[Mesa-dev] [PATCH v4] virgl: Add support for glGetMultisample

[Dave Airlie]

On 10 July 2018 at 16:57, David Airlie <airlied at redhat.com> wrote:
>
>
> On Tue, Jul 10, 2018 at 4:44 PM, Gert Wollny <gert.wollny at collabora.com>
> wrote:
>>
>> Am Dienstag, den 10.07.2018, 09:19 +1000 schrieb Dave Airlie:
>> >
>> > Just FYI in future please don't push mesa patches until the renderer
>> > side patch has landed, this is to avoid the abi accidentally
>> > diverging around the caps.
>> Sure, I'll keep that in mind, and sorry for rushing to push this.
>>
>> However, this actually points to a bigger problem: Given that the
>> mesa/virgl driver is completely separate from the host virglrenderer,
>> how do we ensure in a real world application that host and guest agree
>> on the abi? There is this 'version' in the
>> vrend_renderer_fill_caps_common and the 'max_version' in the caps, but
>> the first one is not used at all, and the second is not used beyond
>> signalling the availability of caps set 2. Maybe we should define some
>> algorithm to bump that latter number so the client can see what values
>> in the caps were actually filled by the host?
>>
>
> We already deal with ABI at runtime. The problem is diverging the virgl_hw.h
> file.
>
> One copy of that file needs to be master and we only add to the end of the
> caps v2
> struct, but the version that is the master copy is the one in virglrenderer.
> So if
> we end up pushing patches to mesa first, and someone pushes another change
> to virglrenderer we get incompatible overlap.

Just in case I didn't answer what you wondered, we use the size of the caps v2
to denote what the two sides support, so a older versions gets a smaller size,
and the newer caps get default values, and new version we don't copy after
the size the renderer expects.

Dave.