On Tue, Aug 15, 2017 at 9:28 AM, Andy Lutomirski <luto@xxxxxxxxxx> wrote: > On Mon, Aug 14, 2017 at 11:12 PM, Dan Williams <dan.j.williams@xxxxxxxxx> wrote: >> The mmap syscall suffers from the ABI anti-pattern of not validating >> unknown flags. However, proposals like MAP_SYNC and MAP_DIRECT need a >> mechanism to define new behavior that is known to fail on older kernels >> without the feature. Use the fact that specifying MAP_SHARED and >> MAP_PRIVATE at the same time is invalid as a cute hack to allow a new >> set of validated flags to be introduced. > > While this is cute, is it actually better than a new syscall? After playing with MAP_DIRECT defined as (MAP_SHARED|MAP_PRIVATE|0x40) I think a new syscall is better. It's very easy to make the mistake that "MAP_DIRECT" defines a single flag vs representing a multi-bit encoding.
