io_uring_register_eventfd - Man Page

register an eventfd with a ring


#include <liburing.h>

int io_uring_register_eventfd(struct io_uring *ring,
                              int fd);

int io_uring_register_eventfd_async(struct io_uring *ring,
                                    int fd);

int io_uring_unregister_eventfd(struct io_uring *ring);


io_uring_register_eventfd(3) registers the eventfd file descriptor fd with the ring identified by ring.

Whenever completions are posted to the CQ ring, an eventfd notification is generated with the registered eventfd descriptor. If io_uring_register_eventfd_async(3) is used, only events that completed out-of-line will trigger a notification.

It notifications are no longer desired, io_uring_unregister_eventfd(3) may be called to remove the eventfd registration. No eventfd argument is needed, as a ring can only have a single eventfd registered.


While io_uring generally takes care to avoid spurious events, they can occur. Similarly, batched completions of CQEs may only trigger a single eventfd notification even if multiple CQEs are posted. The application should make no assumptions on number of events being available having a direct correlation to eventfd notifications posted. An eventfd notification must thus only be treated as a hint to check the CQ ring for completions.

Return Value

Returns 0 on success, or or -errno on error.

See Also


Referenced By

io_uring_register_eventfd(3), io_uring_register_eventfd_async(3), io_uring_unregister_eventfd(3).

April 16, 2022 liburing-2.2 liburing Manual