man-pages/man2/io_getevents.2

.\" Copyright (C) 2003 Free Software Foundation, Inc.
.\" This file is distributed according to the GNU General Public License.
.\" See the file COPYING in the top level source directory for details.
.\"
.TH IO_GETEVENTS 2 2012-05-08 "Linux" "Linux Programmer's Manual"
.SH NAME
io_getevents \- read asynchronous I/O events from the completion queue
.SH "SYNOPSIS"
.nf
.BR "#include <linux/aio_abi.h>" "         /* Defines needed types */"
.BR "#include <linux/time.h>" "            /* Defines 'struct timespec' */"

.sp
.BI "int io_getevents(aio_context_t " ctx_id ", long " min_nr ", long " nr ,
.BI "                 struct io_event *" events \
", struct timespec *" timeout );
.fi
.SH "DESCRIPTION"
.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.
The \fItimeout\fP argument specifies the amount of time to wait for events,
where a NULL timeout waits until at least \fImin_nr\fP events
have been seen.
Note that \fItimeout\fP is relative and will be updated if not NULL
and the operation blocks.
.SH "RETURN VALUE"
On success,
.BR io_getevents ()
returns the number of events read: 0 if no events are
available, or less than \fImin_nr\fP if the \fItimeout\fP has elapsed.
For the failure return, see NOTES.
.SH "ERRORS"
.TP
.B EFAULT
Either \fIevents\fP or \fItimeout\fP is an invalid pointer.
.TP
.B EINVAL
\fIctx_id\fP is invalid.
\fImin_nr\fP is out of range or \fInr\fP is
out of range.
.TP
.B EINTR
Interrupted by a signal handler; see
.BR signal (7).
.TP
.B ENOSYS
.BR io_getevents ()
is not implemented on this architecture.
.SH "VERSIONS"
.PP
The asynchronous I/O system calls first appeared in Linux 2.5.
.SH "CONFORMING TO"
.PP
.BR io_getevents ()
is Linux-specific and should not be used in
programs that are intended to be portable.
.SH NOTES
Glibc does not provide a wrapper function for this system call.
You could invoke it using
.BR syscall (2).
But instead, you probably want to use the
.BR io_getevents ()
wrapper function provided by
.\" http://git.fedorahosted.org/git/?p=libaio.git
.IR libaio .

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 "SEE ALSO"
.PP
.BR io_cancel (2),
.BR io_destroy (2),
.BR io_setup (2),
.BR io_submit (2),
.BR aio (7),
.BR time (7)
.\" .SH AUTHOR
.\" Kent Yoder.