Re: Suggestions for an improvement to the man page "iopl - change I/O privilege level".

[Ingo Schwarze <schwarze@usta.de>]

Hello,

Alejandro Colomar wrote on Sun, Oct 18, 2026 at 01:25:17PM +0200:
> From: Thomas Gleixner <tglx@kernel.org>

>> So in pratice these syscalls and IOCTLs are ancient ballast and any
>> modern distro should not need them anymore.

Same in OpenBSD; by default, securelevel(7) and sysctl(2) block
access to them.  The most important place where they are still
occasionally used are some very old X11 video drivers that that do
not use kernel mode setting but instead use libpciaccess to access
PCI devices directly.  It appears they are also used by some
coreboot-utils programs, but we did not investigate what exactly
the purpose is there.  No other use case came up when i asked around
among developers.

> Thanks!  I'll keep the manual pages unchanged.

An improvement resulted in OpenBSD manual pages though:

  https://man.openbsd.org/?query=iopl&apropos=1        # two related pages
  https://marc.info/?l=openbsd-cvs&m=179214240879202   # commit message

In general, i believe it is valuable when people adhere to standards
and take care to write portable code.  However, this does not apply to
the present case of low-level hardware control where operations are
unavoidably highly system- and hardware-dependent.

Getting rid of these functions may or may not ultimately become a
goal in OpenBSD, but it appears developers working in the area
currently see no urgency.  There is very little risk because these
finctions have been disabled by default for quite some time now.

Yours,
  Ingo