Libvirt driver should reply with a meaningful exception, when connection to libvirt is broken

[Vladik Romanovsky]

Currently, when libvirt connection is broken, there is no meaningful exception being thrown. Instead, every call result in a mutlple traces, as below.
This makes it imposible to handle these exceptions properly in the higher levels.

2013-10-11 15:06:25.179 DEBUG nova.virt.libvirt.driver [req-cd22b4f2-0bfe-4d93-b191-02736ac8a437 None None] Connecting to libvirt: qemu:///system from (pid=28433) _get_connection /home/vladikr/devel/openstack/nova/nova/virt/libvirt/driver.py:600
2013-10-11 15:06:25.180 ERROR nova.virt.libvirt.driver [-] Connection to libvirt failed: Failed to connect socket to '/var/run/libvirt/libvirt-sock': No such file or directory
2013-10-11 15:06:25.180 TRACE nova.virt.libvirt.driver Traceback (most recent call last):
2013-10-11 15:06:25.180 TRACE nova.virt.libvirt.driver File "/home/vladikr/devel/openstack/nova/nova/virt/libvirt/driver.py", line 694, in _connect
2013-10-11 15:06:25.180 TRACE nova.virt.libvirt.driver return libvirt.openAuth(uri, auth, flags)
2013-10-11 15:06:25.180 TRACE nova.virt.libvirt.driver File "/usr/lib64/python2.7/site-packages/libvirt.py", line 102, in openAuth
2013-10-11 15:06:25.180 TRACE nova.virt.libvirt.driver if ret is None:raise libvirtError('virConnectOpenAuth() failed')
2013-10-11 15:06:25.180 TRACE nova.virt.libvirt.driver libvirtError: Failed to connect socket to '/var/run/libvirt/libvirt-sock': No such file or directory
2013-10-11 15:06:25.180 TRACE nova.virt.libvirt.driver
----------------------------------------------------------------------------------------------------------
2013-10-11 15:06:25.188 WARNING nova.virt.libvirt.driver [req-cd22b4f2-0bfe-4d93-b191-02736ac8a437 None None] URI qemu:///system does not support events
Traceback (most recent call last):
  File "/usr/lib64/python2.7/logging/__init__.py", line 851, in emit
2013-10-11 15:06:25.190 ERROR nova.openstack.common.periodic_task [req-cd22b4f2-0bfe-4d93-b191-02736ac8a437 None None] Error during ComputeManager.update_available_resource: 'N
oneType' object has no attribute 'getInfo'
2013-10-11 15:06:25.190 TRACE nova.openstack.common.periodic_task Traceback (most recent call last):
2013-10-11 15:06:25.190 TRACE nova.openstack.common.periodic_task File "/home/vladikr/devel/openstack/nova/nova/openstack/common/periodic_task.py", line 180, in run_periodic_
tasks
2013-10-11 15:06:25.190 TRACE nova.openstack.common.periodic_task task(self, context)
2013-10-11 15:06:25.190 TRACE nova.openstack.common.periodic_task File "/home/vladikr/devel/openstack/nova/nova/compute/manager.py", line 4867, in update_available_resource
2013-10-11 15:06:25.190 TRACE nova.openstack.common.periodic_task rt.update_available_resource(context)
2013-10-11 15:06:25.190 TRACE nova.openstack.common.periodic_task File "/home/vladikr/devel/openstack/nova/nova/openstack/common/lockutils.py", line 246, in inner
2013-10-11 15:06:25.190 TRACE nova.openstack.common.periodic_task return f(*args, **kwargs)
2013-10-11 15:06:25.190 TRACE nova.openstack.common.periodic_task File "/home/vladikr/devel/openstack/nova/nova/compute/resource_tracker.py", line 274, in update_available_resource
2013-10-11 15:06:25.190 TRACE nova.openstack.common.periodic_task resources = self.driver.get_available_resource(self.nodename)
2013-10-11 15:06:25.190 TRACE nova.openstack.common.periodic_task File "/home/vladikr/devel/openstack/nova/nova/virt/libvirt/driver.py", line 3744, in get_available_resource
2013-10-11 15:06:25.190 TRACE nova.openstack.common.periodic_task stats = self.host_state.get_host_stats(refresh=True)
2013-10-11 15:06:25.190 TRACE nova.openstack.common.periodic_task File "/home/vladikr/devel/openstack/nova/nova/virt/libvirt/driver.py", line 4779, in get_host_stats
2013-10-11 15:06:25.190 TRACE nova.openstack.common.periodic_task self.update_status()
2013-10-11 15:06:25.190 TRACE nova.openstack.common.periodic_task File "/home/vladikr/devel/openstack/nova/nova/virt/libvirt/driver.py", line 4813, in update_status
2013-10-11 15:06:25.190 TRACE nova.openstack.common.periodic_task data["memory_mb"] = self.driver.get_memory_mb_total()
2013-10-11 15:06:25.190 TRACE nova.openstack.common.periodic_task File "/home/vladikr/devel/openstack/nova/nova/virt/libvirt/driver.py", line 3383, in get_memory_mb_total
2013-10-11 15:06:25.190 TRACE nova.openstack.common.periodic_task return self._conn.getInfo()[1]
2013-10-11 15:06:25.190 TRACE nova.openstack.common.periodic_task AttributeError: 'NoneType' object has no attribute 'getInfo'
2013-10-11 15:06:25.190 TRACE nova.openstack.common.periodic_task
q

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/52184
Committed: http://github.com/openstack/nova/commit/86be0b7fdf1af20403e0d763b86da06849bcc437
Submitter: Jenkins
Branch: master

commit 86be0b7fdf1af20403e0d763b86da06849bcc437
Author: Vladik Romanovsky <email address hidden>
Date: Tue Oct 22 11:12:37 2013 -0400

    Reply with a meaningful exception, when libvirt connection is broken.

    Libvirt driver will respond with a meaningful error on any
    command, when the connection to the libvirt service is broken.

    Closes-bug: #1240344
    Change-Id: I823fefaffcf969ecf9eb853ac99dc18cef92d137