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Re: [Qemu-devel] Why is SeaBIOS used with -kernel?

From: Richard W.M. Jones
Subject: Re: [Qemu-devel] Why is SeaBIOS used with -kernel?
Date: Tue, 5 Apr 2016 09:04:55 +0100
User-agent: Mutt/1.5.20 (2009-12-10)

On Tue, Apr 05, 2016 at 06:38:36AM +0200, Kevin Wolf wrote:
> Am 01.04.2016 um 13:20 hat Richard W.M. Jones geschrieben:
> > 
> > My patch, plus the configuration and comments from your patch,
> > combined.  Plus I tested it with libguestfs boot-analysis and it works
> > and is still fast.
> > 
> > Integrating this so it happens automatically when the user adds
> > -kernel on x86 seems quite complicated.  The only way I could do it
> > was by adding #ifdef defined(__x86_64__) etc to vl.c, which doesn't
> > seem very nice.  The problem is the machine type code doesn't know
> > that you're using -kernel.
> I would actually find it rather surprising to get differernt BIOSes and
> therefore potentially different behaviour for -kernel and for booting
> from an image. Even if we made sure that Linux really never touches the
> parts that you disable in bios-fast.bin, remember that -kernel is not
> only for Linux, but for arbitrary kernels.
> Requiring an explicit -bios option like you do now seems to make most
> sense to me: The default behaves the same as a normal boot, but if you
> are one of the cases that do need that additional boot speed, you can do
> that and consciously sacrifice the features.

OK so this reminds me of the second problem.  How to detect what
bioses are available, given a qemu binary.  It would be nice if qemu
had an option like:

  qemu -bios \?

Of course we can try to scan /usr/share/qemu/bios.*, except that
Fedora installs extra ROMs in /usr/share/seabios/ (I'm not exactly
sure how qemu deals with those), and the path is different for other
distros and other qemu binaries.


Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
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