linux-kernel - Re: [PATCH v4 2/3] mm: introduce MAP_VALIDATE a mechanism for adding new mmap flags

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Message-ID: <20170918093137.GF32516@quack2.suse.cz>
Date:   Mon, 18 Sep 2017 11:31:37 +0200
From:   Jan Kara <jack@...e.cz>
To:     Christoph Hellwig <hch@....de>
Cc:     Dan Williams <dan.j.williams@...el.com>, Jan Kara <jack@...e.cz>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Arnd Bergmann <arnd@...db.de>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        Linux API <linux-api@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-xfs@...r.kernel.org, linux-mm <linux-mm@...ck.org>,
        Andy Lutomirski <luto@...nel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v4 2/3] mm: introduce MAP_VALIDATE a mechanism for adding
 new mmap flags

On Sun 17-09-17 19:39:45, Christoph Hellwig wrote:
> On Sat, Sep 16, 2017 at 08:44:14PM -0700, Dan Williams wrote:
> > So it wasn't all that easy, and Linus declined to take it. I think we
> > should add a new ->mmap_validate() file operation and save the
> > tree-wide cleanup until later.
> 
> Note that we already have a mmap_capabilities callout for nommu,
> I wonder if we could generalize that.

So if I understood Dan right, Linus refused to merge the patch which adds
'flags' argument to ->mmap callback. That is actually logically independent
change from validating flags passed to mmap(2) syscall. Dan did it just to
save himself from adding a VMA flag for MAP_DIRECT.

For validating flags passed to mmap(2), I agree we could use
->mmap_capabilities() instead of mmap_supported_mask Dan has added. But I
don't have a strong opinion there.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR