Copyright (C) 2022 Jens Axboe <[email protected]>

SPDX-License-Identifier: LGPL-2.0-or-later

io_uring_register_eventfd - 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. Returns 0 on success, or or -errno on error. eventfd (2)