On Tue, Dec 05, 2017 at 08:54:35PM -0800, Matthew Wilcox wrote: > On Wed, Dec 06, 2017 at 03:51:44PM +1100, Michael Ellerman wrote: > > Cyril Hrubis <chrubis@xxxxxxx> writes: > > > > > Hi! > > >> > MAP_FIXED_UNIQUE > > >> > MAP_FIXED_ONCE > > >> > MAP_FIXED_FRESH > > >> > > >> Well, I can open a poll for the best name, but none of those you are > > >> proposing sound much better to me. Yeah, naming sucks... > > > > > > Given that MAP_FIXED replaces the previous mapping MAP_FIXED_NOREPLACE > > > would probably be a best fit. > > > > Yeah that could work. > > > > I prefer "no clobber" as I just suggested, because the existing > > MAP_FIXED doesn't politely "replace" a mapping, it destroys the current > > one - which you or another thread may be using - and clobbers it with > > the new one. > > It's longer than MAP_FIXED_WEAK :-P > > You'd have to be pretty darn strong to clobber an existing mapping. I think we're thinking about this all wrong. We shouldn't document it as "This is a variant of MAP_FIXED". We should document it as "Here's an alternative to MAP_FIXED". 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". Now, we should implement MAP_REQUIRED as having each architecture define _MAP_NOT_A_HINT, and then #define MAP_REQUIRED (MAP_FIXED | _MAP_NOT_A_HINT), but that's not information to confuse users with. Also, that lets us add a third option at some point that is Yet Another Way to interpret the 'addr' argument, by having MAP_FIXED clear and _MAP_NOT_A_HINT set. I'm not set on MAP_REQUIRED. I came up with some awful names (MAP_TODDLER, MAP_TANTRUM, MAP_ULTIMATUM, MAP_BOSS, MAP_PROGRAM_MANAGER, etc). But I think we should drop FIXED from the middle of the name.
