.\" 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_CANCEL 2 2012-07-13 "Linux" "Linux Programmer's Manual"
.SH NAME
io_cancel \- cancel an outstanding asynchronous I/O operation
.SH SYNOPSIS
.nf
.BR "#include <linux/aio_abi.h>" "          /* Defines needed types */"

.BI "int io_cancel(aio_context_t " ctx_id ", struct iocb *" iocb ,
.BI "              struct io_event *" result );
.fi

.IR Note :
There is no glibc wrapper for this system call; see NOTES.
.SH DESCRIPTION
.PP
The
.BR io_cancel ()
system call
attempts to cancel an asynchronous I/O operation previously submitted with
.BR io_submit (2).
The
.I ctx_id
argument is the AIO context ID of the operation to be canceled.
If the AIO context is found, the event will be canceled and then copied
into the memory pointed to by \fIresult\fP without being placed
into the completion queue.
.SH RETURN VALUE
On success,
.BR io_cancel ()
returns 0.
For the failure return, see NOTES.
.SH ERRORS
.TP
.B EAGAIN
The \fIiocb\fP specified was not canceled.
.TP
.B EFAULT
One of the data structures points to invalid data.
.TP
.B EINVAL
The AIO context specified by \fIctx_id\fP is invalid.
.TP
.B ENOSYS
.BR io_cancel ()
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_cancel ()
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_cancel ()
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
.BR io_destroy (2),
.BR io_getevents (2),
.BR io_setup (2),
.BR io_submit (2),
.BR aio (7)
.\" .SH AUTHOR
.\" Kent Yoder.