[XFS] Update c/mtime correctly on truncates

XFS changes the c/mtime of an inode when truncating it to the same size.
The c/mtime is only supposed to change if the size is changed. Not to be
confused with ftruncate, where the c/mtime is supposed to be changed even
if the size is not changed.

The Linux VFS encodes this semantic difference in the flags it sends down
to ->setattr, which XFS currently ignores. We need to make XFS pay
attention to the VFS flags and hence Do The Right Thing.

SGI-PV: 977547
SGI-Modid: xfs-linux-melb:xfs-kern:30536a

Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>

1 files changed, 9 insertions, 4 deletions

diff --git a/fs/xfs/xfs_vnodeops.c b/fs/xfs/xfs_vnodeops.c
index 811ee874d868..b77dede91b71 100644
--- a/fs/xfs/xfs_vnodeops.c
+++ b/fs/xfs/xfs_vnodeops.c
@@ -633,6 +633,15 @@ xfs_setattr(
          * Truncate file.  Must have write permission and not be a directory.
          */
         if (mask & XFS_AT_SIZE) {
+                /*
+                 * Only change the c/mtime if we are changing the size
+                 * or we are explicitly asked to change it. This handles
+                 * the semantic difference between truncate() and ftruncate()
+                 * as implemented in the VFS.
+                 */
+                if (vap->va_size != ip->i_size || (mask & XFS_AT_CTIME))
+                        timeflags |= XFS_ICHGTIME_MOD | XFS_ICHGTIME_CHG;
+
                 if (vap->va_size > ip->i_size) {
                         xfs_igrow_finish(tp, ip, vap->va_size,
                             !(flags & ATTR_DMI));
@@ -661,10 +670,6 @@ xfs_setattr(
                          */
                         xfs_iflags_set(ip, XFS_ITRUNCATED);
                 }
-                /*
-                 * Have to do this even if the file's size doesn't change.
-                 */
-                timeflags |= XFS_ICHGTIME_MOD | XFS_ICHGTIME_CHG;
         }
 
         /*