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

[Max Gurtovoy <mgurtovoy@nvidia.com>]

On 2/7/2022 6:18 PM, Michael S. Tsirkin wrote:
> On Mon, Feb 07, 2022 at 04:58:19PM +0200, Max Gurtovoy wrote:
> > On 2/7/2022 12:39 PM, Michael S. Tsirkin wrote:
> > > On Thu, Feb 03, 2022 at 09:57:13AM +0200, Max Gurtovoy wrote:
> > > > +\begin{lstlisting}
> > > > +struct virtio_admin_cmd {
> > > > +        /* Device-readable part */
> > > > +        u16 command;
> > > > +        u8 command_specific_data[];
> > > > +
> > > > +        /* Device-writable part */
> > > > +        u8 status;
> > > > +        u8 command_specific_error;
> > > > +        u8 command_specific_result[];
> > > > +};
> > > > +\end{lstlisting}
> > > ok this abstraction is an improvement, thanks!
> > >
> > > What I'd like to see is moving a bit more format to this generic structure.
> > >
> > >   From what I could gather, some commands affect a group as a whole, and
> > > some commands just a single member of the group. We could have a
> > > "destination" field for that, and a special "all of the group"
> > > destination for commands affecting the whole group.
> > >
> > >
> > > Next, trying to think about scalable iov extensions. So we
> > > will have groups of VFs and then SFs as the next level.
> > > How does one differentiate between the two?
> > > Maybe reserve a field for "destination type"?
> > For now we have only a PCI group that composed of VFs and the PF.
> >
> > What you suggest, IMO is a definition of a generic virtio group/subsystem
> > that I've mentioned in the discussion of V1.
> >
> > Once we have virtio group - it should have a group id and them the admin
> > command can have a field calld group_id for commands that are targeted to
> > the whole group.
> >
> > Some commands are referring to a specific device in the group so only a
> > vdev_id is needed.
> >
> > Some commands are even targeted to the same device to query some info (we
> > have examples in this series for that), so in this case there is no need for
> > vdev_id nor group_id.
> >
> > So I'm sure sure we can improve common virtio_admin_cmd structure to have
> > these attributes since they are not mandatory because of the reasons I've
> > mentioned.
> I'm not sure I understand 100%, but try to address in the next
> revision and we'll discuss.

I meant to say that I'm *not* sure we can improve the common structure...

It was a typo.

And I don't understand why this info can't be in the 
command_specific_data because of all the reasons I mentioned above.

> > > The point of all this is to allow making sense of commands and
> > > e.g. virtualizing them for nested virt without necessarily
> > > knowing all of the detail about the specific command.
> > I don't understand this, sorry.
> Basically try to move stuff into generic format so it's possible
> to understand things without knowing detail of the command.

But we don't develop a networking protocol here. The management device 
is not sending packets towards its managed devices, right ?

This is an interface for a specific device that can manage others but 
also manage itself.

We didn't introduce a notion of broadcasting admin commands for other 
devices.