Comment 0 for bug 1918427

I used APM Mustang which flash-kernel supported in u-boot mode.
But I used it with UEFI environment.
It will cause fatal error when I used ARM64 ubuntu live server ISO to install system.

In code[1], this will not install `flash-kernel` for APM Mustang because of UEFI.
So that means code[2] will not disable `flash-kernel` in target system, only disable `update-initramfs`.

When curtin execute to `install_kernel` stage, code[3,4] will not install `flash-kernel` either.
But in code[5], it will install `linux-generic`.
`linux-generic` has a long dependency tree and it will get `flash-kernel` in Recommended field.
Apt by default will install Recommended package before kernel is installed.[6]
So it will still execute `zz-flash-kernel` and `flash-kernel` when installing kernel.
But system didn't create any `initrd.img` ever because curtin disable `update-initramfs` in code[2].
This will cause that `flash-kernel` cannot find `initrd.img.<kvers>` and fail when installing it.

This issue didn't effect all ARM64 UEFI platform because `flash-kernel` didn't support them and skip.[7]
I'm not sure which is best solution for this.
But I think we should apply PR-27 in `flash-kernel`[8] for enhancement and fix curtin process with this patch both.

If we only apply PR-27, it should work fine as well because it will be skipped when detecting UEFI
and install `flash-kernel` before `disable_update_initranfs` in ARM platform without UEFI.[9]

[Patch-1,2,3] might have side effect.
Picking one patch for curtin should be enough.
But I need your advice for this to determine which one is better for curtin.
There are two categories
1. avoid installing flash-kernel if no need, [Patch1,2]
2. always install flash-kernel in arm/arm64 and make sure it be installed before code[2] [Patch3]
(I will attach patch in reply.)

Thanks a lot
Regards,
Date

[1] https://github.com/canonical/curtin/blob/master/curtin/deps/__init__.py#L57-L58
[2] https://github.com/canonical/curtin/blob/master/curtin/commands/curthooks.py#L1693-L1699
[3] https://github.com/canonical/curtin/blob/master/curtin/commands/curthooks.py#L365-L370
[4] https://github.com/canonical/curtin/blob/master/curtin/commands/curthooks.py#L311-L327
[5] https://github.com/canonical/curtin/blob/master/curtin/commands/curthooks.py#L372-L374
[6] https://github.com/Debian/apt/blob/master/apt-pkg/init.cc#L132
[7] https://salsa.debian.org/installer-team/flash-kernel/-/blob/master/functions#L787
[8] https://salsa.debian.org/installer-team/flash-kernel/-/merge_requests/27
[9] curtin will insert `flash-kernel` into `REQUIRED_EXECUTABLES` when system is arm/arm64 without UEFI.