Driver hook points for xdp_rxq_info:
  * init+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.

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 <redacted>
---
  drivers/net/tun.c |   25 ++++++++++++++++++++++++-
  1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index e367d6310353..f1df08c2c541 100644
--- a/drivers/net/tun.c
+++ b/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 +731,15 @@ static void tun_detach_all(struct net_device *dev)
  		tun_napi_del(tun, tfile);
  		/* Drop read queue */
  		tun_queue_purge(tfile);
+		skb_array_cleanup(&tfile->tx_array);

+		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);
+		skb_array_cleanup(&tfile->tx_array);
+		xdp_rxq_info_unreg(&tfile->xdp_rxq);
  		sock_put(&tfile->sk);
  	}
  	BUG_ON(tun->numdisabled != 0);

@@ -784,6 +791,21 @@ 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 */
+		xdp_rxq_info_init(&tfile->xdp_rxq);
+		tfile->xdp_rxq.dev = tun->dev;
+		tfile->xdp_rxq.queue_index = tfile->queue_index;
+		xdp_rxq_info_reg(&tfile->xdp_rxq);
+	}
+
  	rcu_assign_pointer(tfile->tun, tun);
  	rcu_assign_pointer(tun->tfiles[tun->numqueues], tfile);
  	tun->numqueues++;

@@ -1508,6 +1530,7 @@ 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);