[dpdk-dev] [PATCH v3] examples/vhost: workaround qemu abort

[Liu, Yong]

> -----Original Message-----
> From: Bie, Tiwei
> Sent: Wednesday, July 25, 2018 2:39 PM
> To: Liu, Yong <yong.liu at intel.com>
> Cc: dev at dpdk.org
> Subject: Re: [PATCH v3] examples/vhost: workaround qemu abort
> 
> On Wed, Jul 25, 2018 at 06:25:56PM +0800, Marvin Liu wrote:
> > Current qemu vhost net ring start has a dependency on feature bit
> > VHOST_USER_F_PROTOCOL_FEATURES. Without this feature, vhost ring can't
> > enabled and ioevent fd won't be deleted after vhost device stop. That
> > will cause qemu abort when reloading driver. Work around qemu issues by
> > enabling feature bit in vhost user backend.
> >
> > Signed-off-by: Marvin Liu <yong.liu at intel.com>
> >
> > diff --git a/examples/vhost/main.c b/examples/vhost/main.c
> > index 2175c1186..8573004dd 100644
> > --- a/examples/vhost/main.c
> > +++ b/examples/vhost/main.c
> > @@ -1520,7 +1520,10 @@ main(int argc, char *argv[])
> >  		}
> >
> >  		if (builtin_net_driver)
> > -			rte_vhost_driver_set_features(file, VIRTIO_NET_FEATURES);
> > +			/* Workaround for qemu vhost net device startup */
> > +			rte_vhost_driver_set_features(file,
> > +				VIRTIO_NET_FEATURES |
> > +				1ULL << VHOST_USER_F_PROTOCOL_FEATURES);
> 
> I have taken a closer look. I think it's not really right
> to just offer this bit like this. Because once this bit is
> negotiated, QEMU will ask the builtin_net_driver for the
> protocol features it supports. Currently, there is no API
> to allow external backends like the builtin_net_driver in
> this example to set the protocol features it supports, and
> instead, the protocol features VHOST_USER_PROTOCOL_FEATURES
> defined in librte_vhost will be returned to QEMU. This will
> cause problems because the builtin_net_driver doesn't really
> support those protocol features.
> 

Agreed, just announce protocol feature may have potential problem. Due to protocol features bits is fixed when no vdpa backend existing. IMHO, it has no benefit that adapt builtin_net_driver into vdpa framework. So just updated this sample's doc about builtin_net_driver compatible issue with QEMU.
Please kindly review that patch.

Regards,
Marvin

> 
> >
> >  		if (mergeable == 0) {
> >  			rte_vhost_driver_disable_features(file,
> > --
> > 2.17.0
> >