On Tue, Oct 17, 2017 at 4:50 AM, Jan Kara <jack@xxxxxxx> wrote: > On Mon 16-10-17 00:45:04, Christoph Hellwig wrote: >> > How about the following incremental update? It allows ->mmap_validate() >> > to be used as a full replacement for ->mmap() and it limits the error >> > code freedom to a centralized mmap_status_errno() routine: >> >> Nah - my earlier comment was simply misinformed because I didn't >> read the whole patch and the _validate name mislead me. >> >> So I think the current calling conventions are ok, I'd just like a >> better name (mmap_flags maybe?) and avoid the need the file system >> also has to implement ->mmap. > > OK, I can do that. But I had just realized that if MAP_DIRECT isn't going > to end up using mmap(2) interface but something else (and I'm not sure > where discussions on this matter ended), we don't need flags argument for > ->mmap at all. MAP_SYNC uses a VMA flag anyway and thus it is fine with the > current ->mmap interface. We still need some opt-in mechanism for > MAP_SHARED_VALIDATE though (probably supported mmap flags as Dan had in one > version of his patch). Thoughts on which way to go for now? The "supported mmap flags" approach also solves the problem you raised about MAP_SYNC being silently accepted by an ->mmap() handler that does not know about the new flag. I.e. leading userpace to potentially assume an invalid data consistency model. I'll revive that approach now that the MAP_DIRECT problem is going to be solved via a different interface.
