Re: [RFC 1/4] vdpa: add VHOST_BACKEND_F_ENABLE_AFTER_DRIVER_OK flag

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, May 24, 2023 at 12:06:47PM +0800, Jason Wang wrote:
> On Tue, May 23, 2023 at 1:55âPM Eugenio Perez Martin
> <eperezma@redhat.com> wrote:
> >
> > On Mon, May 22, 2023 at 11:22âPM Shannon Nelson <shannon.nelson@amd.com> wrote:
> > >
> > > On 5/22/23 1:07 PM, Eugenio Perez Martin wrote:
> > > >
> > > > On Mon, May 22, 2023 at 9:23âPM Michael S. Tsirkin <mst@redhat.com> wrote:
> > > >>
> > > >> On Mon, May 22, 2023 at 08:57:27PM +0200, Eugenio PÃrez wrote:
> > > >>> Signed-off-by: Eugenio PÃrez <eperezma@redhat.com>
> > > >>> ---
> > > >>>   include/uapi/linux/vhost_types.h | 2 ++
> > > >>>   1 file changed, 2 insertions(+)
> > > >>>
> > > >>> diff --git a/include/uapi/linux/vhost_types.h b/include/uapi/linux/vhost_types.h
> > > >>> index c5690a8992d8..a1b316f49b38 100644
> > > >>> --- a/include/uapi/linux/vhost_types.h
> > > >>> +++ b/include/uapi/linux/vhost_types.h
> > > >>> @@ -165,5 +165,7 @@ struct vhost_vdpa_iova_range {
> > > >>>   #define VHOST_BACKEND_F_SUSPEND  0x4
> > > >>>   /* Device can be resumed */
> > > >>>   #define VHOST_BACKEND_F_RESUME  0x5
> > > >>> +/* Device can enable virtqueues after DRIVER_OK */
> > > >>
> > > >> A bit more detail on what does this mean?
> > > >> It's normally driver that enables VQs not device itself ...
> > > >>
> > > >
> > > > I agree, it is not well explained.
> > > >
> > > > What about "Device supports the driver to enable virtqueues after DRIVER_OK"?
> > > >
> > > >>> +#define VHOST_BACKEND_F_ENABLE_AFTER_DRIVER_OK  0x6
> > >
> > > Does this mean it is possible only after DRIVER_OK, or does it mean in
> > > addition to before DRIVER_OK?  It isn't clear to me.
> > >
> > > Maybe something like
> > > "Device supports virtqueue enable only after DRIVER_OK"
> > > or
> > > "Device supports virtqueue enable both before and after DRIVER_OK"
> > >
> >
> > I agree too,
> >
> > With the previous suggestion it would be:
> >
> > "Device supports the driver to enable virtqueues both before and after
> > DRIVER_OK"
> 
> Btw, I think it might be worth clarifying whether or not this is
> supported by the current virtio spec. Spec seems to be unclear on
> this:
> 
> 1) The driver MUST NOT write a 0 to queue_enable.
> 2) if reset is support, driver can wrote 1 to re-enable a virtqueue
> 
> But it doesn't say if the driver can write 1 after DRIVER_OK without reset.
> 
> Thanks

I don't think it can. Do any drivers do this?


> 
> >
> > Does it look better?
> >
> > Thanks!
> >
> > > sln
> > >
> > >
> > > >>>
> > > >>>   #endif
> > > >>> --
> > > >>> 2.31.1
> > > >>
> > > >
> > >
> >