[SeaBIOS] doe's seabios support retry booting from other disk if boot from one disk failed

[Kevin O'Connor]

On Mon, Oct 29, 2012 at 09:32:04AM +0100, Gerd Hoffmann wrote:
> On 10/28/12 02:06, Kevin O'Connor wrote:
> > On Fri, Oct 19, 2012 at 03:52:04PM +0800, Eli wrote:
> >> hi all:
> >>
> >> Does anyone know that if seabiso support booting from other disk if boot
> >> from one failed ?
> >>
> >> For instance, the PC BIOS boot specification allows only one
> >> disk to be bootable.  If boot from disk fails for some reason, the BIOS
> >> won't retry booting from other disk.  It still can try to boot from
> >> floppy or net, though.I want to know that if seabios support retry booting from other disk?
> > 
> > SeaBIOS follows the specifications, and so only the C drive can be
> > booted.  Unfortunately, once the C drive is assigned it can't be
> > changed reliably.  So, ultimately SeaBIOS has the same limitation as
> > other BIOS here.
> 
> What is the problem here?  Fall back to ide/sata hard disk when booting
> from usb stick (which is treated as hard disk too) failed would be useful.
> 
> It certainly would be a non-trivial change to the boot order code as
> this would involve changing the disk mapping, rewriting edd tables and
> maybe more.
> 
> But on a quick glance I can't see why it wouldn't work reliably.

There's no way to remap a drive configured via an option rom.  It is
technically possible to remap the drives if only SeaBIOS internal
drivers are used, but the moment one has a drive configured via an
option rom the behavior will change subtly.  Technically, it's
probably possible to do a complete reboot to change boot order even
with option roms, but I suspect that would also lead to subtle corner
cases.

-Kevin