nixos/profiles/base: support bcachefs

[MakiseKurisu]

Add bcachefs support in the base profile.

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 25.05 Release Notes (or backporting 24.11 and 25.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

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[MakiseKurisu]

Test condition was updated to check the actual underlying kernel package:

nix-repl> pkgs.linuxPackages.kernel == pkgs.linuxPackages_6_6.kernel
true

nix-repl> pkgs.linuxPackages == pkgs.linuxPackages_6_6              
false

However, evaluating with the current bcachefs ISO sample code sans the explicit bcachefs enablement is still causing error:

       … while evaluating 'config.boot.kernelPackages' to select 'kernel' on it
         at /nix/store/py8fn4zjmy5fmfrchrml4rljs0wjngvm-source/nixos/modules/profiles/base.nix:51:19:
           50|     # when bcachefs module no longer defaults to latest kernel
           51|     lib.optional (config.boot.kernelPackages.kernel == pkgs.linuxPackages_latest.kernel) "bcachefs" ++
             |                   ^
           52|     lib.optional (lib.meta.availableOn pkgs.stdenv.hostPlatform config.boot.zfs.package) "zfs";

       … from call site
         at /nix/store/py8fn4zjmy5fmfrchrml4rljs0wjngvm-source/nixos/modules/profiles/base.nix:51:19:
           50|     # when bcachefs module no longer defaults to latest kernel
           51|     lib.optional (config.boot.kernelPackages.kernel == pkgs.linuxPackages_latest.kernel) "bcachefs" ++
             |                   ^
           52|     lib.optional (lib.meta.availableOn pkgs.stdenv.hostPlatform config.boot.zfs.package) "zfs";

       … while calling anonymous lambda
         at /nix/store/py8fn4zjmy5fmfrchrml4rljs0wjngvm-source/lib/attrsets.nix:1204:18:
         1203|         mapAttrs
         1204|           (name: value:
             |                  ^
         1205|             if isAttrs value && cond value

       … from call site
         at /nix/store/py8fn4zjmy5fmfrchrml4rljs0wjngvm-source/lib/attrsets.nix:1207:18:
         1206|             then recurse (path ++ [ name ]) value
         1207|             else f (path ++ [ name ]) value);
             |                  ^
         1208|     in

       … while calling anonymous lambda
         at /nix/store/py8fn4zjmy5fmfrchrml4rljs0wjngvm-source/lib/modules.nix:254:72:
          253|           # For definitions that have an associated option
          254|           declaredConfig = mapAttrsRecursiveCond (v: ! isOption v) (_: v: v.value) options;
             |                                                                        ^
          255|

       … while evaluating the attribute 'value'
         at /nix/store/py8fn4zjmy5fmfrchrml4rljs0wjngvm-source/lib/modules.nix:816:9:
          815|     in warnDeprecation opt //
          816|       { value = addErrorContext "while evaluating the option `${showOption loc}':" value;
             |         ^
          817|         inherit (res.defsFinal') highestPrio;

       error: infinite recursion encountered
       at /nix/store/py8fn4zjmy5fmfrchrml4rljs0wjngvm-source/lib/modules.nix:816:9:
          815|     in warnDeprecation opt //
          816|       { value = addErrorContext "while evaluating the option `${showOption loc}':" value;
             |         ^
          817|         inherit (res.defsFinal') highestPrio;

[Mic92]

Test condition was updated to check the actual underlying kernel package:

nix-repl> pkgs.linuxPackages.kernel == pkgs.linuxPackages_6_6.kernel
true

nix-repl> pkgs.linuxPackages == pkgs.linuxPackages_6_6              
false

However, evaluating with the current bcachefs ISO sample code sans the explicit bcachefs enablement is still causing error:

       … while evaluating 'config.boot.kernelPackages' to select 'kernel' on it
         at /nix/store/py8fn4zjmy5fmfrchrml4rljs0wjngvm-source/nixos/modules/profiles/base.nix:51:19:
           50|     # when bcachefs module no longer defaults to latest kernel
           51|     lib.optional (config.boot.kernelPackages.kernel == pkgs.linuxPackages_latest.kernel) "bcachefs" ++
             |                   ^
           52|     lib.optional (lib.meta.availableOn pkgs.stdenv.hostPlatform config.boot.zfs.package) "zfs";

       … from call site
         at /nix/store/py8fn4zjmy5fmfrchrml4rljs0wjngvm-source/nixos/modules/profiles/base.nix:51:19:
           50|     # when bcachefs module no longer defaults to latest kernel
           51|     lib.optional (config.boot.kernelPackages.kernel == pkgs.linuxPackages_latest.kernel) "bcachefs" ++
             |                   ^
           52|     lib.optional (lib.meta.availableOn pkgs.stdenv.hostPlatform config.boot.zfs.package) "zfs";

       … while calling anonymous lambda
         at /nix/store/py8fn4zjmy5fmfrchrml4rljs0wjngvm-source/lib/attrsets.nix:1204:18:
         1203|         mapAttrs
         1204|           (name: value:
             |                  ^
         1205|             if isAttrs value && cond value

       … from call site
         at /nix/store/py8fn4zjmy5fmfrchrml4rljs0wjngvm-source/lib/attrsets.nix:1207:18:
         1206|             then recurse (path ++ [ name ]) value
         1207|             else f (path ++ [ name ]) value);
             |                  ^
         1208|     in

       … while calling anonymous lambda
         at /nix/store/py8fn4zjmy5fmfrchrml4rljs0wjngvm-source/lib/modules.nix:254:72:
          253|           # For definitions that have an associated option
          254|           declaredConfig = mapAttrsRecursiveCond (v: ! isOption v) (_: v: v.value) options;
             |                                                                        ^
          255|

