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

From: Kevin Wolf
Subject: Re: [Qemu-devel] Why is SeaBIOS used with -kernel?
Date: Tue, 5 Apr 2016 10:11:20 +0200
User-agent: Mutt/1.5.21 (2010-09-15)

Am 05.04.2016 um 10:04 hat Richard W.M. Jones geschrieben:
> 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.

At least in RHEL, /usr/share/qemu-kvm/bios.* seems to have symlinks
pointing to the binaries in /usr/share/seabios/. And I would assume that
that's the only directory besides the working directory where qemu looks
for the files.


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