virtio_net: Check for room in the vq before adding buffer

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

/*
 * Copyright (c) 2000-2005 Silicon Graphics, Inc.
 * All Rights Reserved.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms 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.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write the Free Software Foundation,
 * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */
#include "xfs.h"
#include "xfs_bit.h"
#include "xfs_log.h"
#include "xfs_inum.h"
#include "xfs_sb.h"
#include "xfs_ag.h"
#include "xfs_dir2.h"
#include "xfs_trans.h"
#include "xfs_dmapi.h"
#include "xfs_mount.h"
#include "xfs_bmap_btree.h"
#include "xfs_alloc_btree.h"
#include "xfs_ialloc_btree.h"
#include "xfs_dir2_sf.h"
#include "xfs_attr_sf.h"
#include "xfs_dinode.h"
#include "xfs_inode.h"
#include "xfs_alloc.h"
#include "xfs_btree.h"
#include "xfs_error.h"
#include "xfs_rw.h"
#include "xfs_iomap.h"
#include "xfs_vnodeops.h"
#include <linux/mpage.h>
#include <linux/pagevec.h>
#include <linux/writeback.h>


/*
 * Prime number of hash buckets since address is used as the key.
 */
#define NVSYNC          37
#define to_ioend_wq(v)  (&xfs_ioend_wq[((unsigned long)v) % NVSYNC])
static wait_queue_head_t xfs_ioend_wq[NVSYNC];

void __init
xfs_ioend_init(void)
{
        int i;

        for (i = 0; i < NVSYNC; i++)
                init_waitqueue_head(&xfs_ioend_wq[i]);
}

void
xfs_ioend_wait(
        xfs_inode_t     *ip)
{
        wait_queue_head_t *wq = to_ioend_wq(ip);

        wait_event(*wq, (atomic_read(&ip->i_iocount) == 0));
}

STATIC void
xfs_ioend_wake(
        xfs_inode_t     *ip)
{
        if (atomic_dec_and_test(&ip->i_iocount))
                wake_up(to_ioend_wq(ip));
}

STATIC void
xfs_count_page_state(
        struct page             *page,
        int                     *delalloc,
        int                     *unmapped,
        int                     *unwritten)
{
        struct buffer_head      *bh, *head;

        *delalloc = *unmapped = *unwritten = 0;

        bh = head = page_buffers(page);
        do {
                if (buffer_uptodate(bh) && !buffer_mapped(bh))
                        (*unmapped) = 1;
                else if (buffer_unwritten(bh))
                        (*unwritten) = 1;
                else if (buffer_delay(bh))
                        (*delalloc) = 1;
        } while ((bh = bh->b_this_page) != head);
}

#if defined(XFS_RW_TRACE)
void
xfs_page_trace(
        int             tag,
        struct inode    *inode,
        struct page     *page,
        unsigned long   pgoff)
{
        xfs_inode_t     *ip;
        loff_t          isize = i_size_read(inode);
        loff_t          offset = page_offset(page);
        int             delalloc = -1, unmapped = -1, unwritten = -1;

        if (page_has_buffers(page))
                xfs_count_page_state(page, &delalloc, &unmapped, &unwritten);

        ip = XFS_I(inode);
        if (!ip->i_rwtrace)
                return;

        ktrace_enter(ip->i_rwtrace,
                (void *)((unsigned long)tag),
                (void *)ip,
                (void *)inode,
                (void *)page,
                (void *)pgoff,
                (void *)((unsigned long)((ip->i_d.di_size >> 32) & 0xffffffff)),
                (void *)((unsigned long)(ip->i_d.di_size & 0xffffffff)),
                (void *)((unsigned long)((isize >> 32) & 0xffffffff)),
                (void *)((unsigned long)(isize & 0xffffffff)),
                (void *)((unsigned long)((offset >> 32) & 0xffffffff)),
                (void *)((unsigned long)(offset & 0xffffffff)),
                (void *)((unsigned long)delalloc),
                (void *)((unsigned long)unmapped),
                (void *)((unsigned long)unwritten),
                (void *)((unsigned long)current_pid()),
                (void *)NULL);
}
#else
#define xfs_page_trace(tag, inode, page, pgoff)
#endif

STATIC struct block_device *
xfs_find_bdev_for_inode(
        struct xfs_inode        *ip)
{
        struct xfs_mount        *mp = ip->i_mount;

        if (XFS_IS_REALTIME_INODE(ip))
                return mp->m_rtdev_targp->bt_bdev;
        else
                return mp->m_ddev_targp->bt_bdev;
}

/*
 * We're now finished for good with this ioend structure.
 * Update the page state via the associated buffer_heads,
 * release holds on the inode and bio, and finally free
 * up memory.  Do not use the ioend after this.
 */
STATIC void
xfs_destroy_ioend(
        xfs_ioend_t             *ioend)
{
        struct buffer_head      *bh, *next;
        struct xfs_inode        *ip = XFS_I(ioend->io_inode);

        for (bh = ioend->io_buffer_head; bh; bh = next) {
                next = bh->b_private;
                bh->b_end_io(bh, !ioend->io_error);
        }

        /*
         * Volume managers supporting multiple paths can send back ENODEV
         * when the final path disappears.  In this case continuing to fill
         * the page cache with dirty data which cannot be written out is
         * evil, so prevent that.
         */
        if (unlikely(ioend->io_error == -ENODEV)) {
                xfs_do_force_shutdown(ip->i_mount, SHUTDOWN_DEVICE_REQ,
                                      __FILE__, __LINE__);
        }

        xfs_ioend_wake(ip);
        mempool_free(ioend, xfs_ioend_pool);
}

/*
 * Update on-disk file size now that data has been written to disk.
 * The current in-memory file size is i_size.  If a write is beyond
 * eof i_new_size will be the intended file size until i_size is
 * updated.  If this write does not extend all the way to the valid
 * file size then restrict this update to the end of the write.
 */
STATIC void
xfs_setfilesize(
        xfs_ioend_t             *ioend)
{
        xfs_inode_t             *ip = XFS_I(ioend->io_inode);
        xfs_fsize_t             isize;
        xfs_fsize_t             bsize;

