xfs_aops.c

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/*
 * 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_log.h"
#include "xfs_sb.h"
#include "xfs_ag.h"
#include "xfs_trans.h"
#include "xfs_mount.h"
#include "xfs_bmap_btree.h"
#include "xfs_dinode.h"
#include "xfs_inode.h"
#include "xfs_inode_item.h"
#include "xfs_alloc.h"
#include "xfs_error.h"
#include "xfs_iomap.h"
#include "xfs_vnodeops.h"
#include "xfs_trace.h"
#include "xfs_bmap.h"
#include <linux/gfp.h>
#include <linux/mpage.h>
#include <linux/pagevec.h>
#include <linux/writeback.h>

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

    *delalloc = *unwritten = 0;

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

STATIC struct block_device *
xfs_find_bdev_for_inode(
    struct inode        *inode)
{
    struct xfs_inode    *ip = XFS_I(inode);
    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;

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

    if (ioend->io_iocb) {
        if (ioend->io_isasync) {
            aio_complete(ioend->io_iocb, ioend->io_error ?
                    ioend->io_error : ioend->io_result, 0);
        }
        inode_dio_done(ioend->io_inode);
    }

    mempool_free(ioend, xfs_ioend_pool);
}

/*
 * Fast and loose check if this write could update the on-disk inode size.
 */
static inline bool xfs_ioend_is_append(struct xfs_ioend *ioend)
{
    return ioend->io_offset + ioend->io_size >
        XFS_I(ioend->io_inode)->i_d.di_size;
}

STATIC int
xfs_setfilesize_trans_alloc(
    struct xfs_ioend    *ioend)
{
    struct xfs_mount    *mp = XFS_I(ioend->io_inode)->i_mount;
    struct xfs_trans    *tp;
    int         error;

    tp = xfs_trans_alloc(mp, XFS_TRANS_FSYNC_TS);

    error = xfs_trans_reserve(tp, 0, XFS_FSYNC_TS_LOG_RES(mp), 0, 0, 0);
    if (error) {
        xfs_trans_cancel(tp, 0);
        return error;
    }

    ioend->io_append_trans = tp;

    /*
     * We will pass freeze protection with a transaction.  So tell lockdep
     * we released it.
     */
    rwsem_release(&ioend->io_inode->i_sb->s_writers.lock_map[SB_FREEZE_FS-1],
              1, _THIS_IP_);
    /*
     * We hand off the transaction to the completion thread now, so
     * clear the flag here.
     */
    current_restore_flags_nested(&tp->t_pflags, PF_FSTRANS);
    return 0;
}

/*
 * Update on-disk file size now that data has been written to disk.
 */
STATIC int
xfs_setfilesize(
    struct xfs_ioend    *ioend)
{
    struct xfs_inode    *ip = XFS_I(ioend->io_inode);
    struct xfs_trans    *tp = ioend->io_append_trans;
    xfs_fsize_t     isize;

    /*
     * The transaction was allocated in the I/O submission thread,
     * thus we need to mark ourselves as beeing in a transaction
     * manually.
     */
    current_set_flags_nested(&tp->t_pflags, PF_FSTRANS);

    xfs_ilock(ip, XFS_ILOCK_EXCL);
    isize = xfs_new_eof(ip, ioend->io_offset + ioend->io_size);
    if (!isize) {
        xfs_iunlock(ip, XFS_ILOCK_EXCL);
        xfs_trans_cancel(tp, 0);
        return 0;
    }

    trace_xfs_setfilesize(ip, ioend->io_offset, ioend->io_size);

    ip->i_d.di_size = isize;
    xfs_trans_ijoin(tp, ip, XFS_ILOCK_EXCL);
    xfs_trans_log_inode(tp, ip, XFS_ILOG_CORE);

    return xfs_trans_commit(tp, 0);
}

/*
 * Schedule IO completion handling on the final put of an ioend.
 *
 * If there is no work to do we might as well call it a day and free the
 * ioend right now.
 */
STATIC void
xfs_finish_ioend(
    struct xfs_ioend    *ioend)
{
    if (atomic_dec_and_test(&ioend->io_remaining)) {
        struct xfs_mount    *mp = XFS_I(ioend->io_inode)->i_mount;

        if (ioend->io_type == XFS_IO_UNWRITTEN)
            queue_work(mp->m_unwritten_workqueue, &ioend->io_work);
        else if (ioend->io_append_trans)
            queue_work(mp->m_data_workqueue, &ioend->io_work);
        else
            xfs_destroy_ioend(ioend);
    }
}

