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IO_GETEVENTS(2) Linux Programmer's Manual IO_GETEVENTS(2)
NAME
io_getevents - read asynchronous I/O events from the completion queue
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
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
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.
SEE ALSO
io_cancel(2), io_destroy(2), io_setup(2), io_submit(2), aio(7), time(7)
Linux 2021-03-22 IO_GETEVENTS(2)