        ASSERT((ip->i_d.di_mode & S_IFMT) == S_IFREG);
        ASSERT(ioend->io_type != IOMAP_READ);

        if (unlikely(ioend->io_error))
                return;

        bsize = ioend->io_offset + ioend->io_size;

        xfs_ilock(ip, XFS_ILOCK_EXCL);

        isize = MAX(ip->i_size, ip->i_new_size);
        isize = MIN(isize, bsize);

        if (ip->i_d.di_size < isize) {
                ip->i_d.di_size = isize;
                ip->i_update_core = 1;
                xfs_mark_inode_dirty_sync(ip);
        }

        xfs_iunlock(ip, XFS_ILOCK_EXCL);
}

/*
 * Buffered IO write completion for delayed allocate extents.
 */
STATIC void
xfs_end_bio_delalloc(
        struct work_struct      *work)
{
        xfs_ioend_t             *ioend =
                container_of(work, xfs_ioend_t, io_work);

        xfs_setfilesize(ioend);
        xfs_destroy_ioend(ioend);
}

/*
 * Buffered IO write completion for regular, written extents.
 */
STATIC void
xfs_end_bio_written(
        struct work_struct      *work)
{
        xfs_ioend_t             *ioend =
                container_of(work, xfs_ioend_t, io_work);

        xfs_setfilesize(ioend);
        xfs_destroy_ioend(ioend);
}

/*
 * IO write completion for unwritten extents.
 *
 * Issue transactions to convert a buffer range from unwritten
 * to written extents.
 */
STATIC void
xfs_end_bio_unwritten(
        struct work_struct      *work)
{
        xfs_ioend_t             *ioend =
                container_of(work, xfs_ioend_t, io_work);
        struct xfs_inode        *ip = XFS_I(ioend->io_inode);
        xfs_off_t               offset = ioend->io_offset;
        size_t                  size = ioend->io_size;

        if (likely(!ioend->io_error)) {
                if (!XFS_FORCED_SHUTDOWN(ip->i_mount)) {
                        int error;
                        error = xfs_iomap_write_unwritten(ip, offset, size);
                        if (error)
                                ioend->io_error = error;
                }
                xfs_setfilesize(ioend);
        }
        xfs_destroy_ioend(ioend);
}

/*
 * IO read completion for regular, written extents.
 */
STATIC void
xfs_end_bio_read(
        struct work_struct      *work)
{
        xfs_ioend_t             *ioend =
                container_of(work, xfs_ioend_t, io_work);

        xfs_destroy_ioend(ioend);
}

/*
 * Schedule IO completion handling on a xfsdatad if this was
 * the final hold on this ioend. If we are asked to wait,
 * flush the workqueue.
 */
STATIC void
xfs_finish_ioend(
        xfs_ioend_t     *ioend,
        int             wait)
{
        if (atomic_dec_and_test(&ioend->io_remaining)) {
                struct workqueue_struct *wq = xfsdatad_workqueue;
                if (ioend->io_work.func == xfs_end_bio_unwritten)
                        wq = xfsconvertd_workqueue;

                queue_work(wq, &ioend->io_work);
                if (wait)
                        flush_workqueue(wq);
        }
}

/*
 * Allocate and initialise an IO completion structure.
 * We need to track unwritten extent write completion here initially.
 * We'll need to extend this for updating the ondisk inode size later
 * (vs. incore size).
 */
STATIC xfs_ioend_t *
xfs_alloc_ioend(
        struct inode            *inode,
        unsigned int            type)
{
        xfs_ioend_t             *ioend;

        ioend = mempool_alloc(xfs_ioend_pool, GFP_NOFS);

        /*
         * Set the count to 1 initially, which will prevent an I/O
         * completion callback from happening before we have started
         * all the I/O from calling the completion routine too early.
         */
        atomic_set(&ioend->io_remaining, 1);
        ioend->io_error = 0;
        ioend->io_list = NULL;
        ioend->io_type = type;
        ioend->io_inode = inode;
        ioend->io_buffer_head = NULL;
        ioend->io_buffer_tail = NULL;
        atomic_inc(&XFS_I(ioend->io_inode)->i_iocount);
        ioend->io_offset = 0;
        ioend->io_size = 0;

        if (type == IOMAP_UNWRITTEN)
                INIT_WORK(&ioend->io_work, xfs_end_bio_unwritten);
        else if (type == IOMAP_DELAY)
                INIT_WORK(&ioend->io_work, xfs_end_bio_delalloc);
        else if (type == IOMAP_READ)
                INIT_WORK(&ioend->io_work, xfs_end_bio_read);
        else
                INIT_WORK(&ioend->io_work, xfs_end_bio_written);

        return ioend;
}

STATIC int
xfs_map_blocks(
        struct inode            *inode,
        loff_t                  offset,
        ssize_t                 count,
        xfs_iomap_t             *mapp,
        int                     flags)
{
        int                     nmaps = 1;

        return -xfs_iomap(XFS_I(inode), offset, count, flags, mapp, &nmaps);
}

STATIC_INLINE int
xfs_iomap_valid(
        xfs_iomap_t             *iomapp,
        loff_t                  offset)
{
        return offset >= iomapp->iomap_offset &&
                offset < iomapp->iomap_offset + iomapp->iomap_bsize;
}

/*
 * BIO completion handler for buffered IO.
 */
STATIC void
xfs_end_bio(
        struct bio              *bio,
        int                     error)
{
        xfs_ioend_t             *ioend = bio->bi_private;

        ASSERT(atomic_read(&bio->bi_cnt) >= 1);
        ioend->io_error = test_bit(BIO_UPTODATE, &bio->bi_flags) ? 0 : error;

        /* Toss bio and pass work off to an xfsdatad thread */
        bio->bi_private = NULL;
        bio->bi_end_io = NULL;
        bio_put(bio);

        xfs_finish_ioend(ioend, 0);
}

STATIC void
xfs_submit_ioend_bio(
        xfs_ioend_t     *ioend,
        struct bio      *bio)
{
        atomic_inc(&ioend->io_remaining);

        bio->bi_private = ioend;
        bio->bi_end_io = xfs_end_bio;

        submit_bio(WRITE, bio);
        ASSERT(!bio_flagged(bio, BIO_EOPNOTSUPP));
        bio_put(bio);
}

STATIC struct bio *
xfs_alloc_ioend_bio(
        struct buffer_head      *bh)
{
        struct bio              *bio;
        int                     nvecs = bio_get_nr_vecs(bh->b_bdev);

        do {
                bio = bio_alloc(GFP_NOIO, nvecs);
                nvecs >>= 1;
        } while (!bio);

