io_getevents man page

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


#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.


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.


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


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.


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.


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), aio(7), time(7)

Referenced By

aio(7), io_cancel(2), io_destroy(2), io_setup(2), io_submit(2), signal(7), syscalls(2).

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