PERFORCE change 126230 for review

[Constantine A. Murenin]

On 26/09/2007 11:21, John Baldwin wrote:
> On Sunday 09 September 2007 02:00:36 pm Constantine A. Murenin wrote:
> 
>>http://perforce.freebsd.org/chv.cgi?CH=126230
>>
>>Change 126230 by cnst at dale on 2007/09/09 18:00:16
>>
>>	put in a hack for supporting "Sysctl internal magic",
>>	and now hw.sensors tree magically works in sysctl(8)!
>>	
>>	dale# sysctl hw.sensors.{lm0.volt{0,1,2,3},cpu{0,1}}
>>	hw.sensors.lm0.volt0: 1.23 VDC (VCore)
>>	hw.sensors.lm0.volt1: 12.30 VDC (+12V)
>>	hw.sensors.lm0.volt2: 3.33 VDC (+3.3V)
>>	hw.sensors.lm0.volt3: 3.31 VDC (+3.3V)
>>	hw.sensors.cpu0.temp0: 28.00 degC
>>	hw.sensors.cpu1.temp0: 28.00 degC
>>	dale#
>>	
>>	(All other utilities continue working using a cross-platform
>>	sysctl(3) interface, compatible with OpenBSD.)
>>
>>+#endif /* !NOSYSCTL8HACK */
>>+
>>+
>>+#ifndef NOSYSCTL8HACK
>>+
>>+/*
>>+ * XXX:
>>+ * FreeBSD's sysctl(9) .oid_handler functionality is not accustomed
>>+ * for the CTLTYPE_NODE handler to handle the undocumented sysctl
>>+ * magic calls.  As soon as such functionality is developed, 
>>+ * sysctl_sensors_handler() should be converted to handle all such
>>+ * calls, and these sysctl_add_oid(9) calls should be removed 
>>+ * "with a big axe".  This whole sysctl_add_oid(9) business is solely
>>+ * to please sysctl(8).
> 
> 
> Actually, sysctl_add_oid(9) is how you should add a tree of sysctl's on the
> fly to FreeBSD.  It frees you from having to manually simulate a sysctl
> tree yourself and instead focus on just handling the functionality for the
> leaf nodes.  If you just gave each sensor its own sysctl ctx and tree most
> of your in-kernel code for dealing with 'hw.sensors' would go away as it
> would just be a normal node ala 'dev'.

If you take a closer look, the code for manually keeping track of 
sensors is very straightforward -- mostly a linked list.  sysctl(9) 
interface is much more complicated than that.

This manual accounting of the sensors is a requirement for the sensors 
framework -- it is the basis for the concept of sensor device, which 
stores information about individual sensors each device has (similarly 
to a sysctl_ctx).  It is also required to generate and keep track of the 
numt of each sensor.

Using FreeBSD's internal magic does not make the userland applications 
portable, because there is no documented userland interface for listing 
all leaves of a given sysctl tree.  (If you believe otherwise, a link to 
the manual page is welcome. :)

C.