        ASSERT(bio->bi_private == NULL);
        bio->bi_sector = bh->b_blocknr * (bh->b_size >> 9);
        bio->bi_bdev = bh->b_bdev;
        bio_get(bio);
        return bio;
}

STATIC void
xfs_start_buffer_writeback(
        struct buffer_head      *bh)
{
        ASSERT(buffer_mapped(bh));
        ASSERT(buffer_locked(bh));
        ASSERT(!buffer_delay(bh));
        ASSERT(!buffer_unwritten(bh));

        mark_buffer_async_write(bh);
        set_buffer_uptodate(bh);
        clear_buffer_dirty(bh);
}

STATIC void
xfs_start_page_writeback(
        struct page             *page,
        int                     clear_dirty,
        int                     buffers)
{
        ASSERT(PageLocked(page));
        ASSERT(!PageWriteback(page));
        if (clear_dirty)
                clear_page_dirty_for_io(page);
        set_page_writeback(page);
        unlock_page(page);
        /* If no buffers on the page are to be written, finish it here */
        if (!buffers)
                end_page_writeback(page);
}

static inline int bio_add_buffer(struct bio *bio, struct buffer_head *bh)
{
        return bio_add_page(bio, bh->b_page, bh->b_size, bh_offset(bh));
}

/*
 * Submit all of the bios for all of the ioends we have saved up, covering the
 * initial writepage page and also any probed pages.
 *
 * Because we may have multiple ioends spanning a page, we need to start
 * writeback on all the buffers before we submit them for I/O. If we mark the
 * buffers as we got, then we can end up with a page that only has buffers
 * marked async write and I/O complete on can occur before we mark the other
 * buffers async write.
 *
 * The end result of this is that we trip a bug in end_page_writeback() because
 * we call it twice for the one page as the code in end_buffer_async_write()
 * assumes that all buffers on the page are started at the same time.
 *
 * The fix is two passes across the ioend list - one to start writeback on the
 * buffer_heads, and then submit them for I/O on the second pass.
 */
STATIC void
xfs_submit_ioend(
        xfs_ioend_t             *ioend)
{
        xfs_ioend_t             *head = ioend;
        xfs_ioend_t             *next;
        struct buffer_head      *bh;
        struct bio              *bio;
        sector_t                lastblock = 0;

        /* Pass 1 - start writeback */
        do {
                next = ioend->io_list;
                for (bh = ioend->io_buffer_head; bh; bh = bh->b_private) {
                        xfs_start_buffer_writeback(bh);
                }
        } while ((ioend = next) != NULL);

        /* Pass 2 - submit I/O */
        ioend = head;
        do {
                next = ioend->io_list;
                bio = NULL;

                for (bh = ioend->io_buffer_head; bh; bh = bh->b_private) {

                        if (!bio) {
 retry:
                                bio = xfs_alloc_ioend_bio(bh);
                        } else if (bh->b_blocknr != lastblock + 1) {
                                xfs_submit_ioend_bio(ioend, bio);
                                goto retry;
                        }

                        if (bio_add_buffer(bio, bh) != bh->b_size) {
                                xfs_submit_ioend_bio(ioend, bio);
                                goto retry;
                        }

                        lastblock = bh->b_blocknr;
                }
                if (bio)
                        xfs_submit_ioend_bio(ioend, bio);
                xfs_finish_ioend(ioend, 0);
        } while ((ioend = next) != NULL);
}

/*
 * Cancel submission of all buffer_heads so far in this endio.
 * Toss the endio too.  Only ever called for the initial page
 * in a writepage request, so only ever one page.
 */
STATIC void
xfs_cancel_ioend(
        xfs_ioend_t             *ioend)
{
        xfs_ioend_t             *next;
        struct buffer_head      *bh, *next_bh;

        do {
                next = ioend->io_list;
                bh = ioend->io_buffer_head;
                do {
                        next_bh = bh->b_private;
                        clear_buffer_async_write(bh);
                        unlock_buffer(bh);
                } while ((bh = next_bh) != NULL);

                xfs_ioend_wake(XFS_I(ioend->io_inode));
                mempool_free(ioend, xfs_ioend_pool);
        } while ((ioend = next) != NULL);
}

/*
 * Test to see if we've been building up a completion structure for
 * earlier buffers -- if so, we try to append to this ioend if we
 * can, otherwise we finish off any current ioend and start another.
 * Return true if we've finished the given ioend.
 */
STATIC void
xfs_add_to_ioend(
        struct inode            *inode,
        struct buffer_head      *bh,
        xfs_off_t               offset,
        unsigned int            type,
        xfs_ioend_t             **result,
        int                     need_ioend)
{
        xfs_ioend_t             *ioend = *result;

        if (!ioend || need_ioend || type != ioend->io_type) {
                xfs_ioend_t     *previous = *result;

                ioend = xfs_alloc_ioend(inode, type);
                ioend->io_offset = offset;
                ioend->io_buffer_head = bh;
                ioend->io_buffer_tail = bh;
                if (previous)
                        previous->io_list = ioend;
                *result = ioend;
        } else {
                ioend->io_buffer_tail->b_private = bh;
                ioend->io_buffer_tail = bh;
        }

        bh->b_private = NULL;
        ioend->io_size += bh->b_size;
}

STATIC void
xfs_map_buffer(
        struct buffer_head      *bh,
        xfs_iomap_t             *mp,
        xfs_off_t               offset,
        uint                    block_bits)
{
        sector_t                bn;

        ASSERT(mp->iomap_bn != IOMAP_DADDR_NULL);

        bn = (mp->iomap_bn >> (block_bits - BBSHIFT)) +
              ((offset - mp->iomap_offset) >> block_bits);

        ASSERT(bn || (mp->iomap_flags & IOMAP_REALTIME));

        bh->b_blocknr = bn;
        set_buffer_mapped(bh);
}

STATIC void
xfs_map_at_offset(
        struct buffer_head      *bh,
        loff_t                  offset,
        int                     block_bits,
        xfs_iomap_t             *iomapp)
{
        ASSERT(!(iomapp->iomap_flags & IOMAP_HOLE));
        ASSERT(!(iomapp->iomap_flags & IOMAP_DELAY));

        lock_buffer(bh);
        xfs_map_buffer(bh, iomapp, offset, block_bits);
        bh->b_bdev = iomapp->iomap_target->bt_bdev;
        set_buffer_mapped(bh);
        clear_buffer_delay(bh);
        clear_buffer_unwritten(bh);
}

