notifier_list_notify() has no return value. This is fine when we just want to invoke side-effects.
Sometimes it's useful for notifiers to produce a return value. This allows notifiers to "veto" an operation and will be used by the block layer before-write notifier. Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com> --- include/qemu/notify.h | 25 +++++++++++++++++++++++++ util/notify.c | 30 ++++++++++++++++++++++++++++++ 2 files changed, 55 insertions(+) diff --git a/include/qemu/notify.h b/include/qemu/notify.h index 4e2e7f0..d3103e7 100644 --- a/include/qemu/notify.h +++ b/include/qemu/notify.h @@ -40,4 +40,29 @@ void notifier_remove(Notifier *notifier); void notifier_list_notify(NotifierList *list, void *data); +/* Same as Notifier but allows .notify() to return errors */ +typedef struct NotifierWithReturn NotifierWithReturn; + +struct NotifierWithReturn { + int (*notify)(NotifierWithReturn *notifier, void *data); + QLIST_ENTRY(NotifierWithReturn) node; +}; + +typedef struct NotifierWithReturnList { + QLIST_HEAD(, NotifierWithReturn) notifiers; +} NotifierWithReturnList; + +#define NOTIFIER_WITH_RETURN_LIST_INITIALIZER(head) \ + { QLIST_HEAD_INITIALIZER((head).notifiers) } + +void notifier_with_return_list_init(NotifierWithReturnList *list); + +void notifier_with_return_list_add(NotifierWithReturnList *list, + NotifierWithReturn *notifier); + +void notifier_with_return_remove(NotifierWithReturn *notifier); + +int notifier_with_return_list_notify(NotifierWithReturnList *list, + void *data); + #endif diff --git a/util/notify.c b/util/notify.c index 7b7692a..f215dfc 100644 --- a/util/notify.c +++ b/util/notify.c @@ -39,3 +39,33 @@ void notifier_list_notify(NotifierList *list, void *data) notifier->notify(notifier, data); } } + +void notifier_with_return_list_init(NotifierWithReturnList *list) +{ + QLIST_INIT(&list->notifiers); +} + +void notifier_with_return_list_add(NotifierWithReturnList *list, + NotifierWithReturn *notifier) +{ + QLIST_INSERT_HEAD(&list->notifiers, notifier, node); +} + +void notifier_with_return_remove(NotifierWithReturn *notifier) +{ + QLIST_REMOVE(notifier, node); +} + +int notifier_with_return_list_notify(NotifierWithReturnList *list, void *data) +{ + NotifierWithReturn *notifier, *next; + int ret = 0; + + QLIST_FOREACH_SAFE(notifier, &list->notifiers, node, next) { + ret = notifier->notify(notifier, data); + if (ret != 0) { + break; + } + } + return ret; +} -- 1.8.1.4