Re: [Qemu-devel] [PATCH] tap: set IFF_ONE_QUEUE per default

[Christian Borntraeger]

On 15/02/13 09:27, Peter Lieven wrote:
> historically the kernel queues packets two times. once
> at the device and second in qdisc. this is believed to cause
> interface stalls if one of these queues overruns.
> 
> setting IFF_ONE_QUEUE is the default in kernels >= 3.8. the
> flag is ignored since then. see kernel commit
> 5d097109257c03a71845729f8db6b5770c4bbedc
> 
> Signed-off-by: Peter Lieven <address@hidden>
> ---
>  net/tap-linux.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/tap-linux.c b/net/tap-linux.c
> index a953189..2759b78 100644
> --- a/net/tap-linux.c
> +++ b/net/tap-linux.c
> @@ -49,7 +49,7 @@ int tap_open(char *ifname, int ifname_size, int *vnet_hdr,
>          return -1;
>      }
>      memset(&ifr, 0, sizeof(ifr));
> -    ifr.ifr_flags = IFF_TAP | IFF_NO_PI;
> +    ifr.ifr_flags = IFF_TAP | IFF_NO_PI | IFF_ONE_QUEUE;
> 
>      if (*vnet_hdr) {
>          unsigned int features;

Wouldn't that break macvtap?

there is

        case TUNSETIFF:
                /* ignore the name, just look at flags */
                if (get_user(u, &ifr->ifr_flags))
                        return -EFAULT;

                ret = 0;
                if ((u & ~IFF_VNET_HDR) != (IFF_NO_PI | IFF_TAP))
                        ret = -EINVAL;


in drivers/net/macvtap.c