WIP: nixos/xen: init guest-agent module

[SigmaSquadron]

Description of changes

Turns the profile meant for Xen guests into a proper module that can be enabled as an option.
We also enable it by default on the graphical ISO and differentiate the wording of the xe-guest-agent module, which is the Citrix XenServer guest utilities.

This is based on @matdibu's previous work.

A lot of testing is required before this can be merged. Any and all testers are welcome to help us out!

Things done

• Built on platform(s)
  • x86_64-linux
• Tested, as applicable: Invalid
  • We desperately need an automated testing suite. Manual testing has revealed no issues when providing a separately-built kernel and starting the NixOS activation script from the hypervisor.
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review pr 341129". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of ISO images, HVM domains and PV/PVH domains
• 24.11 Release Notes (or backporting 23.11 and 24.05 Release notes)
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

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[SigmaSquadron]

@matdibu: Hey mate, this is a rough draft so far, but I'd appreciate any comments you may have, as you're more experienced than me with the new rust-based tools.

[matdibu]

@matdibu: Hey mate, this is a rough draft so far, but I'd appreciate any comments you may have, as you're more experienced than me with the new rust-based tools.

you're giving me too much credit, I was just playing around with XCP-ng so I decided to make the experience a bit better for NixOS

that being said, this is nice, thank you!

[SigmaSquadron]

Sooo, this seems to cause a disko rebuild. I have no idea why. because disko depends on the default ISO files.

[wexder]

@SigmaSquadron Trying to run this by copying it into my configurations, I run into issue:

error: builder for '/nix/store/6yh0amr86fxacw7arv7a3i3495pxsdgm-linux-6.6.51-modules-shrunk.drv' failed with exit code 1;
       last 10 log lines:
       > root module: xen_netfront
       >   copying dependency: /nix/store/jhd4b6hjjbsfig5vdanp0z6a82ba8hjd-linux-6.6.51-modules/lib/modules/6.6.51/kernel/drivers/net/xen-netfront.ko.xz
       > root module: xen_pcifront
       >   copying dependency: /nix/store/jhd4b6hjjbsfig5vdanp0z6a82ba8hjd-linux-6.6.51-modules/lib/modules/6.6.51/kernel/drivers/pci/xen-pcifront.ko.xz
       > root module: xen_scsifront
       >   dependency already copied: /nix/store/jhd4b6hjjbsfig5vdanp0z6a82ba8hjd-linux-6.6.51-modules/lib/modules/6.6.51/kernel/drivers/scsi/scsi_common.ko.xz
       >   dependency already copied: /nix/store/jhd4b6hjjbsfig5vdanp0z6a82ba8hjd-linux-6.6.51-modules/lib/modules/6.6.51/kernel/drivers/scsi/scsi_mod.ko.xz
       >   copying dependency: /nix/store/jhd4b6hjjbsfig5vdanp0z6a82ba8hjd-linux-6.6.51-modules/lib/modules/6.6.51/kernel/drivers/scsi/xen-scsifront.ko.xz
       > root module: xen_balloon
       > modprobe: FATAL: Module xen_balloon not found in directory /nix/store/jhd4b6hjjbsfig5vdanp0z6a82ba8hjd-linux-6.6.51-modules/lib/modules/6.6.51
       For full logs, run 'nix log /nix/store/6yh0amr86fxacw7arv7a3i3495pxsdgm-linux-6.6.51-modules-shrunk.drv'.
error: 1 dependencies of derivation '/nix/store/c4y9s9n2f5isbwsdfrnrbw5v6ywnaswq-initrd-linux-6.6.51.drv' failed to build
error: 1 dependencies of derivation '/nix/store/gjpv0lmis474abx92mi34j3ixjplbm3w-nixos-system-nixos-24.11.20240913.537289e.drv' failed to build
error: 1 dependencies of derivation '/nix/store/rzlk3f3dbxwgll6y3sq7si8y8w15pyyx-activatable-nixos-system-nixos-24.11.20240913.537289e.drv' failed to build
error: 1 dependencies of derivation '/nix/store/q8bfq6a1j3pglybjpy7xhdsgcw1r5qvk-deploy-rs-check-activate.drv' failed to build
error: build of '/nix/store/0f5301z5mm0p0p015im4mg3hw1i5fch9-jsonschema-deploy-system.drv', '/nix/store/q8bfq6a1j3pglybjpy7xhdsgcw1r5qvk-deploy-rs-check-activate.drv' failed

Other then that it seems to be working great

[SigmaSquadron]

yep, that and the fact that the ISO image is using the old option is why I just added DO NOT MERGE

will fix it tomorrow

[SigmaSquadron]

cc @ElvishJerricco as the latest ISO maintainer to be touched by the nixpkgs curse.

97cdedf

[SigmaSquadron]

To avoid merge conflicts, I'll wait for #344314 to be merged first and target this for 25.05.

[SigmaSquadron]

Depends on #363388