Re: [PATCHv3 2/2] kvmtool: Restrict virtio queue number to 1 when vhost on

[Andre Przywara <andre.przywara@arm.com>]

Hi,

On 21/07/15 07:18, Fan Du wrote:
> vhost kernel driver does not support mutiple queue yet,
> Tweak queue number will fail with "--net mode=tap,vhost=1,mq=2"
> as below when lkvm trying to set ring kick fd for queue 2:
> 
> VHOST_SET_VRING_KICK failed: No buffer space available
> 
> Error on this scenario, and overide with the default one queue
> configuration.

I don't like the idea of overriding an explicitly given command line
parameter (mq=2).
So why do you provide mq=2 in the first place if you know that the
kernel does not support it?
I'd rather see the error message to be more descriptive in that case.
That would help the user to understand what's going on, also it would
still work should the kernel ever support multiple queues in the future.

Cheers,
Andre.

> 
> Signed-off-by: Fan Du <fan.du@intel.com>
> ---
>  virtio/net.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/virtio/net.c b/virtio/net.c
> index d343615..21a80f3 100644
> --- a/virtio/net.c
> +++ b/virtio/net.c
> @@ -730,6 +730,10 @@ static int set_net_param(struct kvm *kvm, struct virtio_net_params *p,
>  		p->mq = atoi(val);
>  	} else
>  		die("Unknown network parameter %s", param);
> +	if (p->vhost && p->mq > 1) {
> +		p->mq = 1;
> +		pr_err("vhost does not support mq yet, overide mq to 1.");
> +	}
>  
>  	return 0;
>  }
>