[PATCH v8 5/5] xfs: switch to multigrain timestamps

[Jeff Layton <jlayton@kernel.org>]

Enable multigrain timestamps, which should ensure that there is an
apparent change to the internal ctime value whenever a file has been
written after being actively observed via getattr.

Anytime the mtime changes, the ctime must also change, and those are the
only two options for xfs_trans_ichgtime. Have that function
unconditionally bump the ctime, and ASSERT that XFS_ICHGTIME_CHG is
always set.

In getattr, truncate the mtime and ctime at the number of nanoseconds
per jiffy, which should ensure that ordering is preserved. Use the fine
grained ctime to fake up a STATX_CHANGE_COOKIE if one was requested.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
 fs/xfs/libxfs/xfs_trans_inode.c |  6 +++---
 fs/xfs/xfs_iops.c               | 26 +++++++++++++++++++-------
 fs/xfs/xfs_super.c              |  2 +-
 3 files changed, 23 insertions(+), 11 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_trans_inode.c b/fs/xfs/libxfs/xfs_trans_inode.c
index 6b2296ff248a..ad22656376d3 100644
--- a/fs/xfs/libxfs/xfs_trans_inode.c
+++ b/fs/xfs/libxfs/xfs_trans_inode.c
@@ -62,12 +62,12 @@ xfs_trans_ichgtime(
 	ASSERT(tp);
 	ASSERT(xfs_isilocked(ip, XFS_ILOCK_EXCL));
 
-	tv = current_time(inode);
+	/* If the mtime changes, then ctime must also change */
+	ASSERT(flags & XFS_ICHGTIME_CHG);
 
+	tv = inode_set_ctime_current(inode);
 	if (flags & XFS_ICHGTIME_MOD)
 		inode->i_mtime = tv;
-	if (flags & XFS_ICHGTIME_CHG)
-		inode_set_ctime_to_ts(inode, tv);
 	if (flags & XFS_ICHGTIME_CREATE)
 		ip->i_crtime = tv;
 }
diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
index 1c1e6171209d..af4a54756113 100644
--- a/fs/xfs/xfs_iops.c
+++ b/fs/xfs/xfs_iops.c
@@ -559,6 +559,7 @@ xfs_vn_getattr(
 	struct xfs_mount	*mp = ip->i_mount;
 	vfsuid_t		vfsuid = i_uid_into_vfsuid(idmap, inode);
 	vfsgid_t		vfsgid = i_gid_into_vfsgid(idmap, inode);
+	struct timespec64	ctime;
 
 	trace_xfs_getattr(ip);
 
@@ -573,8 +574,23 @@ xfs_vn_getattr(
 	stat->gid = vfsgid_into_kgid(vfsgid);
 	stat->ino = ip->i_ino;
 	stat->atime = inode->i_atime;
-	stat->mtime = inode->i_mtime;
-	stat->ctime = inode_get_ctime(inode);
+	stat->mtime = timestamp_truncate_to_gran(inode->i_mtime, NSEC_PER_SEC/HZ);
+
+	/*
+	 * Don't bother flagging the inode for a fine-grained update unless
+	 * STATX_CHANGE_COOKIE is set, in which case, use the fine-grained
+	 * value to fake up a change_cookie.
+	 */
+	if (request_mask & STATX_CHANGE_COOKIE) {
+		ctime = inode_query_ctime(inode);
+		stat->change_cookie = time_to_chattr(&ctime);
+		stat->result_mask |= STATX_CHANGE_COOKIE;
+	} else {
+		ctime = inode_get_ctime(inode);
+	}
+
+	stat->ctime = timestamp_truncate_to_gran(ctime, NSEC_PER_SEC/HZ);
+
 	stat->blocks = XFS_FSB_TO_BB(mp, ip->i_nblocks + ip->i_delayed_blks);
 
 	if (xfs_has_v3inodes(mp)) {
@@ -914,12 +930,8 @@ xfs_setattr_size(
 	 * these flags set.  For all other operations the VFS set these flags
 	 * explicitly if it wants a timestamp update.
 	 */
-	if (newsize != oldsize &&
-	    !(iattr->ia_valid & (ATTR_CTIME | ATTR_MTIME))) {
-		iattr->ia_ctime = iattr->ia_mtime =
-			current_time(inode);
+	if (newsize != oldsize)
 		iattr->ia_valid |= ATTR_CTIME | ATTR_MTIME;
-	}
 
 	/*
 	 * The first thing we do is set the size to new_size permanently on
diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index b5c202f5d96c..1f77014c6e1a 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -2065,7 +2065,7 @@ static struct file_system_type xfs_fs_type = {
 	.init_fs_context	= xfs_init_fs_context,
 	.parameters		= xfs_fs_parameters,
 	.kill_sb		= xfs_kill_sb,
-	.fs_flags		= FS_REQUIRES_DEV | FS_ALLOW_IDMAP,
+	.fs_flags		= FS_REQUIRES_DEV | FS_ALLOW_IDMAP | FS_MGTIME,
 };
 MODULE_ALIAS_FS("xfs");
 

-- 
2.41.0