/*
 * IO write completion.
 */
STATIC void
xfs_end_io(
    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);
    int     error = 0;

    if (ioend->io_append_trans) {
        /*
         * We've got freeze protection passed with the transaction.
         * Tell lockdep about it.
         */
        rwsem_acquire_read(
            &ioend->io_inode->i_sb->s_writers.lock_map[SB_FREEZE_FS-1],
            0, 1, _THIS_IP_);
    }
    if (XFS_FORCED_SHUTDOWN(ip->i_mount)) {
        ioend->io_error = -EIO;
        goto done;
    }
    if (ioend->io_error)
        goto done;

    /*
     * For unwritten extents we need to issue transactions to convert a
     * range to normal written extens after the data I/O has finished.
     */
    if (ioend->io_type == XFS_IO_UNWRITTEN) {
        /*
         * For buffered I/O we never preallocate a transaction when
         * doing the unwritten extent conversion, but for direct I/O
         * we do not know if we are converting an unwritten extent
         * or not at the point where we preallocate the transaction.
         */
        if (ioend->io_append_trans) {
            ASSERT(ioend->io_isdirect);

            current_set_flags_nested(
                &ioend->io_append_trans->t_pflags, PF_FSTRANS);
            xfs_trans_cancel(ioend->io_append_trans, 0);
        }

        error = xfs_iomap_write_unwritten(ip, ioend->io_offset,
                         ioend->io_size);
        if (error) {
            ioend->io_error = -error;
            goto done;
        }
    } else if (ioend->io_append_trans) {
        error = xfs_setfilesize(ioend);
        if (error)
            ioend->io_error = -error;
    } else {
        ASSERT(!xfs_ioend_is_append(ioend));
    }

done:
    xfs_destroy_ioend(ioend);
}

/*
 * Call IO completion handling in caller context on the final put of an ioend.
 */
STATIC void
xfs_finish_ioend_sync(
    struct xfs_ioend    *ioend)
{
    if (atomic_dec_and_test(&ioend->io_remaining))
        xfs_end_io(&ioend->io_work);
}

/*
 * 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_isasync = 0;
    ioend->io_isdirect = 0;
    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;
    ioend->io_offset = 0;
    ioend->io_size = 0;
    ioend->io_iocb = NULL;
    ioend->io_result = 0;
    ioend->io_append_trans = NULL;

    INIT_WORK(&ioend->io_work, xfs_end_io);
    return ioend;
}

STATIC int
xfs_map_blocks(
    struct inode        *inode,
    loff_t          offset,
    struct xfs_bmbt_irec    *imap,
    int         type,
    int         nonblocking)
{
    struct xfs_inode    *ip = XFS_I(inode);
    struct xfs_mount    *mp = ip->i_mount;
    ssize_t         count = 1 << inode->i_blkbits;
    xfs_fileoff_t       offset_fsb, end_fsb;
    int         error = 0;
    int         bmapi_flags = XFS_BMAPI_ENTIRE;
    int         nimaps = 1;

    if (XFS_FORCED_SHUTDOWN(mp))
        return -XFS_ERROR(EIO);

    if (type == XFS_IO_UNWRITTEN)
        bmapi_flags |= XFS_BMAPI_IGSTATE;

    if (!xfs_ilock_nowait(ip, XFS_ILOCK_SHARED)) {
        if (nonblocking)
            return -XFS_ERROR(EAGAIN);
        xfs_ilock(ip, XFS_ILOCK_SHARED);
    }

    ASSERT(ip->i_d.di_format != XFS_DINODE_FMT_BTREE ||
           (ip->i_df.if_flags & XFS_IFEXTENTS));
    ASSERT(offset <= mp->m_super->s_maxbytes);

    if (offset + count > mp->m_super->s_maxbytes)
        count = mp->m_super->s_maxbytes - offset;
    end_fsb = XFS_B_TO_FSB(mp, (xfs_ufsize_t)offset + count);
    offset_fsb = XFS_B_TO_FSBT(mp, offset);
    error = xfs_bmapi_read(ip, offset_fsb, end_fsb - offset_fsb,
                imap, &nimaps, bmapi_flags);
    xfs_iunlock(ip, XFS_ILOCK_SHARED);

    if (error)
        return -XFS_ERROR(error);

    if (type == XFS_IO_DELALLOC &&
        (!nimaps || isnullstartblock(imap->br_startblock))) {
        error = xfs_iomap_write_allocate(ip, offset, count, imap);
        if (!error)
            trace_xfs_map_blocks_alloc(ip, offset, count, type, imap);
        return -XFS_ERROR(error);
    }

