NFS: Optimise away the close-to-open GETATTR when we have NFSv4 OPEN

NFSv4 should not need to perform an extra close-to-open GETATTR as part
of the process of looking up a regular file, since the OPEN call will
do that for us.
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

fs/nfs/dir.c

@@ -1012,13 +1012,25 @@ int nfs_lookup_verify_inode(struct inode *inode, unsigned int flags)
 
 	if (IS_AUTOMOUNT(inode))
 		return 0;
+
+	if (flags & LOOKUP_OPEN) {
+		switch (inode->i_mode & S_IFMT) {
+		case S_IFREG:
+			/* A NFSv4 OPEN will revalidate later */
+			if (server->caps & NFS_CAP_ATOMIC_OPEN)
+				goto out;
+			/* Fallthrough */
+		case S_IFDIR:
+			if (server->flags & NFS_MOUNT_NOCTO)
+				break;
+			/* NFS close-to-open cache consistency validation */
+			goto out_force;
+		}
+	}
+
 	/* VFS wants an on-the-wire revalidation */
 	if (flags & LOOKUP_REVAL)
 		goto out_force;
-	/* This is an open(2) */
-	if ((flags & LOOKUP_OPEN) && !(server->flags & NFS_MOUNT_NOCTO) &&
-	    (S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode)))
-		goto out_force;
 out:
 	return (inode->i_nlink == 0) ? -ENOENT : 0;
 out_force: