Avoid error during snapshot of ISO booted instance

Fixes bug #1023492

If you boot an instance from an image with disk_format=iso and then
attempt to snapshot (i.e. nova image-create) you currently get a
traceback because we do:

  qemu-img convert -f qcow2 -O iso -s $snap $disk $out

and 'iso' is not a format that qemu-img knows anything about.

When booting the image, we use qemu-img to detect that the file is
a raw image so we avoid having to special case disk_format=iso
there. However, there's no way of avoiding the special casing when
extracting a snapshot.

Note 1 - it's not very clever to take a snapshot of a read-only
disk downloaded from glance and upload it back to glance again.
Adding such smarts would be a nice enhancement.

Note 2 - only the destination format is important here because
we can only be extracting from a qcow2 image since snapshots
only work where use_cow_images=True. See also #1030844.

Change-Id: I21ff6db8ebb59a83d27f224283fb76f582c38a0e

1 files changed, 12 insertions, 3 deletions

diff --git a/nova/tests/test_libvirt.py b/nova/tests/test_libvirt.py
index bb885e8c1..4e6e1ec48 100644
--- a/nova/tests/test_libvirt.py
+++ b/nova/tests/test_libvirt.py
@@ -3303,15 +3303,24 @@ disk size: 4.4M''', ''))
         self.mox.ReplayAll()
         libvirt_utils.chown('/some/path', 'soren')
 
-    def test_extract_snapshot(self):
+    def _do_test_extract_snapshot(self, dest_format='raw', out_format='raw'):
         self.mox.StubOutWithMock(utils, 'execute')
-        utils.execute('qemu-img', 'convert', '-f', 'qcow2', '-O', 'raw',
+        utils.execute('qemu-img', 'convert', '-f', 'qcow2', '-O', out_format,
                       '-s', 'snap1', '/path/to/disk/image', '/extracted/snap')
 
         # Start test
         self.mox.ReplayAll()
         libvirt_utils.extract_snapshot('/path/to/disk/image', 'qcow2',
-                                       'snap1', '/extracted/snap', 'raw')
+                                       'snap1', '/extracted/snap', dest_format)
+
+    def test_extract_snapshot_raw(self):
+        self._do_test_extract_snapshot()
+
+    def test_extract_snapshot_iso(self):
+        self._do_test_extract_snapshot(dest_format='iso')
+
+    def test_extract_snapshot_qcow2(self):
+        self._do_test_extract_snapshot(dest_format='qcow2', out_format='qcow2')
 
     def test_load_file(self):
         dst_fd, dst_path = tempfile.mkstemp()