From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoph Hellwig <hch-jcswGhMUV9g@public.gmane.org>
Subject: Re: [RFC PATCH v8 2/2] mm: introduce MAP_SHARED_VALIDATE, a
 mechanism to safely define new mmap flags
Date: Mon, 11 Sep 2017 13:10:30 +0200
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To: Jan Kara <jack-AlSwsSmVLrQ@public.gmane.org>
Cc: Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org>, linux-nvdimm-hn68Rpc1hR1g9hUCZPvPmw@public.gmane.org, linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, hch-jcswGhMUV9g@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, Andy Lutomirski <luto-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, torvalds-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org, Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>
List-Id: linux-api@vger.kernel.org

On Mon, Sep 11, 2017 at 11:47:14AM +0200, Jan Kara wrote:
> On Fri 08-09-17 12:35:13, Dan Williams wrote:
> > The mmap(2) 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 support. Define a new MAP_SHARED_VALIDATE flag pattern that
> > is guaranteed to fail on all legacy mmap implementations.
> > 
> > With this in place new flags can be defined as:
> > 
> >     #define MAP_new (MAP_SHARED_VALIDATE | val)
> 
> Is this changelog stale? Given MAP_SHARED_VALIDATE will be new mapping
> type, I'd expect we define new flags just as any other mapping flags...
> I see no reason why MAP_SHARED_VALIDATE should be or'ed to that.

Btw, I still think it should be a new hidden flag and not a new mapping
type.  I brought this up last time, so maybe I missed the answer
to my concern.