Add device attribute in Disk class

This attribute hosts the block device associated with this Disk
instance. This can be the original media if the source media is a block
device, a loop device of the original media if the original media is a
regular file or a loop device of a temporary object if the original
media is a directory.

image_creator/dialog_main.py

@@ -61,8 +61,11 @@ def create_image(d, media, out, tmp):
     signal.signal(signal.SIGINT, signal_handler)
     signal.signal(signal.SIGTERM, signal_handler)
     try:
-        snapshot = disk.snapshot()
-        image = disk.get_image(snapshot)
+        # There is no need to snapshot the media if it was created by the Disk
+        # instance as a temporary object.
+        device = disk.device if disk.source == '/' else disk.snapshot()
+
+        image = disk.get_image(device)
 
         out.output("Collecting image metadata ...")
         metadata = {}

image_creator/disk.py

@@ -72,6 +72,7 @@ class Disk(object):
         """
         self._cleanup_jobs = []
         self._images = []
+        self._device = None
         self.source = source
         self.out = output
         self.meta = {}
@@ -123,29 +124,36 @@ class Disk(object):
                 job, args = self._cleanup_jobs.pop()
                 job(*args)
 
-    def snapshot(self):
-        """Creates a snapshot of the original source media of the Disk
-        instance.
-        """
+    @property
+    def device(self):
+        """Convert the source media into a block device"""
+
+        if self._device is not None:
+            return self._device
 
         self.out.output("Examining source media `%s' ..." % self.source, False)
-        sourcedev = self.source
         mode = os.stat(self.source).st_mode
         if stat.S_ISDIR(mode):
             self.out.success('looks like a directory')
-            return self._dir_to_disk()
+            self._device = self._dir_to_disk()
         elif stat.S_ISREG(mode):
             self.out.success('looks like an image file')
-            sourcedev = self._losetup(self.source)
+            self._device = self._losetup(self.source)
         elif not stat.S_ISBLK(mode):
             raise FatalError("Invalid media source. Only block devices, "
                              "regular files and directories are supported.")
         else:
             self.out.success('looks like a block device')
+            self._device = self.source
 
-        # Take a snapshot and return it to the user
+        return self._device
+
+    def snapshot(self):
+        """Creates a snapshot of the original source media of the Disk
+        instance.
+        """
         self.out.output("Snapshotting media source ...", False)
-        size = blockdev('--getsz', sourcedev)
+        size = blockdev('--getsz', self.device)
         cowfd, cow = tempfile.mkstemp(dir=self.tmp)
         os.close(cowfd)
         self._add_cleanup(os.unlink, cow)
@@ -158,7 +166,7 @@ class Disk(object):
         try:
             try:
                 os.write(tablefd, "0 %d snapshot %s %s n 8" %
-                                  (int(size), sourcedev, cowdev))
+                                  (int(size), self.device, cowdev))
             finally:
                 os.close(tablefd)
 

image_creator/main.py

@@ -257,9 +257,10 @@ def image_creator():
     signal.signal(signal.SIGINT, signal_handler)
     signal.signal(signal.SIGTERM, signal_handler)
     try:
-        snapshot = disk.snapshot()
-
-        image = disk.get_image(snapshot, sysprep_params=options.sysprep_params)
+        # There is no need to snapshot the media if it was created by the Disk
+        # instance as a temporary object.
+        device = disk.device if disk.source == '/' else disk.snapshot()
+        image = disk.get_image(device, sysprep_params=options.sysprep_params)
 
         if image.is_unsupported() and not options.allow_unsupported:
             raise FatalError(
@@ -323,7 +324,7 @@ def image_creator():
                                      os.path.basename(options.outfile)))
             out.success('done')
 
-        # Destroy the image instance. We only need the snapshot from now on
+        # Destroy the image instance. We only need the disk device from now on
         disk.destroy_image(image)
 
         out.output()
@@ -331,7 +332,7 @@ def image_creator():
             uploaded_obj = ""
             if options.upload:
                 out.output("Uploading image to the storage service:")
-                with open(snapshot, 'rb') as f:
+                with open(device, 'rb') as f:
                     uploaded_obj = kamaki.upload(
                         f, size, options.upload,
                         "(1/3)  Calculating block hashes",