vn_open_vnode
error = vn_open_vnode(vp, flags, td->td_ucred, td, NULL);
error = vn_open_vnode(vp, flags, td->td_ucred, td, fp);
error = vn_open_vnode(vp, fmode, cred, curthread, fp);
int vn_open_vnode(struct vnode *vp, int fmode, struct ucred *cred,