#ifdef DEBUG
    if (type == XFS_IO_UNWRITTEN) {
        ASSERT(nimaps);
        ASSERT(imap->br_startblock != HOLESTARTBLOCK);
        ASSERT(imap->br_startblock != DELAYSTARTBLOCK);
    }
#endif
    if (nimaps)
        trace_xfs_map_blocks_found(ip, offset, count, type, imap);
    return 0;
}

STATIC int
xfs_imap_valid(
    struct inode        *inode,
    struct xfs_bmbt_irec    *imap,
    xfs_off_t       offset)
{
    offset >>= inode->i_blkbits;

    return offset >= imap->br_startoff &&
        offset < imap->br_startoff + imap->br_blockcount;
}

/*
 * 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);
}

STATIC void
xfs_submit_ioend_bio(
    struct writeback_control *wbc,
    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(wbc->sync_mode == WB_SYNC_ALL ? WRITE_SYNC : WRITE, bio);
}

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

    ASSERT(bio->bi_private == NULL);
    bio->bi_sector = bh->b_blocknr * (bh->b_size >> 9);
    bio->bi_bdev = bh->b_bdev;
    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.
 *
 * If @fail is non-zero, it means that we have a situation where some part of
 * the submission process has failed after we have marked paged for writeback
 * and unlocked them. In this situation, we need to fail the ioend chain rather
 * than submit it to IO. This typically only happens on a filesystem shutdown.
 */
STATIC void
xfs_submit_ioend(
    struct writeback_control *wbc,
    xfs_ioend_t     *ioend,
    int         fail)
{
    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;

        /*
         * If we are failing the IO now, just mark the ioend with an
         * error and finish it. This will run IO completion immediately
         * as there is only one reference to the ioend at this point in
         * time.
         */
        if (fail) {
            ioend->io_error = -fail;
            xfs_finish_ioend(ioend);
            continue;
        }

        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(wbc, ioend, bio);
                goto retry;
            }

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

            lastblock = bh->b_blocknr;
        }
        if (bio)
            xfs_submit_ioend_bio(wbc, ioend, bio);
        xfs_finish_ioend(ioend);
    } 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);

        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 inode        *inode,
    struct buffer_head  *bh,
    struct xfs_bmbt_irec    *imap,
    xfs_off_t       offset)
{
    sector_t        bn;
    struct xfs_mount    *m = XFS_I(inode)->i_mount;
    xfs_off_t       iomap_offset = XFS_FSB_TO_B(m, imap->br_startoff);
    xfs_daddr_t     iomap_bn = xfs_fsb_to_db(XFS_I(inode), imap->br_startblock);

    ASSERT(imap->br_startblock != HOLESTARTBLOCK);
    ASSERT(imap->br_startblock != DELAYSTARTBLOCK);

    bn = (iomap_bn >> (inode->i_blkbits - BBSHIFT)) +
          ((offset - iomap_offset) >> inode->i_blkbits);

    ASSERT(bn || XFS_IS_REALTIME_INODE(XFS_I(inode)));

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

STATIC void
xfs_map_at_offset(
    struct inode        *inode,
    struct buffer_head  *bh,
    struct xfs_bmbt_irec    *imap,
    xfs_off_t       offset)
{
    ASSERT(imap->br_startblock != HOLESTARTBLOCK);
    ASSERT(imap->br_startblock != DELAYSTARTBLOCK);

    xfs_map_buffer(inode, bh, imap, offset);
    set_buffer_mapped(bh);
    clear_buffer_delay(bh);
    clear_buffer_unwritten(bh);
}

/*
 * Test if a given page is suitable for writing as part of an unwritten
 * or delayed allocate extent.
 */
STATIC int
xfs_check_page_type(
    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 == XFS_IO_UNWRITTEN);
            else if (buffer_delay(bh))
                acceptable += (type == XFS_IO_DELALLOC);
            else if (buffer_dirty(bh) && buffer_mapped(bh))
                acceptable += (type == XFS_IO_OVERWRITE);
            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,
    struct xfs_bmbt_irec    *imap,
    xfs_ioend_t     **ioendp,
    struct writeback_control *wbc)
{
    struct buffer_head  *bh, *head;
    xfs_off_t       end_offset;
    unsigned long       p_offset;
    unsigned int        type;
    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_check_page_type(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) ||
            buffer_mapped(bh)) {
            if (buffer_unwritten(bh))
                type = XFS_IO_UNWRITTEN;
            else if (buffer_delay(bh))
                type = XFS_IO_DELALLOC;
            else
                type = XFS_IO_OVERWRITE;

            if (!xfs_imap_valid(inode, imap, offset)) {
                done = 1;
                continue;
            }

            lock_buffer(bh);
            if (type != XFS_IO_OVERWRITE)
                xfs_map_at_offset(inode, bh, imap, offset);
            xfs_add_to_ioend(inode, bh, offset, type,
                     ioendp, done);

            page_dirty--;
            count++;
        } else {
            done = 1;
        }
    } while (offset += len, (bh = bh->b_this_page) != head);

