xfs: bufferhead chains are invalid after end_page_writeback

[mirror_ubuntu-bionic-kernel.git] / fs / xfs / 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_shared.h"
#include "xfs_format.h"
#include "xfs_log_format.h"
#include "xfs_trans_resv.h"
#include "xfs_mount.h"
#include "xfs_inode.h"
#include "xfs_trans.h"
#include "xfs_inode_item.h"
#include "xfs_alloc.h"
#include "xfs_error.h"
#include "xfs_iomap.h"
#include "xfs_trace.h"
#include "xfs_bmap.h"
#include "xfs_bmap_util.h"
#include "xfs_bmap_btree.h"
#include <linux/gfp.h>
#include <linux/mpage.h>
#include <linux/pagevec.h>
#include <linux/writeback.h>

/* flags for direct write completions */
#define XFS_DIO_FLAG_UNWRITTEN  (1 << 0)
#define XFS_DIO_FLAG_APPEND     (1 << 1)

/*
 * structure owned by writepages passed to individual writepage calls
 */
struct xfs_writepage_ctx {
        struct xfs_bmbt_irec    imap;
        bool                    imap_valid;
        unsigned int            io_type;
        struct xfs_ioend        *ioend;
        sector_t                last_block;
};

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);
}

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 page.  Update the page state via the
 * associated buffer_heads, paying attention to the start and end offsets that
 * we need to process on the page.
 *
 * Landmine Warning: bh->b_end_io() will call end_page_writeback() on the last
 * buffer in the IO. Once it does this, it is unsafe to access the bufferhead or
 * the page at all, as we may be racing with memory reclaim and it can free both
 * the bufferhead chain and the page as it will see the page as clean and
 * unused.
 */
static void
xfs_finish_page_writeback(
        struct inode            *inode,
        struct bio_vec          *bvec,
        int                     error)
{
        unsigned int            end = bvec->bv_offset + bvec->bv_len - 1;
        struct buffer_head      *head, *bh, *next;
        unsigned int            off = 0;
        unsigned int            bsize;

        ASSERT(bvec->bv_offset < PAGE_SIZE);
        ASSERT((bvec->bv_offset & ((1 << inode->i_blkbits) - 1)) == 0);
        ASSERT(end < PAGE_SIZE);
        ASSERT((bvec->bv_len & ((1 << inode->i_blkbits) - 1)) == 0);

        bh = head = page_buffers(bvec->bv_page);

        bsize = bh->b_size;
        do {
                next = bh->b_this_page;
                if (off < bvec->bv_offset)
                        goto next_bh;
                if (off > end)
                        break;
                bh->b_end_io(bh, !error);
next_bh:
                off += bsize;
        } while ((bh = next) != head);
}

/*
 * We're now finished for good with this ioend structure.  Update the page
 * state, release holds on bios, and finally free up memory.  Do not use the
 * ioend after this.
 */
STATIC void
xfs_destroy_ioend(
        struct xfs_ioend        *ioend,
        int                     error)
{
        struct inode            *inode = ioend->io_inode;
        struct bio              *last = ioend->io_bio;
        struct bio              *bio, *next;

        for (bio = &ioend->io_inline_bio; bio; bio = next) {
                struct bio_vec  *bvec;
                int             i;

                /*
                 * For the last bio, bi_private points to the ioend, so we
                 * need to explicitly end the iteration here.
                 */
                if (bio == last)
                        next = NULL;
                else
                        next = bio->bi_private;

                /* walk each page on bio, ending page IO on them */
                bio_for_each_segment_all(bvec, bio, i)
                        xfs_finish_page_writeback(inode, bvec, error);

                bio_put(bio);
        }
}

/*
 * 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;

        error = xfs_trans_alloc(mp, &M_RES(mp)->tr_fsyncts, 0, 0, 0, &tp);
        if (error)
                return error;

        ioend->io_append_trans = tp;

        /*
         * We may pass freeze protection with a transaction.  So tell lockdep
         * we released it.
         */
        __sb_writers_release(ioend->io_inode->i_sb, SB_FREEZE_FS);
        /*
         * 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_inode        *ip,
        struct xfs_trans        *tp,
        xfs_off_t               offset,
        size_t                  size)
{
        xfs_fsize_t             isize;

        xfs_ilock(ip, XFS_ILOCK_EXCL);
        isize = xfs_new_eof(ip, offset + size);
        if (!isize) {
                xfs_iunlock(ip, XFS_ILOCK_EXCL);
                xfs_trans_cancel(tp);
                return 0;
        }

        trace_xfs_setfilesize(ip, offset, 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);
}