       … while evaluating the attribute 'value'
         at /nix/store/py8fn4zjmy5fmfrchrml4rljs0wjngvm-source/lib/modules.nix:816:9:
          815|     in warnDeprecation opt //
          816|       { value = addErrorContext "while evaluating the option `${showOption loc}':" value;
             |         ^
          817|         inherit (res.defsFinal') highestPrio;

       error: infinite recursion encountered
       at /nix/store/py8fn4zjmy5fmfrchrml4rljs0wjngvm-source/lib/modules.nix:816:9:
          815|     in warnDeprecation opt //
          816|       { value = addErrorContext "while evaluating the option `${showOption loc}':" value;
             |         ^
          817|         inherit (res.defsFinal') highestPrio;

If you build an image with bcache support based on the installer profile, you can disable zfs like this:

# take from: cd-dvd/installation-cd-minimal-new-kernel-no-zfs.nix
{
  imports = [ ./installation-cd-minimal-new-kernel.nix ]; 
 
  boot.supportedFilesystems.zfs = lib.mkForce false;
} 

Or enable zfsUnstable (which supports a kernel also supported by bcachefs.
However this is not something we can solve in the bcachefs module.
There exist constellations which support both zfs and bcachefs (we have that https://github.com/nix-community/nixos-images). Therefore we should not disable zfs in the bcachefs module.

[MakiseKurisu]

Here is the full code that I'm testing with that got the above infinite recursion, which is already using no-zfs profile:

# nix build --show-trace .#nixosConfigurations.exampleIso.config.system.build.isoImage
{
  description = "Bcachefs enabled installation media";
  inputs.nixos.url = "github:MakiseKurisu/nixpkgs/bcachefs-base";
  outputs = { self, nixos }: {
    nixosConfigurations = {
      exampleIso = nixos.lib.nixosSystem {
        system = "x86_64-linux";
        modules = [
          "${nixos}/nixos/modules/installer/cd-dvd/installation-cd-minimal-new-kernel-no-zfs.nix"
          ({ lib, pkgs, ... }: {
            # Might be required as a workaround for bug
            # https://github.com/NixOS/nixpkgs/issues/32279
            environment.systemPackages = [ pkgs.keyutils ];
            # boot.supportedFilesystems = [ "bcachefs" ];
            # boot.kernelPackages = pkgs.linuxPackages_latest;
          })
        ];
      };
    };
  };
}

Either way I don't think this is related to ZFS, but I'm also not sure how to fix this infinite recursion issue.

[Mic92]

Ah. Actually I noticed you removed the force override filesystems. I think now it's fine actually.

[MakiseKurisu]

Um this PR currently does not build the sample I provided. My guess is that I'm referencing config.boot.kernelPackages which is also touched by bcachefs module if it is enabled. I'm currently out of idea of how to fix it.

[Mic92]

Um this PR currently does not build the sample I provided. My guess is that I'm referencing config.boot.kernelPackages which is also touched by bcachefs module if it is enabled. I'm currently out of idea of how to fix it.

Maybe just enable it in the installer profile that adds the latest kernel?

[Mic92]

But this should be part of the bcachefs module no?

[MakiseKurisu]

In keyctl's man page it says:

       Session keyring: @s or -3
              Each process subscribes to a session keyring that is
              inherited across (v)fork, exec and clone. This is searched
              after the process keyring. Session keyrings can be named
              and an extant keyring can be joined in place of a
              process's current session keyring.

       User specific keyring: @u or -4
              This keyring is shared between all the processes owned by
              a particular user. It isn't searched directly, but is
              **normally linked to from the session keyring.**

So it looks like this might be a more general configuration that are not limited to bcachefs usage. But I'm not sure why we didn't link those 2 keyrings in the first place, and if that actually should be a general setting. So I'm just doing the safe thing as listed in the NixOS Wiki.

[Mic92]

Suggested change

	- `bcachefs` is now enabled in the installation media with a suitable kernel.
	- `bcachefs` is now enabled in the installation media with the latest kernel available.

[MakiseKurisu]

I think we can see 25.05 releases with 6.12 as the default, and hopefully bcachefs module can drop its version override. In that case we just go back to the version check (>=6.7) so a suitable kernel will be more appropriate.

But then it turned out currently it is quite difficult to check if the config.boot.kernelPackages is actually pkgs.linuxPackages_latest, so this PR is no longer the one-liner I was expecting. Might be better to actually wait for those blockages to be fixed first before continuing.

[MakiseKurisu]

6.12 is the default now: #370410

[Mic92]

Yeah that means we could just enable it without any hacks.

[MakiseKurisu]

Locally built the ISO for 6.6 and default, and confirmed nix-store.squashfs contains bcachefs stuff if kernelPackages is commented out. Too lazy to spin up a VM for the night though.

# nix build --show-trace .#nixosConfigurations.exampleIso.config.system.build.isoImage
{
  description = "Bcachefs enabled installation media";
  inputs.nixos.url = "github:MakiseKurisu/nixpkgs/bcachefs-base";
  outputs = { self, nixos }: {
    nixosConfigurations = {
      exampleIso = nixos.lib.nixosSystem {
        system = "x86_64-linux";
        modules = [
          "${nixos}/nixos/modules/installer/cd-dvd/installation-cd-minimal.nix"
          ({ lib, pkgs, ... }: {
            boot.kernelPackages = pkgs.linuxPackages_6_6;
          })
        ];
      };
    };
  };
}