Add submenu to look for some boot files

For each available ISO file, mount it and look for some common boot
files (e.g. GRUB, SYSLINUX, etc.) and show menu entries for each one of
those.

This can be used to test unsupported ISO files.

mbusb.cfg

@@ -16,6 +16,59 @@ if [ -e "$prefix/mbusb.cfg.local" ]; then
   source "$prefix/mbusb.cfg.local"
 fi
 
+# Function to look for boot files
+function search_files {
+  root="$1"
+
+  insmod bitmap
+  insmod jpeg
+  insmod png
+  insmod tga
+
+  for grubfile in \
+    /boot/grub/loopback.cfg \
+    /boot/grub/grub.cfg \
+    /boot/grub/x86_64-efi/grub.cfg \
+    /EFI/BOOT/grub.cfg; do
+    if [ -e "$grubfile" ]; then
+      menuentry "GRUB boot ($grubfile)" "$grubfile" {
+        grub_file="$2"
+        configfile "$grub_file"
+      }
+    fi
+  done
+
+  for syslinuxfile in \
+    /isolinux.cfg \
+    /syslinux.cfg \
+    /isolinux/isolinux.cfg \
+    /isolinux/syslinux.cfg \
+    /syslinux/isolinux.cfg \
+    /boot/isolinux.cfg \
+    /boot/isolinux/isolinux.cfg \
+    /boot/syslinux.cfg \
+    /boot/syslinux/isolinux.cfg \
+    /boot/syslinux/syslinux.cfg; do
+    if [ -e "$syslinuxfile" ]; then
+      menuentry "SYSLINUX boot ($syslinuxfile)" "$syslinuxfile" {
+        syslinux_file="$2"
+        syslinux_configfile -i "$syslinux_file"
+      }
+    fi
+  done
+
+  for legacyfile in \
+    /boot/grub/menu.lst \
+    /menu.lst; do
+    if [ -e "$legacyfile" ]; then
+      menuentry "GRUB legacy boot ($legacyfile)" "$legacyfile" {
+        legacy_file="$2"
+        legacy_configfile "$legacy_file"
+      }
+    fi
+  done
+}
+
 # MultiBoot USB menu
 submenu "Multiboot ->" {
 
@@ -39,6 +92,25 @@ submenu "Multiboot ->" {
     done
   }
 
+  # Search ISO files for boot files
+  submenu "Auto-detect ISO's configfiles ->" {
+    echo -n "Looking for ISO files... "
+    for isofile in $isopath/*.iso $isopath/*.img; do
+      if [ -e "$isofile" ]; then
+        regexp --set=isoname "$isopath/(.*)" "$isofile"
+        submenu "$isoname ->" "$isofile" {
+          iso_path="$2"
+          export iso_path
+          search --set=root --file "$iso_path"
+          loopback loop "$iso_path"
+          root=(loop)
+          # Look for boot files
+          search_files $root
+        }
+      fi
+    done
+  }
+
   # Use MEMDISK to load ISO files
   submenu "Use MEMDISK to boot ISO files ->" {
     echo -n "Looking for ISO files... "