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nikstur 289dd22132 nixos/qemu-vm: simplify building nix store image 
Summary of this change:

- Simplify code.
- Stop a disk image from being cached in the binary cache.
- Make erofs Nix Store image build in an acceptable time outside of
  testing environments (like `darwin.builder`).
- Do not regress on performance for tests that use many store paths in
  their Nix store image.
- Slightly longer startup time for tests where not many store paths are
  included in the image (these probably shouldn't use `useNixStoreImage`
  anyways).
- Slightly longer startup time when inputs of VM do not change because
  the Nix store image is not cached anymore.

Remove the `storeImage` built with make-disk-image.nix. This produced a
separate derivation which is then cached in the binary cache. These
types of images should be avoided because they gunk up the cache as they
change frequently. Now all Nix store images, whether read-only or
writable are based on the erofs image previously only used for read-only
images.

Additionally, simplify the way the erofs image is built by copying the
paths to include to a separate directory and build the erofs image from
there.

Before this change, the list of Nix store paths to include in the Nix
store image was converted to a complex regex that *excludes* all other
paths from a potentially large Nix store.

This previous approach suffers from two issues:

1. The regex is complex and, as admitted in the source code of the
   includes-to-excludes.py script, most likely contains at least one
   error. This means that it's unlikely that anyone will touch this
   piece of software again.

2. When the Nix store image is built from a large Nix store (like when
   you build the VM script to run outside of any testing context) this
   regex becomes painfully slow. There is at least one prominent
   use-case where this matters: `darwin.builder`.

Benchmarking impressions:

- Building Nix store via make-disk-image.nix takes ~25s
- Building Nix store as an erofs image takes ~4s
- Running nixosTests.qemu-vm-writable-store-image takes ~10s when
  building the erofs image with the regex vs ~14s when building by
  copying to a temporary directory.
- nixosTests.gitlab which had the biggest gains from the initial erofs
  change takes the same time as before.
- On a host with ~140k paths in /nix/store, building the erofs image
  with the regex takes 410s as opposed to 6s when copying to a temporary
  directory.
2024-07-18 20:24:58 +02:00
..
doc/manual nixos/hardware.display: init 2024-07-18 16:57:40 +03:00
lib nixos/testing: Add ipv6 configuration 2024-07-18 10:22:32 +02:00
maintainers nixos/amazon-image: avoid top-level with statements in maintainers script 2024-07-15 22:02:39 -07:00
modules nixos/qemu-vm: simplify building nix store image 2024-07-18 20:24:58 +02:00
tests Merge pull request #290730 from nikstur/qemu-vm-refactoring 2024-07-18 19:34:51 +02:00
COPYING
default.nix
README.md Release NixOS 24.05 2024-05-31 20:17:44 +02:00
release-combined.nix nixos/release-combined: fix evaluation 2024-06-05 17:50:37 +02:00
release-small.nix openssh: put tests into passthru 2024-06-14 23:52:56 +02:00
release.nix treewide: rename renamed sddm/displayManager settings 2024-04-08 21:56:38 +02:00

README.md

NixOS

NixOS is a Linux distribution based on the purely functional package management system Nix. More information can be found at https://nixos.org/nixos and in the manual in doc/manual.

Testing changes

You can add new module to your NixOS configuration file (usually it’s /etc/nixos/configuration.nix). And do sudo nixos-rebuild test -I nixpkgs=<path to your local nixpkgs folder> --fast.

Commit conventions

  • Make sure you read about the commit conventions common to Nixpkgs as a whole.

  • Format the commit messages in the following way:

    nixos/(module): (init module | add setting | refactor | etc)

(Motivation for change. Link to release notes. Additional information.)

    Examples:

    • nixos/hydra: add bazBaz option

      Dual baz behavior is needed to do foo.

    • nixos/nginx: refactor config generation

      The old config generation system used impure shell scripts and could break in specific circumstances (see #1234).

Reviewing contributions

When changing the bootloader installation process, extra care must be taken. Grub installations cannot be rolled back, hence changes may break people’s installations forever. For any non-trivial change to the bootloader please file a PR asking for review, especially from @edolstra.

Module updates

Module updates are submissions changing modules in some ways. These often contains changes to the options or introduce new options.

Reviewing process:

  • Ensure that the module maintainers are notified.
    • CODEOWNERS will make GitHub notify users based on the submitted changes, but it can happen that it misses some of the package maintainers.
  • Ensure that the module tests, if any, are succeeding.
    • You may invoke OfBorg with @ofborg test <module> to build nixosTests.<module>
  • Ensure that the introduced options are correct.
    • Type should be appropriate (string related types differs in their merging capabilities, loaOf and string types are deprecated).
    • Description, default and example should be provided.
  • Ensure that option changes are backward compatible.
    • mkRenamedOptionModuleWith provides a way to make renamed option backward compatible.
    • Use lib.versionAtLeast config.system.stateVersion "24.05" on backward incompatible changes which may corrupt, change or update the state stored on existing setups.
  • Ensure that removed options are declared with mkRemovedOptionModule.
  • Ensure that changes that are not backward compatible are mentioned in release notes.
  • Ensure that documentations affected by the change is updated.

Sample template for a module update review is provided below.

##### Reviewed points

- [ ] changes are backward compatible
- [ ] removed options are declared with `mkRemovedOptionModule`
- [ ] changes that are not backward compatible are documented in release notes
- [ ] module tests succeed on ARCHITECTURE
- [ ] options types are appropriate
- [ ] options description is set
- [ ] options example is provided
- [ ] documentation affected by the changes is updated

##### Possible improvements

##### Comments

New modules

New modules submissions introduce a new module to NixOS.

Reviewing process:

  • Ensure that all file paths fit the guidelines.
  • Ensure that the module tests, if any, are succeeding.
  • Ensure that the introduced options are correct.
    • Type should be appropriate (string related types differs in their merging capabilities, loaOf and string types are deprecated).
    • Description, default and example should be provided.
  • Ensure that module meta field is present
    • Maintainers should be declared in meta.maintainers.
    • Module documentation should be declared with meta.doc.
  • Ensure that the module respect other modules functionality.
    • For example, enabling a module should not open firewall ports by default.

Sample template for a new module review is provided below.

##### Reviewed points

- [ ] module path fits the guidelines
- [ ] module tests succeed on ARCHITECTURE
- [ ] options have appropriate types
- [ ] options have default
- [ ] options have example
- [ ] options have descriptions
- [ ] No unneeded package is added to `environment.systemPackages`
- [ ] `meta.maintainers` is set
- [ ] module documentation is declared in `meta.doc`

##### Possible improvements

##### Comments