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

    if (count) {
        if (--wbc->nr_to_write <= 0 &&
            wbc->sync_mode == WB_SYNC_NONE)
            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,
    struct xfs_bmbt_irec    *imap,
    xfs_ioend_t     **ioendp,
    struct writeback_control *wbc,
    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++,
                    imap, ioendp, wbc);
            if (done)
                break;
        }

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

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

/*
 * If the page has delalloc buffers on it, we need to punch them out before we
 * invalidate the page. If we don't, we leave a stale delalloc mapping on the
 * inode that can trip a BUG() in xfs_get_blocks() later on if a direct IO read
 * is done on that same region - the delalloc extent is returned when none is
 * supposed to be there.
 *
 * We prevent this by truncating away the delalloc regions on the page before
 * invalidating it. Because they are delalloc, we can do this without needing a
 * transaction. Indeed - if we get ENOSPC errors, we have to be able to do this
 * truncation without a transaction as there is no space left for block
 * reservation (typically why we see a ENOSPC in writeback).
 *
 * This is not a performance critical path, so for now just do the punching a
 * buffer head at a time.
 */
STATIC void
xfs_aops_discard_page(
    struct page     *page)
{
    struct inode        *inode = page->mapping->host;
    struct xfs_inode    *ip = XFS_I(inode);
    struct buffer_head  *bh, *head;
    loff_t          offset = page_offset(page);

    if (!xfs_check_page_type(page, XFS_IO_DELALLOC))
        goto out_invalidate;

    if (XFS_FORCED_SHUTDOWN(ip->i_mount))
        goto out_invalidate;

    xfs_alert(ip->i_mount,
        "page discard on page %p, inode 0x%llx, offset %llu.",
            page, ip->i_ino, offset);

    xfs_ilock(ip, XFS_ILOCK_EXCL);
    bh = head = page_buffers(page);
    do {
        int     error;
        xfs_fileoff_t   start_fsb;

        if (!buffer_delay(bh))
            goto next_buffer;

        start_fsb = XFS_B_TO_FSBT(ip->i_mount, offset);
        error = xfs_bmap_punch_delalloc_range(ip, start_fsb, 1);
        if (error) {
            /* something screwed, just bail */
            if (!XFS_FORCED_SHUTDOWN(ip->i_mount)) {
                xfs_alert(ip->i_mount,
            "page discard unable to remove delalloc mapping.");
            }
            break;
        }
next_buffer:
        offset += 1 << inode->i_blkbits;

    } while ((bh = bh->b_this_page) != head);

    xfs_iunlock(ip, XFS_ILOCK_EXCL);
out_invalidate:
    xfs_vm_invalidatepage(page, 0);
    return;
}

/*
 * Write out a dirty page.
 *
 * For delalloc space on the page we need to allocate space and flush it.
 * For unwritten space on the page we need to start the conversion to
 * regular allocated space.
 * For any other dirty buffer heads on the page we should flush them.
 */
STATIC int
xfs_vm_writepage(
    struct page     *page,
    struct writeback_control *wbc)
{
    struct inode        *inode = page->mapping->host;
    struct buffer_head  *bh, *head;
    struct xfs_bmbt_irec    imap;
    xfs_ioend_t     *ioend = NULL, *iohead = NULL;
    loff_t          offset;
    unsigned int        type;
    __uint64_t              end_offset;
    pgoff_t                 end_index, last_index;
    ssize_t         len;
    int         err, imap_valid = 0, uptodate = 1;
    int         count = 0;
    int         nonblocking = 0;

    trace_xfs_writepage(inode, page, 0);

    ASSERT(page_has_buffers(page));

    /*
     * Refuse to write the page out if we are called from reclaim context.
     *
     * This avoids stack overflows when called from deeply used stacks in
     * random callers for direct reclaim or memcg reclaim.  We explicitly
     * allow reclaim from kswapd as the stack usage there is relatively low.
     *
     * This should never happen except in the case of a VM regression so
     * warn about it.
     */
    if (WARN_ON_ONCE((current->flags & (PF_MEMALLOC|PF_KSWAPD)) ==
            PF_MEMALLOC))
        goto redirty;

    /*
     * Given that we do not allow direct reclaim to call us, we should
     * never be called while in a filesystem transaction.
     */
    if (WARN_ON(current->flags & PF_FSTRANS))
        goto redirty;

