nixos/networking: add option neededForBoot

[dezren39]

Adds an option neededForBoot which is default set to true (old behavior). If set to false, the network-address-${device} service doesn't set wanted-by and will not block booting if the device is not present.

Fixes #154737
Related #155017

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/)
• 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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[rnhmjoj]

I think the only test to perform here would be: what happens when an interface not-needed-for-boot eventually appears?
The goal is to have network-address-<ifname> start automatically.
If the interface is not virtual (bridge, bond, tun, tap, etc.) network-address-<ifname> should depend on sys-subsystem-net-devices-<ifname>.device, which will be triggered by udev, so theoretically it should work. Otherwise, I'm not sure...

[dezren39]

I think the only test to perform here would be: what happens when an interface not-needed-for-boot eventually appears? The goal is to have network-address-<ifname> start automatically. If the interface is not virtual (bridge, bond, tun, tap, etc.) network-address-<ifname> should depend on sys-subsystem-net-devices-<ifname>.device, which will be triggered by udev, so theoretically it should work. Otherwise, I'm not sure...

before this pr, when i would wait 90s during each boot if not plugged in, my network adapters only worked if they were already plugged-in at-boot or after a nixos-rebuild switch or if i manually executed sudo systemctl start network-address-<ifname>.

my solution to this was:

services.udev.extraRules = lib.concatMapStrings (interface: ''
  SUBSYSTEM=="net", ACTION=="add|move", NAME=="${interface}", TAG+="systemd", ENV{SYSTEMD_WANTS}="network-addresses-${interface}.service"
'') internalInterfaces;

(

• internalInterfaces is a list of interface names within my dnsmasq module;
• also i have networking.usePredictableInterfaceNames = true; in my config.

)
this has been working well for me since then.

i believe if i remove my udev.extraRules, then i wouldn't get a successful connection, but also, at least for me and my usb adapters from amazon, this was already the case before this pr.

i'd be interested in alternatives to test or implement.

[rnhmjoj]

@dezren39 Try running this

$ systemctl list-dependencies network-addresses-<ifname> --type device

It should print sys-subsystem-net-devices-<ifname>.device. Can you also check with

$ systemctl status sys-subsystem-net-devices-<ifname>.device

if the device is active (plugged)?

I think that with BindsTo=sys-subsystem-net-devices-<ifname>.device the network-addresses-<ifname> service should be automatically restarted when the device appears, so the udev rules shouldn't be necessary.