On 2017-11-29 15:42, Michal Hocko wrote: > > The first patch introduced MAP_FIXED_SAFE which enforces the given > address but unlike MAP_FIXED it fails with ENOMEM if the given range > conflicts with an existing one. [s/ENOMEM/EEXIST/, as it seems you also did in the actual patch and changelog] >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. -- Rasmus Villemoes Software Developer Prevas A/S Hedeager 3 DK-8200 Aarhus N +45 51210274 rasmus.villemoes@xxxxxxxxx www.prevas.dk