    /* 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) {
        unsigned offset_into_page = offset & (PAGE_CACHE_SIZE - 1);

        /*
         * Just skip the page if it is fully outside i_size, e.g. due
         * to a truncate operation that is in progress.
         */
        if (page->index >= end_index + 1 || offset_into_page == 0) {
            unlock_page(page);
            return 0;
        }

        /*
         * The page straddles i_size.  It must be zeroed out on each
         * and every writepage invocation because it may be mmapped.
         * "A file is mapped in multiples of the page size.  For a file
         * that is not a multiple of the  page size, the remaining
         * memory is zeroed when mapped, and writes to that region are
         * not written out to the file."
         */
        zero_user_segment(page, offset_into_page, PAGE_CACHE_SIZE);
    }

    end_offset = min_t(unsigned long long,
            (xfs_off_t)(page->index + 1) << PAGE_CACHE_SHIFT,
            offset);
    len = 1 << inode->i_blkbits;

    bh = head = page_buffers(page);
    offset = page_offset(page);
    type = XFS_IO_OVERWRITE;

    if (wbc->sync_mode == WB_SYNC_NONE)
        nonblocking = 1;

    do {
        int new_ioend = 0;

        if (offset >= end_offset)
            break;
        if (!buffer_uptodate(bh))
            uptodate = 0;

        /*
         * set_page_dirty dirties all buffers in a page, independent
         * of their state.  The dirty state however is entirely
         * meaningless for holes (!mapped && uptodate), so skip
         * buffers covering holes here.
         */
        if (!buffer_mapped(bh) && buffer_uptodate(bh)) {
            imap_valid = 0;
            continue;
        }

        if (buffer_unwritten(bh)) {
            if (type != XFS_IO_UNWRITTEN) {
                type = XFS_IO_UNWRITTEN;
                imap_valid = 0;
            }
        } else if (buffer_delay(bh)) {
            if (type != XFS_IO_DELALLOC) {
                type = XFS_IO_DELALLOC;
                imap_valid = 0;
            }
        } else if (buffer_uptodate(bh)) {
            if (type != XFS_IO_OVERWRITE) {
                type = XFS_IO_OVERWRITE;
                imap_valid = 0;
            }
        } else {
            if (PageUptodate(page))
                ASSERT(buffer_mapped(bh));
            /*
             * This buffer is not uptodate and will not be
             * written to disk.  Ensure that we will put any
             * subsequent writeable buffers into a new
             * ioend.
             */
            imap_valid = 0;
            continue;
        }

        if (imap_valid)
            imap_valid = xfs_imap_valid(inode, &imap, offset);
        if (!imap_valid) {
            /*
             * If we didn't have a valid mapping then we need to
             * put the new mapping into a separate ioend structure.
             * This ensures non-contiguous extents always have
             * separate ioends, which is particularly important
             * for unwritten extent conversion at I/O completion
             * time.
             */
            new_ioend = 1;
            err = xfs_map_blocks(inode, offset, &imap, type,
                         nonblocking);
            if (err)
                goto error;
            imap_valid = xfs_imap_valid(inode, &imap, offset);
        }
        if (imap_valid) {
            lock_buffer(bh);
            if (type != XFS_IO_OVERWRITE)
                xfs_map_at_offset(inode, bh, &imap, offset);
            xfs_add_to_ioend(inode, bh, offset, type, &ioend,
                     new_ioend);
            count++;
        }

        if (!iohead)
            iohead = ioend;

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

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

    xfs_start_page_writeback(page, 1, count);

    /* if there is no IO to be submitted for this page, we are done */
    if (!ioend)
        return 0;

    ASSERT(iohead);

    /*
     * Any errors from this point onwards need tobe reported through the IO
     * completion path as we have marked the initial page as under writeback
     * and unlocked it.
     */
    if (imap_valid) {
        xfs_off_t       end_index;

        end_index = imap.br_startoff + imap.br_blockcount;

        /* to bytes */
        end_index <<= inode->i_blkbits;

        /* to pages */
        end_index = (end_index - 1) >> PAGE_CACHE_SHIFT;

        /* check against file size */
        if (end_index > last_index)
            end_index = last_index;

        xfs_cluster_write(inode, page->index + 1, &imap, &ioend,
                  wbc, end_index);
    }


