Re: [libvirt PATCH v2 2/3] conf: support firmware ISA debug console

On Wed, Feb 02, 2022 at 02:32:32PM +0000, Daniel P. Berrangé wrote: > On Wed, Feb 02, 2022 at 06:29:32AM -0800, Andrea Bolognani wrote: > > On Wed, Feb 02, 2022 at 12:44:44PM +0000, Daniel P. Berrangé wrote: > > > Introduce support for > > > > > > <serial type='pty'> > > > <target type='isa-debug'> > > > <model type='isa-debugcon'/> > > > </target> > > > <address type='isa' iobase='0x402'/> > > > </console> > > > > > > which is used as a way to receive debug messages from the > > > firmware on x86 platforms. > > > > > > Note that the default port is 0x0xe9 since that's the original > > > Bochs debug port. Thus for use with SeaBIOS/OVMF, the iobase > > > port needs to be explicitly set to 0x402. > > > > The default is not set anywhere in the code, so I guess we're relying > > on the fact that QEMU has that as the current default. Wouldn't it > > make sense to have it reflected in the XML as well? > > > > The previous version used 0x402 as the default, which apparently > > doesn't match QEMU's own but is what most people will want in > > practice. Wouldn't that be a better default for us? People who care > > about Bochs compatibility can always explicitly set the appropriate > > value themselves. > > The previous bversion was a mistake because I incorrectly thought > 402 was QEMU's own default. I also mistakenly thought we needed > to set it explicitly for ABI compat, but that's not the case because > the machine type ensures that. > > So preferrable to not override QEMU's own defaults in libvirt. I think it would still make sense to reflect QEMU's current default in the XML, which would make sure that the same input XML results in the same device even if QEMU decides to change its defaults later on.