Re: [PATCH net-next 1/3] virtio_net: set multicast filter list to host

[Vlad Yasevich <vyasevich@gmail.com>]

On 12/09/2013 07:16 PM, Stephen Hemminger wrote:
> The virtio_net driver never sends the multicast address list to
> the host. This is because send command takes a pointer to scatter list
> to send but only inserts that one entry into the outgoing scatter list.
> 
> This bug has been there since:
> commit f565a7c259d71cc186753653d978c646d2354b36
> Author: Alex Williamson <alex.williamson@hp.com>
> Date:   Wed Feb 4 09:02:45 2009 +0000
> 
>     virtio_net: Add a MAC filter table
> 
> Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
> 
> --- a/drivers/net/virtio_net.c	2013-12-09 16:12:03.897891975 -0800
> +++ b/drivers/net/virtio_net.c	2013-12-09 16:12:36.353164803 -0800
> @@ -893,7 +893,7 @@ static bool virtnet_send_command(struct
>  	sg_init_one(&hdr, &ctrl, sizeof(ctrl));
>  	sgs[out_num++] = &hdr;
>  
> -	if (out)
> +	for (; out; out = sg_next(out))
>  		sgs[out_num++] = out;
>  	if (in)
>  		sgs[out_num + in_num++] = in;

Hi Stephen

Amos Kong pointed out in your original thread, that this doesn't seem to
be needed and is working for him.  I just checked my VMs and it's
working for me as well without this.  Have you seen it fail?

Amos did a very good job explaining, but it basically boils down to the
fact that virtqueue_add_sgs() treats each entry of the sgs array
as a list and walks each list using exactly the same code as this patch
proposes :).  virtqueue_add() also walks each array element as a list.

-vlad