    /*
     * Reserve log space if we might write beyond the on-disk inode size.
     */
    err = 0;
    if (ioend->io_type != XFS_IO_UNWRITTEN && xfs_ioend_is_append(ioend))
        err = xfs_setfilesize_trans_alloc(ioend);

    xfs_submit_ioend(wbc, iohead, err);

    return 0;

error:
    if (iohead)
        xfs_cancel_ioend(iohead);

    if (err == -EAGAIN)
        goto redirty;

    xfs_aops_discard_page(page);
    ClearPageUptodate(page);
    unlock_page(page);
    return err;

redirty:
    redirty_page_for_writepage(wbc, page);
    unlock_page(page);
    return 0;
}

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. The page should already be clean. We always
 * have buffer heads in this call.
 *
 * Returns 1 if the page is ok to release, 0 otherwise.
 */
STATIC int
xfs_vm_releasepage(
    struct page     *page,
    gfp_t           gfp_mask)
{
    int         delalloc, unwritten;

    trace_xfs_releasepage(page->mapping->host, page, 0);

    xfs_count_page_state(page, &delalloc, &unwritten);

    if (WARN_ON(delalloc))
        return 0;
    if (WARN_ON(unwritten))
        return 0;

    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)
{
    struct xfs_inode    *ip = XFS_I(inode);
    struct xfs_mount    *mp = ip->i_mount;
    xfs_fileoff_t       offset_fsb, end_fsb;
    int         error = 0;
    int         lockmode = 0;
    struct xfs_bmbt_irec    imap;
    int         nimaps = 1;
    xfs_off_t       offset;
    ssize_t         size;
    int         new = 0;

    if (XFS_FORCED_SHUTDOWN(mp))
        return -XFS_ERROR(EIO);

    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;

    /*
     * Direct I/O is usually done on preallocated files, so try getting
     * a block mapping without an exclusive lock first.  For buffered
     * writes we already have the exclusive iolock anyway, so avoiding
     * a lock roundtrip here by taking the ilock exclusive from the
     * beginning is a useful micro optimization.
     */
    if (create && !direct) {
        lockmode = XFS_ILOCK_EXCL;
        xfs_ilock(ip, lockmode);
    } else {
        lockmode = xfs_ilock_map_shared(ip);
    }

    ASSERT(offset <= mp->m_super->s_maxbytes);
    if (offset + size > mp->m_super->s_maxbytes)
        size = mp->m_super->s_maxbytes - offset;
    end_fsb = XFS_B_TO_FSB(mp, (xfs_ufsize_t)offset + size);
    offset_fsb = XFS_B_TO_FSBT(mp, offset);

    error = xfs_bmapi_read(ip, offset_fsb, end_fsb - offset_fsb,
                &imap, &nimaps, XFS_BMAPI_ENTIRE);
    if (error)
        goto out_unlock;

    if (create &&
        (!nimaps ||
         (imap.br_startblock == HOLESTARTBLOCK ||
          imap.br_startblock == DELAYSTARTBLOCK))) {
        if (direct || xfs_get_extsz_hint(ip)) {
            /*
             * Drop the ilock in preparation for starting the block
             * allocation transaction.  It will be retaken
             * exclusively inside xfs_iomap_write_direct for the
             * actual allocation.
             */
            xfs_iunlock(ip, lockmode);
            error = xfs_iomap_write_direct(ip, offset, size,
                               &imap, nimaps);
            if (error)
                return -error;
            new = 1;
        } else {
            /*
             * Delalloc reservations do not require a transaction,
             * we can go on without dropping the lock here. If we
             * are allocating a new delalloc block, make sure that
             * we set the new flag so that we mark the buffer new so
             * that we know that it is newly allocated if the write
             * fails.
             */
            if (nimaps && imap.br_startblock == HOLESTARTBLOCK)
                new = 1;
            error = xfs_iomap_write_delay(ip, offset, size, &imap);
            if (error)
                goto out_unlock;

            xfs_iunlock(ip, lockmode);
        }

        trace_xfs_get_blocks_alloc(ip, offset, size, 0, &imap);
    } else if (nimaps) {
        trace_xfs_get_blocks_found(ip, offset, size, 0, &imap);
        xfs_iunlock(ip, lockmode);
    } else {
        trace_xfs_get_blocks_notfound(ip, offset, size);
        goto out_unlock;
    }

    if (imap.br_startblock != HOLESTARTBLOCK &&
        imap.br_startblock != DELAYSTARTBLOCK) {
        /*
         * For unwritten extents do not report a disk address on
         * the read case (treat as if we're reading into a hole).
         */
        if (create || !ISUNWRITTEN(&imap))
            xfs_map_buffer(inode, bh_result, &imap, offset);
        if (create && ISUNWRITTEN(&imap)) {
            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 = xfs_find_bdev_for_inode(inode);

