netdev - Re: [PATCH net-next 2/2] virtio_net: Implement XDP_FLAGS_NO

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Message-Id: <74a67121-99f6-4321-a54d-888ddf14ae2f@www.fastmail.com>
Date:   Mon, 11 Jan 2021 12:24:11 +1100
From:   "Charlie Somerville" <charlie@...rlie.bz>
To:     "Shay Agroskin" <shayagr@...zon.com>
Cc:     davem@...emloft.net, kuba@...nel.org, mst@...hat.com,
        jasowang@...hat.com, netdev@...r.kernel.org
Subject: Re: [PATCH net-next 2/2] virtio_net: Implement XDP_FLAGS_NO_TX support

On Mon, Jan 11, 2021, at 04:31, Shay Agroskin wrote:

> Is this addition needed ? Seems like we don't set VIRTIO_XDP_TX 
> bit in case of virtnet_xdp_xmit() failure, so the surrounding 'if' 
> won't be taken.

Good catch, it looks like you're right. I'm happy to remove that extra branch although I would like to add a comment explaining that assumption:

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index ed08998765e0..3ae7cd2f1e72 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -1472,8 +1472,10 @@ static int virtnet_poll(struct napi_struct *napi, int budget)
                xdp_do_flush();

        if (xdp_xmit & VIRTIO_XDP_TX) {
+               /* VIRTIO_XDP_TX only set on successful virtnet_xdp_xmit,
+                * implies sq != NULL */
                sq = virtnet_xdp_sq(vi);
-               if (sq && virtqueue_kick_prepare(sq->vq) && virtqueue_notify(sq->vq)) {
+               if (virtqueue_kick_prepare(sq->vq) && virtqueue_notify(sq->vq)) {
                        u64_stats_update_begin(&sq->stats.syncp);
                        sq->stats.kicks++;
                        u64_stats_update_end(&sq->stats.syncp);