STATIC int
xfs_setfilesize_ioend(
        struct xfs_ioend        *ioend,
        int                     error)
{
        struct xfs_inode        *ip = XFS_I(ioend->io_inode);
        struct xfs_trans        *tp = ioend->io_append_trans;

        /*
         * The transaction may have been allocated in the I/O submission thread,
         * thus we need to mark ourselves as being in a transaction manually.
         * Similarly for freeze protection.
         */
        current_set_flags_nested(&tp->t_pflags, PF_FSTRANS);
        __sb_writers_acquired(VFS_I(ip)->i_sb, SB_FREEZE_FS);

        /* we abort the update if there was an IO error */
        if (error) {
                xfs_trans_cancel(tp);
                return error;
        }

        return xfs_setfilesize(ip, tp, ioend->io_offset, ioend->io_size);
}

/*
 * IO write completion.
 */
STATIC void
xfs_end_io(
        struct work_struct *work)
{
        struct xfs_ioend        *ioend =
                container_of(work, struct xfs_ioend, io_work);
        struct xfs_inode        *ip = XFS_I(ioend->io_inode);
        int                     error = ioend->io_bio->bi_error;

        /*
         * Set an error if the mount has shut down and proceed with end I/O
         * processing so it can perform whatever cleanups are necessary.
         */
        if (XFS_FORCED_SHUTDOWN(ip->i_mount))
                error = -EIO;

        /*
         * For unwritten extents we need to issue transactions to convert a
         * range to normal written extens after the data I/O has finished.
         * Detecting and handling completion IO errors is done individually
         * for each case as different cleanup operations need to be performed
         * on error.
         */
        if (ioend->io_type == XFS_IO_UNWRITTEN) {
                if (error)
                        goto done;
                error = xfs_iomap_write_unwritten(ip, ioend->io_offset,
                                                  ioend->io_size);
        } else if (ioend->io_append_trans) {
                error = xfs_setfilesize_ioend(ioend, error);
        } else {
                ASSERT(!xfs_ioend_is_append(ioend));
        }

done:
        xfs_destroy_ioend(ioend, error);
}

STATIC void
xfs_end_bio(
        struct bio              *bio)
{
        struct xfs_ioend        *ioend = bio->bi_private;
        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, bio->bi_error);
}

STATIC int
xfs_map_blocks(
        struct inode            *inode,
        loff_t                  offset,
        struct xfs_bmbt_irec    *imap,
        int                     type)
{
        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 -EIO;

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

        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 error;

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

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)
{
        ASSERT(PageLocked(page));
        ASSERT(!PageWriteback(page));

        /*
         * if the page was not fully cleaned, we need to ensure that the higher
         * layers come back to it correctly. That means we need to keep the page
         * dirty, and for WB_SYNC_ALL writeback we need to ensure the
         * PAGECACHE_TAG_TOWRITE index mark is not removed so another attempt to
         * write this page in this writeback sweep will be made.
         */
        if (clear_dirty) {
                clear_page_dirty_for_io(page);
                set_page_writeback(page);
        } else
                set_page_writeback_keepwrite(page);

        unlock_page(page);
}

static inline int xfs_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 the bio for an ioend. We are passed an ioend with a bio attached to
 * it, and we submit that bio. The ioend may be used for multiple bio
 * submissions, so we only want to allocate an append transaction for the ioend
 * once. In the case of multiple bio submission, each bio will take an IO
 * reference to the ioend to ensure that the ioend completion is only done once
 * all bios have been submitted and the ioend is really done.
 *
 * 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 bio and ioend
 * rather than submit it to IO. This typically only happens on a filesystem
 * shutdown.
 */
STATIC int
xfs_submit_ioend(
        struct writeback_control *wbc,
        struct xfs_ioend        *ioend,
        int                     status)
{
        /* Reserve log space if we might write beyond the on-disk inode size. */
        if (!status &&
            ioend->io_type != XFS_IO_UNWRITTEN &&
            xfs_ioend_is_append(ioend) &&
            !ioend->io_append_trans)
                status = xfs_setfilesize_trans_alloc(ioend);

