);
                        }
                }
                spin_unlock(&pbd_delwrite_lock);

                while (!list_empty(&tmp)) {
                        pb = list_entry(tmp.next, xfs_buf_t, pb_list);
                        target = pb->pb_target;

                        list_del_init(&pb->pb_list);
                        pagebuf_iostrategy(pb);

                        blk_run_address_space(target->pbr_mapping);
                }

                if (as_list_len > 0)
                        purge_addresses();

                force_flush = 0;
        } while (pagebuf_daemon_active);

        complete_and_exit(&pagebuf_daemon_done, 0);
}

/*
 * Go through all incore buffers, and release buffers if they belong to
 * the given device. This is used in filesystem error handling to
 * preserve the consistency of its metadata.
 */
int
xfs_flush_buftarg(
        xfs_buftarg_t           *target,
        int                     wait)
{
        struct list_head        tmp;
        xfs_buf_t               *pb, *n;
        int                     pincount = 0;

        pagebuf_runall_queues(pagebuf_dataio_workqueue);
        pagebuf_runall_queues(pagebuf_logio_workqueue);

        INIT_LIST_HEAD(&tmp);
        spin_lock(&pbd_delwrite_lock);
        list_for_each_entry_safe(pb, n, &pbd_delwrite_queue, pb_list) {

                if (pb->pb_target != target)
                        continue;

                ASSERT(pb->pb_flags & PBF_DELWRI);
                PB_TRACE(pb, "walkq2", (long)pagebuf_ispin(pb));
                if (pagebuf_ispin(pb)) {
                        pincount++;
                        continue;
                }

                pb->pb_flags &= ~PBF_DELWRI;
                pb->pb_flags |= PBF_WRITE;
                list_move(&pb->pb_list, &tmp);
        }
        spin_unlock(&pbd_delwrite_lock);

        /*
         * Dropped the delayed write list lock, now walk the temporary list
         */
        list_for_each_entry_safe(pb, n, &tmp, pb_list) {
                if (wait)
                        pb->pb_flags &= ~PBF_ASYNC;
                else
                        list_del_init(&pb->pb_list);

                pagebuf_lock(pb);
                pagebuf_iostrategy(pb);
        }

        /*
         * Remaining list items must be flushed before returning
         */
        while (!list_empty(&tmp)) {
                pb = list_entry(tmp.next, xfs_buf_t, pb_list);

                list_del_init(&pb->pb_list);
                xfs_iowait(pb);
                xfs_buf_relse(pb);
        }

        if (wait)
                blk_run_address_space(target->pbr_mapping);

        return pincount;
}

STATIC int
pagebuf_daemon_start(void)
{
        int             rval;

        pagebuf_logio_workqueue = create_workqueue("xfslogd");
        if (!pagebuf_logio_workqueue)
                return -ENOMEM;

        pagebuf_dataio_workqueue = create_workqueue("xfsdatad");
        if (!pagebuf_dataio_workqueue) {
                destroy_workqueue(pagebuf_logio_workqueue);
                return -ENOMEM;
        }

        rval = kernel_thread(pagebuf_daemon, NULL, CLONE_FS|CLONE_FILES);
        if (rval < 0) {
                destroy_workqueue(pagebuf_logio_workqueue);
                destroy_workqueue(pagebuf_dataio_workqueue);
        }

        return rval;
}

/*
 * pagebuf_daemon_stop
 *
 * Note: do not mark as __exit, it is called from pagebuf_terminate.
 */
STATIC void
pagebuf_daemon_stop(void)
{
        pagebuf_daemon_active = 0;
        barrier();
        wait_for_completion(&pagebuf_daemon_done);

        destroy_workqueue(pagebuf_logio_workqueue);
        destroy_workqueue(pagebuf_dataio_workqueue);
}

/*
 *      Initialization and Termination
 */

int __init
pagebuf_init(void)
{
        pagebuf_cache = kmem_cache_create("xfs_buf_t", sizeof(xfs_buf_t), 0,
                        SLAB_HWCACHE_ALIGN, NULL, NULL);
        if (pagebuf_cache == NULL) {
                printk("XFS: couldn't init xfs_buf_t cache\n");
                pagebuf_terminate();
                return -ENOMEM;
        }

#ifdef PAGEBUF_TRACE
        pagebuf_trace_buf = ktrace_alloc(PAGEBUF_TRACE_SIZE, KM_SLEEP);
#endif

        pagebuf_daemon_start();

        pagebuf_shake = kmem_shake_register(pagebuf_daemon_wakeup);
        if (pagebuf_shake == NULL) {
                pagebuf_terminate();
                return -ENOMEM;
        }

        return 0;
}


/*
 *      pagebuf_terminate.
 *
 *      Note: do not mark as __exit, this is also called from the __init code.
 */
void
pagebuf_terminate(void)
{
        pagebuf_daemon_stop();

#ifdef PAGEBUF_TRACE
        ktrace_free(pagebuf_trace_buf);
#endif

        kmem_zone_destroy(pagebuf_cache);
        kmem_shake_deregister(pagebuf_shake);
}