Re: [Qemu-devel] [PATCH] pci: fix pci bridge fw path

[Marcel Apfelbaum <marcel.a@redhat.com>]

On Mon, 2013-12-09 at 08:14 +0100, Gerd Hoffmann wrote:
> On So, 2013-12-08 at 13:31 +0200, Michael S. Tsirkin wrote:
> > On Fri, Dec 06, 2013 at 12:24:40PM +0100, Gerd Hoffmann wrote:
> > > qemu uses "pci" as name for pci bridges in the firmware device path.
> > > seabios expects "pci-bridge".  Result is that bootorder is broken for
> > > devices behind pci bridges.
> > > 
> > > Some googling suggests that "pci-bridge" is the correct one.  At least
> > > PPC-based Apple machines are using this.  See question "How do I boot
> > > from a device attached to a PCI card" here:
> > > 	http://www.netbsd.org/ports/macppc/faq.html
> > > 
> > > So lets change qemu to use "pci-bridge" too.
> > > 
> > > Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> > 
> > Sounds good but this needs to be enabled for
> > new machine types only - otherwise guest will read
> > corrupted data since bootindex is in FW CFG.
> 
> Come on, that is seriously over-engineering.
Does this change affects migration in any way?

> 
> First, the chance that you'll find setup in the field where this can
> actually happen in practice is very low as bootorder for devices behind
> pci bridges does not work at all without this patch.
> 
> Second, the race window is so tiny that nobody has ever seen that happen
> in testing.
> 
> > Alternatively, extend
> > 04920fc0faa4760f9c4fc0e73b992b768099be70
> > to work for all fw cfg file entries.
> > 
> > I think the whole boot index thing needs
> > to be reworked: we also have the long-standing feature request to allow
> > booting from a device added by hot add.
> 
> I'm not going to rewrite bootorder just to get a one-liner bugfix
> merged.
Why? You could rewrite Qemu in C++, then rewrite the 
bootorder (easier, because of C++) and finally get your bugfix in...
but again, your patch would look exactly the same :)

Thanks,
Marcel

> 
> cheers,
>   Gerd
> 
>