On Wed, Nov 22, 2017 at 4:02 AM, Vlastimil Babka <vbabka@xxxxxxx> wrote: > On 11/01/2017 04:36 PM, Jan Kara wrote: >> From: Dan Williams <dan.j.williams@xxxxxxxxx> >> >> The mmap(2) syscall suffers from the ABI anti-pattern of not validating >> unknown flags. However, proposals like MAP_SYNC need a mechanism to >> define new behavior that is known to fail on older kernels without the >> support. Define a new MAP_SHARED_VALIDATE flag pattern that is >> guaranteed to fail on all legacy mmap implementations. > > So I'm trying to make sense of this together with Michal's attempt for > MAP_FIXED_SAFE [1] where he has to introduce a completely new flag > instead of flag modifier exactly for the reason of not validating > unknown flags. And my conclusion is that because MAP_SHARED_VALIDATE > implies MAP_SHARED and excludes MAP_PRIVATE, MAP_FIXED_SAFE as a > modifier cannot build on top of this. Wouldn't thus it be really better > long-term to introduce mmap3 at this point? ... We have room to define MAP_PRIVATE_VALIDATE in MAP_TYPE on every arch except parisc. Can we steal an extra bit for MAP_TYPE from somewhere else on parisc?