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

        /*
         * 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 (status) {
                ioend->io_bio->bi_error = status;
                bio_endio(ioend->io_bio);
                return status;
        }

        submit_bio(wbc->sync_mode == WB_SYNC_ALL ? WRITE_SYNC : WRITE,
                   ioend->io_bio);
        return 0;
}

static void
xfs_init_bio_from_bh(
        struct bio              *bio,
        struct buffer_head      *bh)
{
        bio->bi_iter.bi_sector = bh->b_blocknr * (bh->b_size >> 9);
        bio->bi_bdev = bh->b_bdev;
}

static struct xfs_ioend *
xfs_alloc_ioend(
        struct inode            *inode,
        unsigned int            type,
        xfs_off_t               offset,
        struct buffer_head      *bh)
{
        struct xfs_ioend        *ioend;
        struct bio              *bio;

        bio = bio_alloc_bioset(GFP_NOFS, BIO_MAX_PAGES, xfs_ioend_bioset);
        xfs_init_bio_from_bh(bio, bh);

        ioend = container_of(bio, struct xfs_ioend, io_inline_bio);
        INIT_LIST_HEAD(&ioend->io_list);
        ioend->io_type = type;
        ioend->io_inode = inode;
        ioend->io_size = 0;
        ioend->io_offset = offset;
        INIT_WORK(&ioend->io_work, xfs_end_io);
        ioend->io_append_trans = NULL;
        ioend->io_bio = bio;
        return ioend;
}

/*
 * Allocate a new bio, and chain the old bio to the new one.
 *
 * Note that we have to do perform the chaining in this unintuitive order
 * so that the bi_private linkage is set up in the right direction for the
 * traversal in xfs_destroy_ioend().
 */
static void
xfs_chain_bio(
        struct xfs_ioend        *ioend,
        struct writeback_control *wbc,
        struct buffer_head      *bh)
{
        struct bio *new;

        new = bio_alloc(GFP_NOFS, BIO_MAX_PAGES);
        xfs_init_bio_from_bh(new, bh);

        bio_chain(ioend->io_bio, new);
        bio_get(ioend->io_bio);         /* for xfs_destroy_ioend */
        submit_bio(wbc->sync_mode == WB_SYNC_ALL ? WRITE_SYNC : WRITE,
                   ioend->io_bio);
        ioend->io_bio = new;
}

/*
 * 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 the ioend we finished off so that the caller can submit it
 * once it has finished processing the dirty page.
 */
STATIC void
xfs_add_to_ioend(
        struct inode            *inode,
        struct buffer_head      *bh,
        xfs_off_t               offset,
        struct xfs_writepage_ctx *wpc,
        struct writeback_control *wbc,
        struct list_head        *iolist)
{
        if (!wpc->ioend || wpc->io_type != wpc->ioend->io_type ||
            bh->b_blocknr != wpc->last_block + 1 ||
            offset != wpc->ioend->io_offset + wpc->ioend->io_size) {
                if (wpc->ioend)
                        list_add(&wpc->ioend->io_list, iolist);
                wpc->ioend = xfs_alloc_ioend(inode, wpc->io_type, offset, bh);
        }

        /*
         * If the buffer doesn't fit into the bio we need to allocate a new
         * one.  This shouldn't happen more than once for a given buffer.
         */
        while (xfs_bio_add_buffer(wpc->ioend->io_bio, bh) != bh->b_size)
                xfs_chain_bio(wpc->ioend, wbc, bh);

        wpc->ioend->io_size += bh->b_size;
        wpc->last_block = bh->b_blocknr;
        xfs_start_buffer_writeback(bh);
}

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 contains at least one buffer of a given @type.
 * If @check_all_buffers is true, then we walk all the buffers in the page to
 * try to find one of the type passed in. If it is not set, then the caller only
 * needs to check the first buffer on the page for a match.
 */
STATIC bool
xfs_check_page_type(
        struct page             *page,
        unsigned int            type,
        bool                    check_all_buffers)
{
        struct buffer_head      *bh;
        struct buffer_head      *head;

        if (PageWriteback(page))
                return false;
        if (!page->mapping)
                return false;
        if (!page_has_buffers(page))
                return false;

        bh = head = page_buffers(page);
        do {
                if (buffer_unwritten(bh)) {
                        if (type == XFS_IO_UNWRITTEN)
                                return true;
                } else if (buffer_delay(bh)) {
                        if (type == XFS_IO_DELALLOC)
                                return true;
                } else if (buffer_dirty(bh) && buffer_mapped(bh)) {
                        if (type == XFS_IO_OVERWRITE)
                                return true;
                }

                /* If we are only checking the first buffer, we are done now. */
                if (!check_all_buffers)
                        break;
        } while ((bh = bh->b_this_page) != head);

        return false;
}

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

/*
 * 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, true))
                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, PAGE_SIZE);
        return;
}

