io_uring_prep_poll_timeout(3) liburing Manual io_uring_prep_poll_timeout(3)

io_uring_prep_timeout - prepare a timeout request

#include <liburing.h>
void io_uring_prep_timeout(struct io_uring_sqe *sqe,
                           struct __kernel_timespec *ts,
                           unsigned count,
                           unsigned flags);

The io_uring_prep_timeout(3) function prepares a timeout request. The submission queue entry sqe is setup to arm a timeout specified by ts and with a timeout count of count completion entries. The flags argument holds modifier flags for the request.

This request type can be used as a timeout waking anyone sleeping for events on the CQ ring. The flags argument may contain:

The value specified in ts is an absolute value rather than a relative one.
The boottime clock source should be used.
The realtime clock source should be used.
Consider an expired timeout a success in terms of the posted completion. Normally a timeout that triggers would return in a -ETIME CQE res value.
The request will return multiple timeout completions. The completion flag IORING_CQE_F_MORE is set if more timeouts are expected. The value specified in count is the number of repeats. A value of 0 means the timeout is indefinite and can only be stopped by a removal request. Available since the 6.4 kernel.

The timeout completion event will trigger if either the specified timeout has occurred, or the specified number of events to wait for have been posted to the CQ ring.


These are the errors that are reported in the CQE res field. On success, 0 is returned.

The specified timeout occurred and triggered the completion event.
One of the fields set in the SQE was invalid. For example, two clocksources where given, or the specified timeout seconds or nanoseconds where < 0.
io_uring was unable to access the data specified by ts.
The timeout was canceled by a removal request.

As with any request that passes in data in a struct, that data must remain valid until the request has been successfully submitted. It need not remain valid until completion. Once a request has been submitted, the in-kernel state is stable. Very early kernels (5.4 and earlier) required state to be stable until the completion occurred. Applications can test for this behavior by inspecting the IORING_FEAT_SUBMIT_STABLE flag passed back from io_uring_queue_init_params(3).

io_uring_get_sqe(3), io_uring_submit(3), io_uring_prep_timeout_remove(3), io_uring_prep_timeout_update(3)

March 12, 2022 liburing-2.2