rpPPPoE: 3.12 -> 4.0 and build kernel mode plugin

[DictXiong]

The old rpPPPoE package from Roaring Penguin is no longer maintained and the download link is also inaccessible. So I switch the upstream to https://github.com/dfskoll/rp-pppoe. Release note: https://github.com/dfskoll/rp-pppoe/blob/master/doc/CHANGES.

Also, according to the discussions in https://github.com/dfskoll/rp-pppoe/issues/32, it is strongly recommended to use rpPPPoE in the kernel mode, as it is more stable and performant than in the user mode. So I enable the compilation of the kernel mode plugin rp-pppoe.so. It will be available at /run/current-system/sw/lib/rp-pppoe.so.

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.

---

Working example

It functions as expected with the following configuration:

  sops.secrets."pppoe" = {
    # check https://github.com/Distrotech/rp-pppoe/blob/master/configs/pap-secrets for the format
    path = "/etc/ppp/pap-secrets";
    owner = "root";
    mode = "0600";
  };
  services.pppd = {
    enable = true;
    peers = {
      <a custom name> = {
        name = "<a custom name>";
        config = ''
          plugin /run/current-system/sw/lib/rp-pppoe.so
          nic-<physical interface name>
          user "<user name from the isp>"
          debug
          maxfail 0
          holdoff 5
          noipdefault
          defaultroute
          hide-password
          lcp-echo-interval 20
          lcp-echo-failure 3
          noauth
          persist
          noaccomp
          default-asyncmap
          nodetach
          nodeflate
          nopcomp
          novj
          novjccomp
        '';
      };
    };
  };

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[FliegendeWurst]

Would be good to squash the last two commits. LGTM otherwise

[DictXiong]

@FliegendeWurst Thanks for your reviews! I've squashed the last two commits.