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Date: Mon, 11 Sep 2017 10:01:49 -0700 From: Dan Williams <dan.j.williams@...el.com> To: Christoph Hellwig <hch@....de> Cc: Jan Kara <jack@...e.cz>, "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>, Arnd Bergmann <arnd@...db.de>, "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>, Linux API <linux-api@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Linux MM <linux-mm@...ck.org>, Andy Lutomirski <luto@...nel.org>, Andrew Morton <akpm@...ux-foundation.org> Subject: Re: [RFC PATCH v8 2/2] mm: introduce MAP_SHARED_VALIDATE, a mechanism to safely define new mmap flags On Mon, Sep 11, 2017 at 4:10 AM, Christoph Hellwig <hch@....de> wrote: > 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. > I thought you agreed to MAP_SHARED_VALIDATE here: https://marc.info/?l=linux-mm&m=150425124907931&w=2
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