linux-ext4 - Re: [PATCH 6/8] nowait aio: ext4

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Message-ID: <20170410151359.GH3224@quack2.suse.cz>
Date:   Mon, 10 Apr 2017 17:13:59 +0200
From:   Jan Kara <jack@...e.cz>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Jan Kara <jack@...e.cz>, Goldwyn Rodrigues <rgoldwyn@...e.de>,
        linux-fsdevel@...r.kernel.org, jack@...e.com,
        linux-block@...r.kernel.org, linux-btrfs@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org,
        sagi@...mberg.me, avi@...lladb.com, axboe@...nel.dk,
        linux-api@...r.kernel.org, willy@...radead.org,
        tom.leiming@...il.com, Goldwyn Rodrigues <rgoldwyn@...e.com>
Subject: Re: [PATCH 6/8] nowait aio: ext4

On Mon 10-04-17 07:39:43, Christoph Hellwig wrote:
> On Mon, Apr 10, 2017 at 02:37:50PM +0200, Jan Kara wrote:
> > I don't understand here. Do you want that all filesystems support NOWAIT
> > direct IO?
> 
> No.  Per-file_system_type is way to coarse grained.  All feature flag
> needs to be per-file_operation at least for cases like ext4 with our
> without extents (or journal) XFS v4 vs v5, different NFS versions, etc.

Ah, I see your point now. Thanks for patience. I think we could make this
work by making generic_file_write/read_iter() refuse NOWAIT IO with
EOPNOTSUPP and then only modify those few filesystems that implement their
own iter helpers and will not initially support NOWAIT IO. Sounds easy
enough.

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