Re: [PATCH net-next v3 01/11] virtio-pci: Expose generic device capability operations

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

On Thu, Sep 25, 2025 at 11:53:50AM -0500, Dan Jurgens wrote:
> On 9/25/25 8:08 AM, Michael S. Tsirkin wrote:
> > On Thu, Sep 25, 2025 at 05:39:54PM +0530, Parav Pandit wrote:
> >>
> >> On 25-09-2025 05:19 pm, Michael S. Tsirkin wrote:
> >>> On Thu, Sep 25, 2025 at 04:15:19PM +0530, Parav Pandit wrote:
> >>>> On 25-09-2025 04:05 pm, Michael S. Tsirkin wrote:
> >>>>> On Thu, Sep 25, 2025 at 03:21:38PM +0530, Parav Pandit wrote:
> >>>>>> Function pointers are there for multiple transports to implement their own
> >>>>>> implementation.
> >>>>> My understanding is that you want to use flow control admin commands
> >>>>> in virtio net, without making it depend on virtio pci.
> >>>> No flow control in vnet.
> >>>>> This why the callbacks are here. Is that right?
> >>>> No. callbacks are there so that transport agnostic layer can invoke it,
> >>>> which is drivers/virtio/virtio.c.
> >>>>
> >>>> And transport specific code stays in transport layer, which is presently
> >>>> following config_ops design.
> >>>>
> >>>>> That is fair enough, but it looks like every new command then
> >>>>> needs a lot of boilerplate code with a callback a wrapper and
> >>>>> a transport implementation.
> >>>> Not really. I dont see any callbacks or wrapper in current proposed patches.
> >>>>
> >>>> All it has is transport specific implementation of admin commands.
> >>>>
> >>>>>
> >>>>> Why not just put all this code in virtio core? It looks like the
> >>>>> transport just needs to expose an API to find the admin vq.
> >>>> Can you please be specific of which line in the current code can be moved to
> >>>> virtio core?
> >>>>
> >>>> When the spec was drafted, _one_ was thinking of admin command transport
> >>>> over non admin vq also.
> >>>>
> >>>> So current implementation of letting transport decide on how to transport a
> >>>> command seems right to me.
> >>>>
> >>>> But sure, if you can pin point the lines of code that can be shifted to
> >>>> generic layer, that would be good.
> >>> I imagine a get_admin_vq operation in config_ops. The rest of the
> >>> code seems to be transport independent and could be part of
> >>> the core. WDYT?
> >>>
> >> IMHV, the code before vp_modern_admin_cmd_exec() can be part of
> >> drivers/virtio/virtio_admin_cmds.c and admin_cmd_exec() can be part of the
> >> config ops.
> >>
> >> However such refactor can be differed when it actually becomes boiler plate
> >> code where there is more than one transport and/or more than one way to send
> >> admin cmds.
> > 
> > Well administration virtqueue section is currently not a part of a
> > transport section in the spec.  But if you think it will change and so
> > find it cleaner for transports to expose, instead of a VQ, a generic
> > interfaces to send an admin command, that's fine too. That is still a
> > far cry from adding all the object management in the transport. 
> > 
> > 
> > Well we have all the new code you are writing, and hacking around
> > the fact it's in the wrong module with a level of indirection
> > seems wrong.
> > If you need help moving this code let me know, it's not hard.
> > 
> >> Even if its done, it probably will require vfio-virtio-pci to interact with
> >> generic virtio layer. Not sure added value of that complication to be part
> >> of this series.
> >>
> >>
> >> Dan,
> >>
> >> WDYT?
> > 
> > 
> > virtio pci pulls in the core already, and VFIO only uses the SRIOV
> > group, so it can keep using the existing pci device based interfaces,
> > if you prefer.
> > 
> 
> I can make changes here. I'd appreciate if you review the rest of the
> series while I do so. Patches 3+ are isolated from this, so it won't be
> a waste of your time.

OK - will review 3+, thanks!

-- 
MST