Re: [Qemu-devel] [PATCH v3 07/10] check: Only test boot-serial when sga is compiled in

[Gerd Hoffmann]

> > I remember we even discussed that a while back ...
> > Oh yes: 
> > https://git.kraxel.org/cgit/qemu/commit/?h=work/no-sgabios&id=408690999429fdf44011c49b3af6efa50f369b1e
> > Somehow never ended up being merged.
> 
> Sounds like a good idea! Could you repost the patch, with an update to
> qemu-deprecated.texi, please? Maybe also print the deprecation message
> in any case if !use_sgabios, e.g.:
> 
>     } else {
>         /*
>          * For this machine type we expect SeaBIOS to provide a
>          * serial console for -machine graphics=off.  No need to
>          * add the sgabios rom here.
>          */
>         warn_report("sgabios is deprecated and is not required anymore,"
>                     " SeaBIOS now has the same functionality, too");
>     }

Hmm, IIRC libvirt support is a bit tricky here as there is no easy way
to probe for serial console support in seabios.  So the idea was to just
allow both -machine graphics=off and -device sga, by turning -device sga
into a nop in case -machine graphics=off is present.

But given we meanwhile had some releases without this I suspect that
isn't a good idea any more.  With both -machine graphics=off -device sga
seabios and sgabios will fight over the serial device ...

So, maybe take a completely different route.  Add a deprecation_reason
field to DeviceClass.  Make it visible in qapi introspection, so libvirt
can see it and avoid adding it to the command line.  Then we can
deprecate -device sga (and possibly other devices too) that way.

For live migration compatibility reasons it'll be quite a while until we
can actually delete the device (much longer than the usual 2 releases
deprecation cycle).

cheers,
  Gerd