Commit 973fbf96 authored by Vincent Haupert's avatar Vincent Haupert
Browse files

nixos/image/repart: allow replacing `/nix/store`

parent 92127274

nixos/doc/manual/installation/building-images-via-systemd-repart.chapter.md

+46 −4
Original line number Diff line number Diff line
@@ -40,12 +40,18 @@ An example of how to build an image: 
}

```



## Nix Store Partition {#sec-image-repart-store-partition}

## Nix Store Paths {#sec-image-repart-store-paths}



If you want to rewrite Nix store paths, e.g., to remove the `/nix/store` prefix

or to nest it below a parent path, you can do that through the

`nixStorePrefix` option.



### Nix Store Partition {#sec-image-repart-store-partition}



You can define a partition that only contains the Nix store and then mount it

under `/nix/store`. Because the `/nix/store` part of the paths is already

determined by the mount point, you have to set `stripNixStorePrefix = true;` so

that the prefix is stripped from the paths before copying them into the image.

determined by the mount point, you have to set `nixStorePrefix = "/"` so

that `/nix/store` is stripped from the paths before copying them into the image.



```nix

{
@@ -54,7 +60,7 @@ that the prefix is stripped from the paths before copying them into the image. 
  image.repart.partitions = {

    "store" = {

      storePaths = [ config.system.build.toplevel ];

      stripNixStorePrefix = true;

      nixStorePrefix = "/";

      repartConfig = {

        Type = "linux-generic";

        Label = "nix-store";
@@ -65,6 +71,42 @@ that the prefix is stripped from the paths before copying them into the image. 
}

```



### Nix Store Subvolume {#sec-image-repart-store-subvolume}



Alternatively, you can create a Btrfs subvolume `/@nix-store` containing the

Nix store and mount it on `/nix/store`:



```nix

{

  fileSystems."/" = {

    device = "/dev/disk/by-partlabel/root";

    fsType = "btrfs";

    options = [ "subvol=/@" ];

  };



  fileSystems."/nix/store" = {

    device = "/dev/disk/by-partlabel/root";

    fsType = "btrfs";

    options = [ "subvol=/@nix-store" ];

  };



  image.repart.partitions = {

    "root" = {

      storePaths = [ config.system.build.toplevel ];

      nixStorePrefix = "/@nix-store";

      repartConfig = {

        Type = "root";

        Label = "root";

        Format = "btrfs";

        Subvolumes = "/@ /@nix-store";

        MakeDirectories = "/@ /@nix-store";

        # ...

      };

    };

  };

