fuse: optmize missing FUSE_LINK support

If filesystem doesn't support FUSE_LINK (i.e. returns -ENOSYS), then
remember this and next time return immediately, without incurring the
overhead of a round trip to the server.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

Author: Miklos Szeredi

fs/fuse/dir.c

@@ -1123,6 +1123,9 @@ static int fuse_link(struct dentry *entry, struct inode *newdir,
 	struct fuse_mount *fm = get_fuse_mount(inode);
 	FUSE_ARGS(args);
 
+	if (fm->fc->no_link)
+		goto out;
+
 	memset(&inarg, 0, sizeof(inarg));
 	inarg.oldnodeid = get_node_id(inode);
 	args.opcode = FUSE_LINK;
@@ -1138,7 +1141,11 @@ static int fuse_link(struct dentry *entry, struct inode *newdir,
 		fuse_invalidate_attr(inode);
 
 	if (err == -ENOSYS)
-		err = -EPERM;
+		fm->fc->no_link = 1;
+out:
+	if (fm->fc->no_link)
+		return -EPERM;
+
 	return err;
 }
 

fs/fuse/fuse_i.h

@@ -870,6 +870,9 @@ struct fuse_conn {
 	/* Use pages instead of pointer for kernel I/O */
 	unsigned int use_pages_for_kvec_io:1;
 
+	/* Is link not implemented by fs? */
+	unsigned int no_link:1;
+
 	/* Use io_uring for communication */
 	unsigned int io_uring;