/*
 * Look for a page at index that is suitable for clustering.
 */
STATIC unsigned int
xfs_probe_page(
        struct page             *page,
        unsigned int            pg_offset,
        int                     mapped)
{
        int                     ret = 0;

        if (PageWriteback(page))
                return 0;

        if (page->mapping && PageDirty(page)) {
                if (page_has_buffers(page)) {
                        struct buffer_head      *bh, *head;

                        bh = head = page_buffers(page);
                        do {
                                if (!buffer_uptodate(bh))
                                        break;
                                if (mapped != buffer_mapped(bh))
                                        break;
                                ret += bh->b_size;
                                if (ret >= pg_offset)
                                        break;
                        } while ((bh = bh->b_this_page) != head);
                } else
                        ret = mapped ? 0 : PAGE_CACHE_SIZE;
        }

        return ret;
}

STATIC size_t
xfs_probe_cluster(
        struct inode            *inode,
        struct page             *startpage,
        struct buffer_head      *bh,
        struct buffer_head      *head,
        int                     mapped)
{
        struct pagevec          pvec;
        pgoff_t                 tindex, tlast, tloff;
        size_t                  total = 0;
        int                     done = 0, i;

        /* First sum forwards in this page */
        do {
                if (!buffer_uptodate(bh) || (mapped != buffer_mapped(bh)))
                        return total;
                total += bh->b_size;
        } while ((bh = bh->b_this_page) != head);

        /* if we reached the end of the page, sum forwards in following pages */
        tlast = i_size_read(inode) >> PAGE_CACHE_SHIFT;
        tindex = startpage->index + 1;

        /* Prune this back to avoid pathological behavior */
        tloff = min(tlast, startpage->index + 64);

        pagevec_init(&pvec, 0);
        while (!done && tindex <= tloff) {
                unsigned len = min_t(pgoff_t, PAGEVEC_SIZE, tlast - tindex + 1);

                if (!pagevec_lookup(&pvec, inode->i_mapping, tindex, len))
                        break;

                for (i = 0; i < pagevec_count(&pvec); i++) {
                        struct page *page = pvec.pages[i];
                        size_t pg_offset, pg_len = 0;

                        if (tindex == tlast) {
                                pg_offset =
                                    i_size_read(inode) & (PAGE_CACHE_SIZE - 1);
                                if (!pg_offset) {
                                        done = 1;
                                        break;
                                }
                        } else
                                pg_offset = PAGE_CACHE_SIZE;

                        if (page->index == tindex && trylock_page(page)) {
                                pg_len = xfs_probe_page(page, pg_offset, mapped);
                                unlock_page(page);
                        }

                        if (!pg_len) {
                                done = 1;
                                break;
                        }

                        total += pg_len;
                        tindex++;
                }

                pagevec_release(&pvec);
                cond_resched();
        }

        return total;
}

/*
 * Test if a given page is suitable for writing as part of an unwritten
 * or delayed allocate extent.
 */
STATIC int
xfs_is_delayed_page(
        struct page             *page,
        unsigned int            type)
{
        if (PageWriteback(page))
                return 0;

        if (page->mapping && page_has_buffers(page)) {
                struct buffer_head      *bh, *head;
                int                     acceptable = 0;

                bh = head = page_buffers(page);
                do {
                        if (buffer_unwritten(bh))
                                acceptable = (type == IOMAP_UNWRITTEN);
                        else if (buffer_delay(bh))
                                acceptable = (type == IOMAP_DELAY);
                        else if (buffer_dirty(bh) && buffer_mapped(bh))
                                acceptable = (type == IOMAP_NEW);
                        else
                                break;
                } while ((bh = bh->b_this_page) != head);

                if (acceptable)
                        return 1;
        }

        return 0;
}

/*
 * Allocate & map buffers for page given the extent map. Write it out.
 * except for the original page of a writepage, this is called on
 * delalloc/unwritten pages only, for the original page it is possible
 * that the page has no mapping at all.
 */
STATIC int
xfs_convert_page(
        struct inode            *inode,
        struct page             *page,
        loff_t                  tindex,
        xfs_iomap_t             *mp,
        xfs_ioend_t             **ioendp,
        struct writeback_control *wbc,
        int                     startio,
        int                     all_bh)
{
        struct buffer_head      *bh, *head;
        xfs_off_t               end_offset;
        unsigned long           p_offset;
        unsigned int            type;
        int                     bbits = inode->i_blkbits;
        int                     len, page_dirty;
        int                     count = 0, done = 0, uptodate = 1;
        xfs_off_t               offset = page_offset(page);

        if (page->index != tindex)
                goto fail;
        if (!trylock_page(page))
                goto fail;
        if (PageWriteback(page))
                goto fail_unlock_page;
        if (page->mapping != inode->i_mapping)
                goto fail_unlock_page;
        if (!xfs_is_delayed_page(page, (*ioendp)->io_type))
                goto fail_unlock_page;

        /*
         * page_dirty is initially a count of buffers on the page before
         * EOF and is decremented as we move each into a cleanable state.
         *
         * Derivation:
         *
         * End offset is the highest offset that this page should represent.
         * If we are on the last page, (end_offset & (PAGE_CACHE_SIZE - 1))
         * will evaluate non-zero and be less than PAGE_CACHE_SIZE and
         * hence give us the correct page_dirty count. On any other page,
         * it will be zero and in that case we need page_dirty to be the
         * count of buffers on the page.
         */
        end_offset = min_t(unsigned long long,
                        (xfs_off_t)(page->index + 1) << PAGE_CACHE_SHIFT,
                        i_size_read(inode));

        len = 1 << inode->i_blkbits;
        p_offset = min_t(unsigned long, end_offset & (PAGE_CACHE_SIZE - 1),
                                        PAGE_CACHE_SIZE);
        p_offset = p_offset ? roundup(p_offset, len) : PAGE_CACHE_SIZE;
        page_dirty = p_offset / len;

        bh = head = page_buffers(page);
        do {
                if (offset >= end_offset)
                        break;
                if (!buffer_uptodate(bh))
                        uptodate = 0;
                if (!(PageUptodate(page) || buffer_uptodate(bh))) {
                        done = 1;
                        continue;
                }

                if (buffer_unwritten(bh) || buffer_delay(bh)) {
                        if (buffer_unwritten(bh))
                                type = IOMAP_UNWRITTEN;
                        else
                                type = IOMAP_DELAY;

                        if (!xfs_iomap_valid(mp, offset)) {
                                done = 1;
                                continue;
                        }

                        ASSERT(!(mp->iomap_flags & IOMAP_HOLE));
                        ASSERT(!(mp->iomap_flags & IOMAP_DELAY));

                        xfs_map_at_offset(bh, offset, bbits, mp);
                        if (startio) {
                                xfs_add_to_ioend(inode, bh, offset,
                                                type, ioendp, done);
                        } else {
                                set_buffer_dirty(bh);
                                unlock_buffer(bh);
                                mark_buffer_dirty(bh);
                        }
                        page_dirty--;
                        count++;
                } else {
                        type = IOMAP_NEW;
                        if (buffer_mapped(bh) && all_bh && startio) {
                                lock_buffer(bh);
                                xfs_add_to_ioend(inode, bh, offset,
                                                type, ioendp, done);
                                count++;
                                page_dirty--;
                        } else {
                                done = 1;
                        }
                }
        } while (offset += len, (bh = bh->b_this_page) != head);

        if (uptodate && bh == head)
                SetPageUptodate(page);

        if (startio) {
                if (count) {
                        struct backing_dev_info *bdi;

                        bdi = inode->i_mapping->backing_dev_info;
                        wbc->nr_to_write--;
                        if (bdi_write_congested(bdi)) {
                                wbc->encountered_congestion = 1;
                                done = 1;
                        } else if (wbc->nr_to_write <= 0) {
                                done = 1;
                        }
                }
                xfs_start_page_writeback(page, !page_dirty, count);
        }

        return done;
 fail_unlock_page:
        unlock_page(page);
 fail:
        return 1;
}

/*
 * Convert & write out a cluster of pages in the same extent as defined
 * by mp and following the start page.
 */
STATIC void
xfs_cluster_write(
        struct inode            *inode,
        pgoff_t                 tindex,
        xfs_iomap_t             *iomapp,
        xfs_ioend_t             **ioendp,
        struct writeback_control *wbc,
        int                     startio,
        int                     all_bh,
        pgoff_t                 tlast)
{
        struct pagevec          pvec;
        int                     done = 0, i;

        pagevec_init(&pvec, 0);
        while (!done && tindex <= tlast) {
                unsigned len = min_t(pgoff_t, PAGEVEC_SIZE, tlast - tindex + 1);

                if (!pagevec_lookup(&pvec, inode->i_mapping, tindex, len))
                        break;

                for (i = 0; i < pagevec_count(&pvec); i++) {
                        done = xfs_convert_page(inode, pvec.pages[i], tindex++,
                                        iomapp, ioendp, wbc, startio, all_bh);
                        if (done)
                                break;
                }

                pagevec_release(&pvec);
                cond_resched();
        }
}

/*
 * Calling this without startio set means we are being asked to make a dirty
 * page ready for freeing it's buffers.  When called with startio set then
 * we are coming from writepage.
 *
 * When called with startio set it is important that we write the WHOLE
 * page if possible.
 * The bh->b_state's cannot know if any of the blocks or which block for
 * that matter are dirty due to mmap writes, and therefore bh uptodate is
 * only valid if the page itself isn't completely uptodate.  Some layers
 * may clear the page dirty flag prior to calling write page, under the
 * assumption the entire page will be written out; by not writing out the
 * whole page the page can be reused before all valid dirty data is
 * written out.  Note: in the case of a page that has been dirty'd by
 * mapwrite and but partially setup by block_prepare_write the
 * bh->b_states's will not agree and only ones setup by BPW/BCW will have
 * valid state, thus the whole page must be written out thing.
 */

STATIC int
xfs_page_state_convert(
        struct inode    *inode,
        struct page     *page,
        struct writeback_control *wbc,
        int             startio,
        int             unmapped) /* also implies page uptodate */
{
        struct buffer_head      *bh, *head;
        xfs_iomap_t             iomap;
        xfs_ioend_t             *ioend = NULL, *iohead = NULL;
        loff_t                  offset;
        unsigned long           p_offset = 0;
        unsigned int            type;
        __uint64_t              end_offset;
        pgoff_t                 end_index, last_index, tlast;
        ssize_t                 size, len;
        int                     flags, err, iomap_valid = 0, uptodate = 1;
        int                     page_dirty, count = 0;
        int                     trylock = 0;
        int                     all_bh = unmapped;

        if (startio) {
                if (wbc->sync_mode == WB_SYNC_NONE && wbc->nonblocking)
                        trylock |= BMAPI_TRYLOCK;
        }

        /* Is this page beyond the end of the file? */
        offset = i_size_read(inode);
        end_index = offset >> PAGE_CACHE_SHIFT;
        last_index = (offset - 1) >> PAGE_CACHE_SHIFT;
        if (page->index >= end_index) {
                if ((page->index >= end_index + 1) ||
                    !(i_size_read(inode) & (PAGE_CACHE_SIZE - 1))) {
                        if (startio)
                                unlock_page(page);
                        return 0;
                }
        }

        /*
         * page_dirty is initially a count of buffers on the page before
         * EOF and is decremented as we move each into a cleanable state.
         *
         * Derivation:
         *
         * End offset is the highest offset that this page should represent.
         * If we are on the last page, (end_offset & (PAGE_CACHE_SIZE - 1))
         * will evaluate non-zero and be less than PAGE_CACHE_SIZE and
         * hence give us the correct page_dirty count. On any other page,
         * it will be zero and in that case we need page_dirty to be the
         * count of buffers on the page.
         */
        end_offset = min_t(unsigned long long,
                        (xfs_off_t)(page->index + 1) << PAGE_CACHE_SHIFT, offset);
        len = 1 << inode->i_blkbits;
        p_offset = min_t(unsigned long, end_offset & (PAGE_CACHE_SIZE - 1),
                                        PAGE_CACHE_SIZE);
        p_offset = p_offset ? roundup(p_offset, len) : PAGE_CACHE_SIZE;
        page_dirty = p_offset / len;

        bh = head = page_buffers(page);
        offset = page_offset(page);
        flags = BMAPI_READ;
        type = IOMAP_NEW;

