Initial import

1 files changed, 1931 insertions, 0 deletions

diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
new file mode 100644
index 000000000..a56960dd1
--- /dev/null
+++ b/fs/xfs/xfs_aops.c
@@ -0,0 +1,1931 @@
+/*
+ * 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>
+
+void
+xfs_count_page_state(
+	struct page		*page,
+	int			*delalloc,
+	int			*unwritten)
+{
+	struct buffer_head	*bh, *head;
+
+	*delalloc = *unwritten = 0;
+
+	bh = head = page_buffers(page);
+	do {
+		if (buffer_unwritten(bh))
+			(*unwritten) = 1;
+		else if (buffer_delay(bh))
+			(*delalloc) = 1;
+	} while ((bh = bh->b_this_page) != head);
+}
+
+STATIC struct block_device *
+xfs_find_bdev_for_inode(
+	struct inode		*inode)
+{
+	struct xfs_inode	*ip = XFS_I(inode);
+	struct xfs_mount	*mp = ip->i_mount;
+
+	if (XFS_IS_REALTIME_INODE(ip))
+		return mp->m_rtdev_targp->bt_bdev;
+	else
+		return mp->m_ddev_targp->bt_bdev;
+}
+
+/*
+ * We're now finished for good with this ioend structure.
+ * Update the page state via the associated buffer_heads,
+ * release holds on the inode and bio, and finally free
+ * up memory.  Do not use the ioend after this.
+ */
+STATIC void
+xfs_destroy_ioend(
+	xfs_ioend_t		*ioend)
+{
+	struct buffer_head	*bh, *next;
+
+	for (bh = ioend->io_buffer_head; bh; bh = next) {
+		next = bh->b_private;
+		bh->b_end_io(bh, !ioend->io_error);
+	}
+
+	mempool_free(ioend, xfs_ioend_pool);
+}
+
+/*
+ * Fast and loose check if this write could update the on-disk inode size.
+ */
+static inline bool xfs_ioend_is_append(struct xfs_ioend *ioend)
+{
+	return ioend->io_offset + ioend->io_size >
+		XFS_I(ioend->io_inode)->i_d.di_size;
+}
+
+STATIC int
+xfs_setfilesize_trans_alloc(
+	struct xfs_ioend	*ioend)
+{
+	struct xfs_mount	*mp = XFS_I(ioend->io_inode)->i_mount;
+	struct xfs_trans	*tp;
+	int			error;
+
+	tp = xfs_trans_alloc(mp, XFS_TRANS_FSYNC_TS);
+
+	error = xfs_trans_reserve(tp, &M_RES(mp)->tr_fsyncts, 0, 0);
+	if (error) {
+		xfs_trans_cancel(tp, 0);
+		return error;
+	}
+
+	ioend->io_append_trans = tp;
+
+	/*
+	 * We may pass freeze protection with a transaction.  So tell lockdep
+	 * we released it.
+	 */
+	rwsem_release(&ioend->io_inode->i_sb->s_writers.lock_map[SB_FREEZE_FS-1],
+		      1, _THIS_IP_);
+	/*
+	 * We hand off the transaction to the completion thread now, so
+	 * clear the flag here.
+	 */
+	current_restore_flags_nested(&tp->t_pflags, PF_FSTRANS);
+	return 0;
+}
+
+/*
+ * Update on-disk file size now that data has been written to disk.
+ */
+STATIC int
+xfs_setfilesize(
+	struct xfs_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, 0);
+		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, 0);
+}
+
+STATIC int
+xfs_setfilesize_ioend(
+	struct xfs_ioend	*ioend)
+{
+	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);
+	rwsem_acquire_read(&VFS_I(ip)->i_sb->s_writers.lock_map[SB_FREEZE_FS-1],
+			   0, 1, _THIS_IP_);
+
+	return xfs_setfilesize(ip, tp, ioend->io_offset, ioend->io_size);
+}
+
+/*
+ * Schedule IO completion handling on the final put of an ioend.
+ *
+ * If there is no work to do we might as well call it a day and free the
+ * ioend right now.
+ */
+STATIC void
+xfs_finish_ioend(
+	struct xfs_ioend	*ioend)
+{
+	if (atomic_dec_and_test(&ioend->io_remaining)) {
+		struct xfs_mount	*mp = XFS_I(ioend->io_inode)->i_mount;
+
+		if (ioend->io_type == XFS_IO_UNWRITTEN)
+			queue_work(mp->m_unwritten_workqueue, &ioend->io_work);
+		else if (ioend->io_append_trans)
+			queue_work(mp->m_data_workqueue, &ioend->io_work);
+		else
+			xfs_destroy_ioend(ioend);
+	}
+}
+
+/*
+ * IO write completion.
+ */
+STATIC void
+xfs_end_io(
+	struct work_struct *work)
+{
+	xfs_ioend_t	*ioend = container_of(work, xfs_ioend_t, io_work);
+	struct xfs_inode *ip = XFS_I(ioend->io_inode);
+	int		error = 0;
+
+	if (XFS_FORCED_SHUTDOWN(ip->i_mount)) {
+		ioend->io_error = -EIO;
+		goto done;
+	}
+	if (ioend->io_error)
+		goto done;
+
+	/*
+	 * For unwritten extents we need to issue transactions to convert a
+	 * range to normal written extens after the data I/O has finished.
