[libvirt] driver level connection close event

Notify of connection close event from parallels driver (possibly) wrapped in the remote driver. Discussion. In 1 and 2 patch we forced to some decisions because we don't have a weak reference mechanics. 1 patch. ----------- virConnectCloseCallback is introduced because we can not reference the connection object itself when setting a network layer callback because of how connection close works. A connection close procedure is next: 1. client closes connection 2. a this point nobody else referencing a connection and it is disposed 3. connection dispose unreferencing network connection 4. network connection disposes Thus if we referece a connection in network close callback we never get step 2. virConnectCloseCallback broke this cycle but at cost that clients MUST unregister explicitly before closing connection. This is not good as this unregistration is not really neaded. Client is not telling that it does not want to receive events anymore but rather forced to obey some implementation-driven rules. 2 patch. ----------- We impose requirements on driver implementations which is fragile. Moreover we again need to make explicit unregistrations. Implementation of domain events illustrates this point. remoteDispatchConnectDomainEventRegister does not reference NetClient and makes unregistration before NetClient is disposed but drivers do not meet the formulated requirements. Object event system release lock before delivering event for re-entrance purposes. Shortly we have 2 undesired consequences here. 1. Mandatory unregistration. 2. Imposing multi-threading requirements. Introduction of weak pointers could free us from these artifacts. Next weak reference workflow illustrates this. 1. Take weak reference on object of interest before passing to party. This doesn't break disposing mechanics as weak eference does not prevent from disposing object. Object is disposed but memory is not freed yet if there are weak references. 2. When callback is called we are safe to check if pointer dangling as we make a weak reference before. 3. Release weak reference and this trigger memory freeing if there are no more weak references. daemon/libvirtd.h | 1 + daemon/remote.c | 87 ++++++++++++++++++++++++++++++++ src/datatypes.c | 112 +++++++++++++++++++++++++++++++---------- src/datatypes.h | 21 ++++++-- src/driver-hypervisor.h | 12 +++++ src/libvirt-host.c | 79 ++++++++++-------------------- src/remote/remote_driver.c | 108 +++++++++++++++++++++++++++++++--------- src/remote/remote_protocol.x | 24 +++++++++- src/remote_protocol-structs | 6 ++ src/vz/vz_driver.c | 26 ++++++++++ src/vz/vz_sdk.c | 32 +++++++++++- src/vz/vz_utils.h | 3 + 12 files changed, 396 insertions(+), 115 deletions(-)