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notify: add NotiferWithReturn so notifier list can abort

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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.

Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2013-06-24 17:13:09 +02:00 committed by Kevin Wolf
parent a5c5ea3f60
commit 5dae8e5fb8
2 changed files with 59 additions and 0 deletions
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29
include/qemu/notify.h
View File

@ -40,4 +40,33 @@ 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 {
/**
* Return 0 on success (next notifier will be invoked), otherwise
* notifier_with_return_list_notify() will stop and return the value.
*/
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

30
util/notify.c
View File

@ -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;
}