event: server RPC protocol tweaks for domain lifecycle events

event: server RPC protocol tweaks for domain lifecycle events

This patch adds some new RPC call numbers, but for ease of review,
they sit idle until a later patch adds the client counterpart to
drive the new RPCs.  Also for ease of review, I limited this patch
to just the lifecycle event; although converting the remaining
15 domain events will be quite mechanical.  On the server side,
we have to have a function per RPC call, largely with duplicated
bodies (the key difference being that we store in our callback
opaque pointer whether events should be fired with old or new
style); meanwhile, a single function can drive multiple RPC
messages.  With a strategic choice of XDR struct layout, we can
make the event generation code for both styles fairly compact.

I debated about adding a tri-state witness variable per
connection (values 'unknown', 'legacy', 'modern').  It would start
as 'unknown', move to 'legacy' if any RPC call is made to a legacy
event call, and move to 'modern' if the feature probe is made;
then the event code could issue an error if the witness state is
incorrect (a legacy RPC call while in 'modern', a modern RPC call
while in 'unknown' or 'legacy', and a feature probe while in
'legacy' or 'modern').  But while it might prevent odd behavior
caused by protocol fuzzing, I don't see that it would prevent
any security holes, so I considered it bloat.

Note that sticking @acl markers on the new RPCs generates unused
functions in access/viraccessapicheck.c, because there is no new
API call that needs to use the new checks; however, having a
consistent .x file is worth the dead code.

* src/libvirt_internal.h (VIR_DRV_FEATURE_REMOTE_EVENT_CALLBACK):
New feature.
* src/remote/remote_protocol.x
(REMOTE_PROC_CONNECT_DOMAIN_EVENT_CALLBACK_REGISTER_ANY)
(REMOTE_PROC_CONNECT_DOMAIN_EVENT_CALLBACK_DEREGISTER_ANY)
(REMOTE_PROC_DOMAIN_EVENT_CALLBACK_LIFECYCLE): New RPCs.
* daemon/remote.c (daemonClientCallback): Add field.
(remoteDispatchConnectDomainEventCallbackRegisterAny)
(remoteDispatchConnectDomainEventCallbackDeregisterAny): New
functions.
(remoteDispatchConnectDomainEventRegisterAny)
(remoteDispatchConnectDomainEventDeregisterAny): Mark legacy use.
(remoteRelayDomainEventLifecycle): Change message based on legacy
or new use.
(remoteDispatchConnectSupportsFeature): Advertise new feature.
* src/remote_protocol-structs: Regenerate.

Signed-off-by: Eric Blake <eblake@redhat.com>