[syslinux] Is efiboot.img required?

[piranna at gmail.com]

> isohybrid violates UEFI by combining both methods and
> by nesting partitions. The motivation for this is given by
> Matthew Garrett in
>   http://mjg59.dreamwidth.org/11285.html

There it says about creating a third El Torito image only for Macs,
since old ones could fail and this could be the problem I'm having.
I've used the --mac option of IsoHybrid and it's demanding another
disk image, so this should be documented too...


>> > All EFI isohybrid images known to me contain
>> > /efi/boot/bootx64.efi from GRUB Legacy or GRUB2.
>
>> For some hypothetical support of UEFI booting optical media and/or
>> dd'ed isohybrid images, yes, that is currently the case in the Linux
>> world. But if I would want to use a FAT-formatted ESP, I could use
>> 'syslinux.efi' (and/or others too), whether the ISO image is
>> "isohybrid" or not.
>
> Of course, piranna could set up an EFI capable disk boot
> image by help of SYSLINUX. But that would not boot from
> optical media.
> The EFI isohybrid feature is to mark the ESP by both,
> El Torito and partition table.

This is what I've done, a FAT disk image with syslinux.efi and embed
it inside the IsoHybrid disk image, but when dd'd to the USB pendrive,
SysLinux.efi loads the Linux kernel and its initramfs file but doesn't
boot... :-/ As I put in the initial message I'm not using the
/efi/boot/bootx64.efi path but instead just copied all files in the
root directory of the FAT disk image, but since it already load the
kernel and the initramfs maybe the canonical path is not required...
is it? Do I need to use the canonical one (and why)?


>> _ differentiate what _isohybrid_ itself can and cannot do
>
> It equips ISO 9660 filesystem images with partition tables
> which point to the software for the initial boot stage.
> It cannot create the FAT image for the EFI System Partition.

Also add instructions about how to create a FAT image... and maybe add
the hability to craft it with IsoLinux/SysLinux/syslinux.efi instead
of depending to GRUB2 or other bootloaders, ideally by piggy-back over
the real ISO9660 partition (syslinux.efi is the ideal candidate to
support that, but maybe it could be better a custom bootloaded that
only do this task?).


>> _ present the command line options with a minimal very short
>> description, linking to man pages and similar official documentation
>> for further reading;
>
> The only non-expert option is --uefi.
> There is no further non-expert documentation known to me.

I think --mac could fall in this topic too.


>> _ generic examples of isohybrid steps / commands;
>
> For BIOS-only, the user makes the ISO according to
>   http://www.syslinux.org/wiki/index.php/ISOLINUX
> and applies the isohybrid program.
> Or the user makes the ISO by xorriso and lets it do the job
> of isohybrid already when creating the ISO.
>
> For UEFI there are examples with genisoimage and xorriso
> in wiki/index.php/Isohybrid, plus a mkisofs equivalent of
> genisoimage option -e.

Info about creation of the FAT disk image, and if there's any
diference (that seems there are), example for EFI-based Macs.


-- 
"Si quieres viajar alrededor del mundo y ser invitado a hablar en un
monton de sitios diferentes, simplemente escribe un sistema operativo
Unix."
– Linus Tordvals, creador del sistema operativo Linux