Re: [Qemu-devel] Boot order problem and disable iPXE/gPXE

[Gleb Natapov]

On Thu, Jan 05, 2012 at 10:36:29AM +0100, Gerhard Wiesinger wrote:
> On Thu, 5 Jan 2012, Gleb Natapov wrote:
> 
> >On Thu, Jan 05, 2012 at 10:27:44AM +0100, Gerhard Wiesinger wrote:
> >>On Thu, 5 Jan 2012, Gleb Natapov wrote:
> >>
> >>>On Thu, Jan 05, 2012 at 10:09:44AM +0100, Gerhard Wiesinger wrote:
> >>>>On Thu, 5 Jan 2012, Gleb Natapov wrote:
> >>>>
> >>>>>On Thu, Jan 05, 2012 at 09:23:02AM +0100, Gerhard Wiesinger wrote:
> >>>>>>On Thu, 5 Jan 2012, Gerd Hoffmann wrote:
> >>>>>>
> >>>>>>>On 01/04/12 19:02, Gerhard Wiesinger wrote:
> >>>>>>>>Hello,
> >>>>>>>>
> >>>>>>>>I'm having the following boot order problem using an SCSI option ROM:
> >>>>>>>>
> >>>>>>>
> >>>>>>>>Still boots the cdrom instead of harddisk. So it is impossible to 
> >>>>>>>>have a
> >>>>>>>>bootable CDROM in the VM without booting from it.
> >>>>>>>
> >>>>>>>-option-rom romfile=/root/roms/8xx_64.rom,bootindex=1
> >>>>>>
> >>>>>>Ok, works well, but I think than "-boot order=c" is buggy, right?
> >>>>>>
> >>>>>Wrong. "-boot order=c" tells seabios to boot from a HD, but for that
> >>>>>Seabios needs to actually know what is HD and what is not. Since Seabios
> >>>>>does not support scsi controller natively it only sees pci device and
> >>>>>has no idea that you have scsi disk there. It uses pci option rom to
> >>>>>boot from this unknown device.
> >>>>
> >>>>But as far as I remember therefore the option ROM registers through
> >>>>BIOS for INT 19h booting. So Seabios should know it that this is a
> >>>>harddisk.
> >>>It registers BEV. Otherwise you wouldn't be able to boot at all. In fact
> >>>it registers multiple BEVs (one for each attached scsi device). But BIOS
> >>>knows nothing about the device behind the BEV. It just jumps to BEV
> >>>address to boot from it when INT 19h is called. There may be scsi cdrom
> >>>there or even tape.
> >>
> >>But to get rid of this problem typical BIOSes have an option whether
> >>they prefer to BOOT from SCSI (with an option ROM) or
> >>from the other devices. Then the option ROM typically boots from the
> >>first registered device.
> >>
> >>I think this is a missing feature in Seabios.
> >>
> >How is it missing if you just used it and confirmed that it worked?
> 
> It had to specify it on the option ROM itself. But I think a generic
> way would be e.g.:
> boot=SCSI,c,a
> 
boot option is deprecated in favor of bootindex. The later has much more
fine grained control of boot sequence. What if you have 5 SCSI
controllers? Even boot=c does not tell you much if you have more then
one disk.

--
                        Gleb.