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nixos/update-user-groups: Fix encoding issues + atomic writes #98544

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merged 3 commits into from
Nov 20, 2020

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Mic92
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@Mic92 Mic92 commented Sep 23, 2020

Motivation for this change
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.

Ideally we would treat everything as bytes however our database is
already utf-8 encoded so we need to stay compatible.
The issue here is that updateFile expects a unicode string while
encode_json returns a binary string unlike to_json.
Having the .tmp suffix is broken w.r.t. to multiple writers,
as they would overwrite existing files. using the atomic flag
will make write_file to create a unique temporary file it gets renamed
to its target.
updateFile($uidMapFile, encode_json($uidMap));
updateFile($uidMapFile, to_json($uidMap));
updateFile("/etc/passwd", \@lines);
system("nscd --invalidate passwd");
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Note that this still gets inconsistent when multiple writers update multiple files in different order.

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@stigtsp stigtsp left a comment

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I have not tested the changes (yet), but they do look good to me.

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@jonringer jonringer left a comment

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diff LGTM, then again I don't know perl :)

@jonringer jonringer added the 9.needs: port to stable A PR needs a backport to the stable release. label Sep 23, 2020
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grahamc commented Nov 20, 2020

lgtm and I had a friendly perlmonger review it, so going to go ahead and merge it

@grahamc grahamc merged commit 75d7828 into NixOS:master Nov 20, 2020
@Mic92 Mic92 deleted the unfuck-update-user-group branch March 26, 2021 14:36
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4 participants