* use caching for "debian_live" check

src/cryptobox/core/blockdevice.py

@@ -51,6 +51,7 @@ MAJOR_DEVNUM_LOOP = 7
 MAJOR_DEVNUM_FLOPPY = 2
 MAJOR_DEVNUM_RAMDISK = 1
 MAJOR_DEVNUM_MD_RAID = 9
+MOUNT_STATE_FILE = '/proc/mounts'
 
 ## cache settings
 CACHE_ENABLED = True
@@ -248,48 +249,19 @@ class Blockdevice:
         else:
             return False
         
+
     def is_debian_live(self):
         """is the device part of the Debian Live runtime
         """
-        ##Debian Live ("iso" or "usb-hdd" versions) uses two block
-        ##devices as part of its runtime system. The raw boot media
-        ##(such as a usb key or cdrom) is mounted at /live_media,
-        ##and the root filesystem is mounted off of the live media
-        ##using /dev/loop0.
-        deb_live_devs = []
-        for line in file("/proc/mounts"):
-            try:
-                fields = line.split(" ")
-                ##We are looking for, for example:
-                ##/dev/hdc /live_media iso9660 ro 0 0
-                ##and
-                ##/dev/loop0 /filesystem.squashfs squashfs ro 0 0
-                if (fields[1] == "/live_media" and
-                    fields[3] == "ro"):
-                    deb_live_devs.append(fields[0])
-                elif (fields[1] == "/filesystem.squashfs" and
-                      fields[3] == "ro"):
-                    deb_live_devs.append(fields[0])
-            except IndexError:
-                pass
-
-        ##TODO:    
-        ##Since the lines in /proc/mounts that affect deb_live_devs
-        ##don't change after startup, deb_live_devs could be cached here.
-        ##
         ##Check whether any Debian Live devices refer to the
         ##block device we were passed
-        matched = False
-        for dev in deb_live_devs:
-            for node in self.__get_device_nodes():
-                if (node == dev):
-                    matched = True
-                    
+        deb_live_devs = _get_debian_live_devices()
+        ## check for matches in self.__get_device_nodes() and deb_live_devs
+        matching_devices = [ devnode for devnode in self.__get_device_nodes()
+                if devnode in deb_live_devs ]
+        ## return True, if a match was found
+        return len(matching_devices) > 0
                 
-        ##If no nodes of the block device match the Debian Live
-        ##devices, return False            
-        return matched
-        
 
     def is_lvm_pv(self):
         """return if the device is a physical volume of a LVM
@@ -1096,9 +1068,40 @@ def _load_preferences():
             os.chdir(os.path.dirname(config_file))
             return cryptobox.core.settings.CryptoBoxSettings(config_file)
     else:
-        raise CBConfigUnavailableError()
+        raise cryptobox.core.exceptions.CBConfigUnavailableError()
 
 
+def _get_debian_live_devices():
+    ##Debian Live ("iso" or "usb-hdd" versions) uses two block
+    ##devices as part of its runtime system. The raw boot media
+    ##(such as a usb key or cdrom) is mounted at /live_media,
+    ##and the root filesystem is mounted off of the live media
+    ##using /dev/loop0.
+    cache_link = ["debian_live_devices"]
+    cached = CACHE.get(cache_link)
+    if not cached is None:
+        return cached[:]
+
+    ## result is not cached yet - we need to find it
+    deb_live_devs = []
+    for line in file(MOUNT_STATE_FILE):
+        try:
+            fields = line.split(" ")
+            ##We are looking for, for example:
+            ##/dev/hdc /live_media iso9660 ro 0 0
+            ##and
+            ##/dev/loop0 /filesystem.squashfs squashfs ro 0 0
+            if (fields[1] == "/live_media" and
+                fields[3] == "ro"):
+                deb_live_devs.append(fields[0])
+            elif (fields[1] == "/filesystem.squashfs" and
+                  fields[3] == "ro"):
+                deb_live_devs.append(fields[0])
+        except IndexError:
+            pass
+    CACHE.set(cache_link, deb_live_devs)
+    return deb_live_devs[:]
+
 
 ## initialize cache
 CACHE = BlockdeviceCache()