Handle filesystems loop-mounted on file images

Improve prepare_grub_to_access_device to emit appropriate commands for
such filesystems, and ignore them in Linux grub.d scripts.

This is needed for Ubuntu's Wubi installation method.

This patch isn't inherently Debian/Ubuntu-specific.  losetup and
/proc/mounts are Linux-specific, though, so we might need to refine this
before sending it upstream.  The changes to the Linux grub.d scripts
might be better handled by integrating 10_lupin properly instead.

Patch-Name: mkconfig_loopback.patch

util/grub-mkconfig_lib.in

@@ -133,6 +133,22 @@ prepare_grub_to_access_device ()
     esac
   done
 
+  loop_file=
+  case $1 in
+    /dev/loop/*|/dev/loop[0-9])
+      grub_loop_device="${1#/dev/}"
+      loop_file=`losetup "$1" | sed -e "s/^[^(]*(\([^)]\+\)).*/\1/"`
+      case $loop_file in
+        /dev/*) ;;
+        *)
+          loop_device="$1"
+          shift
+          set -- `"${grub_probe}" --target=device "${loop_file}"` "$@"
+        ;;
+      esac
+    ;;
+  esac
+
   # Abstraction modules aren't auto-loaded.
   abstraction="`"${grub_probe}" --device $@ --target=abstraction`"
   for module in ${abstraction} ; do
@@ -165,6 +181,14 @@ prepare_grub_to_access_device ()
     echo "fi"
   fi
   IFS="$old_ifs"
+
+  if [ "x${loop_file}" != x ]; then
+    loop_mountpoint="$(awk '"'${loop_file}'" ~ "^"$2 && $2 != "/" { print $2 }' /proc/mounts | tail -n1)"
+    if [ "x${loop_mountpoint}" != x ]; then
+      echo "loopback ${grub_loop_device} ${loop_file#$loop_mountpoint}"
+      echo "set root=(${grub_loop_device})"
+    fi
+  fi
 }
 
 grub_get_device_id ()

util/grub.d/10_linux.in

@@ -40,6 +40,11 @@ fi
 case ${GRUB_DEVICE} in
   /dev/loop/*|/dev/loop[0-9])
     GRUB_DEVICE=`losetup ${GRUB_DEVICE} | sed -e "s/^[^(]*(\([^)]\+\)).*/\1/"`
+    # We can't cope with devices loop-mounted from files here.
+    case ${GRUB_DEVICE} in
+      /dev/*) ;;
+      *) exit 0 ;;
+    esac
   ;;
 esac
 

util/grub.d/20_linux_xen.in

@@ -40,6 +40,11 @@ fi
 case ${GRUB_DEVICE} in
   /dev/loop/*|/dev/loop[0-9])
     GRUB_DEVICE=`losetup ${GRUB_DEVICE} | sed -e "s/^[^(]*(\([^)]\+\)).*/\1/"`
+    # We can't cope with devices loop-mounted from files here.
+    case ${GRUB_DEVICE} in
+      /dev/*) ;;
+      *) exit 0 ;;
+    esac
   ;;
 esac