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nixos/config/sysfs: init module#391329

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JohnRTitor merged 2 commits intoNixOS:masterfrom
illdefined:nixos-config-sysfs
Aug 11, 2025
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nixos/config/sysfs: init module#391329
JohnRTitor merged 2 commits intoNixOS:masterfrom
illdefined:nixos-config-sysfs

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@illdefined illdefined commented Mar 19, 2025 •
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This module introduces a config option boot.kernel.sysfs, which permits setting of sysfs parameters.

The configuration option accepts a nested attribute set of sysfs path components with arbitrary values, for example:

{
  kernel.mm.transparent_hugepage = {
    enabled = "always";
    defrag = "defer";
    shmem_enabled = "within_size";
  };
}

The options will be applied through systemd path units watching the individual files or glob patterns and writing the configured value through a small service using systemd-tmpfiles once they exist.

The supplied NixOS test checks if configured parameters are actually applied.

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:
  • 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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@github-actions github-actions bot added 6.topic: nixos Issues or PRs affecting NixOS modules, or package usability issues specific to NixOS 8.has: module (update) This PR changes an existing module in `nixos/` 6.topic: systemd Software suite that provides an array of system components for Linux operating systems. 10.rebuild-darwin: 0 This PR does not cause any packages to rebuild on Darwin. 10.rebuild-linux: 1-10 This PR causes between 1 and 10 packages to rebuild on Linux. labels Mar 19, 2025
@illdefined illdefined force-pushed the nixos-config-sysfs branch 3 times, most recently from 09c76cf to c1a036b Compare March 19, 2025 18:04
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illdefined commented Mar 19, 2025

The NixOS manual build failure appears to be unrelated to this change.

I am able to build the manual locally without any issues:
dpc1yk271wl343axkdy7q3h86jx815m4-nixos-manual-html.tar.gz

@illdefined illdefined force-pushed the nixos-config-sysfs branch 4 times, most recently from 4919977 to cd2a1b7 Compare March 19, 2025 19:17
@github-actions github-actions bot added 8.has: changelog This PR adds or changes release notes 8.has: documentation This PR adds or changes documentation labels Mar 19, 2025
@illdefined illdefined force-pushed the nixos-config-sysfs branch 3 times, most recently from 15061d8 to 8461f59 Compare March 20, 2025 00:15
@illdefined illdefined marked this pull request as ready for review March 20, 2025 00:38
@illdefined illdefined changed the title nixos/config/sysfs: init nixos/config/sysfs: init module Mar 20, 2025
@illdefined illdefined force-pushed the nixos-config-sysfs branch 2 times, most recently from 4f517c7 to ebfe568 Compare March 20, 2025 04:03
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r-vdp commented Mar 20, 2025 •
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One issue here, is that a lot of sysfs paths depend on kernel modules being loaded, which may happen at a later time.
On my systems, I use systemd path units to trigger a service whenever a certain path appears (because a module got loaded, e.g. hotplugging a device), and then that service writes a value to the file in sysfs.

I wonder if we'd want to support something like that? Currently the module in this PR will only work for sysfs paths that are present at the time systemd-tmpfiles runs.

SuperSandro2000
SuperSandro2000 reviewed Mar 20, 2025
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types have descriptions? That's new to me.

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The description is usually generated automatically, but due to the nesting this would lead to an infinite recursion. I therefore override the description attribute and describe the type manually.

This description is included in the generated option documentation.

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SuperSandro2000 commented Mar 20, 2025

One issue here, is that a lot of sysfs paths depend on kernel modules being loaded, which may happen at a later time.

sysctl has the same problem. I usually work around it by loading the kernel module already in the initrd.

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illdefined commented Mar 20, 2025

One issue here, is that a lot of sysfs paths depend on kernel modules being loaded, which may happen at a later time.

sysctl has the same problem. I usually work around it by loading the kernel module already in the initrd.

Instead of relying on systemd-tmpfiles, I could create individual path units for every entry.

