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

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Message-ID: <20171017115047.GD24136@quack2.suse.cz>
Date:   Tue, 17 Oct 2017 13:50:47 +0200
From:   Jan Kara <jack@...e.cz>
To:     "hch@...radead.org" <hch@...radead.org>
Cc:     "Williams, Dan J" <dan.j.williams@...el.com>,
        "jack@...e.cz" <jack@...e.cz>,
        "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 Mon 16-10-17 00:45:04, Christoph Hellwig wrote:
> > How about the following incremental update? It allows ->mmap_validate()
> > to be used as a full replacement for ->mmap() and it limits the error
> > code freedom to a centralized mmap_status_errno() routine:
> 
> Nah - my earlier comment was simply misinformed because I didn't
> read the whole patch and the _validate name mislead me.
> 
> So I think the current calling conventions are ok, I'd just like a
> better name (mmap_flags maybe?) and avoid the need the file system
> also has to implement ->mmap.

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?

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