=== modified file 'bin/usb-creator-helper'
--- a/bin/usb-creator-helper	2015-01-14 04:58:42 +0000
+++ b/bin/usb-creator-helper	2015-01-14 10:53:25 +0000
@@ -148,10 +148,10 @@
 
 
     # TODO return boolean success
-    @dbus.service.method(USBCREATOR_IFACE, in_signature='sbsb', out_signature='',
+    @dbus.service.method(USBCREATOR_IFACE, in_signature='sbsbs', out_signature='',
                          sender_keyword='sender', connection_keyword='conn')
     def InstallBootloader(self, device, allow_system_internal, grub_location,
-                          syslinux_legacy, sender=None, conn=None):
+                          syslinux_legacy, sourcefs, sender=None, conn=None):
         '''Install a bootloader to the boot code area, either grub or syslinux.
 
            The function takes a partition device file of the form /dev/sda1
@@ -187,9 +187,23 @@
                 syslinux = 'syslinux-legacy'
             else:
                 syslinux = 'syslinux'
-            popen([syslinux, '-f', device])
+            mbr_file = None
+            if sourcefs and os.path.isdir(sourcefs):
+                for mbrbin in [
+                        os.path.join(sourcefs, 'usr', 'lib', syslinux, 'mbr.bin'),
+                        os.path.join(sourcefs, 'usr', 'lib', syslinux, 'mbr', 'mbr.bin'),
+                        os.path.join(sourcefs, 'usr', 'lib', syslinux.upper(), 'mbr.bin'),
+                        ]:
+                    if os.path.isfile(mbrbin):
+                        mbr_file = mbrbin
+                        break
+            if not mbr_file:
+                # fallback to the host version
+                mbr_file = os.path.join(os.sep, 'usr', 'lib', syslinux, 'mbr.bin'),
+                sourcefs = os.sep
+            popen([os.path.join(sourcefs, 'usr', 'bin', syslinux), '-f', device])
             # Write the syslinux MBR.
-            popen(['dd', 'if=/usr/lib/%s/mbr.bin' % syslinux, 'of=%s' % parent_file,
+            popen(['dd', 'if=%s' % mbr_file, 'of=%s' % parent_file,
                    'bs=446', 'count=1', 'conv=sync'])
 
         part = obj.get_partition()
@@ -266,7 +280,10 @@
         self.check_polkit(sender, conn, 'com.ubuntu.usbcreator.mount')
         import tempfile
         ret = tempfile.mkdtemp()
-        device = device.encode('utf-8')
+        if isinstance(device, dbus.String):
+            device = device.encode('utf-8')
+        if isinstance(device, bytes):
+            device = device.decode('utf-8')
         popen(['mount', '-r', '-o', 'loop', device, ret])
         return ret
 

=== modified file 'usbcreator/backends/base/backend.py'
--- a/usbcreator/backends/base/backend.py	2015-01-14 04:58:42 +0000
+++ b/usbcreator/backends/base/backend.py	2015-01-14 10:08:40 +0000
@@ -189,7 +189,8 @@
         self.install_thread = usbcreator.install.install(
             source, target, persist, device=device,
             allow_system_internal=allow_system_internal,
-            fastboot_mode=fastboot_mode)
+            fastboot_mode=fastboot_mode,
+            sourcefs=self.sourcefs)
         # Connect signals.
         self.install_thread.success = self.success_cb
         self.install_thread.failure = self.failure_cb

=== modified file 'usbcreator/backends/udisks/backend.py'
--- a/usbcreator/backends/udisks/backend.py	2014-04-01 15:04:39 +0000
+++ b/usbcreator/backends/udisks/backend.py	2015-01-14 10:57:19 +0000
@@ -1,3 +1,4 @@
+import os
 import dbus
 import logging
 from dbus.mainloop.glib import DBusGMainLoop, threads_init
@@ -315,6 +316,7 @@
             isofile = self.sources[source]['device']
             source = self.helper.MountISO(isofile)
             self.mounted_source = source
+        self.sourcefs = self.helper.MountISO(os.path.join(source, 'casper', 'filesystem.squashfs'))
 
         dev = self.targets[target]['device']
         if stype == misc.SOURCE_IMG:
@@ -338,6 +340,7 @@
 
     def unmount(self):
         try:
+            self.helper.UnmountFile(self.sourcefs)
             if self.mounted_source:
                 self.helper.UnmountFile(self.mounted_source)
         except:

=== modified file 'usbcreator/install.py'
--- a/usbcreator/install.py	2015-01-14 04:58:42 +0000
+++ b/usbcreator/install.py	2015-01-14 10:11:01 +0000
@@ -66,7 +66,8 @@
 class install(Thread):
     def __init__(self, source, target, persist, device=None,
                  allow_system_internal=False,
-                 fastboot_mode=False):
+                 fastboot_mode=False,
+                 sourcefs=None):
         Thread.__init__(self)
         self.source = source
         self.target = target
@@ -74,6 +75,7 @@
         self.device = device
         self.allow_system_internal = allow_system_internal
         self.fastboot_mode = fastboot_mode
+        self.sourcefs = sourcefs
         self._stopevent = Event()
         self.progress_thread = None
         logging.debug('install thread source: %s' % source)
@@ -249,6 +251,7 @@
                 obj.InstallBootloader(self.device, self.allow_system_internal,
                                       grub_location,
                                       self.need_syslinux_legacy(),
+                                      self.sourcefs,
                                       dbus_interface='com.ubuntu.USBCreator',
                                       timeout=MAX_DBUS_TIMEOUT)
             except dbus.DBusException: