[SeaBIOS] [PATCH 1/3] Add generic qemu detection

[Gleb Natapov]

On Mon, Sep 16, 2013 at 03:14:45PM +0200, Gerd Hoffmann wrote:
> On Mo, 2013-09-16 at 15:34 +0300, Gleb Natapov wrote:
> > On Mon, Sep 16, 2013 at 02:27:37PM +0200, Gerd Hoffmann wrote:
> > > On Mo, 2013-09-16 at 14:10 +0300, Gleb Natapov wrote:
> > > > On Mon, Sep 16, 2013 at 12:36:28PM +0200, Gerd Hoffmann wrote:
> > > > > This patch adds support for detecting whenever SeaBIOS runs on qemu
> > > > > or not.  This is done by looking at the northbridge (pci device 00:00.0)
> > > > > and check the subsystem id.  Most pci devices emulated by qemu -- the
> > > > > two northbridges i440fx and q35 included -- have a subsystem id of
> > > > > "1af4:1100".
> > > > > 
> > > > > In case the subsystem ID matches set PF_QEMU, log a message (including
> > > > > the northbridge found while being at it) and also check for kvm.
> > > > > 
> > > > What if other userspace will want to write enough support to run Seabios
> > > > as a guest? Why kvm detection depends on QEMU?
> > > 
> > > What other userspace?  There is none today.  And if that changes some
> > > day we'll just call kvm_detect() in the init code for $otheruserspace.
> > > 
> > Why seabios code has to be changed at all to support other device model
> > emulator (assuming it will emulate same chipset)?
> 
> That is a purely theoretical thing.  In practice seabios mist likely has
> to be changed for one or another reason.  
> 
It's not have to be this way if Seabios would check for specific HW features
instead of checking for QEMU. For instance if discovery of fw_cfg will
not depend on QEMU detection other userspace can emulate and it will be
detected without changing Seabios.

> kvm detection for CONFIG_QEMU builds only.
> 
Indeed the current logic is the same.

> Also note that in theory seabios should not need to care at all whenever
> it runs on kvm or tcg.  In practice qemu has slightly different behavior
> with kvm enabled and seabios needs adapt to that.  That alone is reason
> enougth that supporting other kvm userspace very likely needs adaptions
> in seabios, unless your theoretical[1] other userspace is bug compatible
> with qemu here.  
I see only one thing that is done based on KVM detection and the logic
would be correct for other userspaces that do not provide e820 map.
> 
> cheers,
>   Gerd
> 
> [1] Or do you know something you don't wanna tell me?
No, all I know is that kvmtool wanted to add seabios support, but I
guess nobody works on that these days.

--
			Gleb.