.\"	$OpenBSD: hotplug.4,v 1.3 2007/05/31 19:19:50 jmc Exp $
.\"
.\" Copyright (c) 2004 Alexander Yurchenko <grange@openbsd.org>
.\"
.\" Permission to use, copy, modify, and distribute this software for any
.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
.\"
.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
.\"
.Dd December 5, 2009
.Dt HOTPLUG 4
.Os
.Sh NAME
.Nm hotplug
.Nd devices hot plugging
.Sh SYNOPSIS
.Cd "pseudo-device hotplug 1"
.Pp
.In sys/types.h
.In sys/device.h
.In sys/hotplug.h
.Sh DESCRIPTION
The
.Nm
pseudo-device passes device attachment and detachment events to
userland.
When a device attaches or detaches, the corresponding event is queued.
The events can then be obtained from the queue through the
.Xr read 2
call on the
.Pa /dev/hotplug
device file.
Once an event has been read, it's deleted from the queue.
The event queue has a limited size and if it's full all new events will be
dropped.
Each event is described with the following structure declared in the
.In sys/hotplug.h
header file:
.Bd -literal -offset indent
struct hotplug_event {
	int		he_type;	/* event type		*/
	enum devclass	he_devclass;	/* device class		*/
	char		he_devname[16];	/* device name		*/
};

.Ed
The
.Va he_type
field describes the event type and can be either
.Dv HOTPLUG_DEVAT
for device attachment or
.Dv HOTPLUG_DEVDT
for detachment.
The
.Va he_devclass
field describes the device class.
All device classes can be found in the
.In sys/device.h
header file:
.Bd -literal -offset indent
enum devclass {
	DV_DULL,	/* generic, no special info */
	DV_CPU,		/* CPU (carries resource utilization) */
	DV_DISK,	/* disk drive (label, etc) */
	DV_IFNET,	/* network interface */
	DV_TAPE,	/* tape device */
	DV_TTY		/* serial line interface */
};

.Ed
The
.Va he_devname
is a device name including unit number, e.g.\&
.Pa sd1 .
.Pp
Only one structure can be read per call.
If there are no events in the queue, the
.Xr read 2
call will block until an event appears.
.Sh DIAGNOSTICS
.Bl -diag
.It "hotplug: event lost, queue full"
New events will be dropped until all pending events have been read.
.El
.Sh SEE ALSO
.Xr read 2 ,
.Xr hotplugd 8
.Sh HISTORY
The
.Nm
device first appeared in
.Ox 3.6 .
The
.Nm
driver was imported to
.Dx 2.5 .
.Sh AUTHORS
The
.Nm
driver was written by
.An Alexander Yurchenko Aq grange@openbsd.org .