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Re: [libvirt] [PATCHv2 09/14] event: properly filter count of remaining events

On 01/06/2014 05:27 PM, Eric Blake wrote:
> On the surface, this sequence of API calls should succeed:
> id1 = virConnectDomainEventRegisterAny(..., VIR_DOMAIN_EVENT_ID_LIFECYCLE,...);
> id2 = virConnectDomainEventRegisterAny(..., VIR_DOMAIN_EVENT_ID_RTC_CHANGE,...);
> virConnectDomainEventDeregisterAny(id1);
> id1 = virConnectDomainEventRegisterAny(..., VIR_DOMAIN_EVENT_ID_LIFECYCLE,...);
> And for test:///default, it does.  But for qemu:///system, it fails:
> libvirt: XML-RPC error : internal error: domain event 0 already registered
> Looking closer, the bug is caused by miscommunication between
> the object event engine and the client side of the remote driver.
> In our implementation, we set up a single server-side event per
> eventID, then the client side replicates that one event to all
> callbacks that have been registered client side.  To know when
> to turn the server side eventID on or off, the client side must
> track how many events for the same eventID have been registered.
> But while our code was filtering by eventID on event registration,
> it did not filter on event deregistration.  So the above API calls
> resulted in the deregister returning 1 instead of 0, so no RPC
> deregister was issued, and the final register detects on the
> server side that the server is already handling eventID 0.
> Unfortunately, since the problem is only observable on remote
> connections, it's not possible to enhance objecteventtest to
> expose the semantics using only public API entry points.
> * src/conf/object_event.c (virObjectEventCallbackListCount): New
> function.
> (virObjectEventCallbackListAddID)
> (virObjectEventCallbackListRemoveID)
> (virObjectEventCallbackListMarkDeleteID): Use it.
> Signed-off-by: Eric Blake <eblake redhat com>
> ---
>  src/conf/object_event.c | 68 ++++++++++++++++++++++++++++++++-----------------
>  1 file changed, 45 insertions(+), 23 deletions(-)

Strangely enough - I was going to remark about the usage of 'deleted' in
the previous patch deleted code as being a bit unusual..



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