From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk0-f197.google.com (mail-qk0-f197.google.com [209.85.220.197]) by kanga.kvack.org (Postfix) with ESMTP id 01F756B02B4 for ; Tue, 15 Aug 2017 18:31:07 -0400 (EDT) Received: by mail-qk0-f197.google.com with SMTP id m84so10010897qki.5 for ; Tue, 15 Aug 2017 15:31:06 -0700 (PDT) Received: from mail-yw0-x22c.google.com (mail-yw0-x22c.google.com. [2607:f8b0:4002:c05::22c]) by mx.google.com with ESMTPS id w4si2857824ybc.314.2017.08.15.15.31.05 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 15 Aug 2017 15:31:05 -0700 (PDT) Received: by mail-yw0-x22c.google.com with SMTP id s143so12958167ywg.1 for ; Tue, 15 Aug 2017 15:31:05 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: References: <150277752553.23945.13932394738552748440.stgit@dwillia2-desk3.amr.corp.intel.com> <150277753660.23945.11500026891611444016.stgit@dwillia2-desk3.amr.corp.intel.com> From: Dan Williams Date: Tue, 15 Aug 2017 15:31:04 -0700 Message-ID: Subject: Re: [PATCH v4 2/3] mm: introduce MAP_VALIDATE a mechanism for adding new mmap flags Content-Type: text/plain; charset="UTF-8" Sender: owner-linux-mm@kvack.org List-ID: To: Andy Lutomirski Cc: "Darrick J. Wong" , Jan Kara , Arnd Bergmann , linux-nvdimm , Linux API , "linux-kernel@vger.kernel.org" , linux-xfs@vger.kernel.org, "linux-mm@kvack.org" , Linux FS Devel , Andrew Morton , Christoph Hellwig On Tue, Aug 15, 2017 at 9:28 AM, Andy Lutomirski wrote: > On Mon, Aug 14, 2017 at 11:12 PM, Dan Williams 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. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org