nixos/stage-1: fix predictable interfaces names

This makes predictable interfaces names available as soon as possible
with udev by adding the default network link units to initrd which are read
by udev. Also adds some udev rules that are needed but which would normally
loaded from the udev store path which is not included in the initrd.

nixos/modules/system/boot/stage-1-init.sh

···
 # Create device nodes in /dev.
 @preDeviceCommands@
 echo "running udev..."
+mkdir -p /etc/systemd
+ln -sfn @linkUnits@ /etc/systemd/network
 mkdir -p /etc/udev
 ln -sfn @udevRules@ /etc/udev/rules.d
 mkdir -p /dev/.mdadm
···
         return 0
     fi
 
-    # Device might be already mounted manually 
+    # Device might be already mounted manually
     # e.g. NBD-device or the host filesystem of the file which contains encrypted root fs
     if mount | grep -q "^$device on "; then
         echo "skip checking already mounted $device"
···
             elif [ "$fsType" = f2fs ]; then
                 echo "resizing $device..."
                 fsck.f2fs -fp "$device"
-                resize.f2fs "$device" 
+                resize.f2fs "$device"
             fi
             ;;
     esac

nixos/modules/system/boot/stage-1.nix

···
 
       # Copy udev.
       copy_bin_and_libs ${udev}/lib/systemd/systemd-udevd
+      copy_bin_and_libs ${udev}/lib/systemd/systemd-sysctl
       copy_bin_and_libs ${udev}/bin/udevadm
       for BIN in ${udev}/lib/udev/*_id; do
         copy_bin_and_libs $BIN
···
     ''; # */
 
 
+  linkUnits = pkgs.runCommand "link-units" {
+      allowedReferences = [ extraUtils ];
+      preferLocalBuild = true;
+    } ''
+      mkdir -p $out
+      cp -v ${udev}/lib/systemd/network/*.link $out/
+    '';
+
   udevRules = pkgs.runCommand "udev-rules" {
       allowedReferences = [ extraUtils ];
       preferLocalBuild = true;
···
 
       cp -v ${udev}/lib/udev/rules.d/60-cdrom_id.rules $out/
       cp -v ${udev}/lib/udev/rules.d/60-persistent-storage.rules $out/
+      cp -v ${udev}/lib/udev/rules.d/75-net-description.rules $out/
       cp -v ${udev}/lib/udev/rules.d/80-drivers.rules $out/
+      cp -v ${udev}/lib/udev/rules.d/80-net-setup-link.rules $out/
       cp -v ${pkgs.lvm2}/lib/udev/rules.d/*.rules $out/
       ${config.boot.initrd.extraUdevRulesCommands}
 
···
             --replace ${pkgs.lvm2}/sbin ${extraUtils}/bin \
             --replace ${pkgs.mdadm}/sbin ${extraUtils}/sbin \
             --replace ${pkgs.bash}/bin/sh ${extraUtils}/bin/sh \
-            --replace ${udev}/bin/udevadm ${extraUtils}/bin/udevadm
+            --replace ${udev} ${extraUtils}
       done
 
       # Work around a bug in QEMU, which doesn't implement the "READ
···
       ${pkgs.buildPackages.busybox}/bin/ash -n $target
     '';
 
-    inherit udevRules extraUtils modulesClosure;
+    inherit linkUnits udevRules extraUtils modulesClosure;
 
     inherit (config.boot) resumeDevice;
 

nixos/tests/predictable-interface-names.nix

···
       networking.useNetworkd = withNetworkd;
       networking.dhcpcd.enable = !withNetworkd;
       networking.useDHCP = !withNetworkd;
+
+      # Check if predictable interface names are working in stage-1
+      boot.initrd.postDeviceCommands = ''
+        ip link
+        ip link show eth0 ${if predictable then "&&" else "||"} exit 1
+      '';
     };
 
     testScript = ''