+	 */
+	if (ioend->io_type == XFS_IO_UNWRITTEN) {
+		error = xfs_iomap_write_unwritten(ip, ioend->io_offset,
+						  ioend->io_size);
+	} else if (ioend->io_append_trans) {
+		error = xfs_setfilesize_ioend(ioend);
+	} else {
+		ASSERT(!xfs_ioend_is_append(ioend));
+	}
+
+done:
+	if (error)
+		ioend->io_error = error;
+	xfs_destroy_ioend(ioend);
+}
+
+/*
+ * Allocate and initialise an IO completion structure.
+ * We need to track unwritten extent write completion here initially.
+ * We'll need to extend this for updating the ondisk inode size later
+ * (vs. incore size).
+ */
+STATIC xfs_ioend_t *
+xfs_alloc_ioend(
+	struct inode		*inode,
+	unsigned int		type)
+{
+	xfs_ioend_t		*ioend;
+
+	ioend = mempool_alloc(xfs_ioend_pool, GFP_NOFS);
+
+	/*
+	 * Set the count to 1 initially, which will prevent an I/O
+	 * completion callback from happening before we have started
+	 * all the I/O from calling the completion routine too early.
+	 */
+	atomic_set(&ioend->io_remaining, 1);
+	ioend->io_error = 0;
+	ioend->io_list = NULL;
+	ioend->io_type = type;
+	ioend->io_inode = inode;
+	ioend->io_buffer_head = NULL;
+	ioend->io_buffer_tail = NULL;
+	ioend->io_offset = 0;
+	ioend->io_size = 0;
+	ioend->io_append_trans = NULL;
+
+	INIT_WORK(&ioend->io_work, xfs_end_io);
+	return ioend;
+}
+
+STATIC int
+xfs_map_blocks(
+	struct inode		*inode,
+	loff_t			offset,
+	struct xfs_bmbt_irec	*imap,
+	int			type,
+	int			nonblocking)
+{
+	struct xfs_inode	*ip = XFS_I(inode);
+	struct xfs_mount	*mp = ip->i_mount;
+	ssize_t			count = 1 << inode->i_blkbits;
+	xfs_fileoff_t		offset_fsb, end_fsb;
+	int			error = 0;
+	int			bmapi_flags = XFS_BMAPI_ENTIRE;
+	int			nimaps = 1;
+
+	if (XFS_FORCED_SHUTDOWN(mp))
+		return -EIO;
+
+	if (type == XFS_IO_UNWRITTEN)
+		bmapi_flags |= XFS_BMAPI_IGSTATE;
+
+	if (!xfs_ilock_nowait(ip, XFS_ILOCK_SHARED)) {
+		if (nonblocking)
+			return -EAGAIN;
+		xfs_ilock(ip, XFS_ILOCK_SHARED);
+	}
+
+	ASSERT(ip->i_d.di_format != XFS_DINODE_FMT_BTREE ||
+	       (ip->i_df.if_flags & XFS_IFEXTENTS));
+	ASSERT(offset <= mp->m_super->s_maxbytes);
+
+	if (offset + count > mp->m_super->s_maxbytes)
+		count = mp->m_super->s_maxbytes - offset;
+	end_fsb = XFS_B_TO_FSB(mp, (xfs_ufsize_t)offset + count);
+	offset_fsb = XFS_B_TO_FSBT(mp, offset);
+	error = xfs_bmapi_read(ip, offset_fsb, end_fsb - offset_fsb,
+				imap, &nimaps, bmapi_flags);
+	xfs_iunlock(ip, XFS_ILOCK_SHARED);
+
+	if (error)
+		return 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 int
+xfs_imap_valid(
+	struct inode		*inode,
+	struct xfs_bmbt_irec	*imap,
+	xfs_off_t		offset)
+{
+	offset >>= inode->i_blkbits;
+
+	return offset >= imap->br_startoff &&
+		offset < imap->br_startoff + imap->br_blockcount;
+}
+
+/*
+ * BIO completion handler for buffered IO.
+ */
+STATIC void
+xfs_end_bio(
+	struct bio		*bio,
+	int			error)
+{
+	xfs_ioend_t		*ioend = bio->bi_private;
+
+	ASSERT(atomic_read(&bio->bi_cnt) >= 1);
+	ioend->io_error = test_bit(BIO_UPTODATE, &bio->bi_flags) ? 0 : error;
+
+	/* Toss bio and pass work off to an xfsdatad thread */
+	bio->bi_private = NULL;
+	bio->bi_end_io = NULL;
+	bio_put(bio);
+
+	xfs_finish_ioend(ioend);
+}
+
+STATIC void
+xfs_submit_ioend_bio(
+	struct writeback_control *wbc,
+	xfs_ioend_t		*ioend,
+	struct bio		*bio)
+{
+	atomic_inc(&ioend->io_remaining);
+	bio->bi_private = ioend;
+	bio->bi_end_io = xfs_end_bio;
+	submit_bio(wbc->sync_mode == WB_SYNC_ALL ? WRITE_SYNC : WRITE, bio);
+}
+
+STATIC struct bio *
+xfs_alloc_ioend_bio(
+	struct buffer_head	*bh)
+{
+	int			nvecs = bio_get_nr_vecs(bh->b_bdev);
+	struct bio		*bio = bio_alloc(GFP_NOIO, nvecs);
+
+	ASSERT(bio->bi_private == NULL);
+	bio->bi_iter.bi_sector = bh->b_blocknr * (bh->b_size >> 9);
+	bio->bi_bdev = bh->b_bdev;
+	return bio;
+}
+
+STATIC void
+xfs_start_buffer_writeback(
+	struct buffer_head	*bh)
+{
+	ASSERT(buffer_mapped(bh));
+	ASSERT(buffer_locked(bh));
+	ASSERT(!buffer_delay(bh));
+	ASSERT(!buffer_unwritten(bh));
+
+	mark_buffer_async_write(bh);
+	set_buffer_uptodate(bh);
+	clear_buffer_dirty(bh);
+}
+
+STATIC void
+xfs_start_page_writeback(
+	struct page		*page,
+	int			clear_dirty,
+	int			buffers)
+{
+	ASSERT(PageLocked(page));
+	ASSERT(!PageWriteback(page));
+
+	/*
+	 * if 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);
+
+	/* If no buffers on the page are to be written, finish it here */
+	if (!buffers)
+		end_page_writeback(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 all of the bios for all of the ioends we have saved up, covering the
+ * initial writepage page and also any probed pages.