    /*
     * 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)) ||
         (new || ISUNWRITTEN(&imap))))
        set_buffer_new(bh_result);

    if (imap.br_startblock == DELAYSTARTBLOCK) {
        BUG_ON(direct);
        if (create) {
            set_buffer_uptodate(bh_result);
            set_buffer_mapped(bh_result);
            set_buffer_delay(bh_result);
        }
    }

    /*
     * If this is O_DIRECT or the mpage code calling tell them how large
     * the mapping is, so that we can avoid repeated get_blocks calls.
     */
    if (direct || size > (1 << inode->i_blkbits)) {
        xfs_off_t       mapping_size;

        mapping_size = imap.br_startoff + imap.br_blockcount - iblock;
        mapping_size <<= inode->i_blkbits;

        ASSERT(mapping_size > 0);
        if (mapping_size > size)
            mapping_size = size;
        if (mapping_size > LONG_MAX)
            mapping_size = LONG_MAX;

        bh_result->b_size = mapping_size;
    }

    return 0;

out_unlock:
    xfs_iunlock(ip, lockmode);
    return -error;
}

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);
}

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);
}

/*
 * Complete a direct I/O write request.
 *
 * If the private argument is non-NULL __xfs_get_blocks signals us that we
 * need to issue a transaction to convert the range from unwritten to written
 * extents.  In case this is regular synchronous I/O we just call xfs_end_io
 * to do this and we are done.  But in case this was a successful AIO
 * request this handler is called from interrupt context, from which we
 * can't start transactions.  In that case offload the I/O completion to
 * the workqueues we also use for buffered I/O completion.
 */
STATIC void
xfs_end_io_direct_write(
    struct kiocb        *iocb,
    loff_t          offset,
    ssize_t         size,
    void            *private,
    int         ret,
    bool            is_async)
{
    struct xfs_ioend    *ioend = iocb->private;

    /*
     * While the generic direct I/O code updates the inode size, it does
     * so only after the end_io handler is called, which means our
     * end_io handler thinks the on-disk size is outside the in-core
     * size.  To prevent this just update it a little bit earlier here.
     */
    if (offset + size > i_size_read(ioend->io_inode))
        i_size_write(ioend->io_inode, offset + size);

    /*
     * 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;

    ioend->io_offset = offset;
    ioend->io_size = size;
    ioend->io_iocb = iocb;
    ioend->io_result = ret;
    if (private && size > 0)
        ioend->io_type = XFS_IO_UNWRITTEN;

    if (is_async) {
        ioend->io_isasync = 1;
        xfs_finish_ioend(ioend);
    } else {
        xfs_finish_ioend_sync(ioend);
    }
}

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

    if (rw & WRITE) {
        size_t size = iov_length(iov, nr_segs);

        /*
         * We need to preallocate a transaction for a size update
         * here.  In the case that this write both updates the size
         * and converts at least on unwritten extent we will cancel
         * the still clean transaction after the I/O has finished.
         */
        iocb->private = ioend = xfs_alloc_ioend(inode, XFS_IO_DIRECT);
        if (offset + size > XFS_I(inode)->i_d.di_size) {
            ret = xfs_setfilesize_trans_alloc(ioend);
            if (ret)
                goto out_destroy_ioend;
            ioend->io_isdirect = 1;
        }

        ret = __blockdev_direct_IO(rw, iocb, inode, bdev, iov,
                        offset, nr_segs,
                        xfs_get_blocks_direct,
                        xfs_end_io_direct_write, NULL, 0);
        if (ret != -EIOCBQUEUED && iocb->private)
            goto out_trans_cancel;
    } else {
        ret = __blockdev_direct_IO(rw, iocb, inode, bdev, iov,
                        offset, nr_segs,
                        xfs_get_blocks_direct,
                        NULL, NULL, 0);
    }

    return ret;

out_trans_cancel:
    if (ioend->io_append_trans) {
        current_set_flags_nested(&ioend->io_append_trans->t_pflags,
                     PF_FSTRANS);
        rwsem_acquire_read(
            &inode->i_sb->s_writers.lock_map[SB_FREEZE_FS-1],
            0, 1, _THIS_IP_);
        xfs_trans_cancel(ioend->io_append_trans, 0);
    }
out_destroy_ioend:
    xfs_destroy_ioend(ioend);
    return ret;
}

