Re: [RFC 02/10] vhost: add 3 commands for vhost-vdpa

[Michael S. Tsirkin]

On Wed, Jan 05, 2022 at 12:35:53PM +0800, Jason Wang wrote:
> On Wed, Jan 5, 2022 at 8:59 AM Longpeng(Mike) <longpeng2@huawei.com> wrote:
> >
> > From: Longpeng <longpeng2@huawei.com>
> >
> > To support generic vdpa deivce, we need add the following ioctls:
> > - GET_VECTORS_NUM: the count of vectors that supported
> 
> Does this mean MSI vectors? If yes, it looks like a layer violation:
> vhost is transport independent.

Well *guest* needs to know how many vectors device supports.
I don't think there's a way around that. Do you?
Otherwise guests will at best be suboptimal.

>  And it reveals device implementation
> details which block (cross vendor) migration.
> 
> Thanks

Not necessarily, userspace can hide this from guest if it
wants to, just validate.


> > - GET_CONFIG_SIZE: the size of the virtio config space
> > - GET_VQS_NUM: the count of virtqueues that exported
> >
> > Signed-off-by: Longpeng <longpeng2@huawei.com>
> > ---
> >  linux-headers/linux/vhost.h | 10 ++++++++++
> >  1 file changed, 10 insertions(+)
> >
> > diff --git a/linux-headers/linux/vhost.h b/linux-headers/linux/vhost.h
> > index c998860d7b..c5edd75d15 100644
> > --- a/linux-headers/linux/vhost.h
> > +++ b/linux-headers/linux/vhost.h
> > @@ -150,4 +150,14 @@
> >  /* Get the valid iova range */
> >  #define VHOST_VDPA_GET_IOVA_RANGE      _IOR(VHOST_VIRTIO, 0x78, \
> >                                              struct vhost_vdpa_iova_range)
> > +
> > +/* Get the number of vectors */
> > +#define VHOST_VDPA_GET_VECTORS_NUM     _IOR(VHOST_VIRTIO, 0x79, int)
> > +
> > +/* Get the virtio config size */
> > +#define VHOST_VDPA_GET_CONFIG_SIZE     _IOR(VHOST_VIRTIO, 0x80, int)
> > +
> > +/* Get the number of virtqueues */
> > +#define VHOST_VDPA_GET_VQS_NUM         _IOR(VHOST_VIRTIO, 0x81, int)
> > +
> >  #endif
> > --
> > 2.23.0
> >