sysctl(3) interface

[Daniel Rudy]

Hello List,

I've been taking apart and analyzing the sysctl(8) program to gain a
better insight into how to use the sysctl(3) interface.  Adding some
debugging code to the program in strategic locations, this is what I
have as an output:

debug: name: dev
debug: all: oid:  0 2 440
debug: name: dev.nexus.%parent
debug: oid:  440 912 913
debug: all: oid:  0 2 440 912 913
debug: name: dev.nexus.0.%desc
debug: oid:  440 912 914 915
debug: all: oid:  0 2 440 912 914 915
debug: name: dev.nexus.0.%driver
debug: oid:  440 912 914 916
debug: value: nexusdev.nexus.0.%driver: nexus
debug: all: oid:  0 2 440 912 914 916
debug: name: dev.nexus.0.%location
debug: oid:  440 912 914 917
debug: all: oid:  0 2 440 912 914 917
debug: name: dev.nexus.0.%pnpinfo
debug: oid:  440 912 914 918
debug: all: oid:  0 2 440 912 914 918
debug: name: dev.nexus.0.%parent
debug: oid:  440 912 914 919
debug: value: root0dev.nexus.0.%parent: root0
debug: all: oid:  0 2 440 912 914 919
debug: name: dev.acpi.%parent
debug: oid:  440 920 921
debug: all: oid:  0 2 440 920 921
debug: name: dev.acpi.0.%desc
debug: oid:  440 920 922 923
debug: value: AMIINT dev.acpi.0.%desc: AMIINT
debug: all: oid:  0 2 440 920 922 923
debug: name: dev.acpi.0.%driver
debug: oid:  440 920 922 924
debug: value: acpidev.acpi.0.%driver: acpi
debug: all: oid:  0 2 440 920 922 924
debug: name: dev.acpi.0.%location
debug: oid:  440 920 922 925
debug: all: oid:  0 2 440 920 922 925
debug: name: dev.acpi.0.%pnpinfo
debug: oid:  440 920 922 926

It's using an oid of 0 and 2 to get something, then it comes up with 440
and then a sequence of numbers that are incrementing in a peculiar
pattern.  I went looking and found that 0 is CTL_UNSPEC which according
to the comment is unused, but I see it here in the program output.


I also noticed this little blurb in the source code too:

/*
 * These functions uses a presently undocumented interface to the kernel
 * to walk the tree and get the type so it can print the value.
 * This interface is under work and consideration, and should probably
 * be killed with a big axe by the first person who can find the time.
 * (be aware though, that the proper interface isn't as obvious as it
 * may seem, there are various conflicting requirements.
 */

But I figure it's for the actual display of the various variables and
not for returning information about the dev tree.


So, my question is, how do I walk the tree to get the PnP info for all
the devices in the system?

-- 
Daniel Rudy