Re: [PATCH v3 1/4] Add virtio Admin virtqueue

[Cornelia Huck <cohuck@redhat.com>]

On Mon, Feb 07 2022, "Michael S. Tsirkin" <mst@redhat.com> wrote:

> On Mon, Feb 07, 2022 at 12:14:33PM +0200, Max Gurtovoy wrote:
>> 
>> On 2/3/2022 3:09 PM, Cornelia Huck wrote:
>> > On Thu, Feb 03 2022, Max Gurtovoy <mgurtovoy@nvidia.com> wrote:

>> > > +commands to manipulate various features of the device and/or to manipulate
>> > > +various features, if possible, of another device within the same group (e.g. PCI VFs
>> > Maybe add
>> > 
>> > "Which devices are actually considered a group is transport specific."
>> > 
>> > ?
>> 
>> Not sure we want to restrict ourselves for that.
>
> do restrict this please, if we want to extend the scope we can
> always do that down the road.

I'm also not sure how grouping can _not_ be transport specific... the
PF/VF example is obviously a pci thing; for ccw, in a non-virtio
context, there's sometimes the concept of some subchannels/devices being
grouped together with no clear hierarchy, and for mmio, I don't really
have an idea how "grouping" might work there.

>> > > +When VIRTIO_F_ADMIN_VQ is negotiated with the device, driver will send all admin commands
>> > > +through the admin virtqueue.
>> > That sounds a bit like the driver might use an alternative interface for
>> > the admin commands as well? What about
>> 
>> Yes if there will be an alternative for AQ and this feature bit will not be
>> negotiated so the driver will use a different channel.
>> 
>> This was explicitly discussed in previous versions.
>> 
>> What is the issue with this assumption ?
>
> it's not an issue down the road but we want to be clear
> that right now that is the only way, to make sure
> reader does not waste time looking for more ways
> in the spec. maybe just say so.

Yes, we should be explicit that admin commands are independent of the
conduit they are using, and that currently the only conduit is the admin
vq. Someone reading the spec does not know about previous discussions on
the mailing list.

Maybe reorder this? First have a section where the admin commands are
defined, and then have a section that lists the different channels admin
commands can use, where the admin vq is the only one currently
supported?