/*
 * We implement an immediate ioend submission policy here to avoid needing to
 * chain multiple ioends and hence nest mempool allocations which can violate
 * forward progress guarantees we need to provide. The current ioend we are
 * adding buffers to is cached on the writepage context, and if the new buffer
 * does not append to the cached ioend it will create a new ioend and cache that
 * instead.
 *
 * If a new ioend is created and cached, the old ioend is returned and queued
 * locally for submission once the entire page is processed or an error has been
 * detected.  While ioends are submitted immediately after they are completed,
 * batching optimisations are provided by higher level block plugging.
 *
 * At the end of a writeback pass, there will be a cached ioend remaining on the
 * writepage context that the caller will need to submit.
 */
static int
xfs_writepage_map(
        struct xfs_writepage_ctx *wpc,
        struct writeback_control *wbc,
        struct inode            *inode,
        struct page             *page,
        loff_t                  offset,
        __uint64_t              end_offset)
{
        LIST_HEAD(submit_list);
        struct xfs_ioend        *ioend, *next;
        struct buffer_head      *bh, *head;
        ssize_t                 len = 1 << inode->i_blkbits;
        int                     error = 0;
        int                     count = 0;
        int                     uptodate = 1;

        bh = head = page_buffers(page);
        offset = page_offset(page);
        do {
                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)) {
                        wpc->imap_valid = false;
                        continue;
                }

                if (buffer_unwritten(bh)) {
                        if (wpc->io_type != XFS_IO_UNWRITTEN) {
                                wpc->io_type = XFS_IO_UNWRITTEN;
                                wpc->imap_valid = false;
                        }
                } else if (buffer_delay(bh)) {
                        if (wpc->io_type != XFS_IO_DELALLOC) {
                                wpc->io_type = XFS_IO_DELALLOC;
                                wpc->imap_valid = false;
                        }
                } else if (buffer_uptodate(bh)) {
                        if (wpc->io_type != XFS_IO_OVERWRITE) {
                                wpc->io_type = XFS_IO_OVERWRITE;
                                wpc->imap_valid = false;
                        }
                } 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.
                         */
                        wpc->imap_valid = false;
                        continue;
                }

                if (wpc->imap_valid)
                        wpc->imap_valid = xfs_imap_valid(inode, &wpc->imap,
                                                         offset);
                if (!wpc->imap_valid) {
                        error = xfs_map_blocks(inode, offset, &wpc->imap,
                                             wpc->io_type);
                        if (error)
                                goto out;
                        wpc->imap_valid = xfs_imap_valid(inode, &wpc->imap,
                                                         offset);
                }
                if (wpc->imap_valid) {
                        lock_buffer(bh);
                        if (wpc->io_type != XFS_IO_OVERWRITE)
                                xfs_map_at_offset(inode, bh, &wpc->imap, offset);
                        xfs_add_to_ioend(inode, bh, offset, wpc, wbc, &submit_list);
                        count++;
                }

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

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

        ASSERT(wpc->ioend || list_empty(&submit_list));

out:
        /*
         * On error, we have to fail the ioend here because we have locked
         * buffers in the ioend. If we don't do this, we'll deadlock
         * invalidating the page as that tries to lock the buffers on the page.
         * Also, because we may have set pages under writeback, we have to make
         * sure we run IO completion to mark the error state of the IO
         * appropriately, so we can't cancel the ioend directly here. That means
         * we have to mark this page as under writeback if we included any
         * buffers from it in the ioend chain so that completion treats it
         * correctly.
         *
         * If we didn't include the page in the ioend, the on error we can
         * simply discard and unlock it as there are no other users of the page
         * or it's buffers right now. The caller will still need to trigger
         * submission of outstanding ioends on the writepage context so they are
         * treated correctly on error.
         */
        if (count) {
                xfs_start_page_writeback(page, !error);

                /*
                 * Preserve the original error if there was one, otherwise catch
                 * submission errors here and propagate into subsequent ioend
                 * submissions.
                 */
                list_for_each_entry_safe(ioend, next, &submit_list, io_list) {
                        int error2;

                        list_del_init(&ioend->io_list);
                        error2 = xfs_submit_ioend(wbc, ioend, error);
                        if (error2 && !error)
                                error = error2;
                }
        } else if (error) {
                xfs_aops_discard_page(page);
                ClearPageUptodate(page);
                unlock_page(page);
        } else {
                /*
                 * We can end up here with no error and nothing to write if we
                 * race with a partial page truncate on a sub-page block sized
                 * filesystem. In that case we need to mark the page clean.
                 */
                xfs_start_page_writeback(page, 1);
                end_page_writeback(page);
        }

        mapping_set_error(page->mapping, error);
        return error;
}

/*
 * 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_do_writepage(
        struct page             *page,
        struct writeback_control *wbc,
        void                    *data)
{
        struct xfs_writepage_ctx *wpc = data;
        struct inode            *inode = page->mapping->host;
        loff_t                  offset;
        __uint64_t              end_offset;
        pgoff_t                 end_index;

        trace_xfs_writepage(inode, page, 0, 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_ONCE(current->flags & PF_FSTRANS))
                goto redirty;

