Move image conversion to privsep.

Following a similar pattern to previous changes, move calls to
qemu-img to convert between image formats to use privsep.

Change-Id: I2c3df909a783e1480d3ab4ca10b34b84ac9e4b5f
blueprint: hurrah-for-privsep

1 files changed, 8 insertions, 23 deletions

diff --git a/nova/virt/images.py b/nova/virt/images.py
index dfd415052d..01bcb4d64c 100644
--- a/nova/virt/images.py
+++ b/nova/virt/images.py
@@ -32,6 +32,7 @@ import nova.conf
 from nova import exception
 from nova.i18n import _
 from nova import image
+import nova.privsep.qemu
 from nova import utils
 
 LOG = logging.getLogger(__name__)
@@ -116,30 +117,14 @@ def convert_image_unsafe(source, dest, out_format, run_as_root=False):
 
 
 def _convert_image(source, dest, in_format, out_format, run_as_root):
-    # NOTE(mdbooth): qemu-img convert defaults to cache=unsafe, which means
-    # that data is not synced to disk at completion. We explicitly use
-    # cache=none here to (1) ensure that we don't interfere with other
-    # applications using the host's io cache, and (2) ensure that the data is
-    # on persistent storage when the command exits. Without (2), a host crash
-    # may leave a corrupt image in the image cache, which Nova cannot recover
-    # automatically.
-    # NOTE(zigo): we cannot use -t none if the instances dir is mounted on a
-    # filesystem that doesn't have support for O_DIRECT, which is the case
-    # for example with tmpfs. This simply crashes "openstack server create"
-    # in environments like live distributions. In such case, the best choice
-    # is writethrough, which is power-failure safe, but still faster than
-    # writeback.
-    if utils.supports_direct_io(CONF.instances_path):
-        cache_mode = 'none'
-    else:
-        cache_mode = 'writethrough'
-    cmd = ('qemu-img', 'convert', '-t', cache_mode, '-O', out_format)
-
-    if in_format is not None:
-        cmd = cmd + ('-f', in_format)
-    cmd = cmd + (source, dest)
     try:
-        utils.execute(*cmd, run_as_root=run_as_root)
+        if not run_as_root:
+            nova.privsep.qemu.unprivileged_convert_image(
+                source, dest, in_format, out_format, CONF.instances_path)
+        else:
+            nova.privsep.qemu.convert_image(
+                source, dest, in_format, out_format, CONF.instances_path)
+
     except processutils.ProcessExecutionError as exp:
         msg = (_("Unable to convert image to %(format)s: %(exp)s") %
                {'format': out_format, 'exp': exp})