+ *
+ * Because we may have multiple ioends spanning a page, we need to start
+ * writeback on all the buffers before we submit them for I/O. If we mark the
+ * buffers as we got, then we can end up with a page that only has buffers
+ * marked async write and I/O complete on can occur before we mark the other
+ * buffers async write.
+ *
+ * The end result of this is that we trip a bug in end_page_writeback() because
+ * we call it twice for the one page as the code in end_buffer_async_write()
+ * assumes that all buffers on the page are started at the same time.
+ *
+ * The fix is two passes across the ioend list - one to start writeback on the
+ * buffer_heads, and then submit them for I/O on the second pass.
+ *
+ * If @fail is non-zero, it means that we have a situation where some part of
+ * the submission process has failed after we have marked paged for writeback
+ * and unlocked them. In this situation, we need to fail the ioend chain rather
+ * than submit it to IO. This typically only happens on a filesystem shutdown.
+ */
+STATIC void
+xfs_submit_ioend(
+	struct writeback_control *wbc,
+	xfs_ioend_t		*ioend,
+	int			fail)
+{
+	xfs_ioend_t		*head = ioend;
+	xfs_ioend_t		*next;
+	struct buffer_head	*bh;
+	struct bio		*bio;
+	sector_t		lastblock = 0;
+
+	/* Pass 1 - start writeback */
+	do {
+		next = ioend->io_list;
+		for (bh = ioend->io_buffer_head; bh; bh = bh->b_private)
+			xfs_start_buffer_writeback(bh);
+	} while ((ioend = next) != NULL);
+
+	/* Pass 2 - submit I/O */
+	ioend = head;
+	do {
+		next = ioend->io_list;
+		bio = NULL;
+
+		/*
+		 * If we are failing the IO now, just mark the ioend with an
+		 * error and finish it. This will run IO completion immediately
+		 * as there is only one reference to the ioend at this point in
+		 * time.
+		 */
+		if (fail) {
+			ioend->io_error = fail;
+			xfs_finish_ioend(ioend);
+			continue;
+		}
+
+		for (bh = ioend->io_buffer_head; bh; bh = bh->b_private) {
+
+			if (!bio) {
+ retry:
+				bio = xfs_alloc_ioend_bio(bh);
+			} else if (bh->b_blocknr != lastblock + 1) {
+				xfs_submit_ioend_bio(wbc, ioend, bio);
+				goto retry;
+			}
+
+			if (xfs_bio_add_buffer(bio, bh) != bh->b_size) {
+				xfs_submit_ioend_bio(wbc, ioend, bio);
+				goto retry;
+			}
+
+			lastblock = bh->b_blocknr;
+		}
+		if (bio)
+			xfs_submit_ioend_bio(wbc, ioend, bio);
+		xfs_finish_ioend(ioend);
+	} while ((ioend = next) != NULL);
+}
+
+/*
+ * Cancel submission of all buffer_heads so far in this endio.
+ * Toss the endio too.  Only ever called for the initial page
+ * in a writepage request, so only ever one page.
+ */
+STATIC void
+xfs_cancel_ioend(
+	xfs_ioend_t		*ioend)
+{
+	xfs_ioend_t		*next;
+	struct buffer_head	*bh, *next_bh;
+
+	do {
+		next = ioend->io_list;
+		bh = ioend->io_buffer_head;
+		do {
+			next_bh = bh->b_private;
+			clear_buffer_async_write(bh);
+			/*
+			 * The unwritten flag is cleared when added to the
+			 * ioend. We're not submitting for I/O so mark the
+			 * buffer unwritten again for next time around.
+			 */
+			if (ioend->io_type == XFS_IO_UNWRITTEN)
+				set_buffer_unwritten(bh);
+			unlock_buffer(bh);
+		} while ((bh = next_bh) != NULL);
+
+		mempool_free(ioend, xfs_ioend_pool);
+	} while ((ioend = next) != NULL);
+}
+
+/*
+ * Test to see if we've been building up a completion structure for
+ * earlier buffers -- if so, we try to append to this ioend if we
+ * can, otherwise we finish off any current ioend and start another.
+ * Return true if we've finished the given ioend.
