Re: [Qemu-devel] seabios serial console vs. sgabios

[Gerd Hoffmann <kraxel@redhat.com>]

On Thu, 2017-11-02 at 16:11 +0000, Daniel P. Berrange wrote:
> On Thu, Nov 02, 2017 at 05:04:20PM +0100, Gerd Hoffmann wrote:
> >   Hi,
> > 
> > One problem we have with the serial console support in seabios and
> > sgabios:  It can happen that both are activated.  We'll go fix that
> > in
> > qemu, but that'll work for new qemu versions only, not for the old
> > already released ones.
> > 
> > So I think it would be useful if seabios makes sure sgabios and
> > serial
> > console are not both active at the same time, i.e. in case we find
> > "vgaroms/sgabios.bin" being present either turn off builtin serial
> > console, or don't load sgabios (and possibly also enable builtin
> > serial
> > console).
> 
> Historically libvirt will always use '-device sgabios' if the user
> has
> requested <bios useserial='yes'/>.  So if that -device arg is given,
> I
> think QEMU must honour it, which implies QEMU must disable Seabios'
> own built-in serial console impl in that scenario.

Hmm, why?  The user asked for a serial console.  Whenever that is
provided by seabios builtin support or the sgabios rom doesn't really
matter, no?

Also, the question is what seabios should do in case both are active. 
Which I think can happen today with libvirt if you configure a virtual
machine without vga (libvirt passes -machine graphics=off which
activates builtin serial console) and with "<bios useserial='yes'/>"
(enables sgabios rom).

cheers,
  Gerd