Re: [PATCH 12/21] vhost-vdpa: introduce uAPI to get the number of virtqueue groups

[Jason Wang]

On 2020/12/29 下午8:24, Eli Cohen wrote:
> On Wed, Dec 16, 2020 at 02:48:09PM +0800, Jason Wang wrote:
> > Follows the vDPA support for multiple address spaces, this patch
> > introduce uAPI for the userspace to know the number of virtqueue
> > groups supported by the vDPA device.
> Can you explain what exactly you mean be userspace?


It's the userspace that uses the uAPI introduced in this patch.


> Is it just qemu or
> is it destined to the virtio_net driver run by the qemu process?


It could be Qemu, DPDK or other userspace program.

The guest virtio-net driver will not use this but talks to the virtio 
device emulated by Qemu.


> Also can you say for what purpose?


This can be used for facilitate the checking of whether the control vq 
could be supported.

E.g if the device support less than 2 groups, qemu won't advertise 
control vq.

Yes, #groups could be inferred from GET_VRING_GROUP. But it's not 
straightforward as this.

Thanks


> > Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
> > ---
> >   drivers/vhost/vdpa.c       | 4 ++++
> >   include/uapi/linux/vhost.h | 3 +++
> >   2 files changed, 7 insertions(+)
> >
> > diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> > index 060d5b5b7e64..1ba5901b28e7 100644
> > --- a/drivers/vhost/vdpa.c
> > +++ b/drivers/vhost/vdpa.c
> > @@ -536,6 +536,10 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
> >   	case VHOST_VDPA_GET_VRING_NUM:
> >   		r = vhost_vdpa_get_vring_num(v, argp);
> >   		break;
> > +	case VHOST_VDPA_GET_GROUP_NUM:
> > +		r = copy_to_user(argp, &v->vdpa->ngroups,
> > +				 sizeof(v->vdpa->ngroups));
> > +		break;
> >   	case VHOST_SET_LOG_BASE:
> >   	case VHOST_SET_LOG_FD:
> >   		r = -ENOIOCTLCMD;
> > diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h
> > index 59c6c0fbaba1..8a4e6e426bbf 100644
> > --- a/include/uapi/linux/vhost.h
> > +++ b/include/uapi/linux/vhost.h
> > @@ -145,4 +145,7 @@
> >   /* Get the valid iova range */
> >   #define VHOST_VDPA_GET_IOVA_RANGE	_IOR(VHOST_VIRTIO, 0x78, \
> >   					     struct vhost_vdpa_iova_range)
> > +/* Get the number of virtqueue groups. */
> > +#define VHOST_VDPA_GET_GROUP_NUM	_IOR(VHOST_VIRTIO, 0x79, unsigned int)
> > +
> >   #endif
> > --
> > 2.25.1