Re: [PATCH RFC 3/4] vsock/virtio: change the maximum packet size allowed

[Stefan Hajnoczi <stefanha@gmail.com>]

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On Thu, Apr 04, 2019 at 12:58:37PM +0200, Stefano Garzarella wrote:
> Since now we are able to split packets, we can avoid limiting
> their sizes to VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE.
> Instead, we can use VIRTIO_VSOCK_MAX_PKT_BUF_SIZE as the max
> packet size.
> 
> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
> ---
>  net/vmw_vsock/virtio_transport_common.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
> index f32301d823f5..822e5d07a4ec 100644
> --- a/net/vmw_vsock/virtio_transport_common.c
> +++ b/net/vmw_vsock/virtio_transport_common.c
> @@ -167,8 +167,8 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
>  	vvs = vsk->trans;
>  
>  	/* we can send less than pkt_len bytes */
> -	if (pkt_len > VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE)
> -		pkt_len = VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE;
> +	if (pkt_len > VIRTIO_VSOCK_MAX_PKT_BUF_SIZE)
> +		pkt_len = VIRTIO_VSOCK_MAX_PKT_BUF_SIZE;

The next line limits pkt_len based on available credits:

  /* virtio_transport_get_credit might return less than pkt_len credit */
  pkt_len = virtio_transport_get_credit(vvs, pkt_len);

I think drivers/vhost/vsock.c:vhost_transport_do_send_pkt() now works
correctly even with pkt_len > VIRTIO_VSOCK_MAX_PKT_BUF_SIZE.

The other ->send_pkt() callback is
net/vmw_vsock/virtio_transport.c:virtio_transport_send_pkt_work() and it
can already send any size packet.

Do you remember why VIRTIO_VSOCK_MAX_PKT_BUF_SIZE still needs to be the
limit?  I'm wondering if we can get rid of it now and just limit packets
to the available credits.

Stefan

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