Re: [PATCH v1] s390/virtio_ccw: don't allocate/assign airqs for non-existing queues

[Michael S. Tsirkin]

On Mon, Apr 07, 2025 at 10:54:00AM +0200, David Hildenbrand wrote:
> On 07.04.25 10:49, Michael S. Tsirkin wrote:
> > On Mon, Apr 07, 2025 at 10:44:21AM +0200, David Hildenbrand wrote:
> > > > 
> > > > 
> > > > 
> > > > > Whoever adds new feat_X *must be aware* about all previous features,
> > > > > otherwise we'd be reusing feature bits and everything falls to pieces.
> > > > 
> > > > 
> > > > The knowledge is supposed be limited to which feature bit to use.
> > > 
> > > I think we also have to know which virtqueue bits can be used, right?
> > > 
> > 
> > what are virtqueue bits? vq number?
> 
> Yes, sorry.

I got confused myself, it's vq index actually now, we made the spec
consistent with that terminology. used to be number/index
interchangeably.

> Assume cross-vm as an example. It would make use of virtqueue indexes 5+6
> with their VIRTIO_BALLOON_F_WS_REPORTING.


crossvm guys really should have reserved the feature bit even if they
did not bother specifying it. Let's reserve it now at least?


> So whatever feature another device implements couldn't use this feature bit
> or these virtqueue indexes.
> 
> (as long the other device never intends to implement
> VIRTIO_BALLOON_F_WS_REPORTING, the virtqueue indexes could be reused. But
> the spec will also be a mess, because virtqueue indexes could also have
> duplicate meanings ... ugh)

what do they do with vq indices btw?



> -- 
> Cheers,
> 
> David / dhildenb