+ */
+STATIC void
+xfs_add_to_ioend(
+	struct inode		*inode,
+	struct buffer_head	*bh,
+	xfs_off_t		offset,
+	unsigned int		type,
+	xfs_ioend_t		**result,
+	int			need_ioend)
+{
+	xfs_ioend_t		*ioend = *result;
+
+	if (!ioend || need_ioend || type != ioend->io_type) {
+		xfs_ioend_t	*previous = *result;
+
+		ioend = xfs_alloc_ioend(inode, type);
+		ioend->io_offset = offset;
+		ioend->io_buffer_head = bh;
+		ioend->io_buffer_tail = bh;
+		if (previous)
+			previous->io_list = ioend;
+		*result = ioend;
+	} else {
+		ioend->io_buffer_tail->b_private = bh;
+		ioend->io_buffer_tail = bh;
+	}
+
+	bh->b_private = NULL;
+	ioend->io_size += bh->b_size;
+}
+
+STATIC void
+xfs_map_buffer(
+	struct inode		*inode,
+	struct buffer_head	*bh,
+	struct xfs_bmbt_irec	*imap,
+	xfs_off_t		offset)
+{
+	sector_t		bn;
+	struct xfs_mount	*m = XFS_I(inode)->i_mount;
+	xfs_off_t		iomap_offset = XFS_FSB_TO_B(m, imap->br_startoff);
+	xfs_daddr_t		iomap_bn = xfs_fsb_to_db(XFS_I(inode), imap->br_startblock);
+
+	ASSERT(imap->br_startblock != HOLESTARTBLOCK);
+	ASSERT(imap->br_startblock != DELAYSTARTBLOCK);
+
+	bn = (iomap_bn >> (inode->i_blkbits - BBSHIFT)) +
+	      ((offset - iomap_offset) >> inode->i_blkbits);
+
+	ASSERT(bn || XFS_IS_REALTIME_INODE(XFS_I(inode)));
+
+	bh->b_blocknr = bn;
+	set_buffer_mapped(bh);
+}
+
+STATIC void
+xfs_map_at_offset(
+	struct inode		*inode,
+	struct buffer_head	*bh,
+	struct xfs_bmbt_irec	*imap,
+	xfs_off_t		offset)
+{
+	ASSERT(imap->br_startblock != HOLESTARTBLOCK);
+	ASSERT(imap->br_startblock != DELAYSTARTBLOCK);
+
+	xfs_map_buffer(inode, bh, imap, offset);
+	set_buffer_mapped(bh);
+	clear_buffer_delay(bh);
+	clear_buffer_unwritten(bh);
+}
+
+/*
+ * Test if a given page 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;
+}
+
+/*
+ * Allocate & map buffers for page given the extent map. Write it out.
+ * except for the original page of a writepage, this is called on
+ * delalloc/unwritten pages only, for the original page it is possible
+ * that the page has no mapping at all.
+ */
+STATIC int
+xfs_convert_page(
+	struct inode		*inode,
+	struct page		*page,
+	loff_t			tindex,
+	struct xfs_bmbt_irec	*imap,
+	xfs_ioend_t		**ioendp,
+	struct writeback_control *wbc)
+{
+	struct buffer_head	*bh, *head;
+	xfs_off_t		end_offset;
+	unsigned long		p_offset;
+	unsigned int		type;
+	int			len, page_dirty;
+	int			count = 0, done = 0, uptodate = 1;
+ 	xfs_off_t		offset = page_offset(page);
+
+	if (page->index != tindex)
+		goto fail;
+	if (!trylock_page(page))
+		goto fail;
+	if (PageWriteback(page))
+		goto fail_unlock_page;
+	if (page->mapping != inode->i_mapping)
+		goto fail_unlock_page;
+	if (!xfs_check_page_type(page, (*ioendp)->io_type, false))
+		goto fail_unlock_page;
+
+	/*
+	 * page_dirty is initially a count of buffers on the page before
+	 * EOF and is decremented as we move each into a cleanable state.
+	 *
+	 * Derivation:
+	 *
+	 * End offset is the highest offset that this page should represent.
+	 * If we are on the last page, (end_offset & (PAGE_CACHE_SIZE - 1))
+	 * will evaluate non-zero and be less than PAGE_CACHE_SIZE and
+	 * hence give us the correct page_dirty count. On any other page,
+	 * it will be zero and in that case we need page_dirty to be the
+	 * count of buffers on the page.
+	 */
+	end_offset = min_t(unsigned long long,
+			(xfs_off_t)(page->index + 1) << PAGE_CACHE_SHIFT,
+			i_size_read(inode));
+
+	/*
+	 * If the current map does not span the entire page we are about to try
+	 * to write, then give up. The only way we can write a page that spans
+	 * multiple mappings in a single writeback iteration is via the
+	 * xfs_vm_writepage() function. Data integrity writeback requires the
+	 * entire page to be written in a single attempt, otherwise the part of
+	 * the page we don't write here doesn't get written as part of the data
+	 * integrity sync.
+	 *
+	 * For normal writeback, we also don't attempt to write partial pages
+	 * here as it simply means that write_cache_pages() will see it under
+	 * writeback and ignore the page until some point in the future, at
+	 * which time this will be the only page in the file that needs
+	 * writeback.  Hence for more optimal IO patterns, we should always
+	 * avoid partial page writeback due to multiple mappings on a page here.
