kernel / Documentation / sysctl / ctl_unnumbered.txt

Except for a few extremely rare exceptions user space applications do not use
the binary sysctl interface.  Instead everyone uses /proc/sys/...  with
readable ascii names.

Recently the kernel has started supporting setting the binary sysctl value to
CTL_UNNUMBERED so we no longer need to assign a binary sysctl path to allow
sysctls to show up in /proc/sys.

Assigning binary sysctl numbers is an endless source of conflicts in sysctl.h,
breaking of the user space ABI (because of those conflicts), and maintenance
problems.  A complete pass through all of the sysctl users revealed multiple
instances where the sysctl binary interface was broken and had gone undetected
for years.

So please do not add new binary sysctl numbers.  They are unneeded and
problematic.

If you really need a new binary sysctl number please first merge your sysctl
into the kernel and then as a separate patch allocate a binary sysctl number.

([e-mail], June 2007)