Enable libvirt driver to use the new BDM format

This patch makes the necessary changes in the libvirt driver to enable
it to use some of the features of the new block device mapping format.

After this patch it will be possible to set the bus, and device_type per
block device, and libvirt driver will honor these when spawning an
instance (note that attaching a volume still does not use the new data
format).

It utilizes some of the existing code in the blockinfo module to be able
to default device names (it does so by overriding the methods introduced
in I84541f8ff6e1b5978734e5def69946d014c66fdf), and also assign default
values to fields like device_type and disk_bus if it is not provided or
if it is bogus. As this implies the driver changing the block devices in
the database, a new virtapi method block_device_mapping_update is added
to accommodate this. Some of the libvirt specific code paths in the
general defaulting function in compute utils have been removed as they
are not needed since the driver now takes care of this.

Further to that, this patch modifies some of the code paths in the
libvirt driver that use the block device info directly (and not through
the blockinfo module) to be aware of the new format. Due to very nicely
factored code - there were only a few instances of this in the driver
itself.

It also overrides the libvirt driver's need_legacy_block_device_info
method to tell the compute manager to feed it the new format when
needed.

This patch concludes the blueprint: improve-block-device-handling

Change-Id: I8efd6af6706a097fb540e040a86ccbeaf131631f

1 files changed, 5 insertions, 0 deletions

diff --git a/nova/block_device.py b/nova/block_device.py
index 9636e81f84..1f0ba62ccf 100644
--- a/nova/block_device.py
+++ b/nova/block_device.py
@@ -406,6 +406,11 @@ def strip_dev(device_name):
     return _dev.sub('', device_name) if device_name else device_name
 
 
+def prepend_dev(device_name):
+    """Make sure there is a leading '/dev/'."""
+    return device_name and '/dev/' + strip_dev(device_name)
+
+
 _pref = re.compile('^((x?v|s)d)')