        /* TODO: cleanup count and page_dirty */

        do {
                if (offset >= end_offset)
                        break;
                if (!buffer_uptodate(bh))
                        uptodate = 0;
                if (!(PageUptodate(page) || buffer_uptodate(bh)) && !startio) {
                        /*
                         * the iomap is actually still valid, but the ioend
                         * isn't.  shouldn't happen too often.
                         */
                        iomap_valid = 0;
                        continue;
                }

                if (iomap_valid)
                        iomap_valid = xfs_iomap_valid(&iomap, offset);

                /*
                 * First case, map an unwritten extent and prepare for
                 * extent state conversion transaction on completion.
                 *
                 * Second case, allocate space for a delalloc buffer.
                 * We can return EAGAIN here in the release page case.
                 *
                 * Third case, an unmapped buffer was found, and we are
                 * in a path where we need to write the whole page out.
                 */
                if (buffer_unwritten(bh) || buffer_delay(bh) ||
                    ((buffer_uptodate(bh) || PageUptodate(page)) &&
                     !buffer_mapped(bh) && (unmapped || startio))) {
                        int new_ioend = 0;

                        /*
                         * Make sure we don't use a read-only iomap
                         */
                        if (flags == BMAPI_READ)
                                iomap_valid = 0;

                        if (buffer_unwritten(bh)) {
                                type = IOMAP_UNWRITTEN;
                                flags = BMAPI_WRITE | BMAPI_IGNSTATE;
                        } else if (buffer_delay(bh)) {
                                type = IOMAP_DELAY;
                                flags = BMAPI_ALLOCATE | trylock;
                        } else {
                                type = IOMAP_NEW;
                                flags = BMAPI_WRITE | BMAPI_MMAP;
                        }

                        if (!iomap_valid) {
                                /*
                                 * if we didn't have a valid mapping then we
                                 * need to ensure that we put the new mapping
                                 * in a new ioend structure. This needs to be
                                 * done to ensure that the ioends correctly
                                 * reflect the block mappings at io completion
                                 * for unwritten extent conversion.
                                 */
                                new_ioend = 1;
                                if (type == IOMAP_NEW) {
                                        size = xfs_probe_cluster(inode,
                                                        page, bh, head, 0);
                                } else {
                                        size = len;
                                }

                                err = xfs_map_blocks(inode, offset, size,
                                                &iomap, flags);
                                if (err)
                                        goto error;
                                iomap_valid = xfs_iomap_valid(&iomap, offset);
                        }
                        if (iomap_valid) {
                                xfs_map_at_offset(bh, offset,
                                                inode->i_blkbits, &iomap);
                                if (startio) {
                                        xfs_add_to_ioend(inode, bh, offset,
                                                        type, &ioend,
                                                        new_ioend);
                                } else {
                                        set_buffer_dirty(bh);
                                        unlock_buffer(bh);
                                        mark_buffer_dirty(bh);
                                }
                                page_dirty--;
                                count++;
                        }
                } else if (buffer_uptodate(bh) && startio) {
                        /*
                         * we got here because the buffer is already mapped.
                         * That means it must already have extents allocated
                         * underneath it. Map the extent by reading it.
                         */
                        if (!iomap_valid || flags != BMAPI_READ) {
                                flags = BMAPI_READ;
                                size = xfs_probe_cluster(inode, page, bh,
                                                                head, 1);
                                err = xfs_map_blocks(inode, offset, size,
                                                &iomap, flags);
                                if (err)
                                        goto error;
                                iomap_valid = xfs_iomap_valid(&iomap, offset);
                        }

                        /*
                         * We set the type to IOMAP_NEW in case we are doing a
                         * small write at EOF that is extending the file but
                         * without needing an allocation. We need to update the
                         * file size on I/O completion in this case so it is
                         * the same case as having just allocated a new extent
                         * that we are writing into for the first time.
                         */
                        type = IOMAP_NEW;
                        if (trylock_buffer(bh)) {
                                ASSERT(buffer_mapped(bh));
                                if (iomap_valid)
                                        all_bh = 1;
                                xfs_add_to_ioend(inode, bh, offset, type,
                                                &ioend, !iomap_valid);
                                page_dirty--;
                                count++;
                        } else {
                                iomap_valid = 0;
                        }
                } else if ((buffer_uptodate(bh) || PageUptodate(page)) &&
                           (unmapped || startio)) {
                        iomap_valid = 0;
                }

                if (!iohead)
                        iohead = ioend;

        } while (offset += len, ((bh = bh->b_this_page) != head));

        if (uptodate && bh == head)
                SetPageUptodate(page);

        if (startio)
                xfs_start_page_writeback(page, 1, count);

        if (ioend && iomap_valid) {
                offset = (iomap.iomap_offset + iomap.iomap_bsize - 1) >>
                                        PAGE_CACHE_SHIFT;
                tlast = min_t(pgoff_t, offset, last_index);
                xfs_cluster_write(inode, page->index + 1, &iomap, &ioend,
                                        wbc, startio, all_bh, tlast);
        }

        if (iohead)
                xfs_submit_ioend(iohead);

        return page_dirty;

error:
        if (iohead)
                xfs_cancel_ioend(iohead);

        /*
         * If it's delalloc and we have nowhere to put it,
         * throw it away, unless the lower layers told
         * us to try again.
         */
        if (err != -EAGAIN) {
                if (!unmapped)
                        block_invalidatepage(page, 0);
                ClearPageUptodate(page);
        }
        return err;
}

/*
 * writepage: Called from one of two places:
 *
 * 1. we are flushing a delalloc buffer head.
 *
 * 2. we are writing out a dirty page. Typically the page dirty
 *    state is cleared before we get here. In this case is it
 *    conceivable we have no buffer heads.
 *
 * For delalloc space on the page we need to allocate space and
 * flush it. For unmapped buffer heads on the page we should
 * allocate space if the page is uptodate. For any other dirty
 * buffer heads on the page we should flush them.
 *
 * If we detect that a transaction would be required to flush
 * the page, we have to check the process flags first, if we
 * are already in a transaction or disk I/O during allocations
 * is off, we need to fail the writepage and redirty the page.
 */

STATIC int
xfs_vm_writepage(
        struct page             *page,
        struct writeback_control *wbc)
{
        int                     error;
        int                     need_trans;
        int                     delalloc, unmapped, unwritten;
        struct inode            *inode = page->mapping->host;

        xfs_page_trace(XFS_WRITEPAGE_ENTER, inode, page, 0);

