On Wed, Nov 22, 2017 at 08:52:37AM -0800, Dan Williams wrote:
On Wed, Nov 22, 2017 at 4:02 AM, Vlastimil Babka
> On 11/01/2017 04:36 PM, Jan Kara wrote:
>> From: Dan Williams <dan.j.williams(a)intel.com>
>> The mmap(2) syscall suffers from the ABI anti-pattern of not validating
>> unknown flags. However, proposals like MAP_SYNC need a mechanism to
>> define new behavior that is known to fail on older kernels without the
>> support. Define a new MAP_SHARED_VALIDATE flag pattern that is
>> guaranteed to fail on all legacy mmap implementations.
> So I'm trying to make sense of this together with Michal's attempt for
> MAP_FIXED_SAFE  where he has to introduce a completely new flag
> instead of flag modifier exactly for the reason of not validating
> unknown flags. And my conclusion is that because MAP_SHARED_VALIDATE
> implies MAP_SHARED and excludes MAP_PRIVATE, MAP_FIXED_SAFE as a
> modifier cannot build on top of this. Wouldn't thus it be really better
> long-term to introduce mmap3 at this point? ...
We have room to define MAP_PRIVATE_VALIDATE in MAP_TYPE on every arch
except parisc. Can we steal an extra bit for MAP_TYPE from somewhere
else on parisc?
It looks like 0x08 should work. But I don't have an HPUX machine around
to check that HP didn't use that bit for something else.
It'd probably help to cc the linux-parisc mailing list when asking
questions about PARISC, eh?