LibvirtDriver创建connection##
在nova.virt.libvirt.driver中，LibvirtDriver是Nova Compute的驱动，通过Libvirt管理虚拟机。
首先看连接过程：
def _get_connection(self):
# multiple concurrent connections are protected by _wrapped_conn_lock
with self._wrapped_conn_lock://给thread加锁
wrapped_conn = self._wrapped_conn
if not wrapped_conn or not self._test_connection(wrapped_conn):
wrapped_conn = self._get_new_connection()//获取新的connection
return wrapped_conn
_conn = property(_get_connection)//将_get_connection当做一个属性来使用
通过_get_new_connection()，获取新的connection：
def _get_new_connection(self):
# call with _wrapped_conn_lock held
LOG.debug(_('Connecting to libvirt: %s'), self.uri())
wrapped_conn = None
try:
wrapped_conn = self._connect(self.uri(), self.read_only)//获取只读connection
finally:
# Enabling the compute service, in case it was disabled
# since the connection was successful.
is_connected = bool(wrapped_conn)
self.set_host_enabled(CONF.host, is_connected)
self._wrapped_conn = wrapped_conn
try:
LOG.debug(_("Registering for lifecycle events %s"), self)
wrapped_conn.domainEventRegisterAny(
None,
libvirt.VIR_DOMAIN_EVENT_ID_LIFECYCLE,
self._event_lifecycle_callback,
self)//注册event，这个随后再讲
except Exception as e:
LOG.warn(_("URI %(uri)s does not support events: %(error)s"),
{'uri': self.uri(), 'error': e})
...
return wrapped_conn
在self._connect()中获取connection：
@staticmethod
def _connect(uri, read_only):
def _connect_auth_cb(creds, opaque):
...
auth = [[libvirt.VIR_CRED_AUTHNAME,
libvirt.VIR_CRED_ECHOPROMPT,
libvirt.VIR_CRED_REALM,
libvirt.VIR_CRED_PASSPHRASE,
libvirt.VIR_CRED_NOECHOPROMPT,
libvirt.VIR_CRED_EXTERNAL],
_connect_auth_cb,
None]
try:
flags = 0
if read_only:
flags = libvirt.VIR_CONNECT_RO
# tpool.proxy_call creates a native thread. Due to limitations
# with eventlet locking we cannot use the logging API inside
# the called function.
//通过eventlet的tpool来获得一个naive thread
return tpool.proxy_call(
(libvirt.virDomain, libvirt.virConnect),
libvirt.openAuth, uri, auth, flags)
except libvirt.libvirtError as ex:
LOG.exception(_("Connection to libvirt failed: %s"), ex)
payload = dict(ip=LibvirtDriver.get_host_ip_addr(),
method='_connect',
reason=ex)
rpc.get_notifier('compute').error(nova_context.get_admin_context(),
'compute.libvirt.error',
payload)
raise exception.HypervisorUnavailable(host=CONF.host)
看tpool.proxy_call()，查eventlet的源码可知，这个函数是用来生成一个naive thread，并将返回值进行wrap。
在eventlet/eventlet/tpool.py里：
def proxy_call(autowrap, f, *args, **kwargs):
"""
Call a function *f* and returns the value. If the type of the return value
is in the *autowrap* collection, then it is wrapped in a :class:`Proxy`
object before return.
Normally *f* will be called in the threadpool with :func:`execute`; if the
keyword argument "nonblocking" is set to ``True``, it will simply be
executed directly. This is useful if you have an object which has methods
that don't need to be called in a separate thread, but which return objects
that should be Proxy wrapped.
"""
if kwargs.pop('nonblocking',False):
rv = f(*args, **kwargs)
else:
rv = execute(f,*args,**kwargs)
if isinstance(rv, autowrap):
return Proxy(rv, autowrap)
else:
return rv
看注释可知，参数autowrap是要包装的值，f是执行的函数，*args是f的参数，**kwargs是keyword argument，比如”nonblocking”。
结合_connect()中的代码：
@staticmethod
def _connect(uri, read_only):
...
return tpool.proxy_call((libvirt.virDomain, libvirt.virConnect), libvirt.openAuth, uri, auth, flags)
意思就是说，开启一个新的naive thread来执行libvirt.openAuth，并将返回的类型为(libvirt.virDomain, libvirt.virtConnect)的值包装起来。
然后通过_conn即可通过libvirt来管理虚拟机，比如：
_conn.listDomainsID()//获取所有domain的id