(Feature request) loopback.cfg files for booting Live ISOs from hard disk

[probonopd]

Please consider generating loopback.cfg files.

A loopback.cfg is basically just a grub.cfg that's designed to be used to boot a live distribution from an ISO file on a filesystem rather than an actual physical CD.

This allows it to make it easy to boot many different ISOs e.g., from an SSD like this:

Without a loopback.cfg file, systems like https://www.ventoy.net/en/index.html and https://github.com/probonopd/SystemImageKit have to take care of each distribution (version) and, as a result, take a lot of maintenance work and/or tend to break frequently, whereas with a loopback.cfg file it "just works" without the tools having to play "catch up" with new distribution releases.

Here is the specification:
https://www.supergrubdisk.org/wiki/Loopback.cfg

Many distributions have started shipping those, including:

• Manjaro
• Ubuntu
• Grml

@Conan-Kudo hinted that with the following, a main showstopper that had prevented loopback.cfg files from being used in the past might be removed: https://fedoraproject.org/wiki/Changes/OptimizeSquashFSOnDVDByRemovingEXT4FilesystemImageLayer

[bcl]

• Would this be for both the boot.iso and the live iso?
• Does it work with UEFI?
• Does it work on all architectures?

It sounds like a pretty minimal change, but I don't use this kind of booting at all so someone is going to need to come up with a working loopback.cfg that I can turn into a template, and test the results for me.

Changes should be:

• Add a template loopback.cfg file to the supported architectures under share/templates.d/99-generic/live/config_files/
• Install it to /boot/grub/ in share/templates.d/99-generic/live/x86.tmpl (and other arches)
• Replace placeholder values with correct ones in the same way we do for isolinux.cfg

[probonopd]

Would this be for both the boot.iso and the live iso?

It would be most helpful for Live ISOs, which this request is about. But if people find it useful for boot.iso, it could be used there as well.

Does it work with UEFI?

Yes.

Does it work on all architectures?

It works on all architectures which GRUB works on, as it is basically just a GRUB config file.

It sounds like a pretty minimal change, but I don't use this kind of booting at all so someone is going to need to come up with a working loopback.cfg that I can turn into a template, and test the results for me.

I volunteer to help with the testing on EFI, non-EFI, and EFI-CSM systems. But I lack the environment and skills to implement the needed changes myself.