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Re: [libvirt] [PATCH] events: Don't fail on registering events for two different domains



On 27.06.2012 14:36, Eric Blake wrote:
> On 06/27/2012 06:12 AM, Michal Privoznik wrote:
>> virConnectDomainEventRegisterAny() takes a domain as an argument.
>> So it should be possible to register the same event (be it
>> VIR_DOMAIN_EVENT_ID_LIFECYCLE for example) for two different domains.
>> That is, we need to take domain into account when searching for
>> duplicate event being already registered.
>> ---
>>  src/conf/domain_event.c |    6 +++++-
>>  1 files changed, 5 insertions(+), 1 deletions(-)
>>
>> diff --git a/src/conf/domain_event.c b/src/conf/domain_event.c
>> index 4ecc413..3cfd940 100644
>> --- a/src/conf/domain_event.c
>> +++ b/src/conf/domain_event.c
>> @@ -363,7 +363,11 @@ virDomainEventCallbackListAddID(virConnectPtr conn,
>>      for (i = 0 ; i < cbList->count ; i++) {
>>          if (cbList->callbacks[i]->cb == VIR_DOMAIN_EVENT_CALLBACK(callback) &&
>>              cbList->callbacks[i]->eventID == eventID &&
>> -            cbList->callbacks[i]->conn == conn) {
>> +            cbList->callbacks[i]->conn == conn &&
>> +            ((dom && cbList->callbacks[i]->dom &&
>> +              memcmp(cbList->callbacks[i]->dom->uuid,
>> +                     dom->uuid, VIR_UUID_BUFLEN) == 0) ||
>> +             (!dom && !cbList->callbacks[i]->dom))) {
> 
> This misses the case of registering a catchall against NULL domain then
> attempting to re-register the same event against a specific domain
> (which one of the two would fire?).  It also misses the case of
> registering a domain-specific handler, then attempting to broaden things
> into a global handler.

Yes, but that's intentional. In both cases both events are fired.

> 
> I think the idea of double registration makes sense (in particular, if I
> have a per-domain callback, but then want to switch to global, I would
> rather have a window with both handlers at once than a window with no
> handler at all), but I have not tested whether we actually handle it by
> firing both the global and domain-specific callback.

I've tested it and it works.

> 
> If we are happy with double registration, then your patch looks correct
> on the registration side (although it may be incomplete, if we mishandle
> double firing).  On the other hand, if we want to prevent double
> registration, then you need to further forbid registration when ((dom &&
> !cbList->callbacks[i]->dom) || (!dom && cblist->callbacks[i]->dom)).
> 
> 
> 
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