Re: [PATCH 2/3] vdpa: Add dummy receive callbacks

[Jason Wang]

On Fri, Nov 19, 2021 at 6:20 PM Eugenio Pérez <eperezma@redhat.com> wrote:
>
> Qemu falls back on userland handlers even if vhost-user and vhost-vdpa
> cases. These assumes a tap device can handle the packets.
>
> If a vdpa device fail to start, it can trigger a sigsegv because of
> that. Add dummy receivers that return no progress so it can keep
> running.
>
> Fixes: 1e0a84ea49 ("vhost-vdpa: introduce vhost-vdpa net client")
> Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> ---
>  net/vhost-vdpa.c | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
>
> diff --git a/net/vhost-vdpa.c b/net/vhost-vdpa.c
> index 2e3c22a8c7..4c75b78304 100644
> --- a/net/vhost-vdpa.c
> +++ b/net/vhost-vdpa.c
> @@ -170,9 +170,25 @@ static bool vhost_vdpa_check_peer_type(NetClientState 
> *nc, ObjectClass *oc,
>      return true;
>  }
>
> +/** Dummy receive in case qemu falls back to userland tap networking */
> +static ssize_t vhost_vdpa_receive_iov(NetClientState *nc,
> +                                      const struct iovec *iov, int iovcnt)
> +{
> +    return 0;
> +}
> +
> +/** Dummy receive in case qemu falls back to userland tap networking */
> +static ssize_t vhost_vdpa_receive_raw(NetClientState *nc, const uint8_t *buf,
> +                                      size_t size)
> +{
> +    return 0;
> +}

It looks to me the .receive_raw is not need, in nc_sendv_compat() we had:

=>  if (flags & QEMU_NET_PACKET_FLAG_RAW && nc->info->receive_raw) {
        ret = nc->info->receive_raw(nc, buffer, offset);
    } else {
        ret = nc->info->receive(nc, buffer, offset);
    }

Thanks

> +
>  static NetClientInfo net_vhost_vdpa_info = {
>          .type = NET_CLIENT_DRIVER_VHOST_VDPA,
>          .size = sizeof(VhostVDPAState),
> +        .receive_iov = vhost_vdpa_receive_iov,
> +        .receive_raw = vhost_vdpa_receive_raw,
>          .cleanup = vhost_vdpa_cleanup,
>          .has_vnet_hdr = vhost_vdpa_has_vnet_hdr,
>          .has_ufo = vhost_vdpa_has_ufo,
> --
> 2.27.0
>