[syslinux] Is efiboot.img required?

[piranna at gmail.com]

> I am replying to this email, but the content of your prior email might
> be relevant too.

Thank you :-)


> IMHO, the current content of the Isohybrid page in the Syslinux Wiki is
> not clear enough (in the past we have had here some discussion about
> the target audience of such page). The current generic information is
> rather focused on _potential_ capabilities of _isohybrid_ tools and
> some of their internal technical characteristics, and less focused on
> actual practical steps for ends users.

I think the content although is not a step-by-step is good in general,
but I need to expend several hours looking for internet to understand
what the h*ll was the efiboot.img, what format it had and how to build
it. Later I see it's explained there but not too clear since the text
give the impression the file it's already there in the SysLinux files
(similar to mbr.bin and others) and that it did a loopback from the
EFI boot to the actual IsoLinux partition, not that it's an actual
boot partition itself. This text definitely needs an update, because I
was totally wrong here...


> Currently (as of v.6.03), 'syslinux.efi' does not support multiple
> volumes in the way that is currently described in the 'isohybrid' wiki
> page, so 'syslinux.efi' cannot simultaneously access both volumes, the
> ISO9660 volume and a FAT volume in an "efi.img". Additionally,
> currently 'syslinux.efi' has no support for ISO9660.
>
> So, even before evaluating whichever potential conflicts with specific
> hardware or with any variant of (U)EFI (e.g. EFI-based Macs) or with
> specific kernels, the fact is that 'syslinux.efi' could help you boot,
> for example, a USB flash drive formatted with FAT32, or a FAT EFI
> System Partition in your local disk drive, or network booting UEFI
> clients, but currently 'syslinux.efi' has no use for "efi.img" in a
> ISO9660 volume, and it cannot boot optical media in UEFI mode (with or
> without an "efi.img").

Ok, since I'm mostly interested on using USB pendrives so we can
consider that almost nobody will use a CD on an EFI-based computer
(CDs are a good thing too, but who use them today? With BIOS-based
computers support is just enough) and I'm writting the IsoHybrid image
to an USB pendrive for my tests, crafting by hand (without the --uefi
isohybrid argument) a volume (the ISO9660 one that later will be
written to the USB, setting there the files from efiboot.img) marked
with the esp flag and with the syslinux.efi file would work (so no
need for efiboot.img), or does syslinux.efi needs support for ISO9660
first? As I said, syslinux.efi is reading the kernel.img and initrd.gz
files from the efiboot.img image, but not booting them... :-/


> If you want to be able to boot a (FAT) storage media (such as a USB
> drive, among others) in UEFI mode, or network boot UEFI clients, then
> 'syslinux.efi' v.6.03 might be useful for you. The same ISO(hybrid)
> image could be used in systems with CSM mode in the same way as it is
> used in BIOS-based hardware (by means of ISOLINUX, for example).

Well, that's what tried first and didn't worked, on BIOS-based systems
it boot but on my MacBook as Legacy OS didn't ("Operating System not
found -- Insert disk and press any key"), that's why I started to
experiment with EFI... :-/


> If you really need to boot optical media in UEFI mode, then you/we
> could wait some (long) time for potential developments in Syslinux, or
> you might want to consider other UEFI bootloaders, unfortunately.

Not at all. As I've said, booting from USB from an IsoHybrid-generated
image on my MacBook is just enough, and in fact if I could do it in
CSM mode I would remove EFI at all :-D


-- 
"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