From d2af7ca7a5c862f53f18c00ac76fc85336fa79e6 Mon Sep 17 00:00:00 2001
From: esubramanian <esubramanian@godaddy.com>
Date: Mon, 8 Jun 2020 23:08:30 -0700
Subject: [PATCH] Removes the delta file once image is extracted

When creating a live snapshot of an instance, nova creates a
copy of the instance disk using a QEMU shallow rebase. This
copy - the delta file - is then extracted and uploaded. The
delta file will eventually be deleted, when the temporary
working directory nova is using for the live snapshot is
discarded, however, until this happens, we will use 3x the
size of the image of host disk space: the original disk,
the delta file, and the extracted file. This can be problematic
when concurrent snapshots of multiple instances are requested
at once.

The solution is simple: delete the delta file after it has
been extracted and is no longer necessary.

Change-Id: I15e9975fa516d81e7d34206e5a4069db5431caa9
Closes-Bug: #1881727
---
 nova/tests/unit/virt/libvirt/test_driver.py | 4 +++-
 nova/virt/libvirt/driver.py                 | 4 ++++
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/nova/tests/unit/virt/libvirt/test_driver.py b/nova/tests/unit/virt/libvirt/test_driver.py
index 1a9c111b0bc6..b34f8d72ce2a 100644
--- a/nova/tests/unit/virt/libvirt/test_driver.py
+++ b/nova/tests/unit/virt/libvirt/test_driver.py
@@ -19868,10 +19868,11 @@ class LibvirtConnTestCase(test.NoDBTestCase,
         disconnect_volume.assert_called_once_with(self.context,
                 mock.sentinel.new_connection_info, instance)
 
+    @mock.patch.object(fileutils, 'delete_if_exists')
     @mock.patch('nova.virt.libvirt.guest.BlockDevice.is_job_complete')
     @mock.patch('nova.privsep.path.chown')
     def _test_live_snapshot(
-            self, mock_chown, mock_is_job_complete,
+            self, mock_chown, mock_is_job_complete, mock_delete,
             can_quiesce=False, require_quiesce=False):
         drvr = libvirt_driver.LibvirtDriver(fake.FakeVirtAPI())
         mock_dom = mock.MagicMock()
@@ -19929,6 +19930,7 @@ class LibvirtConnTestCase(test.NoDBTestCase,
             mock_chown.assert_called_once_with(dltfile, uid=os.getuid())
             mock_snapshot.assert_called_once_with(dltfile, "qcow2",
                                                   dstfile, "qcow2")
+            mock_delete.assert_called_once_with(dltfile)
             mock_define.assert_called_once_with(xmldoc)
             mock_quiesce.assert_any_call(mock.ANY, self.test_instance,
                                          mock.ANY, True)
diff --git a/nova/virt/libvirt/driver.py b/nova/virt/libvirt/driver.py
index 5443e55472da..58e4dfbb2f4d 100644
--- a/nova/virt/libvirt/driver.py
+++ b/nova/virt/libvirt/driver.py
@@ -2675,6 +2675,10 @@ class LibvirtDriver(driver.ComputeDriver):
         libvirt_utils.extract_snapshot(disk_delta, 'qcow2',
                                        out_path, image_format)
 
+        # Remove the disk_delta file once the snapshot extracted, so that
+        # it doesn't hang around till the snapshot gets uploaded
+        fileutils.delete_if_exists(disk_delta)
+
     def _volume_snapshot_update_status(self, context, snapshot_id, status):
         """Send a snapshot status update to Cinder.