fs: handle delegated timestamps in setattr_copy_mgtime

An update to the inode ctime typically requires the latest clock
value possible. The exception to this rule is when there is a nfsd write
delegation and the server is proxying timestamps from the client.

When nfsd gets a CB_GETATTR response, update the timestamp value in the
inode to the values that the client is tracking. The client doesn't send
a ctime value (since that's always determined by the exported
filesystem), but it can send a mtime value. In the case where it does,
update the ctime to a value commensurate with that instead of the
current time.

If ATTR_DELEG is set, then use ia_ctime value instead of setting the
timestamp to the current time.

With the addition of delegated timestamps, the server may receive a
request to update only the atime, which doesn't involve a ctime update.
Trust the ATTR_CTIME flag in the update and only update the ctime when
it's set.

Tested-by: Randy Dunlap <rdunlap@infradead.org> # documentation bits
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Link: https://lore.kernel.org/r/20241002-mgtime-v10-5-d1c4717f5284@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

1 files changed, 19 insertions, 10 deletions

diff --git a/fs/attr.c b/fs/attr.c
index 0309c2bd8afa..9caf63d20d03 100644
--- a/fs/attr.c
+++ b/fs/attr.c
@@ -286,16 +286,21 @@ static void setattr_copy_mgtime(struct inode *inode, const struct iattr *attr)
 	unsigned int ia_valid = attr->ia_valid;
 	struct timespec64 now;
 
-	/*
-	 * If the ctime isn't being updated then nothing else should be
-	 * either.
-	 */
-	if (!(ia_valid & ATTR_CTIME)) {
-		WARN_ON_ONCE(ia_valid & (ATTR_ATIME|ATTR_MTIME));
-		return;
+	if (ia_valid & ATTR_CTIME) {
+		/*
+		 * In the case of an update for a write delegation, we must respect
+		 * the value in ia_ctime and not use the current time.
+		 */
+		if (ia_valid & ATTR_DELEG)
+			now = inode_set_ctime_deleg(inode, attr->ia_ctime);
+		else
+			now = inode_set_ctime_current(inode);
+	} else {
+		/* If ATTR_CTIME isn't set, then ATTR_MTIME shouldn't be either. */
+		WARN_ON_ONCE(ia_valid & ATTR_MTIME);
+		now = current_time(inode);
 	}
 
-	now = inode_set_ctime_current(inode);
 	if (ia_valid & ATTR_ATIME_SET)
 		inode_set_atime_to_ts(inode, attr->ia_atime);
 	else if (ia_valid & ATTR_ATIME)
@@ -354,8 +359,12 @@ void setattr_copy(struct mnt_idmap *idmap, struct inode *inode,
 		inode_set_atime_to_ts(inode, attr->ia_atime);
 	if (ia_valid & ATTR_MTIME)
 		inode_set_mtime_to_ts(inode, attr->ia_mtime);
-	if (ia_valid & ATTR_CTIME)
-		inode_set_ctime_to_ts(inode, attr->ia_ctime);
+	if (ia_valid & ATTR_CTIME) {
+		if (ia_valid & ATTR_DELEG)
+			inode_set_ctime_deleg(inode, attr->ia_ctime);
+		else
+			inode_set_ctime_to_ts(inode, attr->ia_ctime);
+	}
 }
 EXPORT_SYMBOL(setattr_copy);