bpf, xdp: Implement LINK_UPDATE for BPF XDP link

	kfree(xdp_link);

}

static int bpf_xdp_link_update(struct bpf_link *link, struct bpf_prog *new_prog,

			       struct bpf_prog *old_prog)

{

	struct bpf_xdp_link *xdp_link = container_of(link, struct bpf_xdp_link, link);

	enum bpf_xdp_mode mode;

	bpf_op_t bpf_op;

	int err = 0;

	rtnl_lock();

	/* link might have been auto-released already, so fail */

	if (!xdp_link->dev) {

		err = -ENOLINK;

		goto out_unlock;

	}

	if (old_prog && link->prog != old_prog) {

		err = -EPERM;

		goto out_unlock;

	}

	old_prog = link->prog;

	if (old_prog == new_prog) {

		/* no-op, don't disturb drivers */

		bpf_prog_put(new_prog);

		goto out_unlock;

	}

	mode = dev_xdp_mode(xdp_link->flags);

	bpf_op = dev_xdp_bpf_op(xdp_link->dev, mode);

	err = dev_xdp_install(xdp_link->dev, mode, bpf_op, NULL,

			      xdp_link->flags, new_prog);

	if (err)

		goto out_unlock;

	old_prog = xchg(&link->prog, new_prog);

	bpf_prog_put(old_prog);

out_unlock:

	rtnl_unlock();

	return err;

}

static const struct bpf_link_ops bpf_xdp_link_lops = {

	.release = bpf_xdp_link_release,

	.dealloc = bpf_xdp_link_dealloc,

	.update_prog = bpf_xdp_link_update,

};

int bpf_xdp_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)