Re: [PATCH] virtio-net: Add check for mac address while peer is vdpa

["Michael S. Tsirkin" <mst@redhat.com>]

> [PATCH] virtio-net: Add check for mac address while peer is vdpa
please do keep numbering patch versions.


On Wed, Feb 24, 2021 at 03:33:33PM +0800, Cindy Lu wrote:
> Sometime vdpa get an all zero mac address from the hardware, this will cause the
> traffic down, So we add the check for in part.if we get an zero mac address we will
> use the default/cmdline mac address instead

How does this differ from v4 of same patch?

Lots of typos above. I guess I can just rewrite the whole log ...

> 
> Signed-off-by: Cindy Lu <lulu@redhat.com>
> ---
>  hw/net/virtio-net.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> index 9179013ac4..f1648fc47d 100644
> --- a/hw/net/virtio-net.c
> +++ b/hw/net/virtio-net.c
> @@ -126,6 +126,7 @@ static void virtio_net_get_config(VirtIODevice *vdev, uint8_t *config)
>      VirtIONet *n = VIRTIO_NET(vdev);
>      struct virtio_net_config netcfg;
>      NetClientState *nc = qemu_get_queue(n->nic);
> +    static const MACAddr zero = { .a = { 0, 0, 0, 0, 0, 0 } };
>  
>      int ret = 0;
>      memset(&netcfg, 0 , sizeof(struct virtio_net_config));
> @@ -151,7 +152,11 @@ static void virtio_net_get_config(VirtIODevice *vdev, uint8_t *config)
>          ret = vhost_net_get_config(get_vhost_net(nc->peer), (uint8_t *)&netcfg,
>                                     n->config_size);
>          if (ret != -1) {
> -            memcpy(config, &netcfg, n->config_size);

Below needs a huge code comment explaining what is going on.

E.g.  if we get a valid mac from peer, use it.

If we get 0 instead
then we don't know the peer mac but since the
mac is 0 and that is not a legal value,
try to proceed assume something else (management, hardware) sets up the mac
correctly and consistently with the qemu configuration.


> +            if (memcmp(&netcfg.mac, &zero, sizeof(zero)) != 0) {

!= 0 is not necessary

> +                memcpy(config, &netcfg, n->config_size);

> +        } else {
> +                error_report("Get an all zero mac address from hardware");

So why are you skipping the copying of the whole config space? Why not
just skip the mac? Seems quite risky e.g. looks like it will break
things like reporting the link status, right?

> +            }
>          }
>      }
>  }
> -- 
> 2.21.3