xfs: fix behaviour of XFS_IOC_FSSETXATTR on directories

Currently, the ioctl handling code for XFS_IOC_FSSETXATTR treats all
targets as regular files: it refuses to change the extent size if
extents are allocated. This is wrong for directories, as there the
extent size is only used as a default for children.

The patch fixes this issue and improves validation of flag
combinations:

- only disallow extent size changes after extents have been allocated
  for regular files
- only allow XFS_XFLAG_EXTSIZE for regular files
- only allow XFS_XFLAG_EXTSZINHERIT for directories
- automatically clear the flags if the extent size is zero

Thanks to Dave Chinner for guidance on the proper fix for this issue.

[dchinner: ported changes onto cleanup series. Makes changes clear
	   and obvious.]
[dchinner: added comments documenting validity checking rules.]
Signed-off-by: Iustin Pop <iustin@k1024.org>
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

fs/xfs/xfs_ioctl.c

@@ -1098,6 +1098,20 @@ xfs_ioctl_setattr_get_trans(
 	return ERR_PTR(error);
 }
 
+/*
+ * extent size hint validation is somewhat cumbersome. Rules are:
+ *
+ * 1. extent size hint is only valid for directories and regular files
+ * 2. XFS_XFLAG_EXTSIZE is only valid for regular files
+ * 3. XFS_XFLAG_EXTSZINHERIT is only valid for directories.
+ * 4. can only be changed on regular files if no extents are allocated
+ * 5. can be changed on directories at any time
+ * 6. extsize hint of 0 turns off hints, clears inode flags.
+ * 7. Extent size must be a multiple of the appropriate block size.
+ * 8. for non-realtime files, the extent size hint must be limited
+ *    to half the AG size to avoid alignment extending the extent beyond the
+ *    limits of the AG.
+ */
 int
 xfs_ioctl_setattr_check_extsize(
 	struct xfs_inode	*ip,
@@ -1105,20 +1119,17 @@ xfs_ioctl_setattr_check_extsize(
 {
 	struct xfs_mount	*mp = ip->i_mount;
 
-	/* Can't change extent size if any extents are allocated. */
-	if (ip->i_d.di_nextents &&
+	if ((fa->fsx_xflags & XFS_XFLAG_EXTSIZE) && !S_ISREG(ip->i_d.di_mode))
+		return -EINVAL;
+
+	if ((fa->fsx_xflags & XFS_XFLAG_EXTSZINHERIT) &&
+	    !S_ISDIR(ip->i_d.di_mode))
+		return -EINVAL;
+
+	if (S_ISREG(ip->i_d.di_mode) && ip->i_d.di_nextents &&
 	    ((ip->i_d.di_extsize << mp->m_sb.sb_blocklog) != fa->fsx_extsize))
 		return -EINVAL;
 
-	/*
-	 * Extent size must be a multiple of the appropriate block size, if set
-	 * at all. It must also be smaller than the maximum extent size
-	 * supported by the filesystem.
-	 *
-	 * Also, for non-realtime files, limit the extent size hint to half the
-	 * size of the AGs in the filesystem so alignment doesn't result in
-	 * extents larger than an AG.
-	 */
 	if (fa->fsx_extsize != 0) {
 		xfs_extlen_t    size;
 		xfs_fsblock_t   extsize_fsb;
@@ -1138,7 +1149,9 @@ xfs_ioctl_setattr_check_extsize(
 
 		if (fa->fsx_extsize % size)
 			return -EINVAL;
-	}
+	} else
+		fa->fsx_xflags &= ~(XFS_XFLAG_EXTSIZE | XFS_XFLAG_EXTSZINHERIT);
+
 	return 0;
 }
 
@@ -1169,8 +1182,6 @@ xfs_ioctl_setattr_check_projid(
 	return 0;
 }
 
-
-
 STATIC int
 xfs_ioctl_setattr(
 	xfs_inode_t		*ip,