[PATCH] xfs: flush the range before zero range conversion

[Brian Foster]

XFS currently discards delalloc blocks within the target range of a zero
range request. Unaligned start and end offsets are zeroed through the
page cache and the internal, aligned blocks are converted to unwritten
extents.

If EOF is page aligned and covered by a delayed allocation extent. The
inode size is not updated until I/O completion. If a zero range request
discards a delalloc range that covers page aligned EOF as such, the
inode size update never occurs. For example:

$ rm -f /mnt/file
$ xfs_io -fc "pwrite 0 64k" -c "zero 60k 4k" /mnt/file
$ stat -c "%s" /mnt/file
65536
$ umount /mnt
$ mount <dev> /mnt
$ stat -c "%s" /mnt/file
61440

Update xfs_zero_file_space() to flush the range rather than discard
delalloc blocks to ensure that inode size updates occur appropriately.

Signed-off-by: Brian Foster <bfoster at redhat.com>
---

I suppose we could be more clever here and only flush the range in this
particular scenario, but I'm not sure if there's a major benefit there.
FWIW, this implicitly addresses the indlen==0 assert failures described
in the xfs_bmap_del_extent() rfc, but doesn't necessarily mean we
shouldn't fix that code IMO.

Brian

 fs/xfs/xfs_bmap_util.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
index d8b77b5..24d634d 100644
--- a/fs/xfs/xfs_bmap_util.c
+++ b/fs/xfs/xfs_bmap_util.c
@@ -1394,14 +1394,14 @@ xfs_zero_file_space(
 
 	if (start_boundary < end_boundary - 1) {
 		/*
-		 * punch out delayed allocation blocks and the page cache over
-		 * the conversion range
+		 * Writeback the range to ensure any inode size updates due to
+		 * appending writes make it to disk (otherwise we could just
+		 * punch out the delalloc blocks).
 		 */
-		xfs_ilock(ip, XFS_ILOCK_EXCL);
-		error = xfs_bmap_punch_delalloc_range(ip,
-				XFS_B_TO_FSBT(mp, start_boundary),
-				XFS_B_TO_FSB(mp, end_boundary - start_boundary));
-		xfs_iunlock(ip, XFS_ILOCK_EXCL);
+		error = filemap_write_and_wait_range(VFS_I(ip)->i_mapping,
+				start_boundary, end_boundary - 1);
+		if (error)
+			goto out;
 		truncate_pagecache_range(VFS_I(ip), start_boundary,
 					 end_boundary - 1);
 
-- 
1.8.3.1