grub: Add support for forcing devices to be identified with labels or UUIDs

nixos/modules/system/boot/loader/grub/grub.nix

@@ -26,11 +26,11 @@ let
       inherit (cfg)
         version extraConfig extraPerEntryConfig extraEntries
         extraEntriesBeforeNixOS extraPrepareConfig configurationLimit copyKernels timeout
-        default devices;
+        default devices fsIdentifier;
       path = (makeSearchPath "bin" [
         pkgs.coreutils pkgs.gnused pkgs.gnugrep pkgs.findutils pkgs.diffutils
       ]) + ":" + (makeSearchPath "sbin" [
-        pkgs.mdadm
+        pkgs.mdadm pkgs.utillinux
       ]);
     });
 
@@ -210,6 +210,21 @@ in
         '';
       };
 
+      fsIdentifier = mkOption {
+        default = "uuid";
+        type = types.addCheck types.string
+          (type: type == "uuid" || type == "label" || type = "provided");
+        description = ''
+          Determines how grub will identify devices when generating the
+          configuration file. A value of uuid / label signifies that grub
+          will always resolve the uuid or label of the device before using
+          it in the configuration. A value of provided means that grub will
+          use the device name as show in <command>df</command> or
+          <command>mount</command>. Note, zfs zpools / datasets are ignored
+          and will always be mounted using their labels.
+        '';
+      };
+
       zfsSupport = mkOption {
         default = false;
         type = types.bool;

nixos/modules/system/boot/loader/grub/install-grub.pl

@@ -8,6 +8,7 @@ use File::stat;
 use File::Copy;
 use POSIX;
 use Cwd;
+use Switch;
 
 my $defaultConfig = $ARGV[1] or die;
 
@@ -40,6 +41,7 @@ my $configurationLimit = int(get("configurationLimit"));
 my $copyKernels = get("copyKernels") eq "true";
 my $timeout = int(get("timeout"));
 my $defaultEntry = int(get("default"));
+my $fsIdentifier = get("fsIdentifier");
 $ENV{'PATH'} = get("path");
 
 die "unsupported GRUB version\n" if $grubVersion != 1 && $grubVersion != 2;
@@ -87,6 +89,15 @@ sub GrubFs {
                 $path = "/" . substr($fs->device, $sid) . "/@" . $path;
             }
         } else {
+            my $idCmd = "\$(blkid -o export $fs->device) 2>/dev/null; echo"
+            switch ($fsIdentifier) {
+                case "uuid" {
+                    $search = "--fs-uuid " . `$idCmd \$UUID`;
+                }
+                case "label" {
+                    $search = "--label " . `$idCmd \$LABEL`;
+                }
+                case "provided" {
                     my $lbl = "/dev/disk/by-label/";
                     if (index($fs->device, $lbl) == 0) {
                         $search = "--label " . substr($fs->device, length($lbl));
@@ -96,6 +107,11 @@ sub GrubFs {
                         $search = "--fs-uuid " . substr($fs->device, length($uuid));
                     }
                 }
+                else {
+                    die "invalid fs identifier type\n";
+                }
+            }
+        }
         if (not $search eq "") {
             $search = "search --set=drive$driveid " . $search;
             $path = "(\$drive$driveid)" . $path;