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.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 .