iso-image: add loopback.cfg support to boot iso from grub

nixos/modules/installer/cd-dvd/iso-image.nix

@@ -24,7 +24,7 @@ let
         # Name appended to menuentry defaults to params if no specific name given.
         option.name or (if option ? params then "(${option.params})" else "")
         }' ${if option ? class then " --class ${option.class}" else ""} {
-          linux ${defaults.image} ${defaults.params} ${
+          linux ${defaults.image} \''${isoboot} ${defaults.params} ${
             option.params or ""
           }
           initrd ${defaults.initrd}
@@ -268,6 +268,12 @@ let
     set timeout=10
     ${grubMenuCfg}
 
+    # If the parameter iso_path is set, append the findiso parameter to the kernel
+    # line. We need this to allow the nixos iso to be booted from grub directly.
+    if [ \''${iso_path} ] ; then
+      set isoboot="findiso=\''${iso_path}"
+    fi
+
     #
     # Menu entries
     #
@@ -616,6 +622,9 @@ in
         { source = "${efiDir}/EFI";
           target = "/EFI";
         }
+        { source = pkgs.writeText "loopback.cfg" "source /EFI/boot/grub.cfg";
+          target = "/boot/grub/loopback.cfg";
+        }
       ] ++ optionals (config.boot.loader.grub.memtest86.enable && canx86BiosBoot) [
         { source = "${pkgs.memtest86plus}/memtest.bin";
           target = "/boot/memtest.bin";

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

@@ -183,6 +183,12 @@ for o in $(cat /proc/cmdline); do
         copytoram)
             copytoram=1
             ;;
+        findiso=*)
+            # if an iso name is supplied, try to find the device where
+            # the iso resides on
+            set -- $(IFS==; echo $o)
+            isoPath=$2
+            ;;
     esac
 done
 
@@ -442,6 +448,27 @@ if test -e /sys/power/resume -a -e /sys/power/disk; then
     fi
 fi
 
+# If we have a path to an iso file, find the iso and link it to /dev/root
+if [ -n "$isoPath" ]; then
+  mkdir -p /findiso
+
+  for delay in 5 10; do
+    blkid | while read -r line; do
+      device=$(echo "$line" | sed 's/:.*//')
+      type=$(echo "$line" | sed 's/.*TYPE="\([^"]*\)".*/\1/')
+
+      mount -t "$type" "$device" /findiso
+      if [ -e "/findiso$isoPath" ]; then
+        ln -sf "/findiso$isoPath" /dev/root
+        break 2
+      else
+        umount /findiso
+      fi
+    done
+
+    sleep "$delay"
+  done
+fi
 
 # Try to find and mount the root device.
 mkdir -p $targetRoot