}

```



## Appliance Image {#sec-image-repart-appliance}



The `image/repart.nix` module can also be used to build self-contained [software

nixos/doc/manual/redirects.json

+6 −0
Original line number Diff line number Diff line
@@ -287,9 +287,15 @@ 
  "sec-image-repart": [

    "index.html#sec-image-repart"

  ],

  "sec-image-repart-store-paths": [

    "index.html#sec-image-repart-store-paths"

  ],

  "sec-image-repart-store-partition": [

    "index.html#sec-image-repart-store-partition"

  ],

  "sec-image-repart-store-subvolume": [

    "index.html#sec-image-repart-store-subvolume"

  ],

  "sec-image-repart-appliance": [

    "index.html#sec-image-repart-appliance"

  ],

nixos/modules/image/amend-repart-definitions.py

+9 −7
Original line number Diff line number Diff line
@@ -36,11 +36,11 @@ def add_contents_to_definition( 




def add_closure_to_definition(

    definition: Path, closure: Path | None, strip_nix_store_prefix: bool | None

    definition: Path, closure: Path | None, nix_store_prefix: str | None

) -> None:

    """Add CopyFiles= instructions to a definition for all paths in the closure.



    If strip_nix_store_prefix is True, `/nix/store` is stripped from the target path.

    Replace `/nix/store` with the value of nix_store_prefix.

    """

    if not closure:

        return
@@ -52,10 +52,12 @@ def add_closure_to_definition( 
                continue



            source = Path(line.strip())

            target = str(source.relative_to("/nix/store/"))

            target = f":/{target}" if strip_nix_store_prefix else ""

            option = f"CopyFiles={source}"

            if nix_store_prefix:

                target = nix_store_prefix / source.relative_to("/nix/store/")

                option = f"{option}:{target}"



            copy_files_lines.append(f"CopyFiles={source}{target}\n")

            copy_files_lines.append(f"{option}\n")



    with open(definition, "a") as f:

        f.writelines(copy_files_lines)
@@ -102,8 +104,8 @@ def main() -> None: 
        add_contents_to_definition(definition, contents)



        closure = config.get("closure")

        strip_nix_store_prefix = config.get("stripNixStorePrefix")

        add_closure_to_definition(definition, closure, strip_nix_store_prefix)

        nix_store_prefix = config.get("nixStorePrefix")

        add_closure_to_definition(definition, closure, nix_store_prefix)



    print(target_dir.absolute())

nixos/modules/image/repart.nix

+87 −70
Original line number Diff line number Diff line
@@ -15,7 +15,9 @@ let 


  inherit (utils.systemdUtils.lib) GPTMaxLabelLength;



  partitionOptions = {

  partitionOptions =

    { config, ... }:

    {

      options = {

        storePaths = lib.mkOption {

          type = with lib.types; listOf path;
@@ -23,13 +25,21 @@ let 
          description = "The store paths to include in the partition.";

        };



        # Superseded by `nixStorePrefix`. Unfortunately, `mkChangedOptionModule`

        # does not support submodules.

        stripNixStorePrefix = lib.mkOption {

        type = lib.types.bool;

        default = false;

          default = "_mkMergedOptionModule";

          visible = false;

        };



        nixStorePrefix = lib.mkOption {

          type = lib.types.path;

          default = "/nix/store";

          description = ''

          Whether to strip `/nix/store/` from the store paths. This is useful

          when you want to build a partition that only contains store paths and

          is mounted under `/nix/store`.

            The prefix to use for store paths. Defaults to `/nix/store`. This is

            useful when you want to build a partition that only contains store

            paths and is mounted under `/nix/store` or if you want to create the

            store paths below a parent path (e.g., `/@nix/nix/store`).

          '';

        };
@@ -77,6 +87,10 @@ let 
          '';

        };

      };



      config = lib.mkIf (config.stripNixStorePrefix == true) {

        nixStorePrefix = "/";

      };

    };



  mkfsOptionsToEnv =
@@ -350,7 +364,7 @@ in 
          }

        ) cfg.partitions;



        warnings = lib.filter (v: v != null) (

        warnings = lib.flatten (

          lib.mapAttrsToList (

            fileName: partitionConfig:

            let
@@ -358,8 +372,7 @@ in 
              suggestedMaxLabelLength = GPTMaxLabelLength - 2;

              labelLength = builtins.stringLength repartConfig.Label;

            in

            if (repartConfig ? Label && labelLength >= suggestedMaxLabelLength) then

              ''

            lib.optional (repartConfig ? Label && labelLength >= suggestedMaxLabelLength) ''

              The partition label '${repartConfig.Label}'

              defined for '${fileName}' is ${toString labelLength} characters long.

              The suggested maximum label length is ${toString suggestedMaxLabelLength}.
@@ -370,8 +383,12 @@ in 
              ${toString GPTMaxLabelLength} characters long (the maximum enforced by UEFI) and

              you're at version 9, you cannot increment this to 10.

            ''

            else

              null

            ++ lib.optional (partitionConfig.stripNixStorePrefix != "_mkMergedOptionModule") ''

              The option definition `image.repart.paritions.${fileName}.stripNixStorePrefix`

              has changed to `image.repart.paritions.${fileName}.nixStorePrefix` and now

              accepts the path to use as prefix directly. Use `nixStorePrefix = "/"` to

              achieve the same effect as setting `stripNixStorePrefix = true`.

            ''

          ) cfg.partitions

        );

      };