add "is_parent_of" function to blockdevice module

improve pre-defined exceptions
improve few failure behaviours

src/cryptobox/core/blockdevice.py

@@ -33,6 +33,7 @@ import subprocess
 import time
 import logging
 import cryptobox.core.settings
+import cryptobox.core.exceptions
 
 OPTIONAL_PROGS = { "lvm": True }
 """remember which programs don't exist to avoid calling them in vain
@@ -99,6 +100,10 @@ class Blockdevices:
 
 
 class Blockdevice:
+    """don't instantiate this class directly!
+
+    use "_get_blockdevice" instead
+    """
 
     def __init__(self, dev,
             sysblock_dir=DEFAULT_SYSBLOCK_DIR,
@@ -115,6 +120,11 @@ class Blockdevice:
         self.devdir = dev
         self.devnode_dir = devnode_dir
         self.sysblock_dir = sysblock_dir
+        ## check if the device is valid
+        if not os.path.isdir(os.path.join(self.devnode_dir, dev)):
+            raise cryptobox.core.exceptions.CBInternalError(
+                    "invalid blockdevice given: %s (%s)" % \
+                    (self.devdir, self.sysblock_dir))
         self.name = os.path.basename(self.devdir)
         ## "reset" below will fill these values
         self.devnum = None
@@ -358,6 +368,38 @@ class Blockdevice:
         return result
 
 
+    def is_parent_of(self, ask_child):
+        """check if the blockdevice or any of its children contains the given child
+
+        the result of "foo.is_parent_of(foo)" returns False
+
+        invalid (None) "ask_child" devices return False
+
+        @param ask_child: the blockdevice that is considered to be a possible child
+        @type ask_child: BlockDevice
+        @return: True if the child is (even recursively) part of the blockdevice, otherwise False
+        @rtype: bool
+        """
+        ## return False for non existing device
+        if ask_child is None:
+            return False
+        ## throw exception for invalid call
+        if not isinstance(ask_child, Blockdevice):
+            raise cryptobox.core.exceptions.CBInternalError(\
+                    "invalid arguments for 'is_parent_of'")
+        ## recursively go through all the children
+        for child_devname in self.children:
+            child_dev = get_blockdevice(child_devname)
+            ## direct child?
+            if child_dev == ask_child:
+                return True
+            ## indirect child?
+            if child_dev.is_parent_of(ask_child):
+                return True
+        ## no matches found
+        return False
+
+
     def __get_dev_related(self, subdir):
         """return the content of sub directories (e.g. 'holders' or 'slaves')
         """

src/cryptobox/core/exceptions.py

@@ -22,30 +22,65 @@
 exceptions of the cryptobox package
 """
 
+
 __revision__ = "$Id$"
 
 
 class CBError(Exception):
     """base class for exceptions of the cryptobox"""
-    pass
 
+    prefix = "general cryptobox error"
+
+    def __init__(self, desc):
+        self.desc = desc
+
+    def __str__(self):
+        """Return the error description.
+        """
+        if self.desc:
+            return "%s: %s" % (self.prefix, self.desc)
+        else:
+            return self.prefix
+
+
+
+# main exception classes
 
 class CBConfigError(CBError):
     """any kind of error related to the configuration of a cryptobox"""
     pass
 
 
+class CBContainerError(CBError):
+    """Any error raised while manipulating a cryptobox container.
+    """
+
+    prefix = "cryptobox container error"
+
+
+class CBEnvironmentError(CBError):
+    """some part of the environment of the cryptobox is broken
+    e.g. the wrong version of a required program
+    """
+
+    prefix = "cryptobox environment error"
+
+
+class CBInternalError(CBError):
+    """report any failing internal assertions
+
+    this is always a bug
+    """
+
+    prefix = "internal error detected"
+
+
+# specialized exceptions
+    
 class CBConfigUnavailableError(CBConfigError):
     """config file/input was not available at all"""
     
-    def __init__(self, source=None):
-        self.source = source
-    
-    def __str__(self):
-        if self.source:
-            return "failed to access the configuration of the cryptobox: %s" % self.source
-        else:
-            return "failed to access the configuration of the cryptobox"
+    prefix = "failed to access the configuration of the cryptobox"
 
 
 class CBConfigUndefinedError(CBConfigError):
@@ -86,25 +121,6 @@ class CBConfigInvalidValueError(CBConfigError):
                 (self.section, self.name, self.value, self.reason)
 
 
-class CBEnvironmentError(CBError):
-    """some part of the environment of the cryptobox is broken
-    e.g. the wrong version of a required program
-    """
-
-    def __init__(self, desc):
-        self.desc = desc
-
-    def __str__(self):
-        """Return the error description.
-        """
-        return "misconfiguration detected: %s" % self.desc
-
-
-class CBContainerError(CBError):
-    """Any error raised while manipulating a cryptobox container.
-    """
-
-    
 class CBCreateError(CBContainerError):
     """Raised if a container could not be created (formatted).
     """

src/cryptobox/core/settings.py

@@ -317,9 +317,13 @@ class CryptoBoxSettings:
             else: 
                 raise CBConfigUnavailableError(
                         "failed to load the config file: %s" % config_file)
-        except IOError:
+        except IOError, err_msgg:
             raise CBConfigUnavailableError(
-                    "unable to open the config file: %s" % config_file)
+                    "unable to open the config file (%s): %s" % \
+                            (config_file, err_msg))
+        except configobj.ConfigObjError, err_msg:
+            raise CBConfigError("failed to load config file (%s): %s" % \
+                (config_file, err_msg))
         return prefs