xfs: reclaim speculative preallocations for append only files

The XFS XFS_DIFLAG_APPEND maps to the VFS S_APPEND flag, which forbids
writes that don't append at the current EOF.

But the commit originally adding XFS_DIFLAG_APPEND support (commit
a23321e766d in xfs xfs-import repository) also checked it to skip
releasing speculative preallocations, which doesn't make any sense.

Another commit (dd9f438 in the xfs-import repository) later extended
that flag to also report these speculation preallocations which should
not exist in getbmap.

Remove these checks as nothing XFS_DIFLAG_APPEND implies that
preallocations beyond EOF should exist, but explicitly check for
XFS_DIFLAG_APPEND in xfs_file_release to bypass the algorithm that
discard preallocations on the first close as append only files aren't
expected to be written to only once.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>

Author: Christoph Hellwig

fs/xfs/xfs_bmap_util.c

@@ -331,8 +331,7 @@ xfs_getbmap(
 		}
 
 		if (xfs_get_extsz_hint(ip) ||
-		    (ip->i_diflags &
-		     (XFS_DIFLAG_PREALLOC | XFS_DIFLAG_APPEND)))
+		    (ip->i_diflags & XFS_DIFLAG_PREALLOC))
 			max_len = mp->m_super->s_maxbytes;
 		else
 			max_len = XFS_ISIZE(ip);
@@ -524,12 +523,11 @@ xfs_can_free_eofblocks(
 		return false;
 
 	/*
-	 * Only free real extents for inodes with persistent preallocations or
-	 * the append-only flag.
+	 * Do not free real extents in preallocated files unless the file has
+	 * delalloc blocks and we are forced to remove them.
 	 */
-	if (ip->i_diflags & (XFS_DIFLAG_PREALLOC | XFS_DIFLAG_APPEND))
-		if (ip->i_delayed_blks == 0)
-			return false;
+	if ((ip->i_diflags & XFS_DIFLAG_PREALLOC) && !ip->i_delayed_blks)
+		return false;
 
 	/*
 	 * Do not try to free post-EOF blocks if EOF is beyond the end of the

fs/xfs/xfs_file.c

@@ -1220,6 +1220,9 @@ xfs_file_release(
 	 * one file after another without going back to it while keeping the
 	 * preallocation for files that have recurring open/write/close cycles.
 	 *
+	 * This heuristic is skipped for inodes with the append-only flag as
+	 * that flag is rather pointless for inodes written only once.
+	 *
 	 * There is no point in freeing blocks here for open but unlinked files
 	 * as they will be taken care of by the inactivation path soon.
 	 *
@@ -1234,6 +1237,7 @@ xfs_file_release(
 	 */
 	if (inode->i_nlink &&
 	    (file->f_mode & FMODE_WRITE) &&
+	    !(ip->i_diflags & XFS_DIFLAG_APPEND) &&
 	    !xfs_iflags_test(ip, XFS_EOFBLOCKS_RELEASED) &&
 	    xfs_ilock_nowait(ip, XFS_IOLOCK_EXCL)) {
 		if (xfs_can_free_eofblocks(ip) &&

fs/xfs/xfs_icache.c

@@ -1159,7 +1159,7 @@ xfs_inode_free_eofblocks(
 	if (xfs_can_free_eofblocks(ip))
 		return xfs_free_eofblocks(ip);
 
-	/* inode could be preallocated or append-only */
+	/* inode could be preallocated */
 	trace_xfs_inode_free_eofblocks_invalid(ip);
 	xfs_inode_clear_eofblocks_tag(ip);
 	return 0;