Import OpenBSD's sysctl hardware sensors framework.

This commit includes the following core components:

 * sample configuration file for sensorsd
 * rc(8) script and glue code for sensorsd(8)
 * sysctl(3) doc fixes for CTL_HW tree
 * sysctl(3) documentation for hardware sensors
 * sysctl(8) documentation for hardware sensors
 * support for the sensor structure for sysctl(8)
 * rc.conf(5) documentation for starting sensorsd(8)
 * sensor_attach(9) et al documentation
 * /sys/kern/kern_sensors.c
   o sensor_attach(9) API for drivers to register ksensors
   o sensor_task_register(9) API for the update task
   o sysctl(3) glue code
   o hw.sensors shadow tree for sysctl(8) internal magic
 * <sys/sensors.h>
 * HW_SENSORS definition for <sys/sysctl.h>
 * sensors display for systat(1), including documentation
 * sensorsd(8) and all applicable documentation

The userland part of the framework is entirely source-code
compatible with OpenBSD 4.1, 4.2 and  -current as of today.

All sensor readings can be viewed with `sysctl hw.sensors`,
monitored in semi-realtime with `systat -sensors` and also
logged with `sensorsd`.

Submitted by:	Constantine A. Murenin <cnst@FreeBSD.org>
Sponsored by:	Google Summer of Code 2007 (GSoC2007/cnst-sensors)
Mentored by:	syrinx
Tested by:	many
OKed by:	kensmith
Obtained from:	OpenBSD (parts)

1 files changed, 34 insertions, 6 deletions

diff --git a/lib/libc/gen/sysctl.3 b/lib/libc/gen/sysctl.3
index 1f0807b..8386678 100644
--- a/lib/libc/gen/sysctl.3
+++ b/lib/libc/gen/sysctl.3
@@ -280,10 +280,10 @@ privilege may change the value.
 .It "HW_PHYSMEM	integer	no"
 .It "HW_USERMEM	integer	no"
 .It "HW_PAGESIZE	integer	no"
-.It "HW_FLOATINGPOINT	integer	no"
+.It "HW_FLOATINGPT	integer	no"
 .It "HW_MACHINE_ARCH	string	no"
-.\".It "HW_DISKNAMES	integer	no"
-.\".It "HW_DISKSTATS	integer	no"
+.It "HW_REALMEM	integer	no"
+.It "HW_SENSORS	node	not applicable"
 .El
 .Pp
 .Bl -tag -width 6n
@@ -301,12 +301,40 @@ The bytes of physical memory.
 The bytes of non-kernel memory.
 .It Li HW_PAGESIZE
 The software page size.
-.It Li HW_FLOATINGPOINT
+.It Li HW_FLOATINGPT
 Nonzero if the floating point support is in hardware.
 .It Li HW_MACHINE_ARCH
 The machine dependent architecture type.
-.\".It Fa HW_DISKNAMES
-.\".It Fa HW_DISKSTATS
+.It Li HW_REALMEM
+The bytes of real memory.
+.It Li HW_SENSORS
+Third level comprises an array of
+.Li struct sensordev
+structures containing information about devices 
+that may attach hardware monitoring sensors. 
+.Pp
+Third, fourth and fifth levels together comprise an array of
+.Li struct sensor
+structures containing snapshot readings of hardware monitoring sensors.
+In such usage, third level indicates the numerical representation 
+of the sensor device name to which the sensor is attached 
+(device's xname and number shall be matched with the help of 
+.Li struct sensordev
+structure above), 
+fourth level indicates sensor type and 
+fifth level is an ordinal sensor number (unique to
+the specified sensor type on the specified sensor device).
+.Pp
+The
+.Sy sensordev
+and
+.Sy sensor
+structures
+and
+.Sy sensor_type
+enumeration
+are defined in
+.In sys/sensors.h .
 .El
 .Ss CTL_KERN
 The string and integer information available for the CTL_KERN level