Re: find_vqs operation starting at arbitrary index

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

On Tue, Jun 02, 2009 at 08:53:07AM +0930, Rusty Russell wrote:
> On Mon, 1 Jun 2009 05:33:48 pm Amit Shah wrote:
> > Hello,
> >
> > The recent find_vqs operation doesn't allow for a vq to be found at an
> > arbitrary location; it's meant to be called once at startup to find all
> > possible queues and never called again.
> >
> > This doesn't work for devices which can have queues hot-plugged at
> > run-time. This can be made to work by passing the 'start_index' value as
> > was done earlier for find_vq, but I doubt something like the following
> > will work. The MSI vectors might need some changing as well.
> 
> There's a fundamental conflict here: find_vqs was added so the PCI MSI code 
> knows exactly how many virtqueues there are.
> 
> So you'll need to sort this out with Michael...
> 
> Thanks,
> Rusty.

I'd like to understand the expected usage some more.  If there's still a
small # of hotpluggable queues known in advance, you can request all
vectors but have the queues disabled, and then enable as queues arrive.
In that case, something like resize_queue or enable_queue might be a
good idea.

OTOH, if you want to have a potentially unlimited number of queues,
you will have to allocate a common vector for all of them
as on intel we are limited to 256 total vectors for all devices
taken together.  Not sure what a good API for that would be.

-- 
MST