nixos/iosched: init module

[illdefined]

Description of changes

This module introduces the following options to set I/O schedulers for block devices and generates appropriate udev rules:

• hardware.block.defaultScheduler: Default scheduler for all block devices.
• hardware.block.defaultSchedulerRotational: Default scheduler for rotational drives, such as hard drives.
• hardware.block.scheduler: Schedulers for specific block devices.

This solves #57577. My personal motivation is that I often run workloads that do not perform well with the default scheduler and I would like to have a way to override it without writing individual udev rules for simple cases.

hardware.block.scheduler is an attribute set assigning schedulers by device name pattern. Using an attrset limits its use to non‐overlapping patterns. Overlapping patterns could be supported by instead using a list of attrsets, but I believe that users requiring these are served better by producing their own custom udev rules.

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/)
• 24.11 Release Notes (or backporting 23.11 and 24.05 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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