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

Gleb Natapov gleb at redhat.com
Tue Sep 17 09:29:50 CEST 2013

On Mon, Sep 16, 2013 at 08:03:01PM -0400, Kevin O'Connor wrote:
> On Mon, Sep 16, 2013 at 07:58:42PM +0300, Gleb Natapov wrote:
> > On Mon, Sep 16, 2013 at 03:14:45PM +0200, Gerd Hoffmann wrote:
> > > 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.
> For the most part, this is what SeaBIOS does today.  There are very
> few places in the code that check CONFIG_QEMU.
> In particular, Gerd has already changed the fw_cfg support to not
> depend on CONFIG_QEMU.
Cool. That's definitely an improvement.

> > > 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.
> One of the places where CONFIG_QEMU is used is in determining how to
> get the memory map.  Any new emulator that uses SeaBIOS is going to
> have to define the mechanism for passing the memory map and that's
> going to be a SeaBIOS code change anyway.  (It's different on qemu,
> xen, coreboot, and csm.)  It's theoretically possible to use the QEMU
> memory map passing (magic cmos variables), but if that path is taken
> one might as well just enable CONFIG_QEMU then..
As far as I see the memory map is passed through fw_cfg, so it is enough
to implement it.


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