Linux-libre 4.19.20-gnu

[librecmc/linux-libre.git] / fs / xfs / xfs_aops.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (c) 2000-2005 Silicon Graphics, Inc.
 * Copyright (c) 2016-2018 Christoph Hellwig.
 * All Rights Reserved.
 */
#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 "xfs_reflink.h"
#include <linux/writeback.h>

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

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;
}

struct dax_device *
xfs_find_daxdev_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_daxdev;
        else
                return mp->m_ddev_targp->bt_daxdev;
}

static void
xfs_finish_page_writeback(
        struct inode            *inode,
        struct bio_vec          *bvec,
        int                     error)
{
        struct iomap_page       *iop = to_iomap_page(bvec->bv_page);

        if (error) {
                SetPageError(bvec->bv_page);
                mapping_set_error(inode->i_mapping, -EIO);
        }

        ASSERT(iop || i_blocksize(inode) == PAGE_SIZE);
        ASSERT(!iop || atomic_read(&iop->write_count) > 0);

        if (!iop || atomic_dec_and_test(&iop->write_count))
                end_page_writeback(bvec->bv_page);
}

/*
 * 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              *bio = &ioend->io_inline_bio;
        struct bio              *last = ioend->io_bio, *next;
        u64                     start = bio->bi_iter.bi_sector;
        bool                    quiet = bio_flagged(bio, BIO_QUIET);

        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);
        }

        if (unlikely(error && !quiet)) {
                xfs_err_ratelimited(XFS_I(inode)->i_mount,
                        "writeback error on sector %llu", start);
        }
}

/*
 * 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,
                                XFS_TRANS_NOFS, &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_MEMALLOC_NOFS);
        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);
}

int
xfs_setfilesize(
        struct xfs_inode        *ip,
        xfs_off_t               offset,
        size_t                  size)
{
        struct xfs_mount        *mp = ip->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;

        return __xfs_setfilesize(ip, tp, offset, size);
}

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_MEMALLOC_NOFS);
        __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);
        xfs_off_t               offset = ioend->io_offset;
        size_t                  size = ioend->io_size;
        int                     error;

        /*
         * Just clean up the in-memory strutures if the fs has been shut down.
         */
        if (XFS_FORCED_SHUTDOWN(ip->i_mount)) {
                error = -EIO;
                goto done;
        }

        /*
         * Clean up any COW blocks on an I/O error.
         */
        error = blk_status_to_errno(ioend->io_bio->bi_status);
        if (unlikely(error)) {
                switch (ioend->io_type) {
                case XFS_IO_COW:
                        xfs_reflink_cancel_cow_range(ip, offset, size, true);
                        break;
                }

                goto done;
        }

        /*
         * Success:  commit the COW or unwritten blocks if needed.
         */
        switch (ioend->io_type) {
        case XFS_IO_COW:
                error = xfs_reflink_end_cow(ip, offset, size);
                break;
        case XFS_IO_UNWRITTEN:
                /* writeback should never update isize */
                error = xfs_iomap_write_unwritten(ip, offset, size, false);
                break;
        default:
                ASSERT(!xfs_ioend_is_append(ioend) || ioend->io_append_trans);
                break;
        }

done:
        if (ioend->io_append_trans)
                error = xfs_setfilesize_ioend(ioend, error);
        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 || ioend->io_type == XFS_IO_COW)
                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, blk_status_to_errno(bio->bi_status));
}

STATIC int
xfs_map_blocks(
        struct xfs_writepage_ctx *wpc,
        struct inode            *inode,
        loff_t                  offset)
{
        struct xfs_inode        *ip = XFS_I(inode);
        struct xfs_mount        *mp = ip->i_mount;
        ssize_t                 count = i_blocksize(inode);
        xfs_fileoff_t           offset_fsb = XFS_B_TO_FSBT(mp, offset), end_fsb;
        xfs_fileoff_t           cow_fsb = NULLFILEOFF;
        struct xfs_bmbt_irec    imap;
        int                     whichfork = XFS_DATA_FORK;
        struct xfs_iext_cursor  icur;
        bool                    imap_valid;
        int                     error = 0;