        /*
         * Is this page beyond the end of the file?
         *
         * The page index is less than the end_index, adjust the end_offset
         * to the highest offset that this page should represent.
         * -----------------------------------------------------
         * |                    file mapping           | <EOF> |
         * -----------------------------------------------------
         * | Page ... | Page N-2 | Page N-1 |  Page N  |       |
         * ^--------------------------------^----------|--------
         * |     desired writeback range    |      see else    |
         * ---------------------------------^------------------|
         */
        offset = i_size_read(inode);
        end_index = offset >> PAGE_SHIFT;
        if (page->index < end_index)
                end_offset = (xfs_off_t)(page->index + 1) << PAGE_SHIFT;
        else {
                /*
                 * Check whether the page to write out is beyond or straddles
                 * i_size or not.
                 * -------------------------------------------------------
                 * |            file mapping                    | <EOF>  |
                 * -------------------------------------------------------
                 * | Page ... | Page N-2 | Page N-1 |  Page N   | Beyond |
                 * ^--------------------------------^-----------|---------
                 * |                                |      Straddles     |
                 * ---------------------------------^-----------|--------|
                 */
                unsigned offset_into_page = offset & (PAGE_SIZE - 1);

                /*
                 * Skip the page if it is fully outside i_size, e.g. due to a
                 * truncate operation that is in progress. We must redirty the
                 * page so that reclaim stops reclaiming it. Otherwise
                 * xfs_vm_releasepage() is called on it and gets confused.
                 *
                 * Note that the end_index is unsigned long, it would overflow
                 * if the given offset is greater than 16TB on 32-bit system
                 * and if we do check the page is fully outside i_size or not
                 * via "if (page->index >= end_index + 1)" as "end_index + 1"
                 * will be evaluated to 0.  Hence this page will be redirtied
                 * and be written out repeatedly which would result in an
                 * infinite loop, the user program that perform this operation
                 * will hang.  Instead, we can verify this situation by checking
                 * if the page to write is totally beyond the i_size or if it's
                 * offset is just equal to the EOF.
                 */
                if (page->index > end_index ||
                    (page->index == end_index && offset_into_page == 0))
                        goto redirty;

                /*
                 * 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_SIZE);

                /* Adjust the end_offset to the end of file */
                end_offset = offset;
        }

        return xfs_writepage_map(wpc, wbc, inode, page, offset, end_offset);

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

STATIC int
xfs_vm_writepage(
        struct page             *page,
        struct writeback_control *wbc)
{
        struct xfs_writepage_ctx wpc = {
                .io_type = XFS_IO_INVALID,
        };
        int                     ret;

        ret = xfs_do_writepage(page, wbc, &wpc);
        if (wpc.ioend)
                ret = xfs_submit_ioend(wbc, wpc.ioend, ret);
        return ret;
}

STATIC int
xfs_vm_writepages(
        struct address_space    *mapping,
        struct writeback_control *wbc)
{
        struct xfs_writepage_ctx wpc = {
                .io_type = XFS_IO_INVALID,
        };
        int                     ret;

        xfs_iflags_clear(XFS_I(mapping->host), XFS_ITRUNCATED);
        if (dax_mapping(mapping))
                return dax_writeback_mapping_range(mapping,
                                xfs_find_bdev_for_inode(mapping->host), wbc);

        ret = write_cache_pages(mapping, wbc, xfs_do_writepage, &wpc);
        if (wpc.ioend)
                ret = xfs_submit_ioend(wbc, wpc.ioend, ret);
        return ret;
}

/*
 * 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, 0);

        /*
         * mm accommodates an old ext3 case where clean pages might not have had
         * the dirty bit cleared. Thus, it can send actual dirty pages to
         * ->releasepage() via shrink_active_list(). Conversely,
         * block_invalidatepage() can send pages that are still marked dirty
         * but otherwise have invalidated buffers.
         *
         * We've historically freed buffers on the latter. Instead, quietly
         * filter out all dirty pages to avoid spurious buffer state warnings.
         * This can likely be removed once shrink_active_list() is fixed.
         */
        if (PageDirty(page))
                return 0;

        xfs_count_page_state(page, &delalloc, &unwritten);

