int xfrm_alloc_spi(struct xfrm_state *x, u32 low, u32 high)
{
	struct net *net = xs_net(x);
	unsigned int h;
	struct xfrm_state *x0;
	int err = -ENOENT;
	__be32 minspi = htonl(low);
	__be32 maxspi = htonl(high);
	u32 mark = x->mark.v & x->mark.m;

	spin_lock_bh(&x->lock);
	if (x->km.state == XFRM_STATE_DEAD)
		goto unlock;

	err = 0;
	if (x->id.spi)
		goto unlock;

	err = -ENOENT;

	if (minspi == maxspi) {
		x0 = xfrm_state_lookup(net, mark, &x->id.daddr, minspi, x->id.proto, x->props.family);
		if (x0) {
			xfrm_state_put(x0);
			goto unlock;
		}
		x->id.spi = minspi;
	} else {
		u32 spi = 0;
		for (h = 0; h < high-low+1; h++) {
			spi = low + prandom_u32()%(high-low+1);
			x0 = xfrm_state_lookup(net, mark, &x->id.daddr, htonl(spi), x->id.proto, x->props.family);
			if (x0 == NULL) {
				x->id.spi = htonl(spi);
				break;
			}
			xfrm_state_put(x0);
		}
	}
	if (x->id.spi) {
		spin_lock_bh(&net->xfrm.xfrm_state_lock);
		h = xfrm_spi_hash(net, &x->id.daddr, x->id.spi, x->id.proto, x->props.family);
		hlist_add_head_rcu(&x->byspi, net->xfrm.state_byspi + h);
		spin_unlock_bh(&net->xfrm.xfrm_state_lock);

		err = 0;
	}

unlock:
	spin_unlock_bh(&x->lock);

	return err;
}
Unknown