+	 */
+	if (!xfs_imap_valid(inode, imap, end_offset))
+		goto fail_unlock_page;
+
+	len = 1 << inode->i_blkbits;
+	p_offset = min_t(unsigned long, end_offset & (PAGE_CACHE_SIZE - 1),
+					PAGE_CACHE_SIZE);
+	p_offset = p_offset ? roundup(p_offset, len) : PAGE_CACHE_SIZE;
+	page_dirty = p_offset / len;
+
+	/*
+	 * The moment we find a buffer that doesn't match our current type
+	 * specification or can't be written, abort the loop and start
+	 * writeback. As per the above xfs_imap_valid() check, only
+	 * xfs_vm_writepage() can handle partial page writeback fully - we are
+	 * limited here to the buffers that are contiguous with the current
+	 * ioend, and hence a buffer we can't write breaks that contiguity and
+	 * we have to defer the rest of the IO to xfs_vm_writepage().
+	 */
+	bh = head = page_buffers(page);
+	do {
+		if (offset >= end_offset)
+			break;
+		if (!buffer_uptodate(bh))
+			uptodate = 0;
+		if (!(PageUptodate(page) || buffer_uptodate(bh))) {
+			done = 1;
+			break;
+		}
+
+		if (buffer_unwritten(bh) || buffer_delay(bh) ||
+		    buffer_mapped(bh)) {
+			if (buffer_unwritten(bh))
+				type = XFS_IO_UNWRITTEN;
+			else if (buffer_delay(bh))
+				type = XFS_IO_DELALLOC;
+			else
+				type = XFS_IO_OVERWRITE;
+
+			/*
+			 * imap should always be valid because of the above
+			 * partial page end_offset check on the imap.
+			 */
+			ASSERT(xfs_imap_valid(inode, imap, offset));
+
+			lock_buffer(bh);
+			if (type != XFS_IO_OVERWRITE)
+				xfs_map_at_offset(inode, bh, imap, offset);
+			xfs_add_to_ioend(inode, bh, offset, type,
+					 ioendp, done);
+
+			page_dirty--;
+			count++;
+		} else {
+			done = 1;
+			break;
+		}
+	} while (offset += len, (bh = bh->b_this_page) != head);
+
+	if (uptodate && bh == head)
+		SetPageUptodate(page);
+
+	if (count) {
+		if (--wbc->nr_to_write <= 0 &&
+		    wbc->sync_mode == WB_SYNC_NONE)
+			done = 1;
+	}
+	xfs_start_page_writeback(page, !page_dirty, count);
+
+	return done;
+ fail_unlock_page:
+	unlock_page(page);
+ fail:
+	return 1;
+}
+
+/*
+ * Convert & write out a cluster of pages in the same extent as defined
+ * by mp and following the start page.
+ */
+STATIC void
+xfs_cluster_write(
+	struct inode		*inode,
+	pgoff_t			tindex,
+	struct xfs_bmbt_irec	*imap,
+	xfs_ioend_t		**ioendp,
+	struct writeback_control *wbc,
+	pgoff_t			tlast)
+{
+	struct pagevec		pvec;
+	int			done = 0, i;
+
+	pagevec_init(&pvec, 0);
+	while (!done && tindex <= tlast) {
+		unsigned len = min_t(pgoff_t, PAGEVEC_SIZE, tlast - tindex + 1);
+
+		if (!pagevec_lookup(&pvec, inode->i_mapping, tindex, len))
+			break;
+
+		for (i = 0; i < pagevec_count(&pvec); i++) {
+			done = xfs_convert_page(inode, pvec.pages[i], tindex++,
+					imap, ioendp, wbc);
+			if (done)
+				break;
+		}
+
+		pagevec_release(&pvec);
+		cond_resched();
+	}
+}
+
+STATIC void
+xfs_vm_invalidatepage(
+	struct page		*page,
+	unsigned 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_CACHE_SIZE);
+	return;
+}
+
+/*
+ * Write out a dirty page.
+ *
+ * For delalloc space on the page we need to allocate space and flush it.
+ * For unwritten space on the page we need to start the conversion to
+ * regular allocated space.
+ * For any other dirty buffer heads on the page we should flush them.
+ */
+STATIC int
+xfs_vm_writepage(
+	struct page		*page,
+	struct writeback_control *wbc)
+{
+	struct inode		*inode = page->mapping->host;
+	struct buffer_head	*bh, *head;
+	struct xfs_bmbt_irec	imap;
+	xfs_ioend_t		*ioend = NULL, *iohead = NULL;
+	loff_t			offset;
+	unsigned int		type;
+	__uint64_t              end_offset;
+	pgoff_t                 end_index, last_index;
+	ssize_t			len;
+	int			err, imap_valid = 0, uptodate = 1;
+	int			count = 0;
+	int			nonblocking = 0;
+
+	trace_xfs_writepage(inode, page, 0, 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? */
+	offset = i_size_read(inode);
+	end_index = offset >> PAGE_CACHE_SHIFT;
+	last_index = (offset - 1) >> PAGE_CACHE_SHIFT;
+
+	/*
+	 * 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    |
+	 * ---------------------------------^------------------|
+	 */
+	if (page->index < end_index)
+		end_offset = (xfs_off_t)(page->index + 1) << PAGE_CACHE_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_CACHE_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_CACHE_SIZE);
+
+		/* Adjust the end_offset to the end of file */
+		end_offset = offset;
+	}
+
+	len = 1 << inode->i_blkbits;
+
+	bh = head = page_buffers(page);
+	offset = page_offset(page);
+	type = XFS_IO_OVERWRITE;
+
+	if (wbc->sync_mode == WB_SYNC_NONE)
+		nonblocking = 1;
+
+	do {
+		int new_ioend = 0;
+
+		if (offset >= end_offset)
+			break;
+		if (!buffer_uptodate(bh))
+			uptodate = 0;
+
+		/*
+		 * set_page_dirty dirties all buffers in a page, independent
+		 * of their state.  The dirty state however is entirely
+		 * meaningless for holes (!mapped && uptodate), so skip
+		 * buffers covering holes here.