        /*
         * We need a transaction if:
         *  1. There are delalloc buffers on the page
         *  2. The page is uptodate and we have unmapped buffers
         *  3. The page is uptodate and we have no buffers
         *  4. There are unwritten buffers on the page
         */

        if (!page_has_buffers(page)) {
                unmapped = 1;
                need_trans = 1;
        } else {
                xfs_count_page_state(page, &delalloc, &unmapped, &unwritten);
                if (!PageUptodate(page))
                        unmapped = 0;
                need_trans = delalloc + unmapped + unwritten;
        }

        /*
         * If we need a transaction and the process flags say
         * we are already in a transaction, or no IO is allowed
         * then mark the page dirty again and leave the page
         * as is.
         */
        if (current_test_flags(PF_FSTRANS) && need_trans)
                goto out_fail;

        /*
         * Delay hooking up buffer heads until we have
         * made our go/no-go decision.
         */
        if (!page_has_buffers(page))
                create_empty_buffers(page, 1 << inode->i_blkbits, 0);


        /*
         *  VM calculation for nr_to_write seems off.  Bump it way
         *  up, this gets simple streaming writes zippy again.
         *  To be reviewed again after Jens' writeback changes.
         */
        wbc->nr_to_write *= 4;

        /*
         * Convert delayed allocate, unwritten or unmapped space
         * to real space and flush out to disk.
         */
        error = xfs_page_state_convert(inode, page, wbc, 1, unmapped);
        if (error == -EAGAIN)
                goto out_fail;
        if (unlikely(error < 0))
                goto out_unlock;

        return 0;

out_fail:
        redirty_page_for_writepage(wbc, page);
        unlock_page(page);
        return 0;
out_unlock:
        unlock_page(page);
        return error;
}

STATIC int
xfs_vm_writepages(
        struct address_space    *mapping,
        struct writeback_control *wbc)
{
        xfs_iflags_clear(XFS_I(mapping->host), XFS_ITRUNCATED);
        return generic_writepages(mapping, wbc);
}

/*
 * Called to move a page into cleanable state - and from there
 * to be released. Possibly the page is already clean. We always
 * have buffer heads in this call.
 *
 * Returns 0 if the page is ok to release, 1 otherwise.
 *
 * Possible scenarios are:
 *
 * 1. We are being called to release a page which has been written
 *    to via regular I/O. buffer heads will be dirty and possibly
 *    delalloc. If no delalloc buffer heads in this case then we
 *    can just return zero.
 *
 * 2. We are called to release a page which has been written via
 *    mmap, all we need to do is ensure there is no delalloc
 *    state in the buffer heads, if not we can let the caller
 *    free them and we should come back later via writepage.
 */
STATIC int
xfs_vm_releasepage(
        struct page             *page,
        gfp_t                   gfp_mask)
{
        struct inode            *inode = page->mapping->host;
        int                     dirty, delalloc, unmapped, unwritten;
        struct writeback_control wbc = {
                .sync_mode = WB_SYNC_ALL,
                .nr_to_write = 1,
        };

        xfs_page_trace(XFS_RELEASEPAGE_ENTER, inode, page, 0);

        if (!page_has_buffers(page))
                return 0;

        xfs_count_page_state(page, &delalloc, &unmapped, &unwritten);
        if (!delalloc && !unwritten)
                goto free_buffers;

        if (!(gfp_mask & __GFP_FS))
                return 0;

        /* If we are already inside a transaction or the thread cannot
         * do I/O, we cannot release this page.
         */
        if (current_test_flags(PF_FSTRANS))
                return 0;

        /*
         * Convert delalloc space to real space, do not flush the
         * data out to disk, that will be done by the caller.
         * Never need to allocate space here - we will always
         * come back to writepage in that case.
         */
        dirty = xfs_page_state_convert(inode, page, &wbc, 0, 0);
        if (dirty == 0 && !unwritten)
                goto free_buffers;
        return 0;

free_buffers:
        return try_to_free_buffers(page);
}

STATIC int
__xfs_get_blocks(
        struct inode            *inode,
        sector_t                iblock,
        struct buffer_head      *bh_result,
        int                     create,
        int                     direct,
        bmapi_flags_t           flags)
{
        xfs_iomap_t             iomap;
        xfs_off_t               offset;
        ssize_t                 size;
        int                     niomap = 1;
        int                     error;

        offset = (xfs_off_t)iblock << inode->i_blkbits;
        ASSERT(bh_result->b_size >= (1 << inode->i_blkbits));
        size = bh_result->b_size;

        if (!create && direct && offset >= i_size_read(inode))
                return 0;

        error = xfs_iomap(XFS_I(inode), offset, size,
                             create ? flags : BMAPI_READ, &iomap, &niomap);
        if (error)
                return -error;
        if (niomap == 0)
                return 0;

        if (iomap.iomap_bn != IOMAP_DADDR_NULL) {
                /*
                 * For unwritten extents do not report a disk address on
                 * the read case (treat as if we're reading into a hole).
                 */
                if (create || !(iomap.iomap_flags & IOMAP_UNWRITTEN)) {
                        xfs_map_buffer(bh_result, &iomap, offset,
                                       inode->i_blkbits);
                }
                if (create && (iomap.iomap_flags & IOMAP_UNWRITTEN)) {
                        if (direct)
                                bh_result->b_private = inode;
                        set_buffer_unwritten(bh_result);
                }
        }

        /*
         * If this is a realtime file, data may be on a different device.
         * to that pointed to from the buffer_head b_bdev currently.
         */
        bh_result->b_bdev = iomap.iomap_target->bt_bdev;

        /*
         * If we previously allocated a block out beyond eof and we are now
         * coming back to use it then we will need to flag it as new even if it
         * has a disk address.
         *
         * With sub-block writes into unwritten extents we also need to mark
         * the buffer as new so that the unwritten parts of the buffer gets
         * correctly zeroed.
         */
        if (create &&
            ((!buffer_mapped(bh_result) && !buffer_uptodate(bh_result)) ||
             (offset >= i_size_read(inode)) ||
             (iomap.iomap_flags & (IOMAP_NEW|IOMAP_UNWRITTEN))))
                set_buffer_new(bh_result);

        if (iomap.iomap_flags & IOMAP_DELAY) {
                BUG_ON(direct);
                if (create) {
                        set_buffer_uptodate(bh_result);
                        set_buffer_mapped(bh_result);
                        set_buffer_delay(bh_result);
                }
        }

        if (direct || size > (1 << inode->i_blkbits)) {
                ASSERT(iomap.iomap_bsize - iomap.iomap_delta > 0);
                offset = min_t(xfs_off_t,
                                iomap.iomap_bsize - iomap.iomap_delta, size);
                bh_result->b_size = (ssize_t)min_t(xfs_off_t, LONG_MAX, offset);
        }

        return 0;
}

int
xfs_get_blocks(
        struct inode            *inode,
        sector_t                iblock,
        struct buffer_head      *bh_result,
        int                     create)
{
        return __xfs_get_blocks(inode, iblock,
                                bh_result, create, 0, BMAPI_WRITE);
}