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

        return try_to_free_buffers(page);
}

/*
 * When we map a DIO buffer, we may need to pass flags to
 * xfs_end_io_direct_write to tell it what kind of write IO we are doing.
 *
 * Note that for DIO, an IO to the highest supported file block offset (i.e.
 * 2^63 - 1FSB bytes) will result in the offset + count overflowing a signed 64
 * bit variable. Hence if we see this overflow, we have to assume that the IO is
 * extending the file size. We won't know for sure until IO completion is run
 * and the actual max write offset is communicated to the IO completion
 * routine.
 */
static void
xfs_map_direct(
        struct inode            *inode,
        struct buffer_head      *bh_result,
        struct xfs_bmbt_irec    *imap,
        xfs_off_t               offset)
{
        uintptr_t               *flags = (uintptr_t *)&bh_result->b_private;
        xfs_off_t               size = bh_result->b_size;

        trace_xfs_get_blocks_map_direct(XFS_I(inode), offset, size,
                ISUNWRITTEN(imap) ? XFS_IO_UNWRITTEN : XFS_IO_OVERWRITE, imap);

        if (ISUNWRITTEN(imap)) {
                *flags |= XFS_DIO_FLAG_UNWRITTEN;
                set_buffer_defer_completion(bh_result);
        } else if (offset + size > i_size_read(inode) || offset + size < 0) {
                *flags |= XFS_DIO_FLAG_APPEND;
                set_buffer_defer_completion(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 the mapping spans EOF, then we have to break the mapping up as the mapping
 * for blocks beyond EOF must be marked new so that sub block regions can be
 * correctly zeroed. We can't do this for mappings within EOF unless the mapping
 * was just allocated or is unwritten, otherwise the callers would overwrite
 * existing data with zeros. Hence we have to split the mapping into a range up
 * to and including EOF, and a second mapping for beyond EOF.
 */
static void
xfs_map_trim_size(
        struct inode            *inode,
        sector_t                iblock,
        struct buffer_head      *bh_result,
        struct xfs_bmbt_irec    *imap,
        xfs_off_t               offset,
        ssize_t                 size)
{
        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 (offset < i_size_read(inode) &&
            offset + mapping_size >= i_size_read(inode)) {
                /* limit mapping to block that spans EOF */
                mapping_size = roundup_64(i_size_read(inode) - offset,
                                          1 << inode->i_blkbits);
        }
        if (mapping_size > LONG_MAX)
                mapping_size = LONG_MAX;

        bh_result->b_size = mapping_size;
}

STATIC int
__xfs_get_blocks(
        struct inode            *inode,
        sector_t                iblock,
        struct buffer_head      *bh_result,
        int                     create,
        bool                    direct,
        bool                    dax_fault)
{
        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 -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_data_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;

        /* for DAX, we convert unwritten extents directly */
        if (create &&
            (!nimaps ||
             (imap.br_startblock == HOLESTARTBLOCK ||
              imap.br_startblock == DELAYSTARTBLOCK) ||
             (IS_DAX(inode) && ISUNWRITTEN(&imap)))) {
                if (direct || xfs_get_extsz_hint(ip)) {
                        /*
                         * xfs_iomap_write_direct() expects the shared lock. It
                         * is unlocked on return.
                         */
                        if (lockmode == XFS_ILOCK_EXCL)
                                xfs_ilock_demote(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,
                                ISUNWRITTEN(&imap) ? XFS_IO_UNWRITTEN
                                                   : XFS_IO_DELALLOC, &imap);
        } else if (nimaps) {
                trace_xfs_get_blocks_found(ip, offset, size,
                                ISUNWRITTEN(&imap) ? XFS_IO_UNWRITTEN
                                                   : XFS_IO_OVERWRITE, &imap);
                xfs_iunlock(ip, lockmode);
        } else {
                trace_xfs_get_blocks_notfound(ip, offset, size);
                goto out_unlock;
        }

        if (IS_DAX(inode) && create) {
                ASSERT(!ISUNWRITTEN(&imap));
                /* zeroing is not needed at a higher layer */
                new = 0;
        }

        /* trim mapping down to size requested */
        if (direct || size > (1 << inode->i_blkbits))
                xfs_map_trim_size(inode, iblock, bh_result,
                                  &imap, offset, size);

        /*
         * For unwritten extents do not report a disk address in the buffered
         * read case (treat as if we're reading into a hole).
         */
        if (imap.br_startblock != HOLESTARTBLOCK &&
            imap.br_startblock != DELAYSTARTBLOCK &&
            (create || !ISUNWRITTEN(&imap))) {
                xfs_map_buffer(inode, bh_result, &imap, offset);
                if (ISUNWRITTEN(&imap))
                        set_buffer_unwritten(bh_result);
                /* direct IO needs special help */
                if (create && direct) {
                        if (dax_fault)
                                ASSERT(!ISUNWRITTEN(&imap));
                        else
                                xfs_map_direct(inode, bh_result, &imap, offset);
                }
        }

