linux-kernel - Re: [PATCH net] vsock/virtio: postpone packet delivery to monitoring devices

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Date:   Tue, 21 Apr 2020 16:42:46 +0100
From:   Stefan Hajnoczi <stefanha@...il.com>
To:     Stefano Garzarella <sgarzare@...hat.com>
Cc:     davem@...emloft.net, Gerard Garcia <ggarcia@...a.uab.cat>,
        kvm@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Jakub Kicinski <kuba@...nel.org>
Subject: Re: [PATCH net] vsock/virtio: postpone packet delivery to monitoring
 devices

On Tue, Apr 21, 2020 at 11:25:27AM +0200, Stefano Garzarella wrote:
> We delivering packets to monitoring devices, before to check if
> the virtqueue has enough space.

"We [are] delivering packets" and "before to check" -> "before
checking".  Perhaps it can be rewritten as:

  Packets are delivered to monitoring devices before checking if the
  virtqueue has enough space.

> 
> If the virtqueue is full, the transmitting packet is queued up
> and it will be sent in the next iteration. This causes the same
> packet to be delivered multiple times to monitoring devices.
> 
> This patch fixes this issue, postponing the packet delivery
> to monitoring devices, only when it is properly queued in the

s/,//

> virqueue.

s/virqueue/virtqueue/

> @@ -137,6 +135,11 @@ virtio_transport_send_pkt_work(struct work_struct *work)
>  			break;
>  		}
>  
> +		/* Deliver to monitoring devices all correctly transmitted
> +		 * packets.
> +		 */
> +		virtio_transport_deliver_tap_pkt(pkt);
> +

The device may see the tx packet and therefore receive a reply to it
before we can call virtio_transport_deliver_tap_pkt().  Does this mean
that replies can now appear in the packet capture before the transmitted
packet?

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