+		 */
+		if (!buffer_mapped(bh) && buffer_uptodate(bh)) {
+			imap_valid = 0;
+			continue;
+		}
+
+		if (buffer_unwritten(bh)) {
+			if (type != XFS_IO_UNWRITTEN) {
+				type = XFS_IO_UNWRITTEN;
+				imap_valid = 0;
+			}
+		} else if (buffer_delay(bh)) {
+			if (type != XFS_IO_DELALLOC) {
+				type = XFS_IO_DELALLOC;
+				imap_valid = 0;
+			}
+		} else if (buffer_uptodate(bh)) {
+			if (type != XFS_IO_OVERWRITE) {
+				type = XFS_IO_OVERWRITE;
+				imap_valid = 0;
+			}
+		} else {
+			if (PageUptodate(page))
+				ASSERT(buffer_mapped(bh));
+			/*
+			 * This buffer is not uptodate and will not be
+			 * written to disk.  Ensure that we will put any
+			 * subsequent writeable buffers into a new
+			 * ioend.
+			 */
+			imap_valid = 0;
+			continue;
+		}
+
+		if (imap_valid)
+			imap_valid = xfs_imap_valid(inode, &imap, offset);
+		if (!imap_valid) {
+			/*
+			 * If we didn't have a valid mapping then we need to
+			 * put the new mapping into a separate ioend structure.
+			 * This ensures non-contiguous extents always have
+			 * separate ioends, which is particularly important
+			 * for unwritten extent conversion at I/O completion
+			 * time.
+			 */
+			new_ioend = 1;
+			err = xfs_map_blocks(inode, offset, &imap, type,
+					     nonblocking);
+			if (err)
+				goto error;
+			imap_valid = xfs_imap_valid(inode, &imap, offset);
+		}
+		if (imap_valid) {
+			lock_buffer(bh);
+			if (type != XFS_IO_OVERWRITE)
+				xfs_map_at_offset(inode, bh, &imap, offset);
+			xfs_add_to_ioend(inode, bh, offset, type, &ioend,
+					 new_ioend);
+			count++;
+		}
+
+		if (!iohead)
+			iohead = ioend;
+
+	} while (offset += len, ((bh = bh->b_this_page) != head));
+
+	if (uptodate && bh == head)
+		SetPageUptodate(page);
+
+	xfs_start_page_writeback(page, 1, count);
+
+	/* if there is no IO to be submitted for this page, we are done */
+	if (!ioend)
+		return 0;
+
+	ASSERT(iohead);
+
+	/*
+	 * Any errors from this point onwards need tobe reported through the IO
+	 * completion path as we have marked the initial page as under writeback
+	 * and unlocked it.
+	 */
+	if (imap_valid) {
+		xfs_off_t		end_index;
+
+		end_index = imap.br_startoff + imap.br_blockcount;
+
+		/* to bytes */
+		end_index <<= inode->i_blkbits;
+
+		/* to pages */
+		end_index = (end_index - 1) >> PAGE_CACHE_SHIFT;
+
+		/* check against file size */
+		if (end_index > last_index)
+			end_index = last_index;
+
+		xfs_cluster_write(inode, page->index + 1, &imap, &ioend,
+				  wbc, end_index);
+	}
+
+
+	/*
+	 * Reserve log space if we might write beyond the on-disk inode size.
+	 */
+	err = 0;
+	if (ioend->io_type != XFS_IO_UNWRITTEN && xfs_ioend_is_append(ioend))
+		err = xfs_setfilesize_trans_alloc(ioend);
+
+	xfs_submit_ioend(wbc, iohead, err);
+
+	return 0;
+
+error:
+	if (iohead)
+		xfs_cancel_ioend(iohead);
+
+	if (err == -EAGAIN)
+		goto redirty;
+
+	xfs_aops_discard_page(page);
+	ClearPageUptodate(page);
+	unlock_page(page);
+	return err;
+
+redirty:
+	redirty_page_for_writepage(wbc, page);
+	unlock_page(page);
+	return 0;
+}
+
+STATIC int
+xfs_vm_writepages(
+	struct address_space	*mapping,
+	struct writeback_control *wbc)
+{
+	xfs_iflags_clear(XFS_I(mapping->host), XFS_ITRUNCATED);
+	return generic_writepages(mapping, wbc);
+}
+
+/*
+ * Called to move a page into cleanable state - and from there
+ * to be released. The page should already be clean. We always
+ * have buffer heads in this call.
+ *
+ * Returns 1 if the page is ok to release, 0 otherwise.
