Porting OpenBSD's sysctl hw.sensors framework to FreeBSD

[Poul-Henning Kamp]

In message <200707130740.17680.jhb at freebsd.org>, John Baldwin writes:

>ifconfig doesn't use strings from sysctl.  It uses a more sophisticated 
>interface with data structures, etc.  If you wanted to add a standard RAID 
>monitoring interface, then I would add ioctl's for different RAID operations 
>along with a set of generic RAID structures [...]

I wouldn't.

The amount of time and code it takes to encapsulate instructions in
binary structures, and then unpack and validate those same structures
is utterly wasted for complex interfaces like that.

The reason why we started out on the struct+bitmap method, was that
the structs were copies of the hardware or kernel structures, so there
were no work involved in receiving and sending them from the kernel.

But we are increasingly using abstract representations for reasons
of portability and multi-everything-support, and now we end up having
to treat the binary structures and bitmaps as very complex communication
protocols and look for all the sorts of evil you can have in binary
data (overruns, underruns etc etc.)

For complex low-frequency interfaces, like RAID management,
I would (and have: see GEOM) simply send text strings to the kernel
and deal with all the parsing and validation there.

Part of the reason for this is that their very complex nature makes
the struct representation particularly unwieldy, whereas the good
old command line metaphor manages to capture complex data forms
in a readable and easily parseable format:

	find . -type file -name '*.c -print

>Strings are a horrible data interface.  The stuff I work on needs to send 
>e-mails that are more like:
>
>volume X on controller Y is degraded
>the following disks(s) need to be replaced: drive 5 (enclosure 1, slot 2),
>  drive 7 (enclosure 1, slot 4)
>
>To do that sanely, I need to have access to data structures, not just 
>arbitrary strings from a sysctl.

I thought a lot about that with GEOM, and that's why the output from the
kernel is highly structured, but free form (ie: XML).

Overall I think the assymetric API GEOM got, and in a lighter degree
nmount, are the way forward.

The age of the intricate struct + bitmap is a cul-de-sac, which leads
to unreadable and buggy code to encapsulate and decode a binary format
at the syscall interface, which nobody really cares about.

ifconfig is a primary candidate for being rototilled like this: if
you compare the length of the average ifconfig argument list to the
number of structures and bitflags manipulated, it will soon be
seen that shipping argv[] to the kernel and only parsing once would
be much more economical and less bugprone.

Move with the times people...

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.