@github-actions github-actions bot added 10.rebuild-darwin: 1 This PR causes 1 package to rebuild on Darwin. 10.rebuild-darwin: 1-10 This PR causes between 1 and 10 packages to rebuild on Darwin. and removed 10.rebuild-darwin: 0 This PR does not cause any packages to rebuild on Darwin. labels Apr 6, 2025
@wegank wegank added the 2.status: merge conflict This PR has merge conflicts with the target branch label Apr 17, 2025
This was referenced Apr 28, 2025
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pigsinablanket commented Apr 28, 2025 •
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I tested enabling zram zswap with boot.kernel.sysfs.module.zswap.parameters.enabled = 1; and it worked and was persistent through a reboot.

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ShamrockLee commented Apr 28, 2025 •
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I tested enabling zram with boot.kernel.sysfs.module.zswap.parameters.enabled = 1; and it worked and was persistent through a reboot.

Did you mean "zswap"? That's a great news!

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ShamrockLee commented May 3, 2025

It also works well configuring zswap on my system.

jopejoe1
jopejoe1 reviewed Jun 12, 2025
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This looks interesting, would be nice to get this merged.

@illdefined illdefined force-pushed the nixos-config-sysfs branch from b07085f to 1305aee Compare June 17, 2025 19:00
@ofborg ofborg bot removed the 2.status: merge conflict This PR has merge conflicts with the target branch label Jun 17, 2025
@github-actions github-actions bot added 10.rebuild-darwin: 0 This PR does not cause any packages to rebuild on Darwin. and removed 10.rebuild-darwin: 1-10 This PR causes between 1 and 10 packages to rebuild on Darwin. 10.rebuild-darwin: 1 This PR causes 1 package to rebuild on Darwin. labels Jun 17, 2025
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illdefined commented Jun 18, 2025

nixpkgs-review result

Generated using nixpkgs-review.

Command: nixpkgs-review pr 391329 --checkout commit --package nixosTests.sysfs
Commit: 1305aee196b53922abfc0959d03ac90f34c8c4f9

x86_64-linux

✅ 1 test built:
  • nixosTests.sysfs

aarch64-linux

✅ 1 test built:
  • nixosTests.sysfs

@nixpkgs-ci nixpkgs-ci bot added the 12.approvals: 1 This PR was reviewed and approved by one person. label Jun 26, 2025
@JohnRTitor JohnRTitor enabled auto-merge (rebase) August 11, 2025 06:46
@JohnRTitor JohnRTitor disabled auto-merge August 11, 2025 06:46
@JohnRTitor JohnRTitor merged commit 6d98ba9 into NixOS:master Aug 11, 2025
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wolfgangwalther commented Aug 11, 2025

I think this has broken nixfmt formatting, because the treefmt job ran last before the nixfmt 1.0.0 bump. PRs are failing now.

@wolfgangwalther wolfgangwalther mentioned this pull request Aug 11, 2025
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wolfgangwalther commented Aug 11, 2025

I think this has broken nixfmt formatting, because the treefmt job ran last before the nixfmt 1.0.0 bump. PRs are failing now.

Fix in #432729.

@wolfgangwalther wolfgangwalther mentioned this pull request Aug 11, 2025
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JohnRTitor added a commit to JohnRTitor/nix-conf that referenced this pull request Aug 11, 2025
@JohnRTitor
hardware/disk: set label to Bcachefs disk via new sysfs option
c0fbde0 
CC: NixOS/nixpkgs#391329
@illdefined illdefined deleted the nixos-config-sysfs branch August 11, 2025 09:54
@dblsaiko dblsaiko mentioned this pull request Sep 22, 2025
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6.topic: nixos Issues or PRs affecting NixOS modules, or package usability issues specific to NixOS 8.has: changelog This PR adds or changes release notes 8.has: documentation This PR adds or changes documentation 8.has: module (new) This PR adds a module in `nixos/` 8.has: module (update) This PR changes an existing module in `nixos/` 8.has: tests This PR has tests 10.rebuild-darwin: 0 This PR does not cause any packages to rebuild on Darwin. 10.rebuild-linux: 1-10 This PR causes between 1 and 10 packages to rebuild on Linux. 12.approvals: 1 This PR was reviewed and approved by one person.

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