This should make the xorriso-based ISO build path respect the
'efiparttable' and 'gpt_hybrid_mbr' settings when building a
UEFI-compatible image, making it write a GPT disk label by default
instead of an MBR (msdos) one. If it's building an image that is not
UEFI-compatible it will always write an MBR label, regardless of
this setting.
If 'gpt_hybrid_mbr' is set, xorriso will write an Ubuntu-style
MBR/GPT hybrid partition table, where the MBR partition table
includes a partition with type 00 and the bootable flag, as well
as the partition with type ee required by the UEFI spec. This
mildly violates the UEFI spec but may make the image bootable on
native BIOS or CSM firmwares which refuse to boot from a disk with
no partition marked 'bootable' in the MBR. If 'gpt_hybrid_mbr' is
not set, xorriso will write a strictly UEFI-spec compliant label,
with just the 'protective MBR' required by the UEFI spec (no
bootable partition) and the correct GPT partition table. Note
this is somewhat different from what gpt_hybrid_mbr does for
disk images.
Also, we now pass -compliance no_emul_toc when building ISOs, as
recommended by upstream in
https://lists.gnu.org/archive/html/bug-xorriso/2024-11/msg00012.html
This tool is generally always going to be building ISOs intended
for write-once use, not multi-session use (and which are rarely,
these days, written to physical discs at all anyway).
Signed-off-by: Adam Williamson <awilliam@redhat.com>
75c9939f84