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[Bug-xorriso] Re: EFI boot option in mkisofs emulation of xorriso

From: Thomas Schmitt
Subject: [Bug-xorriso] Re: EFI boot option in mkisofs emulation of xorriso
Date: Sat, 14 Aug 2010 20:10:02 +0200


> I always prefer the exaggerated form as I can understand what
> parameter is being used. I get confused with -v and -V and all the
> single alphabet options.

Yeah. Single letter options are for 16-bit
systems. :))

The shortest xorriso option is "-as".
Matchingly, -as emulates mkisofs or cdreord
which indulge heavily in single letter options.

> > EFI boot facility which does not use the El Torito
> > Boot record on CD/DVD/Blu-ray media.
> having this kind of setup enables me to launch
> (iso-root)/efi/boot/bootx64.efi using the EFI shell

But the EFI image which is known to the
El Torito Boot Catalog will start automatically
if the mainboard does not like PC-BIOS booting ?

> I tried dd copy of the isohybrid image to a 4 GB pendrive, but my efi
> did not detect it.

This is why i proposed to have a look at what
grub-mkrescue does. It sets the El Torito boot
info similar to yours, and it includes an MBR
by mkisofs option -embedded-boot. See
especially variable grub_mkisofs_arguments
througout the script and the xorriso command
at the end.

The -embedded-boot data go to the ISO 9660 System
Area, which reaches from block 0 to block 15.
There is room for 32 kB, which the ISO 9660
filesystem drivers will ignore.

Other than with isohybrid, the GRUB2 System Area
image has no block address pointers which need to
be updated by xorriso. It has its own ways to
find the necessary GRUB2 files in the ISO image.

The only thing that xorriso does for GRUB2 in
that System Area image is to patch-in a primitive
DOS Partition Table which tells the size of the
ISO image. (-as mkisofs --protective-msdos-label)
This is not needed for booting, but shall tell
partitioning tools that the ISO image is not
unused media space.

> If you make any changes to --efi-boot option, please tell me.

There are no changes planned, except eventual
fixing of obvious bugs.
If other behavior is desired, then i would rather
introduce a new option.

(I am undecided whether i shall support
 -efi-boot with a single dash as alias of -e.
 Maybe it is better not to confuse the user
 by having --efi-boot and -efi-boot with
 different behavior.)

Have a nice day :)


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