Re: [virtio-dev] [RFC RESEND] virtio-video: Add virtio video device specification

Dmitry Sepp
2019-12-09T11:38:35Z

Hi,

On Montag, 9. Dezember 2019 11:46:15 CET Gerd Hoffmann wrote:
> Hi,
>
> > > For (1) you'll simply do a QUEUE_BUFFER. The command carries references
> > > to the buffer pages. No resource management needed.
> > >
> > > For (2) you'll have RESOURCE_CREATE + RESOURCE_DESTROY + QUEUE_RESOURCE,
> > > where RESOURCE_CREATE passes the scatter list of buffer pages to the
> > > host and QUEUE_RESOURCE will carry just the resource id.
> > >
> > > For (3) you'll have RESOURCE_IMPORT + RESOURCE_DESTROY + QUEUE_RESOURCE.
> >
> > Thanks for the clarification.
> > On second thought, however, I'm wondering if we should keep all
> > RESOURCE controls.
> > This should be an option (4).
>
> Well, that's actually (2), aka "we use RESOURCE_* commands to manage
> resources". With the commands in the latest draft that would be:
>
> (1) RESOURCE_CREATE
> (2) RESOURCE_ATTACH_BACKING
> (3) RESOURCE_QUEUE (resource can be used multiple times here)
> (4) RESOURCE_DETACH_BACKING
> (5) RESOURCE_DESTROY
>
> I'm not sure we need the separate *_BACKING commands. I think we could
> also have RESOURCE_CREATE pass the buffer pages scatter list instead.
>
> Why it is done this way? Just because the design was copied from
> virtio-gpu? Or is there some specific reason?

Yes, the design was just derived from virtio-gpu at early stages.

I do agree we should merge the two steps.

>
> cheers,
> Gerd