[SeaBIOS] [Qemu-devel] [RFC] Passing boot order from qemu to seabios

[Gleb Natapov]

On Tue, Oct 12, 2010 at 10:11:09AM +0200, Peter Stuge wrote:
> > How about:
> > 
> > 1) QEMU let's user choose device boot order based on something that
> >    makes sense to QEMU and it's users.  It places this info in fw_cfg
> >    by providing a list of "path names" for each device.
> > 2) SeaBIOS creates a list of bootable devices based on the BBS and
> >    anything else it thinks it can boot from.  It prioritizes devices
> >    in this list if their "path name" is found in the fw_cfg boot order
> >    list provided by qemu.
> 
> I think it may be more difficult for QEMU to predict how SeaBIOS will
> enumerate boot devices and what paths they will have than for QEMU to
> work with the boot devices that were found by SeaBIOS after the fact.
> 
Why do you think so? Path to a device is HW topology thing. It does not
change no matter who enumerates it QEMU or Seabios. The same exact
problem exists between a BIOS and an OS when EDD describes storage
devices. 

> 
> > 3) SeaBIOS then allows a user to reorder boot devices.
> > 
> > I'm not sure why step 4 (SeaBIOS tells QEMU the new boot order) is
> > needed.
> 
> To save the boot order in NV storage.
> 
We do not have NV storage and we'd rather not introduce it. In
virtualization user configs VM through virt-manager or using qemu command
line directly. Bios reads config using fw_cgf interface and obeys it.

--
			Gleb.