NAME¶

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

LIBRARY¶

Standard C library (libc, -lc)

Alternatively, Asynchronous I/O library (libaio, -laio); see VERSIONS.

SYNOPSIS¶

#include <linux/aio_abi.h>    /* Definition of *io_* types */
#include <sys/syscall.h>      /* Definition of SYS_* constants */
#include <unistd.h>

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

Note: glibc provides no wrapper for io_getevents(), necessitating the use of syscall(2).

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 VERSIONS.

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 timespec(3) structure.

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 VERSIONS.

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¶

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.

STANDARDS¶

Linux.

HISTORY¶

Linux 2.5.

BUGS¶

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

SEE ALSO¶

io_cancel(2), io_destroy(2), io_setup(2), io_submit(2), timespec(3), aio(7), time(7)