linux-ext4 - Re: [PATCH 01/19] mm: introduce MAP_SHARED_VALIDATE, a mechanism to safely define new mmap flags

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Date:   Tue, 17 Oct 2017 23:59:38 -0700
From:   "hch@...radead.org" <hch@...radead.org>
To:     Jan Kara <jack@...e.cz>
Cc:     "hch@...radead.org" <hch@...radead.org>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "linux-xfs@...r.kernel.org" <linux-xfs@...r.kernel.org>,
        "darrick.wong@...cle.com" <darrick.wong@...cle.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "luto@...nel.org" <luto@...nel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "ross.zwisler@...ux.intel.com" <ross.zwisler@...ux.intel.com>,
        "linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
        "tytso@....edu" <tytso@....edu>, "arnd@...db.de" <arnd@...db.de>
Subject: Re: [PATCH 01/19] mm: introduce MAP_SHARED_VALIDATE, a mechanism to
 safely define new mmap flags

On Tue, Oct 17, 2017 at 01:50:47PM +0200, Jan Kara wrote:
> OK, I can do that. But I had just realized that if MAP_DIRECT isn't going
> to end up using mmap(2) interface but something else (and I'm not sure
> where discussions on this matter ended), we don't need flags argument for
> ->mmap at all. MAP_SYNC uses a VMA flag anyway and thus it is fine with the
> current ->mmap interface. We still need some opt-in mechanism for
> MAP_SHARED_VALIDATE though (probably supported mmap flags as Dan had in one
> version of his patch). Thoughts on which way to go for now?

Yes, I'd much prefer the mmap_flags in file_operations.  The other
option would be a new FMODE_* flag which is what Al did for various
other optional features, but I generally thing that is a confusing
interface.