Re: [Qemu-devel] [PATCH] libvhost-user: Start VQs on SET_VRING_CALL

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

On Thu, Jan 12, 2017 at 05:14:07PM -0800, Felipe Franciosi wrote:
> Currently, VQs are started as soon as a SET_VRING_KICK is received. That
> is too early in the VQ setup process, as the backend might not yet have
> a callfd to notify in case it received a kick and fully processed the
> request/command. This patch only starts a VQ when a SET_VRING_CALL is
> received.
> 
> Signed-off-by: Felipe Franciosi <felipe@nutanix.com>

Doesn't look right to me.
It should happen when the fd supplies becomes readable.

> ---
>  contrib/libvhost-user/libvhost-user.c | 26 +++++++++++++-------------
>  1 file changed, 13 insertions(+), 13 deletions(-)
> 
> diff --git a/contrib/libvhost-user/libvhost-user.c b/contrib/libvhost-user/libvhost-user.c
> index af4faad..a46ef90 100644
> --- a/contrib/libvhost-user/libvhost-user.c
> +++ b/contrib/libvhost-user/libvhost-user.c
> @@ -607,19 +607,6 @@ vu_set_vring_kick_exec(VuDev *dev, VhostUserMsg *vmsg)
>          DPRINT("Got kick_fd: %d for vq: %d\n", vmsg->fds[0], index);
>      }
>  
> -    dev->vq[index].started = true;
> -    if (dev->iface->queue_set_started) {
> -        dev->iface->queue_set_started(dev, index, true);
> -    }
> -
> -    if (dev->vq[index].kick_fd != -1 && dev->vq[index].handler) {
> -        dev->set_watch(dev, dev->vq[index].kick_fd, VU_WATCH_IN,
> -                       vu_kick_cb, (void *)(long)index);
> -
> -        DPRINT("Waiting for kicks on fd: %d for vq: %d\n",
> -               dev->vq[index].kick_fd, index);
> -    }
> -
>      return false;
>  }
>  
> @@ -661,6 +648,19 @@ vu_set_vring_call_exec(VuDev *dev, VhostUserMsg *vmsg)
>  
>      DPRINT("Got call_fd: %d for vq: %d\n", vmsg->fds[0], index);
>  
> +    dev->vq[index].started = true;
> +    if (dev->iface->queue_set_started) {
> +        dev->iface->queue_set_started(dev, index, true);
> +    }
> +
> +    if (dev->vq[index].kick_fd != -1 && dev->vq[index].handler) {
> +        dev->set_watch(dev, dev->vq[index].kick_fd, VU_WATCH_IN,
> +                       vu_kick_cb, (void *)(long)index);
> +
> +        DPRINT("Waiting for kicks on fd: %d for vq: %d\n",
> +               dev->vq[index].kick_fd, index);
> +    }
> +
>      return false;
>  }
>  
> -- 
> 1.9.4