Re: [Qemu-devel] [Spice-devel] [PATCH] Add new client_present and client capabilities fields to QXLRom

[Gerd Hoffmann <kraxel@redhat.com>]

  Hi,

>> Hmm, when the server is able to translate a8 ops into non-a8 ops using
>> server-side rendering, then there is no need to notify the guest about
>> the client capabilities.
> 
> To be clear, this ability doesn't exist at the moment, and it would be a
> significant chunk of work to add it.
> 
>>> But it's much simpler to just say that the guest should stop referring
>>> to a8 surfaces if the client can't handle them.
>>
>> Not sure about that, this move might just shift the complexity from
>> spice-server to the guest qxl driver.
> 
> The ability to handle this is already pretty much present in at least
> the X driver (and I'm pretty sure the Windows driver has it as well)
> because any time something can't be expressed in the SPICE protocol, it
> has to fall back to software rendering. Ie., it has to read all the
> involved surfaces back from video memory, do software rendering, then
> upload the result as an image.
> 
> Dealing with a disappearing ability to handle a8 surfaces would simply
> be a matter of reading back the a8 surfaces to guest RAM and then not
> attempt to acccelerate any operations involving them any more.
> 
> It looks much more involved to do it in spice-server because it would
> probably involve adding a new concept of "emulated surface" that needs
> to be handled specially in a bunch of cases.

Ok, so the tradeoff seems clear.  I trust you on that one, you know the
guest drivers alot better than I do.  Lets go forward with the client
capability notification for the guest, /me awaits a new revision of the
patches.

cheers,
  Gerd