[Ksummit-2013-discuss] [ATTEND] Interface stability guarantees

[Jan Kara]

On Sun 21-07-13 15:58:49, H. Peter Anvin wrote:
> We all, hopefully, know that the maxim is "don't break userspace".
> However, there are clearly some limitations to that.  For example, Linus
> recently made the distinction between "userspace" and "kernel support",
> when some scripts designed to set up Grub2 groped around the kernel
> configuration file left by the build and broke.
> 
> However, "broken kernel support" itself is not a killer, obviously; we
> already have a whole bunch of workarounds for broken bootloaders (which
> gets really gnarly, because different bootloaders are broken in
> different ways.)
> 
> "Breaking userspace" clearly also doesn't extend to userspace which does
> things like "build a kernel module and insert it" (and yes, there are
> applications that do that), or a number of similar extremely low level
> manipulations.  In the extreme case, fixing a security holes is
> "breaking userspace" in the sense that some malware would no longer run
> -- but neither might some very bizarre real-life usecase.
  Yeah, tracepoints are another grey area where opinions differ I think.
E.g. AFAIK Al Viro refuses any tracepoints in VFS because he doesn't want
to maintain the interface they possibly create (which I can understand as
much as I'd be happy to have some tracepoints in VFS to be able to
occasionally debug issues). Others take tracepoints more freely, possibly
mitigating userspace impact of tracepoint changes by maintaing tools
consuming tracepoints in tools/ directory. Maybe some discussion what has
worked and what has not when dealing with tracepoints would be useful?

								Honza
-- 
Jan Kara <jack at suse.cz>
SUSE Labs, CR