        /*
         * We have to make sure the cached mapping is within EOF to protect
         * against eofblocks trimming on file release leaving us with a stale
         * mapping. Otherwise, a page for a subsequent file extending buffered
         * write could get picked up by this writeback cycle and written to the
         * wrong blocks.
         *
         * Note that what we really want here is a generic mapping invalidation
         * mechanism to protect us from arbitrary extent modifying contexts, not
         * just eofblocks.
         */
        xfs_trim_extent_eof(&wpc->imap, ip);

        /*
         * COW fork blocks can overlap data fork blocks even if the blocks
         * aren't shared.  COW I/O always takes precedent, so we must always
         * check for overlap on reflink inodes unless the mapping is already a
         * COW one, or the COW fork hasn't changed from the last time we looked
         * at it.
         *
         * It's safe to check the COW fork if_seq here without the ILOCK because
         * we've indirectly protected against concurrent updates: writeback has
         * the page locked, which prevents concurrent invalidations by reflink
         * and directio and prevents concurrent buffered writes to the same
         * page.  Changes to if_seq always happen under i_lock, which protects
         * against concurrent updates and provides a memory barrier on the way
         * out that ensures that we always see the current value.
         */
        imap_valid = offset_fsb >= wpc->imap.br_startoff &&
                     offset_fsb < wpc->imap.br_startoff + wpc->imap.br_blockcount;
        if (imap_valid &&
            (!xfs_inode_has_cow_data(ip) ||
             wpc->io_type == XFS_IO_COW ||
             wpc->cow_seq == READ_ONCE(ip->i_cowfp->if_seq)))
                return 0;

        if (XFS_FORCED_SHUTDOWN(mp))
                return -EIO;

        /*
         * If we don't have a valid map, now it's time to get a new one for this
         * offset.  This will convert delayed allocations (including COW ones)
         * into real extents.  If we return without a valid map, it means we
         * landed in a hole and we skip the block.
         */
        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 > mp->m_super->s_maxbytes - count)
                count = mp->m_super->s_maxbytes - offset;
        end_fsb = XFS_B_TO_FSB(mp, (xfs_ufsize_t)offset + count);

        /*
         * Check if this is offset is covered by a COW extents, and if yes use
         * it directly instead of looking up anything in the data fork.
         */
        if (xfs_inode_has_cow_data(ip) &&
            xfs_iext_lookup_extent(ip, ip->i_cowfp, offset_fsb, &icur, &imap))
                cow_fsb = imap.br_startoff;
        if (cow_fsb != NULLFILEOFF && cow_fsb <= offset_fsb) {
                wpc->cow_seq = READ_ONCE(ip->i_cowfp->if_seq);
                xfs_iunlock(ip, XFS_ILOCK_SHARED);
                /*
                 * Truncate can race with writeback since writeback doesn't
                 * take the iolock and truncate decreases the file size before
                 * it starts truncating the pages between new_size and old_size.
                 * Therefore, we can end up in the situation where writeback
                 * gets a CoW fork mapping but the truncate makes the mapping
                 * invalid and we end up in here trying to get a new mapping.
                 * bail out here so that we simply never get a valid mapping
                 * and so we drop the write altogether.  The page truncation
                 * will kill the contents anyway.
                 */
                if (offset > i_size_read(inode)) {
                        wpc->io_type = XFS_IO_HOLE;
                        return 0;
                }
                whichfork = XFS_COW_FORK;
                wpc->io_type = XFS_IO_COW;
                goto allocate_blocks;
        }

        /*
         * Map valid and no COW extent in the way?  We're done.
         */
        if (imap_valid) {
                xfs_iunlock(ip, XFS_ILOCK_SHARED);
                return 0;
        }

