Merge "Rework base file checksums."

2 files changed, 45 insertions, 13 deletions

diff --git a/nova/virt/libvirt/connection.py b/nova/virt/libvirt/connection.py
index e8fdcd792..634acdeca 100644
--- a/nova/virt/libvirt/connection.py
+++ b/nova/virt/libvirt/connection.py
@@ -921,6 +921,11 @@ class LibvirtConnection(driver.ComputeDriver):
         If size is specified, we attempt to resize up to that size.
         """
 
+        # NOTE(mikal): Checksums aren't created here, even if the image cache
+        # manager is enabled, as that would slow down VM startup. If both
+        # cache management and checksumming are enabled, then the checksum
+        # will be created on the first pass of the image cache manager.
+
         generating = 'image_id' not in kwargs
         if not os.path.exists(target):
             base_dir = os.path.join(FLAGS.instances_path, '_base')
diff --git a/nova/virt/libvirt/imagecache.py b/nova/virt/libvirt/imagecache.py
index bd714ea7f..6226e8d4e 100644
--- a/nova/virt/libvirt/imagecache.py
+++ b/nova/virt/libvirt/imagecache.py
@@ -55,6 +55,9 @@ imagecache_opts = [
                default=(24 * 3600),
                help='Unused unresized base images younger than this will not '
                     'be removed'),
+    cfg.BoolOpt('checksum_base_images',
+                default=False,
+                help='Write a checksum for files in _base to disk'),
     ]
 
 flags.DECLARE('instances_path', 'nova.compute.manager')
@@ -77,6 +80,23 @@ def read_stored_checksum(base_file):
     return stored_checksum
 
 
+def write_stored_checksum(target):
+    """Write a checksum to disk for a file in _base."""
+
+    checksum_filename = '%s.sha1' % target
+    if os.path.exists(target) and not os.path.exists(checksum_filename):
+        # NOTE(mikal): Create the checksum file first to exclude possible
+        # overlap in checksum operations. An empty checksum file is ignored if
+        # encountered during verification.
+        sum_file = open(checksum_filename, 'w')
+        img_file = open(target, 'r')
+        checksum = utils.hash_file(img_file)
+        img_file.close()
+
+        sum_file.write(checksum)
+        sum_file.close()
+
+
 class ImageCacheManager(object):
     def __init__(self):
         self.unexplained_images = []
@@ -200,13 +220,13 @@ class ImageCacheManager(object):
         action occurs. This is something sysadmins should monitor for and
         handle manually when it occurs.
         """
-        f = open(base_file, 'r')
-        current_checksum = utils.hash_file(f)
-        f.close()
 
         stored_checksum = read_stored_checksum(base_file)
-
         if stored_checksum:
+            f = open(base_file, 'r')
+            current_checksum = utils.hash_file(f)
+            f.close()
+
             if current_checksum != stored_checksum:
                 LOG.error(_('%(container_format)s-%(id)s '
                             '(%(base_file)s): '
@@ -225,6 +245,13 @@ class ImageCacheManager(object):
                       {'container_format': img['container_format'],
                        'id': img['id'],
                        'base_file': base_file})
+
+            # NOTE(mikal): If the checksum file is missing, then we should
+            # create one. We don't create checksums when we download images
+            # from glance because that would delay VM startup.
+            if FLAGS.checksum_base_images:
+                write_stored_checksum(base_file)
+
             return None
 
     def _remove_base_file(self, base_file):
@@ -335,15 +362,15 @@ class ImageCacheManager(object):
         # TODO(mikal): Write a unit test for this method
         # TODO(mikal): Handle "generated" images
 
-        # The new scheme for base images is as follows -- an image is streamed
-        # from the image service to _base (filename is the sha1 hash of the
-        # image id). If CoW is enabled, that file is then resized to be the
-        # correct size for the instance (filename is the same as the original,
-        # but with an underscore and the resized size in bytes). This second
-        # file is then CoW'd to the instance disk. If CoW is disabled, the
-        # resize occurs as part of the copy from the cache to the instance
-        # directory. Files ending in _sm are no longer created, but may remain
-        # from previous versions.
+        # NOTE(mikal): The new scheme for base images is as follows -- an
+        # image is streamed from the image service to _base (filename is the
+        # sha1 hash of the image id). If CoW is enabled, that file is then
+        # resized to be the correct size for the instance (filename is the
+        # same as the original, but with an underscore and the resized size
+        # in bytes). This second file is then CoW'd to the instance disk. If
+        # CoW is disabled, the resize occurs as part of the copy from the
+        # cache to the instance directory. Files ending in _sm are no longer
+        # created, but may remain from previous versions.
 
         self.unexplained_images = []
         self.active_base_files = []