Re: [dpdk-dev] [PATCH] vhost: return ready when at least 1 vring is configured

["Liu, Changpeng" <changpeng.liu@intel.com>]

Hi Maxime,

> -----Original Message-----
> From: Maxime Coquelin <maxime.coquelin@redhat.com>
> Sent: Friday, September 18, 2020 5:54 PM
> To: Liu, Changpeng <changpeng.liu@intel.com>; dev@dpdk.org
> Cc: matan@mellanox.com; Xia, Chenbo <chenbo.xia@intel.com>; Zawadzki,
> Tomasz <tomasz.zawadzki@intel.com>
> Subject: Re: [PATCH] vhost: return ready when at least 1 vring is configured
> 
> Hi Changpeng,
> 
> On 9/1/20 9:07 AM, Changpeng Liu wrote:
> > Commit d0fcc38f "vhost: improve device readiness notifications"
> > needs at least 2 vrings before changing the device state to
> > ready, this is fine for NET device but not correct for BLK
> > device.
> >
> > The number of vring required should be based on the device
> > type, e.g. virtio_scsi device needs at least 3 vrings, and
> > virtio_net needs at least 2 vrings, virtio_blk needs at least
> > 1 vring. So instead of doing it in vhost library it's better
> > that the application who uses this library do this check.
> >
> > Signed-off-by: Changpeng Liu <changpeng.liu@intel.com>
> > ---
> >  lib/librte_vhost/vhost_user.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/lib/librte_vhost/vhost_user.c b/lib/librte_vhost/vhost_user.c
> > index c3c924f..4d1883c 100644
> > --- a/lib/librte_vhost/vhost_user.c
> > +++ b/lib/librte_vhost/vhost_user.c
> > @@ -1343,7 +1343,7 @@
> >  	       vq->enabled;
> >  }
> >
> > -#define VIRTIO_DEV_NUM_VQS_TO_BE_READY 2u
> > +#define VIRTIO_DEV_NUM_VQS_TO_BE_READY 1u
> 
> I think it would be better to rely on VIRTIO_DEV_BUILTIN_VIRTIO_NET to
> know whether it should wait for 1 or 2 queues to determine if ready.
virtio_scsi needs at least 3 vrings, so both 1 and 2 can't work for virtio_scsi device.
Can we expose an API to let the caller to set the minimum number of vrings required by
virtio device?
> 
> 
> >  static int
> >  virtio_is_ready(struct virtio_net *dev)
> >