+ */
+STATIC int
+xfs_vm_releasepage(
+	struct page		*page,
+	gfp_t			gfp_mask)
+{
+	int			delalloc, unwritten;
+
+	trace_xfs_releasepage(page->mapping->host, page, 0, 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 attach an ioend that describes the
+ * type of write IO we are doing. This passes to the completion function the
+ * operations it needs to perform. If the mapping is for an overwrite wholly
+ * within the EOF then we don't need an ioend and so we don't allocate one.
+ * This avoids the unnecessary overhead of allocating and freeing ioends for
+ * workloads that don't require transactions on IO completion.
+ *
+ * If we get multiple mappings in a single IO, we might be mapping different
+ * types. But because the direct IO can only have a single private pointer, we
+ * need to ensure that:
+ *
+ * a) i) the ioend spans the entire region of unwritten mappings; or
+ *    ii) the ioend spans all the mappings that cross or are beyond EOF; and
+ * b) if it contains unwritten extents, it is *permanently* marked as such
+ *
+ * We could do this by chaining ioends like buffered IO does, but we only
+ * actually get one IO completion callback from the direct IO, and that spans
+ * the entire IO regardless of how many mappings and IOs are needed to complete
+ * the DIO. There is only going to be one reference to the ioend and its life
+ * cycle is constrained by the DIO completion code. hence we don't need
+ * reference counting here.
+ */
+static void
+xfs_map_direct(
+	struct inode		*inode,
+	struct buffer_head	*bh_result,
+	struct xfs_bmbt_irec	*imap,
+	xfs_off_t		offset)
+{
+	struct xfs_ioend	*ioend;
+	xfs_off_t		size = bh_result->b_size;
+	int			type;
+
+	if (ISUNWRITTEN(imap))
+		type = XFS_IO_UNWRITTEN;
+	else
+		type = XFS_IO_OVERWRITE;
+
+	trace_xfs_gbmap_direct(XFS_I(inode), offset, size, type, imap);
+
+	if (bh_result->b_private) {
+		ioend = bh_result->b_private;
+		ASSERT(ioend->io_size > 0);
+		ASSERT(offset >= ioend->io_offset);
+		if (offset + size > ioend->io_offset + ioend->io_size)
+			ioend->io_size = offset - ioend->io_offset + size;
+
+		if (type == XFS_IO_UNWRITTEN && type != ioend->io_type)
+			ioend->io_type = XFS_IO_UNWRITTEN;
+
+		trace_xfs_gbmap_direct_update(XFS_I(inode), ioend->io_offset,
+					      ioend->io_size, ioend->io_type,
+					      imap);
+	} else if (type == XFS_IO_UNWRITTEN ||
+		   offset + size > i_size_read(inode)) {
+		ioend = xfs_alloc_ioend(inode, type);
+		ioend->io_offset = offset;
+		ioend->io_size = size;
+
+		bh_result->b_private = ioend;
+		set_buffer_defer_completion(bh_result);
+
+		trace_xfs_gbmap_direct_new(XFS_I(inode), offset, size, type,
+					   imap);
+	} else {
+		trace_xfs_gbmap_direct_none(XFS_I(inode), offset, size, type,
+					    imap);
+	}
+}
+
+/*
+ * 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,
+	int			direct)
+{
+	struct xfs_inode	*ip = XFS_I(inode);
+	struct xfs_mount	*mp = ip->i_mount;
+	xfs_fileoff_t		offset_fsb, end_fsb;
+	int			error = 0;
+	int			lockmode = 0;
+	struct xfs_bmbt_irec	imap;
+	int			nimaps = 1;
+	xfs_off_t		offset;
+	ssize_t			size;
+	int			new = 0;
+
+	if (XFS_FORCED_SHUTDOWN(mp))
+		return -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;
+
+	if (create &&
+	    (!nimaps ||
+	     (imap.br_startblock == HOLESTARTBLOCK ||
+	      imap.br_startblock == DELAYSTARTBLOCK))) {
+		if (direct || xfs_get_extsz_hint(ip)) {
+			/*
+			 * Drop the ilock in preparation for starting the block
+			 * allocation transaction.  It will be retaken
+			 * exclusively inside xfs_iomap_write_direct for the
+			 * actual allocation.
+			 */
+			xfs_iunlock(ip, lockmode);
+			error = xfs_iomap_write_direct(ip, offset, size,
+						       &imap, nimaps);
+			if (error)
+				return error;
+			new = 1;
+		} else {
+			/*
+			 * Delalloc reservations do not require a transaction,
+			 * we can go on without dropping the lock here. If we
+			 * are allocating a new delalloc block, make sure that
+			 * we set the new flag so that we mark the buffer new so
+			 * that we know that it is newly allocated if the write
+			 * fails.
+			 */
+			if (nimaps && imap.br_startblock == HOLESTARTBLOCK)
+				new = 1;
+			error = xfs_iomap_write_delay(ip, offset, size, &imap);
+			if (error)
+				goto out_unlock;
+
+			xfs_iunlock(ip, lockmode);
+		}
+		trace_xfs_get_blocks_alloc(ip, offset, size,
+				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;
+	}
+
+	/* 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)
+			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, 0);
+}
+
+STATIC int
+xfs_get_blocks_direct(
+	struct inode		*inode,
+	sector_t		iblock,
+	struct buffer_head	*bh_result,
+	int			create)
+{
+	return __xfs_get_blocks(inode, iblock, bh_result, create, 1);
+}
+
+/*
+ * Complete a direct I/O write request.
