On 01/06/2014 05:27 PM, Eric Blake wrote:
Right now, the older virConnectDomainEventRegister (takes a function pointer, returns 0 on success) and the newer virConnectDomainEventRegisterID (takes an eventID, returns a callbackID) share the underlying implementation (the older API ends up consuming a callbackID for eventID 0 under the hood). We implemented that by a lot of copy and pasted code between object_event.c and domain_event.c, according to whether we are dealing with a function pointer or an eventID. However, our copy and paste is not symmetric. Consider this sequence:
id1 = virConnectDomainEventRegisterAny(conn, dom, VIR_DOMAIN_EVENT_ID_LIFECYCLE, VIR_DOMAIN_EVENT_CALLBACK(callback), NULL, NULL); virConnectDomainEventRegister(conn, callback, NULL, NULL); virConnectDomainEventDeregister(conn, callback); virConnectDomainEventDeregsiterAny(conn, id1);
the first three calls would succeed, but the third call ended up nuking the id1 callbackID (the per-domain new-style handler), then the fourth call failed with an error about an unknown callbackID, leaving us with the global handler (old-style) still live and receiving events. It required another old-style deregister to clean up the mess. Root cause was that virDomainEventCallbackList{Remove,MarkDelete} were only checking for function pointer match, rather than also checking for whether the registration was global.
Rather than playing with the guts of object_event ourselves in domain_event, it is nicer to add a mapping function for the internal callback id, then share common code for event removal. For now, the function-to-id mapping is used only internally; I thought about whether a new public API to let a user learn the callback would be useful, but decided exposing this to the user is probably a disservice, since we already publicly document that they should avoid the old style, and since this patch already demonstrates that older libvirt versions have weird behavior when mixing old and new styles.
* src/conf/object_event.c (virObjectEventCallbackLookup) (virObjectEventStateCallbackID): New functions. (virObjectEventCallbackLookup): Use helper function. * src/conf/object_event_private.h (virObjectEventStateCallbackID): Declare new function. * src/conf/domain_event.c (virDomainEventStateRegister) (virDomainEventStateDeregister): Let common code handle the complexity. (virDomainEventCallbackListRemove) (virDomainEventCallbackListMarkDelete) (virDomainEventCallbackListAdd): Drop unused functions.
Signed-off-by: Eric Blake <eblake@redhat.com> --- src/conf/domain_event.c | 171 ++++------------------------------------ src/conf/object_event.c | 96 +++++++++++++++++++--- src/conf/object_event_private.h | 9 +++ 3 files changed, 109 insertions(+), 167 deletions(-)
ACK the pair (6 & 7)... The intro comment to 6 had me do a double take though thinking I messed up the pair! John