Re: [Qemu-devel] [PATCH 3/4] libvhost-user: implement VHOST_USER_PROTOCOL_F_MQ

[Marc-André Lureau]

On Fri, Jun 21, 2019 at 11:40 AM Stefan Hajnoczi <address@hidden> wrote:
>
> Existing vhost-user device backends, including vhost-user-scsi and
> vhost-user-blk, support multiqueue but libvhost-user currently does not
> advertise this.
>
> VHOST_USER_PROTOCOL_F_MQ enables the VHOST_USER_GET_QUEUE_NUM request
> needed for a vhost-user master to query the number of queues.  For
> example, QEMU's vhost-user-net master depends on
> VHOST_USER_PROTOCOL_F_MQ for multiqueue.
>
> If you're wondering how any device backend with more than one virtqueue
> functions today, it's because device types with a fixed number of
> virtqueues do not require querying the number of queues.  Therefore the
> vhost-user master for vhost-user-input with 2 virtqueues, for example,
> doesn't actually depend on VHOST_USER_PROTOCOL_F_MQ.  It just enables
> virtqueues 0 and 1 without asking.
>
> Let there be multiqueue!
>
> Suggested-by: Sebastien Boeuf <address@hidden>
> Signed-off-by: Stefan Hajnoczi <address@hidden>

Reviewed-by: Marc-André Lureau <address@hidden>

> ---
>  contrib/libvhost-user/libvhost-user.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/contrib/libvhost-user/libvhost-user.c 
> b/contrib/libvhost-user/libvhost-user.c
> index 0c88431e8f..312c54f260 100644
> --- a/contrib/libvhost-user/libvhost-user.c
> +++ b/contrib/libvhost-user/libvhost-user.c
> @@ -1160,7 +1160,8 @@ vu_set_vring_err_exec(VuDev *dev, VhostUserMsg *vmsg)
>  static bool
>  vu_get_protocol_features_exec(VuDev *dev, VhostUserMsg *vmsg)
>  {
> -    uint64_t features = 1ULL << VHOST_USER_PROTOCOL_F_LOG_SHMFD |
> +    uint64_t features = 1ULL << VHOST_USER_PROTOCOL_F_MQ |
> +                        1ULL << VHOST_USER_PROTOCOL_F_LOG_SHMFD |
>                          1ULL << VHOST_USER_PROTOCOL_F_SLAVE_REQ |
>                          1ULL << VHOST_USER_PROTOCOL_F_HOST_NOTIFIER |
>                          1ULL << VHOST_USER_PROTOCOL_F_SLAVE_SEND_FD;
> @@ -1200,8 +1201,8 @@ vu_set_protocol_features_exec(VuDev *dev, VhostUserMsg 
> *vmsg)
>  static bool
>  vu_get_queue_num_exec(VuDev *dev, VhostUserMsg *vmsg)
>  {
> -    DPRINT("Function %s() not implemented yet.\n", __func__);
> -    return false;
> +    vmsg_set_reply_u64(vmsg, dev->max_queues);
> +    return true;
>  }
>
>  static bool
> --
> 2.21.0
>