+ *
+ * The ioend structure is passed from __xfs_get_blocks() to tell us what to do.
+ * If no ioend exists (i.e. @private == NULL) then the write IO is an overwrite
+ * wholly within the EOF 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 an
+ * ioend we will always be called in task context (i.e. from a workqueue).
+ */
+STATIC void
+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;
+	struct xfs_ioend	*ioend = private;
+
+	trace_xfs_gbmap_direct_endio(ip, offset, size,
+				     ioend ? ioend->io_type : 0, NULL);
+
+	if (!ioend) {
+		ASSERT(offset + size <= i_size_read(inode));
+		return;
+	}
+
+	if (XFS_FORCED_SHUTDOWN(mp))
+		goto out_end_io;
+
+	/*
+	 * dio completion end_io functions are only called on writes if more
+	 * than 0 bytes was written.
+	 */
+	ASSERT(size > 0);
+
+	/*
+	 * The ioend only maps whole blocks, while the IO may be sector aligned.
+	 * Hence the ioend offset/size may not match the IO offset/size exactly.
+	 * Because we don't map overwrites within EOF into the ioend, the offset
+	 * may not match, but only if the endio spans EOF.  Either way, write
+	 * the IO sizes into the ioend so that completion processing does the
+	 * right thing.
+	 */
+	ASSERT(offset + size <= ioend->io_offset + ioend->io_size);
+	ioend->io_size = size;
+	ioend->io_offset = offset;
+
+	/*
+	 * The ioend tells us whether we are doing unwritten extent conversion
+	 * 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.
+	 *
+	 * 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 we are doing an append IO that needs to update the EOF on disk,
+	 * do the transaction reserve now so we can use common end io
+	 * processing. Stashing the error (if there is one) in the ioend will
+	 * result in the ioend processing passing on the error if it is
+	 * possible as we can't return it from here.
+	 */
+	if (ioend->io_type == XFS_IO_OVERWRITE)
+		ioend->io_error = xfs_setfilesize_trans_alloc(ioend);
+
+out_end_io:
+	xfs_end_io(&ioend->io_work);
+	return;
+}
+
+STATIC ssize_t
+xfs_vm_direct_IO(
+	struct kiocb		*iocb,
+	struct iov_iter		*iter,
+	loff_t			offset)
+{
+	struct inode		*inode = iocb->ki_filp->f_mapping->host;
+	struct block_device	*bdev = xfs_find_bdev_for_inode(inode);
+
+	if (iov_iter_rw(iter) == WRITE) {
+		return __blockdev_direct_IO(iocb, inode, bdev, iter, offset,
+					    xfs_get_blocks_direct,
+					    xfs_end_io_direct_write, NULL,
+					    DIO_ASYNC_EXTEND);
+	}
+	return __blockdev_direct_IO(iocb, inode, bdev, iter, offset,
+				    xfs_get_blocks_direct, NULL, NULL, 0);
+}
+
+/*
+ * 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_CACHE_SIZE - 1);
+	loff_t			to = from + len;
+	struct buffer_head	*bh, *head;
+
+	/*
+	 * 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_CACHE_SHIFT) << PAGE_CACHE_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;
+
+		if (!buffer_delay(bh))
+			continue;
+
+		if (!buffer_new(bh) && block_offset < i_size_read(inode))
+			continue;
+
+		xfs_vm_kill_delalloc_range(inode, block_offset,
+					   block_offset + bh->b_size);
+
+		/*
+		 * This 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);
+	}
+
+}
+
+/*
+ * This used to call block_write_begin(), but it unlocks and releases the page
+ * on error, and we need that page to be able to punch stale delalloc blocks out
+ * on failure. hence we copy-n-waste it here and call xfs_vm_write_failed() at
+ * the appropriate point.
+ */
+STATIC int
+xfs_vm_write_begin(
+	struct file		*file,
+	struct address_space	*mapping,
+	loff_t			pos,
+	unsigned		len,
+	unsigned		flags,
+	struct page		**pagep,
+	void			**fsdata)
+{
+	pgoff_t			index = pos >> PAGE_CACHE_SHIFT;
+	struct page		*page;
+	int			status;
+
+	ASSERT(len <= PAGE_CACHE_SIZE);
+
+	page = grab_cache_page_write_begin(mapping, index, flags);
+	if (!page)
+		return -ENOMEM;
+
+	status = __block_write_begin(page, pos, len, xfs_get_blocks);
+	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 (pos + len > isize) {
+			ssize_t start = max_t(ssize_t, pos, isize);
+
+			truncate_pagecache_range(inode, start, pos + len);
+		}
+
+		page_cache_release(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_CACHE_SIZE);
+
+	ret = generic_write_end(file, mapping, pos, len, copied, page, fsdata);
+	if (unlikely(ret < len)) {
+		struct inode	*inode = mapping->host;
+		size_t		isize = i_size_read(inode);
+		loff_t		to = pos + len;
+
+		if (to > isize) {
+			/* 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)
+{
+	return mpage_readpage(page, xfs_get_blocks);
+}
+
+STATIC int
+xfs_vm_readpages(
+	struct file		*unused,
+	struct address_space	*mapping,
+	struct list_head	*pages,
+	unsigned		nr_pages)
+{
+	return mpage_readpages(mapping, pages, nr_pages, xfs_get_blocks);
+}
+
+/*
+ * 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);
+	}
+	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);
+		__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,
+};