stage-1: Hardcoded udev usage for device detection

This should be extracted into a self-contained module.

modules/stage-2.nix

@@ -1,14 +1,24 @@
 { config, lib, pkgs, ... }:
 
+# FIXME: Add hook for mounting, right now it's hardcoded to only mount "/".
+#        (This'll allow complex schemes like LVM)
+# FIXME: Move udev stuff out.
+
+let
+  rootfs = config.fileSystems."/".device;
+in
 with import ./initrd-order.nix;
 {
-  mobile.boot.stage-1.init = lib.mkOrder SWITCH_ROOT_INIT ''
+  mobile.boot.stage-1.init =
+  lib.mkOrder SWITCH_ROOT_INIT ''
     set -x
-    targetRoot=/mnt
 
-    _fs_id() {
-      blkid | grep ' LABEL="'"$1"'" ' | cut -d':' -f1
-    }
+    # FIXME : udev stuff out of here...
+    systemd-udevd --daemon
+    udevadm trigger --action=add
+    udevadm settle
+
+    targetRoot=/mnt
 
     _init_path() {
       local _system=""
@@ -40,18 +50,8 @@ with import ./initrd-order.nix;
       echo "$_system/init"
     }
 
-    _fs_id NIXOS_SD
-    _fs_id NIXOS_BOOT
-    # FIXME : LESS FLIMSY!
     mkdir -p $targetRoot
-    mount $(_fs_id NIXOS_SD) $targetRoot
-
-    # mkdir -p $targetRoot/boot
-    # mount $(_fs_id NIXOS_BOOT) $targetRoot/boot
-
-    # mount "$(blkid | grep ' LABEL="'"NIXOS_SD"'" ' | cut -d':' -f1)" /mnt
-    # mkdir -p /mnt/boot/
-    # mount "$(blkid | grep ' LABEL="'"NIXOS_BOOT"'" ' | cut -d':' -f1)" /mnt/boot
+    mount "${rootfs}" $targetRoot
 
     echo ""
     echo "***"
@@ -61,12 +61,17 @@ with import ./initrd-order.nix;
     echo "***"
     echo ""
 
-
     for mp in /proc /sys /dev /run; do
       mkdir -m 0755 -p $targetRoot/$mp
       mount --move $mp $targetRoot/$mp
     done
 
+    # TODO : hook "AT" switch root
+
+    # FIXME : udev stuff out of here...
+    # Stop udevd.
+    udevadm control --exit
+
     exec env -i $(type -P switch_root) $targetRoot $(_init_path)
   '';
 

systems/initrd.nix

@@ -11,8 +11,18 @@
 
   lib,
   mkExtraUtils,
+
+  # FIXME : udev specifics
+  runCommandNoCC,
+  udev,
+  pkgs
 }:
 
+# FIXME: get the udev specifics out of here.
+# The main issue is how `udevRules` needs a reference to `extraUtils`.
+# This means that `extraUtils` should be a build product of stage-1 in
+# system.build, that we can refer to when required.
+
 let
   inherit (lib) optionals flatten;
 
@@ -24,11 +34,74 @@ let
       busybox
     ]
       ++ optionals (stage-1 ? extraUtils) stage-1.extraUtils
+      ++ [{
+      package = runCommandNoCC "empty" {} "mkdir -p $out";
+      extraCommand =
+        let
+          inherit (pkgs) udev;
+        in
+        ''
+          # Copy udev.
+          copy_bin_and_libs ${udev}/lib/systemd/systemd-udevd
+          copy_bin_and_libs ${udev}/bin/udevadm
+          for BIN in ${udev}/lib/udev/*_id; do
+            copy_bin_and_libs $BIN
+          done
+        ''
+      ;
+    }]
     ;
   };
 
   shell = "${extraUtils}/bin/ash";
 
+  udevRules = runCommandNoCC "udev-rules" {
+    allowedReferences = [ extraUtils ];
+    preferLocalBuild = true;
+  } ''
+    mkdir -p $out
+
+    echo 'ENV{LD_LIBRARY_PATH}="${extraUtils}/lib"' > $out/00-env.rules
+
+    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/80-drivers.rules $out/
+    cp -v ${pkgs.lvm2}/lib/udev/rules.d/*.rules $out/
+
+    for i in $out/*.rules; do
+        substituteInPlace $i \
+          --replace ata_id ${extraUtils}/bin/ata_id \
+          --replace scsi_id ${extraUtils}/bin/scsi_id \
+          --replace cdrom_id ${extraUtils}/bin/cdrom_id \
+          --replace ${pkgs.coreutils}/bin/basename ${extraUtils}/bin/basename \
+          --replace ${pkgs.utillinux}/bin/blkid ${extraUtils}/bin/blkid \
+          --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
+    done
+
+    # Work around a bug in QEMU, which doesn't implement the "READ
+    # DISC INFORMATION" SCSI command:
+    #   https://bugzilla.redhat.com/show_bug.cgi?id=609049
+    # As a result, `cdrom_id' doesn't print
+    # ID_CDROM_MEDIA_TRACK_COUNT_DATA, which in turn prevents the
+    # /dev/disk/by-label symlinks from being created.  We need these
+    # in the NixOS installation CD, so use ID_CDROM_MEDIA in the
+    # corresponding udev rules for now.  This was the behaviour in
+    # udev <= 154.  See also
+    #   http://www.spinics.net/lists/hotplug/msg03935.html
+    substituteInPlace $out/60-persistent-storage.rules \
+      --replace ID_CDROM_MEDIA_TRACK_COUNT_DATA ID_CDROM_MEDIA
+  ''; # */
+
+  # Just to keep track of this bit.
+  udevFragment = ''
+    mkdir -p /etc/udev
+
+    ln -sfn ${udevRules} /etc/udev/rules.d
+  '';
+
   stage1 = writeScript "stage1" ''
     #!${shell}
 
@@ -41,6 +114,7 @@ let
     ln -sv ${shell} /bin/sh
 
     # ---- stage-1.init START ----
+    ${udevFragment}
     ${stage-1.init}
     # ---- stage-1.init END ----
   '';