Matthew Wilcox <willy@xxxxxxxxxxxxx> writes: > On Thu, Dec 07, 2017 at 11:14:27AM -0800, Kees Cook wrote: >> On Wed, Dec 6, 2017 at 9:46 PM, Michael Ellerman <mpe@xxxxxxxxxxxxxx> wrote: >> > Matthew Wilcox <willy@xxxxxxxxxxxxx> writes: >> >> So, just like we currently say "exactly one of MAP_SHARED or MAP_PRIVATE", >> >> we could add a new paragraph saying "at most one of MAP_FIXED or >> >> MAP_REQUIRED" and "any of the following values". >> > >> > MAP_REQUIRED doesn't immediately grab me, but I don't actively dislike >> > it either :) >> > >> > What about MAP_AT_ADDR ? >> > >> > It's short, and says what it does on the tin. The first argument to mmap >> > is actually called "addr" too. >> >> "FIXED" is supposed to do this too. >> >> Pavel suggested: >> >> MAP_ADD_FIXED >> >> (which is different from "use fixed", and describes why it would fail: >> can't add since it already exists.) >> >> Perhaps "MAP_FIXED_NEW"? >> >> There has been a request to drop "FIXED" from the name, so these: >> >> MAP_FIXED_NOCLOBBER >> MAP_FIXED_NOREPLACE >> MAP_FIXED_ADD >> MAP_FIXED_NEW >> >> Could be: >> >> MAP_NOCLOBBER >> MAP_NOREPLACE >> MAP_ADD >> MAP_NEW >> >> and we still have the unloved, but acceptable: >> >> MAP_REQUIRED >> >> My vote is still for "NOREPLACE" or "NOCLOBBER" since it's very >> specific, though "NEW" is pretty clear too. > > How about MAP_NOFORCE? It doesn't tell me that addr is not a hint. That's a crucial detail. Without MAP_FIXED mmap never "forces/replaces/clobbers", so why would I need MAP_NOFORCE if I don't have MAP_FIXED? So it needs something in there to indicate that the addr is not a hint, that's the only thing that flag actually *does*. If we had a time machine, the right set of flags would be: - MAP_FIXED: don't treat addr as a hint, fail if addr is not free - MAP_REPLACE: replace an existing mapping (or force or clobber) But the two were conflated for some reason in the current MAP_FIXED. Given we can't go back and fix it, the closest we can get is to add a variant of MAP_FIXED which subtracts the "REPLACE" semantic. ie: MAP_FIXED_NOREPLACE cheers
