Re: [PATCH v4 2/3] mm: introduce MAP_VALIDATE a mechanism for adding new mmap flags

[Andy Lutomirski]

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?