stevedoreize the drivers

I don't expect these to be plugable, mostly just wrapping my head
around stevedores codebase.

Of note, because of the stevedore-ness, we _must_ install ekko to use
it. No longer will it work in the local dir, it must be installed on
the system (or in a venv)

Change-Id: I5037f6877e623614ef7ecf991b0009f49824ec0a

ekko/manifest/_drivers/osdk.py

@@ -20,10 +20,10 @@
 import os
 from struct import pack
 
-from ekko.manifest import driver
+from ekko.manifest import drivers
 
 
-class OSDKDriver(driver.ManifestDriver):
+class OSDKManifest(drivers.BaseManifest):
 
     def initialize(self):
         with open(self.manifest_file, 'wb', 4096) as f:

ekko/manifest/_drivers/sqlite.py

@@ -17,11 +17,11 @@ from contextlib import closing
 from contextlib import contextmanager
 import sqlite3
 
-from ekko.manifest import driver
+from ekko.manifest import drivers
 from ekko.manifest import structure
 
 
-class SQLiteDriver(driver.ManifestDriver):
+class SQLiteManifest(drivers.BaseManifest):
 
     def initialize(self):
         with self.get_conn() as conn:

ekko/manifest/drivers.py

@@ -13,35 +13,53 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from oslo_utils import importutils
+import abc
+
+import six
 
 
-def load_manifest_driver(manifest_location, manifest_driver=None):
-    if not manifest_driver:
-        manifest_driver = 'sqlite.SQLiteDriver'
-
-    return importutils.import_object_ns('ekko.manifest',
-                                        manifest_driver,
-                                        manifest_location)
-
-
-class ManifestDriver(object):
-    """Base class for manifest drivers
+@six.add_metaclass(abc.ABCMeta)
+class BaseManifest(object):
+    """Base class for Manifest drivers
 
+    :params manifest_file: File location for manifest
     """
 
     def __init__(self, manifest_file):
         self.conn = None
         self.manifest_file = manifest_file
 
+    @abc.abstractmethod
     def get_metadata(self):
+        """Get segments from manifest
+
+        :returns: An object of class manifest.structure.Metadata
+        """
         raise NotImplementedError()
 
+    @abc.abstractmethod
     def get_segments(self):
+        """Get segments from manifest
+
+        :returns: A generator of with objects of class
+          manifest.structure.Segment
+        """
         raise NotImplementedError()
 
+    @abc.abstractmethod
     def put_metadata(self, metadata):
+        """Puts given metadata into manifest
+
+        :params metadata: An object of class manifest.structure.Metadata
+        """
         raise NotImplementedError()
 
+    @abc.abstractmethod
     def put_segments(self, segments, metadata):
+        """Puts given segment information into manifest
+
+        :params segments: An interable with objects of class
+          manifest.structure.Segment
+        :params metadata: An object of class manifest.structure.Metadata
+        """
         raise NotImplementedError()

requirements.txt

@@ -5,3 +5,4 @@
 pbr>=1.6
 six>=1.9.0
 oslo.utils>=3.2.0                       # Apache-2.0
+stevedore>=1.5.0  # Apache-2.0

setup.cfg

@@ -19,6 +19,11 @@ classifier =
     Programming Language :: Python :: 3.3
     Programming Language :: Python :: 3.4
 
+[entry_points]
+ekko.manifest.drivers =
+    osdk = ekko.manifest._drivers.osdk:OSDKManifest
+    sqlite = ekko.manifest._drivers.sqlite:SQLiteManifest
+
 [files]
 packages =
     ekko

tools/generate_manifest.py

@@ -21,16 +21,9 @@ import argparse
 import os
 import sys
 
-sys.path.insert(0, '/root/ekko/')
-from ekko.manifest import driver as manifest_driver
 from ekko.manifest import structure as manifest_structure
 from six.moves import range
-
-
-DRIVERS = {
-    'osdk': 'osdk.OSDKDriver',
-    'sqlite': 'sqlite.SQLiteDriver'
-}
+from stevedore import driver
 
 
 def parse_args():
@@ -68,8 +61,12 @@ def main():
         print('manifest exists; exiting')
         return
 
-    manifest = manifest_driver.load_manifest_driver(args.manifest,
-                                                    DRIVERS[args.driver])
+    manifest = driver.DriverManager(
+        namespace='ekko.manifest.drivers',
+        name=args.driver,
+        invoke_on_load=True,
+        invoke_args=[args.manifest]
+    ).driver
 
     size_of_disk = args.backupsize * 1024**3  # Convert GB to B
     num_of_sectors = int(size_of_disk / 512)