Bug#731709: grub-efi UEFI support based on debian-cd work complete (repos)

["Thomas Schmitt" <scdbackup@gmx.net>]

Hi,

Michal Suchanek wrote:
> -eltorito-alt-boot is not documented option of xorriso.

You need to look into man xorrisofs for the options of the -as mkisofs
emulation.

 -eltorito-alt-boot
      Finalize the current El Torito boot catalog entry  and  begin  a
      new  one.  A boot image file and all its necessary options shall
      be specified before option -eltorito-alt-boot.  All  further  El
      Torito  boot  options  apply  to the new catalog entry. Up to 32
      catalog entries are possible.


> So any bootloader is made primary by leaving out -eltorito-alt-boot.

There is no "primary" or "secondary" on the level of boot images
and loaders. (Of course you may call them this way in your project.)

There are first, second, third ... El Torito boot images or MBR, GPT,
APM partition entries.
The sequence is just needed because not all can be first in the list.

The boot firmware inspects the medium for its known lures,
picks a tasty one, and follows it to the boot loader or kernel.


> You can probably use only one legacy bootloader but syslinux-efi and
> grub-efi use different files so it should be possible to install both.
> I am not sure how selecting one or the other would work, though.

You can offer several EL Torito boot images for BIOS, indeed.
It will depend on your BIOS what it does in this case.

There can be only one MBR, though. So you would have to hop
by MBR x86 code to a standalone program which chooses among
the BIOS suitable El Torito boot images.

With EFI it makes few sense to offer more than one El Torito
boot image or EFI System Partition. UEFI 2.4 rather prescribes to
handle all alternatives inside the FAT filesystem. The firmware
will start the \EFI\BOOT\BOOT*.EFI binary which it deems suitable
for its processor type.
This binary is quite free in its further proceedings.


Have a nice day :)

Thomas