rem: struct vnode *vnode = descriptor->vnode;
add: struct vnode *vnode = descriptor->u.vnode;
context: file_free_fd(struct file_descriptor *descriptor){	struct vnode *vnode = descriptor->vnode;	if (vnode != NULL) {		FS_CALL(vnode, free_cookie)(vnode->mount->cookie, vnode->private_node, descriptor->cookie);		put_vnode(vnode);	}}