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Reintroduce lib output for systemd #99382

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Reintroduce lib output for systemd #99382

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arianvp
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@arianvp arianvp commented Oct 2, 2020

Motivation for this change

#94354 removed $lib output but this causes significant closure bloat
See #98094

This reintroduces $lib, by getting rid of the problematic cyclic dependency

Things done
  • Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
  • Built on platform(s)
    • NixOS
    • macOS
    • other Linux distributions
  • Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
  • Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
  • Tested execution of all binary files (usually in ./result/bin/)
  • Determined the impact on package closure size (by running nix path-info -S before and after)
  • Ensured that relevant documentation is up to date
  • Fits CONTRIBUTING.md.

arianvp added 2 commits October 2, 2020 14:00
@arianvp
systemd: set rootprefix to /run/current-system/systemd
353fb8d 
sd_path_lookup_*  returns $rootprefix, which was making a cyclic
dependency to $out and $lib

We also patch systemd in  ./0014-add-rootprefix-to-lookup-dir-paths.patch
to look for all config files (except unit files; they have their
own lookup path logic) in rootprefix. This will keep working
@arianvp
systemd: reintroduce lib output
bb21fd4 
Now that $lib doesn't refer to rootprefixdir anymore,  the
cyclic dependnecy should be gone
@arianvp arianvp requested review from flokli and edolstra October 2, 2020 12:05
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arianvp commented Oct 2, 2020 •
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@edolstra PTAL. I don't have time to make a backport PR to 20.09. Would love if somebody else could do this.

We should also probably make the base-branch staging instead of master

I didn't test yet if this works.

@arianvp arianvp mentioned this pull request Oct 2, 2020
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arianvp commented Oct 2, 2020

cc @NixOS/systemd

@arianvp arianvp added 1.severity: blocker This is preventing another PR or issue from being completed 6.topic: closure size The final size of a derivation, including its dependencies 6.topic: nixos Issues or PRs affecting NixOS modules, or package usability issues specific to NixOS labels Oct 2, 2020
@arianvp arianvp added this to the 20.09 milestone Oct 2, 2020
@arianvp arianvp marked this pull request as draft October 2, 2020 12:11
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arianvp commented Oct 2, 2020 •
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Nevermind this doesn't work. As systemd tries to install files in rootprefixdir in meson.build. we'd have to patch sd_path_ instead so that it doesn't refer to ROOTPREFIXDIR

@ofborg ofborg bot removed the 6.topic: nixos Issues or PRs affecting NixOS modules, or package usability issues specific to NixOS label Oct 2, 2020
@ofborg ofborg bot requested a review from andir October 2, 2020 15:26
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arianvp commented Oct 2, 2020 •
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The "problematic" patch that causes these issues is systemd/systemd@9c5bb20

The systemd folks are refactoring the path-related code and AFAIK sd-path should be the source of truth of all path-prefix related things after that refactoring is complete. But it's not there yet.

As it adds a reference to src/basic/path-lookup.h (which has references to both PREFIX and ROOTPREFIX, which we both set to $out) to libsystemd/sd-path/sd-path.c
it causes systemd.lib to depend on systemd.out

It also directly pulls in ROOTPREFIX , USER_DATA_UNIT_PATH , SYSTEM_DATA_UNIT_PATH , SYSTEM_GENERATOR_PATH USER_GENERATOR_PATH, which also all refer to $out

Three ideas:

  1. Revert systemd/systemd@9c5bb20 as non of these code paths are actively used in systemd as of 246. It's not sustainable but it will quickly fix our issues

  2. Patch both path-lookup.h/path-lookup.c and sd-path.c to not refer to PREFIX and ROOTPREFIX but to /run/current-system/systemd consistently

  3. don't do anything. Simply return the lib output without fixing the cycle, and fix Support cyclic references in multi-output derivations nix#494 instead

I honestly don't see upstream accommodating us here. As they don't think it's problematic to have references between libsystemd and systemd proper. So option 3 sounds very attractive as we do not have to keep playing cat and mouse with changes inside systemd.

@edolstra edolstra removed the 1.severity: blocker This is preventing another PR or issue from being completed label Oct 2, 2020
@flokli flokli mentioned this pull request Oct 9, 2020
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flokli commented Nov 24, 2020

Based on

So option 3 sounds very attractive as we do not have to keep playing cat and mouse with changes inside systemd.

let's close this :-)

@flokli flokli closed this Nov 24, 2020
@wegank wegank deleted the systemd-lib-reintroduce branch May 27, 2023 12:51
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@flokli flokli Awaiting requested review from flokli

@edolstra edolstra Awaiting requested review from edolstra

@andir andir Awaiting requested review from andir

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6.topic: closure size The final size of a derivation, including its dependencies 10.rebuild-darwin: 101-500 10.rebuild-linux: 501+ 10.rebuild-linux: 5001+
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systemd
Status: Done
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20.09
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