Re: [PATCH 0/2] mm: introduce MAP_FIXED_SAFE

[Michal Hocko]

On Wed 29-11-17 16:13:53, Rasmus Villemoes wrote:
> On 2017-11-29 15:42, Michal Hocko wrote:
[...]
> >The flag is introduced as a completely
> > new one rather than a MAP_FIXED extension because of the backward
> > compatibility. We really want a never-clobber semantic even on older
> > kernels which do not recognize the flag. Unfortunately mmap sucks wrt.
> > flags evaluation because we do not EINVAL on unknown flags. On those
> > kernels we would simply use the traditional hint based semantic so the
> > caller can still get a different address (which sucks) but at least not
> > silently corrupt an existing mapping. I do not see a good way around
> > that.
> 
> I think it would be nice if this rationale was in the 1/2 changelog,
> along with the hint about what userspace that wants to be compatible
> with old kernels will have to do (namely, check that it got what it
> requested) - which I see you did put in the man page.

OK, I've added there.

-- 
Michal Hocko
SUSE Labs