[SeaBIOS] [PATCH v3 4/6] pci: init boot devices only on address space shortage

[Gleb Natapov]

On Wed, Jul 06, 2011 at 12:18:13PM +0300, Michael S. Tsirkin wrote:
> On Wed, Jul 06, 2011 at 10:57:41AM +0200, Gerd Hoffmann wrote:
> > On 07/05/11 18:23, Michael S. Tsirkin wrote:
> > >On Tue, Jul 05, 2011 at 05:27:03PM +0200, Gerd Hoffmann wrote:
> > >>Try to handle address space shortage by skipping any device
> > >>which isn't essential for boot.
> > >>
> > >>Signed-off-by: Gerd Hoffmann<kraxel at redhat.com>
> > >
> > >At least in a virt setup, it's much easier to debug
> > >things if boot just fails. Partial boot could be an option I guess.
> > 
> > Yea, I think that is pretty much the fundamental question.  Does it
> > make sense to try boot up even if we can't fit some devices into the
> > pci memory hole.
> 
> Well, the real fix is for the management to remove the offending
> devices, so I think we should make it as easy as possible to detect the
> problem and implement the fix.
> 
> We could also implement an interface allowing the user to select which
> devices to disable.
> 
Interface that requires device identifications between qemu and the BIOS
involve device paths. Not sure you want to go there :) (Although for PCI
devices this is solved problem).

> > At least linux guests will try to map devices below the pci memory
> > hole in case seabios didn't assign an address.
> > 
> > Of course this works
> > only if the guest hasn't too much memory so there is some free space
> > between end of ram and the start of the pci memory hole.
> 
> IO port memory is a problem too, BTW, and not that easily worked
> around. It's becoming rare in the non-virtualized systems
> but is unfortunately the mechanism of choice for virtualization.
> 
> > >We usually have a list of bootable devices we got from qemu -
> > >want to use that?
> > 
> > Why?  seabios knows itself which devices it can use to boot.  Also
> > the list from qemu is incomplete, the boot menu can have more
> > entries than what we get passed in from qemu as boot order list.
> > 
> > cheers,
> >   Gerd
> 
> 
> 
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--
			Gleb.