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modules-shrunk: preserve module priorities from build #75181

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merged 1 commit into from Dec 12, 2019
Merged

modules-shrunk: preserve module priorities from build #75181

merged 1 commit into from Dec 12, 2019

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wamserma
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@wamserma wamserma commented Dec 7, 2019

depmod looks for files modules.order and modules.builtin which are
generated at kernel build time but were previously not passed to
the modules-shrunk derivation.

Motivation for this change
depmod: WARNING: could not open modules.order at /nix/store/fprfhcrkzbnqlivj146j57sjccm5kjpf-linux-4.19.87-modules-shrunk/lib/modules/4.19.87: No such file or directory
depmod: WARNING: could not open modules.builtin at /nix/store/fprfhcrkzbnqlivj146j57sjccm5kjpf-linux-4.19.87-modules-shrunk/lib/modules/4.19.87: No such file or directory

on nixos-rebuild.

see also: #75178

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 nix-review --run "nix-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.
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cc @

@wamserma
modules-shrunk: preserve module priorities from build
34b04a6 
depmod looks for files modules.order and modules.builtin which are
generated at kernel build time but were previously not passed to
the modules-shrunk derivation
@wamserma wamserma mentioned this pull request Dec 7, 2019
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@andir
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andir commented Dec 12, 2019

@wamserma could you maybe fill in if there is some actual functional difference here? Right now I just see two warnings. What is the size difference of the resulting output?

@wamserma
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@andir The main motivation was actually to get rid of these warnings. For the functional difference, well let me quote from https://lwn.net/Articles/260856/, because I couldn't phrase it better:

When multiple built-in [kernel] modules (especially drivers) provide
the same capability, they're prioritized by link order specified by the
order listed in Makefile. This implicit ordering is lost for loadable
modules.

When driver modules are loaded by udev, what comes first in
modules.alias file is selected. However, the order in this file is
indeterministic (depends on filesystem listing order of installed
modules). This causes confusion.

modules.order [...] contains the name of modules ordered
according to Makefile [of the Kernel]. [...] depmod [...]
generates output files according to this file.

For this to work the file must be available to depmod and temporarily copying it over is the simplest and most reliable solution for that. Note that the file is removed after depmod has been run, so it should not impact the size of the output beyond adjusting module preferences to what has actually been chosen for the kernel.

Granted, the proper Nix way would be to adjust the search path used by depmod to the nix store path where modules.order and its sibling live, but I expect endless pain and horror from going that route.
Similar arguments apply for modules.builtin.

@andir
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andir commented Dec 12, 2019

Thank you for double checking that. It is about ~200K on my system right now so that should be fine.

@andir andir merged commit 8964705 into NixOS:master Dec 12, 2019
@wamserma wamserma deleted the fix-modules-shrunk branch December 12, 2019 22:00
@wamserma wamserma mentioned this pull request Dec 12, 2019
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