        /*
         * If we don't have a valid map, now it's time to get a new one for this
         * offset.  This will convert delayed allocations (including COW ones)
         * into real extents.
         */
        if (!xfs_iext_lookup_extent(ip, &ip->i_df, offset_fsb, &icur, &imap))
                imap.br_startoff = end_fsb;     /* fake a hole past EOF */
        xfs_iunlock(ip, XFS_ILOCK_SHARED);

        if (imap.br_startoff > offset_fsb) {
                /* landed in a hole or beyond EOF */
                imap.br_blockcount = imap.br_startoff - offset_fsb;
                imap.br_startoff = offset_fsb;
                imap.br_startblock = HOLESTARTBLOCK;
                wpc->io_type = XFS_IO_HOLE;
        } else {
                /*
                 * Truncate to the next COW extent if there is one.  This is the
                 * only opportunity to do this because we can skip COW fork
                 * lookups for the subsequent blocks in the mapping; however,
                 * the requirement to treat the COW range separately remains.
                 */
                if (cow_fsb != NULLFILEOFF &&
                    cow_fsb < imap.br_startoff + imap.br_blockcount)
                        imap.br_blockcount = cow_fsb - imap.br_startoff;

                if (isnullstartblock(imap.br_startblock)) {
                        /* got a delalloc extent */
                        wpc->io_type = XFS_IO_DELALLOC;
                        goto allocate_blocks;
                }

                if (imap.br_state == XFS_EXT_UNWRITTEN)
                        wpc->io_type = XFS_IO_UNWRITTEN;
                else
                        wpc->io_type = XFS_IO_OVERWRITE;
        }

        wpc->imap = imap;
        trace_xfs_map_blocks_found(ip, offset, count, wpc->io_type, &imap);
        return 0;
allocate_blocks:
        error = xfs_iomap_write_allocate(ip, whichfork, offset, &imap,
                        &wpc->cow_seq);
        if (error)
                return error;
        ASSERT(whichfork == XFS_COW_FORK || cow_fsb == NULLFILEOFF ||
               imap.br_startoff + imap.br_blockcount <= cow_fsb);
        wpc->imap = imap;
        trace_xfs_map_blocks_alloc(ip, offset, count, wpc->io_type, &imap);
        return 0;
}

/*
 * 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)
{
        /* Convert CoW extents to regular */
        if (!status && ioend->io_type == XFS_IO_COW) {
                /*
                 * Yuk. This can do memory allocation, but is not a
                 * transactional operation so everything is done in GFP_KERNEL
                 * context. That can deadlock, because we hold pages in
                 * writeback state and GFP_KERNEL allocations can block on them.
                 * Hence we must operate in nofs conditions here.
                 */
                unsigned nofs_flag;

                nofs_flag = memalloc_nofs_save();
                status = xfs_reflink_convert_cow(XFS_I(ioend->io_inode),
                                ioend->io_offset, ioend->io_size);
                memalloc_nofs_restore(nofs_flag);
        }

        /* 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;
        ioend->io_bio->bi_opf = REQ_OP_WRITE | wbc_to_write_flags(wbc);

        /*
         * 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_status = errno_to_blk_status(status);
                bio_endio(ioend->io_bio);
                return status;
        }

        ioend->io_bio->bi_write_hint = ioend->io_inode->i_write_hint;
        submit_bio(ioend->io_bio);
        return 0;
}

static struct xfs_ioend *
xfs_alloc_ioend(
        struct inode            *inode,
        unsigned int            type,
        xfs_off_t               offset,
        struct block_device     *bdev,
        sector_t                sector)
{
        struct xfs_ioend        *ioend;
        struct bio              *bio;

        bio = bio_alloc_bioset(GFP_NOFS, BIO_MAX_PAGES, &xfs_ioend_bioset);
        bio_set_dev(bio, bdev);
        bio->bi_iter.bi_sector = sector;

