NFS: Allow applications to speed up readdir+statx() using AT_STATX_DONT_SYNC

If the application uses the AT_STATX_DONT_SYNC flag after doing readdir(),
then we should still mark the parent inode as seeing a readdirplus hit.
That ensures that we continue to use readdirplus in the 'ls -l' type
of workflow to do fast lookups of the dentries.
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

fs/nfs/inode.c

@@ -794,8 +794,10 @@ int nfs_getattr(const struct path *path, struct kstat *stat,
 
 	trace_nfs_getattr_enter(inode);
 
-	if ((query_flags & AT_STATX_DONT_SYNC) && !force_sync)
+	if ((query_flags & AT_STATX_DONT_SYNC) && !force_sync) {
+		nfs_readdirplus_parent_cache_hit(path->dentry);
 		goto out_no_update;
+	}
 
 	/* Flush out writes to the server in order to update c/mtime.  */
 	if ((request_mask & (STATX_CTIME|STATX_MTIME)) &&