        /*
         * 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);
                }
        }

        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, false, false);
}

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, true, false);
}

int
xfs_get_blocks_dax_fault(
        struct inode            *inode,
        sector_t                iblock,
        struct buffer_head      *bh_result,
        int                     create)
{
        return __xfs_get_blocks(inode, iblock, bh_result, create, true, true);
}

/*
 * Complete a direct I/O write request.
 *
 * xfs_map_direct passes us some flags in the private data to tell us what to
 * do.  If no flags are set, then the write IO is an overwrite wholly within
 * the existing allocated file size and so there is nothing for us to do.
 *
 * Note that in this case the completion can be called in interrupt context,
 * whereas if we have flags set we will always be called in task context
 * (i.e. from a workqueue).
 */
int
xfs_end_io_direct_write(
        struct kiocb            *iocb,
        loff_t                  offset,
        ssize_t                 size,
        void                    *private)
{
        struct inode            *inode = file_inode(iocb->ki_filp);
        struct xfs_inode        *ip = XFS_I(inode);
        struct xfs_mount        *mp = ip->i_mount;
        uintptr_t               flags = (uintptr_t)private;
        int                     error = 0;

        trace_xfs_end_io_direct_write(ip, offset, size);

        if (XFS_FORCED_SHUTDOWN(mp))
                return -EIO;

        if (size <= 0)
                return size;

        /*
         * The flags tell us whether we are doing unwritten extent conversions
         * or an append transaction that updates the on-disk file size. These
         * cases are the only cases where we should *potentially* be needing
         * to update the VFS inode size.
         */
        if (flags == 0) {
                ASSERT(offset + size <= i_size_read(inode));
                return 0;
        }

        /*
         * We need to update the in-core inode size here so that we don't end up
         * with the on-disk inode size being outside the in-core inode size. We
         * have no other method of updating EOF for AIO, so always do it here
         * if necessary.
         *
         * We need to lock the test/set EOF update as we can be racing with
         * other IO completions here to update the EOF. Failing to serialise
         * here can result in EOF moving backwards and Bad Things Happen when
         * that occurs.
         */
        spin_lock(&ip->i_flags_lock);
        if (offset + size > i_size_read(inode))
                i_size_write(inode, offset + size);
        spin_unlock(&ip->i_flags_lock);

        if (flags & XFS_DIO_FLAG_UNWRITTEN) {
                trace_xfs_end_io_direct_write_unwritten(ip, offset, size);

                error = xfs_iomap_write_unwritten(ip, offset, size);
        } else if (flags & XFS_DIO_FLAG_APPEND) {
                struct xfs_trans *tp;

                trace_xfs_end_io_direct_write_append(ip, offset, size);

                error = xfs_trans_alloc(mp, &M_RES(mp)->tr_fsyncts, 0, 0, 0,
                                &tp);
                if (!error)
                        error = xfs_setfilesize(ip, tp, offset, size);
        }

        return error;
}

STATIC ssize_t
xfs_vm_direct_IO(
        struct kiocb            *iocb,
        struct iov_iter         *iter)
{
        /*
         * We just need the method present so that open/fcntl allow direct I/O.
         */
        return -EINVAL;
}

/*
 * 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;
        loff_t                  block_start;
        loff_t                  block_end;
        loff_t                  from = pos & (PAGE_SIZE - 1);
        loff_t                  to = from + len;
        struct buffer_head      *bh, *head;
        struct xfs_mount        *mp = XFS_I(inode)->i_mount;

        /*
         * The request pos offset might be 32 or 64 bit, this is all fine
         * on 64-bit platform.  However, for 64-bit pos request on 32-bit
         * platform, the high 32-bit will be masked off if we evaluate the
         * block_offset via (pos & PAGE_MASK) because the PAGE_MASK is
         * 0xfffff000 as an unsigned long, hence the result is incorrect
         * which could cause the following ASSERT failed in most cases.
         * In order to avoid this, we can evaluate the block_offset of the
         * start of the page by using shifts rather than masks the mismatch
         * problem.
         */
        block_offset = (pos >> PAGE_SHIFT) << PAGE_SHIFT;

        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;

                /*
                 * Process delalloc and unwritten buffers beyond EOF. We can
                 * encounter unwritten buffers in the event that a file has
                 * post-EOF unwritten extents and an extending write happens to
                 * fail (e.g., an unaligned write that also involves a delalloc
                 * to the same page).
                 */
                if (!buffer_delay(bh) && !buffer_unwritten(bh))
                        continue;