        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 block_device     *bdev,
        sector_t                sector)
{
        struct bio *new;

        new = bio_alloc(GFP_NOFS, BIO_MAX_PAGES);
        bio_set_dev(new, bdev);
        new->bi_iter.bi_sector = sector;
        bio_chain(ioend->io_bio, new);
        bio_get(ioend->io_bio);         /* for xfs_destroy_ioend */
        ioend->io_bio->bi_opf = REQ_OP_WRITE | wbc_to_write_flags(wbc);
        ioend->io_bio->bi_write_hint = ioend->io_inode->i_write_hint;
        submit_bio(ioend->io_bio);
        ioend->io_bio = new;
}

/*
 * Test to see if we have an existing ioend structure that we could append to
 * first, otherwise finish off the current ioend and start another.
 */
STATIC void
xfs_add_to_ioend(
        struct inode            *inode,
        xfs_off_t               offset,
        struct page             *page,
        struct iomap_page       *iop,
        struct xfs_writepage_ctx *wpc,
        struct writeback_control *wbc,
        struct list_head        *iolist)
{
        struct xfs_inode        *ip = XFS_I(inode);
        struct xfs_mount        *mp = ip->i_mount;
        struct block_device     *bdev = xfs_find_bdev_for_inode(inode);
        unsigned                len = i_blocksize(inode);
        unsigned                poff = offset & (PAGE_SIZE - 1);
        sector_t                sector;

        sector = xfs_fsb_to_db(ip, wpc->imap.br_startblock) +
                ((offset - XFS_FSB_TO_B(mp, wpc->imap.br_startoff)) >> 9);

        if (!wpc->ioend || wpc->io_type != wpc->ioend->io_type ||
            sector != bio_end_sector(wpc->ioend->io_bio) ||
            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,
                                bdev, sector);
        }

        if (!__bio_try_merge_page(wpc->ioend->io_bio, page, len, poff)) {
                if (iop)
                        atomic_inc(&iop->write_count);
                if (bio_full(wpc->ioend->io_bio))
                        xfs_chain_bio(wpc->ioend, wbc, bdev, sector);
                __bio_add_page(wpc->ioend->io_bio, page, len, poff);
        }

        wpc->ioend->io_size += len;
}

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

/*
 * If the page has delalloc blocks 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 up a later direct I/O read operation on the same region.
 *
 * We prevent this by truncating away the delalloc regions on the page.  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).
 */
STATIC void
xfs_aops_discard_page(
        struct page             *page)
{
        struct inode            *inode = page->mapping->host;
        struct xfs_inode        *ip = XFS_I(inode);
        struct xfs_mount        *mp = ip->i_mount;
        loff_t                  offset = page_offset(page);
        xfs_fileoff_t           start_fsb = XFS_B_TO_FSBT(mp, offset);
        int                     error;

        if (XFS_FORCED_SHUTDOWN(mp))
                goto out_invalidate;

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

        error = xfs_bmap_punch_delalloc_range(ip, start_fsb,
                        PAGE_SIZE / i_blocksize(inode));
        if (error && !XFS_FORCED_SHUTDOWN(mp))
                xfs_alert(mp, "page discard unable to remove delalloc mapping.");
out_invalidate:
        xfs_vm_invalidatepage(page, 0, PAGE_SIZE);
}

/*
 * 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 blocks to is cached on the writepage context, and if the new block
 * 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,
        uint64_t                end_offset)
{
        LIST_HEAD(submit_list);
        struct iomap_page       *iop = to_iomap_page(page);
        unsigned                len = i_blocksize(inode);
        struct xfs_ioend        *ioend, *next;
        uint64_t                file_offset;    /* file offset of page */
        int                     error = 0, count = 0, i;

        ASSERT(iop || i_blocksize(inode) == PAGE_SIZE);
        ASSERT(!iop || atomic_read(&iop->write_count) == 0);

