.\" Copyright (C) 2003 Free Software Foundation, Inc.
.\"
.\" SPDX-License-Identifier: GPL-1.0-or-later
.\"
.TH io_getevents 2 2022-10-30 "Linux man-pages 6.03"
.SH NAME
io_getevents \- read asynchronous I/O events from the completion queue
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.BR "#include <linux/aio_abi.h>" "    /* Definition of " *io_* " types */"
.BR "#include <sys/syscall.h>" "      /* Definition of " SYS_* " constants */"
.B #include <unistd.h>
.PP
.BI "int syscall(SYS_io_getevents, aio_context_t " ctx_id ,
.BI "            long " min_nr ", long " nr ", struct io_event *" events ,
.BI "            struct timespec *" timeout );
.fi
.PP
.IR Note :
glibc provides no wrapper for
.BR io_getevents (),
necessitating the use of
.BR syscall (2).
.SH DESCRIPTION
.IR Note :
this page describes the raw Linux system call interface.
The wrapper function provided by
.I libaio
uses a different type for the
.I ctx_id
argument.
See NOTES.
.PP
The
.BR io_getevents ()
system call
attempts to read at least \fImin_nr\fP events and
up to \fInr\fP events from the completion queue of the AIO context
specified by \fIctx_id\fP.
.PP
The \fItimeout\fP argument specifies the amount of time to wait for events,
and is specified as a relative timeout in a
.BR timespec (3)
structure.
.PP
The specified time will be rounded up to the system clock granularity
and is guaranteed not to expire early.
.PP
Specifying
.I timeout
as NULL means block indefinitely until at least
.I min_nr
events have been obtained.
.SH RETURN VALUE
On success,
.BR io_getevents ()
returns the number of events read.
This may be 0, or a value less than
.IR min_nr ,
if the
.I timeout
expired.
It may also be a nonzero value less than
.IR min_nr ,
if the call was interrupted by a signal handler.
.PP
For the failure return, see NOTES.
.SH ERRORS
.TP
.B EFAULT
Either \fIevents\fP or \fItimeout\fP is an invalid pointer.
.TP
.B EINTR
Interrupted by a signal handler; see
.BR signal (7).
.TP
.B EINVAL
\fIctx_id\fP is invalid.
\fImin_nr\fP is out of range or \fInr\fP is
out of range.
.TP
.B ENOSYS
.BR io_getevents ()
is not implemented on this architecture.
.SH VERSIONS
The asynchronous I/O system calls first appeared in Linux 2.5.
.SH STANDARDS
.BR io_getevents ()
is Linux-specific and should not be used in
programs that are intended to be portable.
.SH NOTES
You probably want to use the
.BR io_getevents ()
wrapper function provided by
.\" http://git.fedorahosted.org/git/?p=libaio.git
.IR libaio .
.PP
Note that the
.I libaio
wrapper function uses a different type
.RI ( io_context_t )
.\" But glibc is confused, since <libaio.h> uses 'io_context_t' to declare
.\" the system call.
for the
.I ctx_id
argument.
Note also that the
.I 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
.BR syscall (2),
then the return value follows the usual conventions for
indicating an error: \-1, with
.I errno
set to a (positive) value that indicates the error.
.SH BUGS
An invalid
.I ctx_id
may cause a segmentation fault instead of generating the error
.BR EINVAL .
.SH SEE ALSO
.BR io_cancel (2),
.BR io_destroy (2),
.BR io_setup (2),
.BR io_submit (2),
.BR timespec (3),
.BR aio (7),
.BR time (7)
.\" .SH AUTHOR
.\" Kent Yoder.