Verify that the bootflag is enabled

diff --git a/grml2usb b/grml2usb
index 68565db..16b53cd 100755 (executable)
--- a/grml2usb
+++ b/grml2usb
@@ -128,6 +128,12 @@ class CriticalException(Exception):
     @Exception: message"""
     pass
 
+class VerifyException(Exception):
+    """Throw critical exception if there is an fatal error when verifying something.
+
+    @Exception: message"""
+    pass
+
 
 # The following two functions help to operate on strings as
 # array (list) of bytes (octets). In Python 3000, the bytes
@@ -305,6 +311,18 @@ def check_uid_root():
         sys.exit("Error: please run this script with uid 0 (root).")
 
 
+def check_boot_flag(device):
+    with open(device, 'r') as image:
+        data = image.read(512)
+        bootcode = data[440:]
+        if bootcode[6] == '\x80':
+            logging.debug("bootflag is enabled")
+        else:
+            logging.debug("bootflag is NOT enabled")
+            raise VerifyException("Device %s does not have the bootflag set. "
+                "Please enable it to be able to boot." % device)
+
+
 def mkfs_fat16(device):
     """Format specified device with VFAT/FAT16 filesystem.
 
@@ -1475,7 +1493,11 @@ def install_grml(mountpoint, device):
         remove_device_mountpoint = True
         try:
             check_for_fat(device)
+            check_boot_flag(device)
             mount(device, device_mountpoint, ['-o', 'utf8,iocharset=iso8859-1'])
+        except VerifyException, error:
+            logging.critical("Fatal: %s", error)
+            raise
         except CriticalException, error:
             try:
                 mount(device, device_mountpoint, "")