Directly copy a file URL from glance.

That patch allows nova to use shutil to copy a file directly from the
glance store.  For this to work glance needs to enable direct_url
descriptions in the image metadata.  This is done by setting
show_image_direct_url to True in glance-api.conf.  The path used to back
glance also must match the path used to back nova instance storage.  This
should be a large performance increase for the cases where both glance
and nova instance storage are backed by a shared file system like gluster
or ceph.

A new option has been added to nova: allowed_direct_url_schemes
This option is set to a list of schemes that can be directly accessed.
For this first simple patch only file:// is valid, and the
implementation is simple and inline.  In the future it would be better
to make this into propagation modules which are dynamically loaded
according to the scheme.

DocImpact
Implements: blueprint direct-file-copy
Change-Id: I041b5524f8a0ea59e89ece0202f0503abf2f9d8e

1 files changed, 37 insertions, 0 deletions

diff --git a/nova/tests/image/test_glance.py b/nova/tests/image/test_glance.py
index 7c13796a6..9dd9e5121 100644
--- a/nova/tests/image/test_glance.py
+++ b/nova/tests/image/test_glance.py
@@ -17,7 +17,10 @@
 
 
 import datetime
+import filecmp
+import os
 import random
+import tempfile
 import time
 
 import glanceclient.exc
@@ -468,6 +471,40 @@ class TestGlanceImageService(test.TestCase):
         self.flags(glance_num_retries=1)
         service.download(self.context, image_id, writer)
 
+    def test_download_file_url(self):
+        class MyGlanceStubClient(glance_stubs.StubGlanceClient):
+            """A client that returns a file url."""
+
+            (outfd, s_tmpfname) = tempfile.mkstemp(prefix='directURLsrc')
+            outf = os.fdopen(outfd, 'w')
+            inf = open('/dev/urandom', 'r')
+            for i in range(10):
+                _data = inf.read(1024)
+                outf.write(_data)
+            outf.close()
+
+            def get(self, image_id):
+                return type('GlanceTestDirectUrlMeta', (object,),
+                            {'direct_url': 'file://%s' + self.s_tmpfname})
+
+        client = MyGlanceStubClient()
+        (outfd, tmpfname) = tempfile.mkstemp(prefix='directURLdst')
+        writer = os.fdopen(outfd, 'w')
+
+        service = self._create_image_service(client)
+        image_id = 1  # doesn't matter
+
+        self.flags(allowed_direct_url_schemes=['file'])
+        service.download(self.context, image_id, writer)
+        writer.close()
+
+        # compare the two files
+        rc = filecmp.cmp(tmpfname, client.s_tmpfname)
+        self.assertTrue(rc, "The file %s and %s should be the same" %
+                        (tmpfname, client.s_tmpfname))
+        os.remove(client.s_tmpfname)
+        os.remove(tmpfname)
+
     def test_client_forbidden_converts_to_imagenotauthed(self):
         class MyGlanceStubClient(glance_stubs.StubGlanceClient):
             """A client that raises a Forbidden exception."""