.\" Copyright (C) 2003 Free Software Foundation, Inc.
.\"
.\" %%%LICENSE_START(GPL_NOVERSION_ONELINE)
.\" This file is distributed according to the GNU General Public License.
.\" %%%LICENSE_END
.\"
.TH IO_SETUP 2 2017-09-15 "Linux" "Linux Programmer's Manual"
.SH NAME
io_setup \- create an asynchronous I/O context
.SH SYNOPSIS
.nf
.BR "#include <linux/aio_abi.h>" "          /* Defines needed types */"
.PP
.BI "int io_setup(unsigned " nr_events ", aio_context_t *" ctx_idp );
.fi
.PP
.IR Note :
There is no glibc wrapper for this system call; see NOTES.
.SH DESCRIPTION
.PP
The
.BR io_setup ()
system call
creates an asynchronous I/O context suitable for concurrently processing
\fInr_events\fP operations.
The
.I ctx_idp
argument must not point to an AIO context that already exists, and must
be initialized to 0 prior to the call.
On successful creation of the AIO context, \fI*ctx_idp\fP is filled in
with the resulting handle.
.SH RETURN VALUE
On success,
.BR io_setup ()
returns 0.
For the failure return, see NOTES.
.SH ERRORS
.TP
.B EAGAIN
The specified \fInr_events\fP exceeds the user's limit of available events,
as defined in
.IR /proc/sys/fs/aio-max-nr .
.TP
.B EFAULT
An invalid pointer is passed for \fIctx_idp\fP.
.TP
.B EINVAL
\fIctx_idp\fP is not initialized, or the specified \fInr_events\fP
exceeds internal limits.
\fInr_events\fP should be greater than 0.
.TP
.B ENOMEM
Insufficient kernel resources are available.
.TP
.B ENOSYS
.BR io_setup ()
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_setup ()
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_setup ()
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_idp
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
.BR io_cancel (2),
.BR io_destroy (2),
.BR io_getevents (2),
.BR io_submit (2),
.BR aio (7)
.\" .SH AUTHOR
.\" Kent Yoder.
.SH COLOPHON
This page is part of release 4.16 of the Linux
.I man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
\%https://www.kernel.org/doc/man\-pages/.