Add submenu to look for bootable partitions

Look for partitions in the current USB drive that have either some
common boot files (e.g. GRUB, SYSLINUX, etc.) or an EFI binary.

This can be used to boot a Windows installation CD by creating a
partition and dumping the contents of the CD into it.

mbusb.cfg

@@ -1,7 +1,9 @@
 # Partition holding files
+regexp --set=rootdisk "^(.*),.*" "$root"
+regexp --set=rootpartnum "^.*,.*([0-9]+)" "$root"
 probe -u $root --set=rootuuid
 set imgdevpath="/dev/disk/by-uuid/$rootuuid"
-export imgdevpath rootuuid
+export imgdevpath rootuuid rootdisk rootpartnum
 
 # Custom variables
 set isopath="/boot/isos"
@@ -67,6 +69,18 @@ function search_files {
       }
     fi
   done
+
+  if [ "x$grub_platform" == "xefi" ]; then
+    for efifile in /efi/boot/bootx64.efi; do
+      if [ -e "$efifile" ]; then
+        menuentry "EFI boot ($efifile)" "$efifile" {
+          efi_file="$2"
+          chainloader "$efi_file"
+        }
+      fi
+    done
+  fi
+
 }
 
 # MultiBoot USB menu
@@ -92,6 +106,22 @@ submenu "Multiboot ->" {
     done
   }
 
+  # Search partitions for boot files
+  submenu "Auto-detect bootable partitions ->" {
+    echo -n "Searching pendrive's partitions... "
+    for part in ($rootdisk,*); do
+      regexp --set=partnum "^.*,.*([0-9]+)" "$part"
+      if [ "$partnum" -le "$rootpartnum" ]; then continue; fi
+      submenu "$part ->" "$part" {
+        part_name="$2"
+        probe --fs-uuid $part_name --set=part_uuid
+        search --fs-uuid --no-floppy --hint=$part_name --set=root $part_uuid
+        # Look for boot files
+        search_files $root
+      }
+    done
+  }
+
   # Search ISO files for boot files
   submenu "Auto-detect ISO's configfiles ->" {
     echo -n "Looking for ISO files... "