linux-ext4 - Re: [RFC PATCH 0/7] dax, ext4: Synchronous page faults

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Message-ID: <CAPcyv4hgqh8tHeWDNRnJnvwDh7hiFU8+3O0VWAHFQOEvPna11Q@mail.gmail.com>
Date:   Sat, 12 Aug 2017 19:44:14 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Jan Kara <jack@...e.cz>, linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Dave Chinner <david@...morbit.com>, linux-xfs@...r.kernel.org,
        Andy Lutomirski <luto@...nel.org>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        "linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>
Subject: Re: [RFC PATCH 0/7] dax, ext4: Synchronous page faults

On Fri, Aug 11, 2017 at 3:03 AM, Christoph Hellwig <hch@...radead.org> wrote:
> On Mon, Aug 07, 2017 at 05:24:08PM -0700, Dan Williams wrote:
>> Does sys_mmap() reject unknown flag values today? I'm either not
>> looking in the right place or it's missing and we'll need some
>> interface/mechanism to check if MAP_SYNC is honored.
>
> It doesn't seem to reject unknown flags.
>
> The lack of flags checking strikes back once more, sighṫ.

How about MAP_SYNC == (MAP_SHARED|MAP_PRIVATE)? On older kernels that
should get -EINVAL, and on new kernels it means SYNC+SHARED.