Re: How can we identify an ISO file is an EFI bootable ISO image?

[Rod Smith <rodsmith@rodsbooks.com>]

On 06/20/2017 12:47 PM, Laszlo Ersek wrote:
> On 06/20/17 14:34, Heyi Guo wrote:
> 
>> Several tools like mount in Linux will show all files together
>> including EFI/BOOT directory,
> 
> That directory, displayed as part of the ISO9660 filesystem that was
> written to the ISO image / CD-ROM, is entirely irrelevant when it comes
> to UEFI-bootability. I doesn't even need to exist, and if it does, it's
> likely there only for convenience reasons (so that people don't have to
> run "dumpet" or similar tools to extract the FAT image first, and then
> the EFI binaries second, if they want to investigate the EFI binaries).
> 
> For UEFI boot, only the ElTorito image matters.

MOSTLY, yes; however, some EFI implementations include ISO-9660 drivers.
This is definitely true of the EFI used by VirtualBox. I think I've seen
this feature on one or two UEFI-based PCs, too, but I don't recall the
details and I can't say I'm 100% certain of this. There are also
ISO-9660 drivers floating around that can be loaded from a FAT
partition. In either of these cases, the files on the ISO-9660
filesystem can be used to boot from an optical disc, even if it lacks
the El Torito image.

This is admittedly a corner case at best; but IMHO it's worth keeping in
mind, since non-matching El Torito and ISO-9660 files could lead to user
(or developer) confusion.

-- 
Rod Smith
rodsmith@rodsbooks.com
http://www.rodsbooks.com