On 16/07/2024 at 08:55, Michael Chang via Grub-devel wrote:
4. When booting from an ISO, the ESP is treated as an El Torito image in
the boot catalog. It is therefore presented by firmware and
interpreted by grub as a disk (cd0).
In my limited experience, (cd0) is the whole CD/DVD/BD and GRUB does not
show the EFI El Torito image as such.
Tested with debian-12.6.0-amd64-netinst.iso on QEMU+OVMF and real hardware:
grub> echo $cmdpath
(cd0)/EFI/BOOT
grub> ls
(proc) (memdisk) (cd0) (cd0,apple2) (cd0,apple1) (cd0,msdos2)
grub> ls (cd0)
Device cd0: Filesystem type iso9660 - Label 'Debian 12.6.0 amd64 n' ...
grub> ls (cd0)/
/boot /css /debian /dists /doc /EFI ...
The /EFI directory in the ISO9660 filesystem contains a copy of the EFI
El Torito image contents so that GRUB can find its config file
(cd0)/EFI/debian/grub.cfg.
The Apple and MSDOS partitions are caused by the hybrid structure of the
Debian installation image. Partition (cd0,apple2) matches the position
of the EFI El Torito image but would not exist on a "pure" ISO9660 image.
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