tun: setup xdp_rxq_info

Driver hook points for xdp_rxq_info:
 * reg  : tun_attach
 * unreg: __tun_detach

I've done some manual testing of this tun driver, but I would
appriciate good review and someone else running their use-case tests,
as I'm not 100% sure I understand the tfile->detached semantics.

V2: Removed the skb_array_cleanup() call from V1 by request from Jason Wang.

Cc: Jason Wang <jasowang@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Willem de Bruijn <willemb@google.com>
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Reviewed-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

drivers/net/tun.c

@@ -180,6 +180,7 @@ struct tun_file {
 	struct list_head next;
 	struct tun_struct *detached;
 	struct skb_array tx_array;
+	struct xdp_rxq_info xdp_rxq;
 };
 
 struct tun_flow_entry {
@@ -687,8 +688,10 @@ static void __tun_detach(struct tun_file *tfile, bool clean)
 			    tun->dev->reg_state == NETREG_REGISTERED)
 				unregister_netdevice(tun->dev);
 		}
-		if (tun)
+		if (tun) {
 			skb_array_cleanup(&tfile->tx_array);
+			xdp_rxq_info_unreg(&tfile->xdp_rxq);
+		}
 		sock_put(&tfile->sk);
 	}
 }
@@ -728,11 +731,13 @@ static void tun_detach_all(struct net_device *dev)
 		tun_napi_del(tun, tfile);
 		/* Drop read queue */
 		tun_queue_purge(tfile);
+		xdp_rxq_info_unreg(&tfile->xdp_rxq);
 		sock_put(&tfile->sk);
 	}
 	list_for_each_entry_safe(tfile, tmp, &tun->disabled, next) {
 		tun_enable_queue(tfile);
 		tun_queue_purge(tfile);
+		xdp_rxq_info_unreg(&tfile->xdp_rxq);
 		sock_put(&tfile->sk);
 	}
 	BUG_ON(tun->numdisabled != 0);
@@ -784,6 +789,22 @@ static int tun_attach(struct tun_struct *tun, struct file *file,
 
 	tfile->queue_index = tun->numqueues;
 	tfile->socket.sk->sk_shutdown &= ~RCV_SHUTDOWN;
+
+	if (tfile->detached) {
+		/* Re-attach detached tfile, updating XDP queue_index */
+		WARN_ON(!xdp_rxq_info_is_reg(&tfile->xdp_rxq));
+
+		if (tfile->xdp_rxq.queue_index    != tfile->queue_index)
+			tfile->xdp_rxq.queue_index = tfile->queue_index;
+	} else {
+		/* Setup XDP RX-queue info, for new tfile getting attached */
+		err = xdp_rxq_info_reg(&tfile->xdp_rxq,
+				       tun->dev, tfile->queue_index);
+		if (err < 0)
+			goto out;
+		err = 0;
+	}
+
 	rcu_assign_pointer(tfile->tun, tun);
 	rcu_assign_pointer(tun->tfiles[tun->numqueues], tfile);
 	tun->numqueues++;
@@ -1508,6 +1529,7 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
 		xdp.data = buf + pad;
 		xdp_set_data_meta_invalid(&xdp);
 		xdp.data_end = xdp.data + len;
+		xdp.rxq = &tfile->xdp_rxq;
 		orig_data = xdp.data;
 		act = bpf_prog_run_xdp(xdp_prog, &xdp);