IO_GETEVENTS

Section: Linux Programmer's Manual (2)
Updated: 2020-12-21
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NAME

io_getevents - read asynchronous I/O events from the completion queue

SYNOPSIS

#include <linux/aio_abi.h>         /* Defines needed types */
#include <linux/time.h>            /* Defines 'struct timespec' */

int io_getevents(aio_context_t ctx_id, long min_nr, long nr,
                 struct io_event *events, struct timespec *timeout);

Note: There is no glibc wrapper for this system call; see NOTES.

DESCRIPTION

Note: this page describes the raw Linux system call interface. The wrapper function provided by libaio uses a different type for the ctx_id argument. See NOTES.

The io_getevents() system call attempts to read at least min_nr events and up to nr events from the completion queue of the AIO context specified by ctx_id.

The timeout argument specifies the amount of time to wait for events, and is specified as a relative timeout in a structure of the following form:

struct timespec {
time_t tv_sec; /* seconds */
long tv_nsec; /* nanoseconds [0 .. 999999999] */ };

The specified time will be rounded up to the system clock granularity and is guaranteed not to expire early.

Specifying timeout as NULL means block indefinitely until at least min_nr events have been obtained.

RETURN VALUE

On success, io_getevents() returns the number of events read. This may be 0, or a value less than min_nr, if the timeout expired. It may also be a nonzero value less than min_nr, if the call was interrupted by a signal handler.

For the failure return, see NOTES.

ERRORS

EFAULT: Either events or timeout is an invalid pointer.
EINTR: Interrupted by a signal handler; see signal(7).
EINVAL: ctx_id is invalid. min_nr is out of range or nr is out of range.
ENOSYS: io_getevents() is not implemented on this architecture.

VERSIONS

The asynchronous I/O system calls first appeared in Linux 2.5.

CONFORMING TO

io_getevents() is Linux-specific and should not be used in programs that are intended to be portable.

NOTES

Glibc does not provide a wrapper function for this system call. You could invoke it using syscall(2). But instead, you probably want to use the io_getevents() wrapper function provided by libaio.

Note that the libaio wrapper function uses a different type (io_context_t) for the ctx_id argument. Note also that the libaio wrapper does not follow the usual C library conventions for indicating errors: on error it returns a negated error number (the negative of one of the values listed in ERRORS). If the system call is invoked via syscall(2), then the return value follows the usual conventions for indicating an error: -1, with errno set to a (positive) value that indicates the error.

BUGS

An invalid ctx_id may cause a segmentation fault instead of generating the error EINVAL.

COLOPHON

This page is part of release 5.10 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.