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.\"-
.\" Copyright (c) 2002 Dag-Erling Coïdan Smørgrav
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. The name of the author may not be used to endorse or promote products
.\" derived from this software without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" $FreeBSD$
.\"
.Dd July 15, 2016
.Dt AIO 4
.Os
.Sh NAME
.Nm aio
.Nd asynchronous I/O
.Sh SYNOPSIS
To link into the kernel:
.Cd "options VFS_AIO"
.Pp
To load as a kernel loadable module:
.Dl kldload aio
.Sh DESCRIPTION
The
.Nm
facility provides system calls for asynchronous I/O.
It is available both as a kernel option for static inclusion and as a
dynamic kernel module.
.Pp
Asynchronous I/O control buffers should be zeroed before initializing
individual fields.
This ensures all fields are initialized.
.Pp
All asynchronous I/O control buffers contain a
.Vt sigevent
structure in the
.Va aio_sigevent
field which can be used to request notification when an operation completes.
.Pp
For
.Dv SIGEV_KEVENT
notifications,
the posted kevent will contain:
.Bl -column ".Va filter"
.It Sy Member Ta Sy Value
.It Va ident Ta asynchronous I/O control buffer pointer
.It Va filter Ta Dv EVFILT_AIO
.It Va udata Ta
value stored in
.Va aio_sigevent.sigev_value
.El
.Pp
For
.Dv SIGEV_SIGNO
and
.Dv SIGEV_THREAD_ID
notifications,
the information for the queued signal will include
.Dv SI_ASYNCIO
in the
.Va si_code
field and the value stored in
.Va sigevent.sigev_value
in the
.Va si_value
field.
.Pp
For
.Dv SIGEV_THREAD
notifications,
the value stored in
.Va aio_sigevent.sigev_value
is passed to the
.Va aio_sigevent.sigev_notify_function
as described in
.Xr sigevent 3 .
.Sh SEE ALSO
.Xr aio_cancel 2 ,
.Xr aio_error 2 ,
.Xr aio_read 2 ,
.Xr aio_return 2 ,
.Xr aio_suspend 2 ,
.Xr aio_waitcomplete 2 ,
.Xr aio_write 2 ,
.Xr lio_listio 2 ,
.Xr sigevent 3 ,
.Xr config 8 ,
.Xr kldload 8 ,
.Xr kldunload 8
.Sh HISTORY
The
.Nm
facility appeared as a kernel option in
.Fx 3.0 .
The
.Nm
kernel module appeared in
.Fx 5.0 .
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