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

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

                /*
                 * This buffer does not contain data anymore. make sure anyone
                 * who finds it knows that for certain.
                 */
                clear_buffer_delay(bh);
                clear_buffer_uptodate(bh);
                clear_buffer_mapped(bh);
                clear_buffer_new(bh);
                clear_buffer_dirty(bh);
                clear_buffer_unwritten(bh);
        }

}

/*
 * 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_SHIFT;
        struct page             *page;
        int                     status;
        struct xfs_mount        *mp = XFS_I(mapping->host)->i_mount;

        ASSERT(len <= PAGE_SIZE);

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

        status = __block_write_begin(page, pos, len, xfs_get_blocks);
        if (xfs_mp_fail_writes(mp))
                status = -EIO;
        if (unlikely(status)) {
                struct inode    *inode = mapping->host;
                size_t          isize = i_size_read(inode);

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

                /*
                 * If the write is beyond EOF, we only want to kill blocks
                 * allocated in this write, not blocks that were previously
                 * written successfully.
                 */
                if (xfs_mp_fail_writes(mp))
                        isize = 0;
                if (pos + len > isize) {
                        ssize_t start = max_t(ssize_t, pos, isize);

                        truncate_pagecache_range(inode, start, pos + len);
                }

                put_page(page);
                page = NULL;
        }

        *pagep = page;
        return status;
}

/*
 * On failure, we only need to kill delalloc blocks beyond EOF in the range of
 * this specific write because they will never be written. Previous writes
 * beyond EOF where block allocation succeeded do not need to be trashed, so
 * only new blocks from this write should be trashed. 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_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) {
                        /* only kill blocks in this write beyond EOF */
                        if (pos > isize)
                                isize = pos;
                        xfs_vm_kill_delalloc_range(inode, isize, to);
                        truncate_pagecache_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);
        filemap_write_and_wait(mapping);
        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)
{
        trace_xfs_vm_readpage(page->mapping->host, 1);
        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)
{
        trace_xfs_vm_readpages(mapping->host, nr_pages);
        return mpage_readpages(mapping, pages, nr_pages, xfs_get_blocks);
}

/*
 * This is basically a copy of __set_page_dirty_buffers() with one
 * small tweak: buffers beyond EOF do not get marked dirty. If we mark them
 * dirty, we'll never be able to clean them because we don't write buffers
 * beyond EOF, and that means we can't invalidate pages that span EOF
 * that have been marked dirty. Further, the dirty state can leak into
 * the file interior if the file is extended, resulting in all sorts of
 * bad things happening as the state does not match the underlying data.
 *
 * XXX: this really indicates that bufferheads in XFS need to die. Warts like
 * this only exist because of bufferheads and how the generic code manages them.
 */
STATIC int
xfs_vm_set_page_dirty(
        struct page             *page)
{
        struct address_space    *mapping = page->mapping;
        struct inode            *inode = mapping->host;
        loff_t                  end_offset;
        loff_t                  offset;
        int                     newly_dirty;

        if (unlikely(!mapping))
                return !TestSetPageDirty(page);

        end_offset = i_size_read(inode);
        offset = page_offset(page);

        spin_lock(&mapping->private_lock);
        if (page_has_buffers(page)) {
                struct buffer_head *head = page_buffers(page);
                struct buffer_head *bh = head;

                do {
                        if (offset < end_offset)
                                set_buffer_dirty(bh);
                        bh = bh->b_this_page;
                        offset += 1 << inode->i_blkbits;
                } while (bh != head);
        }
        /*
         * Lock out page->mem_cgroup migration to keep PageDirty
         * synchronized with per-memcg dirty page counters.
         */
        lock_page_memcg(page);
        newly_dirty = !TestSetPageDirty(page);
        spin_unlock(&mapping->private_lock);

        if (newly_dirty) {
                /* sigh - __set_page_dirty() is static, so copy it here, too */
                unsigned long flags;

                spin_lock_irqsave(&mapping->tree_lock, flags);
                if (page->mapping) {    /* Race with truncate? */
                        WARN_ON_ONCE(!PageUptodate(page));
                        account_page_dirtied(page, mapping);
                        radix_tree_tag_set(&mapping->page_tree,
                                        page_index(page), PAGECACHE_TAG_DIRTY);
                }
                spin_unlock_irqrestore(&mapping->tree_lock, flags);
        }
        unlock_page_memcg(page);
        if (newly_dirty)
                __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
        return newly_dirty;
}

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,
        .set_page_dirty         = xfs_vm_set_page_dirty,
        .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,
};