[SeaBIOS] [Qemu-devel] seabios serial console vs. sgabios

[Daniel P. Berrange]

On Fri, Nov 03, 2017 at 07:49:03AM +0100, Gerd Hoffmann wrote:
> 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?

Surely it has ABI implications for the guest if we stop putting the
sgabios option ROM into memory - changing layout of ROMS

> 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).

Libvirt doesn't use  '-machine graphics=off' AFAIK, only '-nographic'. 

Regards,
Daniel
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