Adding upstream version 4.19.249.upstream/4.19.249

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1043 insertions, 0 deletions

diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
new file mode 100644
index 000000000..b69786694
--- /dev/null
+++ b/fs/xfs/xfs_aops.c
@@ -0,0 +1,1043 @@
+// 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;
+	xfs_trim_extent_eof(&wpc->imap, ip);
+	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;
+	xfs_trim_extent_eof(&wpc->imap, ip);
+	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,
+};