        /*
         * Walk through the page to find areas to write back. If we run off the
         * end of the current map or find the current map invalid, grab a new
         * one.
         */
        for (i = 0, file_offset = page_offset(page);
             i < (PAGE_SIZE >> inode->i_blkbits) && file_offset < end_offset;
             i++, file_offset += len) {
                if (iop && !test_bit(i, iop->uptodate))
                        continue;

                error = xfs_map_blocks(wpc, inode, file_offset);
                if (error)
                        break;
                if (wpc->io_type == XFS_IO_HOLE)
                        continue;
                xfs_add_to_ioend(inode, file_offset, page, iop, wpc, wbc,
                                 &submit_list);
                count++;
        }

        ASSERT(wpc->ioend || list_empty(&submit_list));
        ASSERT(PageLocked(page));
        ASSERT(!PageWriteback(page));

        /*
         * On error, we have to fail the ioend here 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 blocks 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
         * now.  The caller will still need to trigger submission of outstanding
         * ioends on the writepage context so they are treated correctly on
         * error.
         */
        if (unlikely(error)) {
                if (!count) {
                        xfs_aops_discard_page(page);
                        ClearPageUptodate(page);
                        unlock_page(page);
                        goto done;
                }

                /*
                 * 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.
                 */
                set_page_writeback_keepwrite(page);
        } else {
                clear_page_dirty_for_io(page);
                set_page_writeback(page);
        }

        unlock_page(page);

        /*
         * 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;
        }

        /*
         * We can end up here with no error and nothing to write only if we race
         * with a partial page truncate on a sub-page block sized filesystem.
         */
        if (!count)
                end_page_writeback(page);
done:
        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.
 */
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);

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

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

STATIC int
xfs_vm_releasepage(
        struct page             *page,
        gfp_t                   gfp_mask)
{
        trace_xfs_releasepage(page->mapping->host, page, 0, 0);
        return iomap_releasepage(page, gfp_mask);
}

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

        trace_xfs_vm_bmap(ip);

        /*
         * The swap code (ab-)uses ->bmap to get a block mapping and then
         * bypasses the file system for actual I/O.  We really can't allow
         * that on reflinks inodes, so we have to skip out here.  And yes,
         * 0 is the magic code for a bmap error.
         *
         * Since we don't pass back blockdev info, we can't return bmap
         * information for rt files either.
         */
        if (xfs_is_reflink_inode(ip) || XFS_IS_REALTIME_INODE(ip))
                return 0;
        return iomap_bmap(mapping, block, &xfs_iomap_ops);
}

STATIC int
xfs_vm_readpage(
        struct file             *unused,
        struct page             *page)
{
        trace_xfs_vm_readpage(page->mapping->host, 1);
        return iomap_readpage(page, &xfs_iomap_ops);
}

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 iomap_readpages(mapping, pages, nr_pages, &xfs_iomap_ops);
}

static int
xfs_iomap_swapfile_activate(
        struct swap_info_struct         *sis,
        struct file                     *swap_file,
        sector_t                        *span)
{
        sis->bdev = xfs_find_bdev_for_inode(file_inode(swap_file));
        return iomap_swapfile_activate(sis, swap_file, span, &xfs_iomap_ops);
}

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         = iomap_set_page_dirty,
        .releasepage            = xfs_vm_releasepage,
        .invalidatepage         = xfs_vm_invalidatepage,
        .bmap                   = xfs_vm_bmap,
        .direct_IO              = noop_direct_IO,
        .migratepage            = iomap_migrate_page,
        .is_partially_uptodate  = iomap_is_partially_uptodate,
        .error_remove_page      = generic_error_remove_page,
        .swap_activate          = xfs_iomap_swapfile_activate,
};

const struct address_space_operations xfs_dax_aops = {
        .writepages             = xfs_dax_writepages,
        .direct_IO              = noop_direct_IO,
        .set_page_dirty         = noop_set_page_dirty,
        .invalidatepage         = noop_invalidatepage,
        .swap_activate          = xfs_iomap_swapfile_activate,
};