STATIC int
xfs_get_blocks_direct(
        struct inode            *inode,
        sector_t                iblock,
        struct buffer_head      *bh_result,
        int                     create)
{
        return __xfs_get_blocks(inode, iblock,
                                bh_result, create, 1, BMAPI_WRITE|BMAPI_DIRECT);
}

STATIC void
xfs_end_io_direct(
        struct kiocb    *iocb,
        loff_t          offset,
        ssize_t         size,
        void            *private)
{
        xfs_ioend_t     *ioend = iocb->private;

        /*
         * Non-NULL private data means we need to issue a transaction to
         * convert a range from unwritten to written extents.  This needs
         * to happen from process context but aio+dio I/O completion
         * happens from irq context so we need to defer it to a workqueue.
         * This is not necessary for synchronous direct I/O, but we do
         * it anyway to keep the code uniform and simpler.
         *
         * Well, if only it were that simple. Because synchronous direct I/O
         * requires extent conversion to occur *before* we return to userspace,
         * we have to wait for extent conversion to complete. Look at the
         * iocb that has been passed to us to determine if this is AIO or
         * not. If it is synchronous, tell xfs_finish_ioend() to kick the
         * workqueue and wait for it to complete.
         *
         * The core direct I/O code might be changed to always call the
         * completion handler in the future, in which case all this can
         * go away.
         */
        ioend->io_offset = offset;
        ioend->io_size = size;
        if (ioend->io_type == IOMAP_READ) {
                xfs_finish_ioend(ioend, 0);
        } else if (private && size > 0) {
                xfs_finish_ioend(ioend, is_sync_kiocb(iocb));
        } else {
                /*
                 * A direct I/O write ioend starts it's life in unwritten
                 * state in case they map an unwritten extent.  This write
                 * didn't map an unwritten extent so switch it's completion
                 * handler.
                 */
                INIT_WORK(&ioend->io_work, xfs_end_bio_written);
                xfs_finish_ioend(ioend, 0);
        }

        /*
         * blockdev_direct_IO can return an error even after the I/O
         * completion handler was called.  Thus we need to protect
         * against double-freeing.
         */
        iocb->private = NULL;
}

STATIC ssize_t
xfs_vm_direct_IO(
        int                     rw,
        struct kiocb            *iocb,
        const struct iovec      *iov,
        loff_t                  offset,
        unsigned long           nr_segs)
{
        struct file     *file = iocb->ki_filp;
        struct inode    *inode = file->f_mapping->host;
        struct block_device *bdev;
        ssize_t         ret;

        bdev = xfs_find_bdev_for_inode(XFS_I(inode));

        if (rw == WRITE) {
                iocb->private = xfs_alloc_ioend(inode, IOMAP_UNWRITTEN);
                ret = blockdev_direct_IO_own_locking(rw, iocb, inode,
                        bdev, iov, offset, nr_segs,
                        xfs_get_blocks_direct,
                        xfs_end_io_direct);
        } else {
                iocb->private = xfs_alloc_ioend(inode, IOMAP_READ);
                ret = blockdev_direct_IO_no_locking(rw, iocb, inode,
                        bdev, iov, offset, nr_segs,
                        xfs_get_blocks_direct,
                        xfs_end_io_direct);
        }

        if (unlikely(ret != -EIOCBQUEUED && iocb->private))
                xfs_destroy_ioend(iocb->private);
        return ret;
}

STATIC int
xfs_vm_write_begin(
        struct file             *file,
        struct address_space    *mapping,
        loff_t                  pos,
        unsigned                len,
        unsigned                flags,
        struct page             **pagep,
        void                    **fsdata)
{
        *pagep = NULL;
        return block_write_begin(file, mapping, pos, len, flags, pagep, fsdata,
                                                                xfs_get_blocks);
}

STATIC sector_t
xfs_vm_bmap(
        struct address_space    *mapping,
        sector_t                block)
{
        struct inode            *inode = (struct inode *)mapping->host;
        struct xfs_inode        *ip = XFS_I(inode);

        xfs_itrace_entry(XFS_I(inode));
        xfs_ilock(ip, XFS_IOLOCK_SHARED);
        xfs_flush_pages(ip, (xfs_off_t)0, -1, 0, FI_REMAPF);
        xfs_iunlock(ip, XFS_IOLOCK_SHARED);
        return generic_block_bmap(mapping, block, xfs_get_blocks);
}

STATIC int
xfs_vm_readpage(
        struct file             *unused,
        struct page             *page)
{
        return mpage_readpage(page, xfs_get_blocks);
}

STATIC int
xfs_vm_readpages(
        struct file             *unused,
        struct address_space    *mapping,
        struct list_head        *pages,
        unsigned                nr_pages)
{
        return mpage_readpages(mapping, pages, nr_pages, xfs_get_blocks);
}

STATIC void
xfs_vm_invalidatepage(
        struct page             *page,
        unsigned long           offset)
{
        xfs_page_trace(XFS_INVALIDPAGE_ENTER,
                        page->mapping->host, page, offset);
        block_invalidatepage(page, offset);
}

const struct address_space_operations xfs_address_space_operations = {
        .readpage               = xfs_vm_readpage,
        .readpages              = xfs_vm_readpages,
        .writepage              = xfs_vm_writepage,
        .writepages             = xfs_vm_writepages,
        .sync_page              = block_sync_page,
        .releasepage            = xfs_vm_releasepage,
        .invalidatepage         = xfs_vm_invalidatepage,
        .write_begin            = xfs_vm_write_begin,
        .write_end              = generic_write_end,
        .bmap                   = xfs_vm_bmap,
        .direct_IO              = xfs_vm_direct_IO,
        .migratepage            = buffer_migrate_page,
        .is_partially_uptodate  = block_is_partially_uptodate,
};