/*
 * Punch out the delalloc blocks we have already allocated.
 *
 * Don't bother with xfs_setattr given that nothing can have made it to disk yet
 * as the page is still locked at this point.
 */
STATIC void
xfs_vm_kill_delalloc_range(
    struct inode        *inode,
    loff_t          start,
    loff_t          end)
{
    struct xfs_inode    *ip = XFS_I(inode);
    xfs_fileoff_t       start_fsb;
    xfs_fileoff_t       end_fsb;
    int         error;

    start_fsb = XFS_B_TO_FSB(ip->i_mount, start);
    end_fsb = XFS_B_TO_FSB(ip->i_mount, end);
    if (end_fsb <= start_fsb)
        return;

    xfs_ilock(ip, XFS_ILOCK_EXCL);
    error = xfs_bmap_punch_delalloc_range(ip, start_fsb,
                        end_fsb - start_fsb);
    if (error) {
        /* something screwed, just bail */
        if (!XFS_FORCED_SHUTDOWN(ip->i_mount)) {
            xfs_alert(ip->i_mount,
        "xfs_vm_write_failed: unable to clean up ino %lld",
                    ip->i_ino);
        }
    }
    xfs_iunlock(ip, XFS_ILOCK_EXCL);
}

STATIC void
xfs_vm_write_failed(
    struct inode        *inode,
    struct page     *page,
    loff_t          pos,
    unsigned        len)
{
    loff_t          block_offset = pos & PAGE_MASK;
    loff_t          block_start;
    loff_t          block_end;
    loff_t          from = pos & (PAGE_CACHE_SIZE - 1);
    loff_t          to = from + len;
    struct buffer_head  *bh, *head;

    ASSERT(block_offset + from == pos);

    head = page_buffers(page);
    block_start = 0;
    for (bh = head; bh != head || !block_start;
         bh = bh->b_this_page, block_start = block_end,
                   block_offset += bh->b_size) {
        block_end = block_start + bh->b_size;

        /* skip buffers before the write */
        if (block_end <= from)
            continue;

        /* if the buffer is after the write, we're done */
        if (block_start >= to)
            break;

        if (!buffer_delay(bh))
            continue;

        if (!buffer_new(bh) && block_offset < i_size_read(inode))
            continue;

        xfs_vm_kill_delalloc_range(inode, block_offset,
                       block_offset + bh->b_size);
    }

}

/*
 * This used to call block_write_begin(), but it unlocks and releases the page
 * on error, and we need that page to be able to punch stale delalloc blocks out
 * on failure. hence we copy-n-waste it here and call xfs_vm_write_failed() at
 * the appropriate point.
 */
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)
{
    pgoff_t         index = pos >> PAGE_CACHE_SHIFT;
    struct page     *page;
    int         status;

    ASSERT(len <= PAGE_CACHE_SIZE);

    page = grab_cache_page_write_begin(mapping, index,
                       flags | AOP_FLAG_NOFS);
    if (!page)
        return -ENOMEM;

    status = __block_write_begin(page, pos, len, xfs_get_blocks);
    if (unlikely(status)) {
        struct inode    *inode = mapping->host;

        xfs_vm_write_failed(inode, page, pos, len);
        unlock_page(page);

        if (pos + len > i_size_read(inode))
            truncate_pagecache(inode, pos + len, i_size_read(inode));

        page_cache_release(page);
        page = NULL;
    }

    *pagep = page;
    return status;
}

/*
 * On failure, we only need to kill delalloc blocks beyond EOF because they
 * will never be written. For blocks within EOF, generic_write_end() zeros them
 * so they are safe to leave alone and be written with all the other valid data.
 */
STATIC int
xfs_vm_write_end(
    struct file     *file,
    struct address_space    *mapping,
    loff_t          pos,
    unsigned        len,
    unsigned        copied,
    struct page     *page,
    void            *fsdata)
{
    int         ret;

    ASSERT(len <= PAGE_CACHE_SIZE);

    ret = generic_write_end(file, mapping, pos, len, copied, page, fsdata);
    if (unlikely(ret < len)) {
        struct inode    *inode = mapping->host;
        size_t      isize = i_size_read(inode);
        loff_t      to = pos + len;

        if (to > isize) {
            truncate_pagecache(inode, to, isize);
            xfs_vm_kill_delalloc_range(inode, isize, to);
        }
    }
    return ret;
}

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);

    trace_xfs_vm_bmap(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);
}

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,
    .releasepage        = xfs_vm_releasepage,
    .invalidatepage     = xfs_vm_invalidatepage,
    .write_begin        = xfs_vm_write_begin,
    .write_end      = xfs_vm_write_end,
    .bmap           = xfs_vm_bmap,
    .direct_IO      = xfs_vm_direct_IO,
    .migratepage        = buffer_migrate_page,
    .is_partially_uptodate  = block_is_partially_uptodate,
    .error_remove_page  = generic_error_remove_page,
};