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

[Gerd Hoffmann]

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 <address@hidden>
> 
> 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.

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.

cheers,
  Gerd