[wishlist] Make the GRUB installation procedure smarter

Every time the operating system is instantiated the GRUB boot-loader is inexplicitly re-installed. This behaviour leads to unsolicited changes to the user's boot configuration on UEFI systems; and leads to unnecessary write operations on the ESP, and/or the MBR, which, in case they are abruptly aborted during the building of the install-bootloader derivation, can leave the system in an unbootable state. Futhermore, frequent writes to the platform's NV-RAM may negatively impact its lifespan.

NixOS stores the GRUB derivation as well as boot parameters in a state file, and only re-installs the boot-loader if the computed state is different from the stored state: https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/system/boot/loader/grub/install-grub.pl#L626.However, unless I am mistaken, that alone will not prevent GRUB from altering the user's boot configuration in a scenario, in which we want GRUB to be re-installed because it has received an update.

To summarize, I think that consecutive grub-install invocations should not be allowed to modify the user's boot configuration on UEFI systems, and that we should teach Guix to only re-install the boot-loader if the boot parameters has been changed and/or the GRUB package has been upgraded.

Although other boot-loaders are not in the scope of this wish, brining their installation procedures to the same high standard would be beneficial, too.

I would like to clarify that whenever I wrote "boot parameters", I meant installation arguments passed to grub-install.

First I was using Guix on Lenovo Carbon X1 in parallel with Arch.

Few times I experiences "NVRAM full" or similar problem, I don't

recall now. Solution was to reset NVRAM by some procedure. Half a

year now, I moved to System76 Lemur Pro, where I have only Guix

alone. Here I have another problem, sometimes it simply does not

boot, then I have to plug USB, and run grub-install manually to

recover.

As per discussion on IRC today, I would suggest the folowing

regarding grub efi, I'm not using other bootloaders, but I suppose

same logic may apply.

There are two things about grub:

1) /boot/efi/EFI/Guix/grubx64.efi & NVRAM - these are changing

very very rarely, only when grub version change, boot partition

change.

2) /boot/grub/* - these are changing only when grub version change

or new guix generation is created, then grub.cfg is getting

updated.

Currently, as far as I understand, both of them are getting

installed with one script from this derivation:

/gnu/store/...-install-bootloader.scm.drv

It could be split into two, one which runs grub-install, i.e. #1

above, the other which covers #2 above, let's say

bootloader-phase-1-install and bootloader-phase-2-install

respectively.

Then, each script can be executed only when derivation is

changing. With the following exceptions:

- must be executed anyway on "guix system init ..."

- must be executed only if "guix system reconfigure

--force-bootloader ..."

Scripts them selves store grub version (via absolute path), thus

if grub updated, derivations will change.

If for some reason, grub and/or nvram getting broken on boot, user

has to boot with some kind recovery media anyway.