linux-kernel - Re: [PATCH 1/1 linux-next] ext4: add compatibility flag check

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Message-ID: <20161125052639.3v56ef3clt7r52hr@thunk.org>
Date:   Fri, 25 Nov 2016 00:26:39 -0500
From:   Theodore Ts'o <tytso@....edu>
To:     Fabian Frederick <fabf@...net.be>
Cc:     Jan Kara <jack@...e.com>, Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1 linux-next] ext4: add compatibility flag check

On Thu, Nov 24, 2016 at 08:47:41PM +0100, Fabian Frederick wrote:
> data=journal mount option should disable O_DIRECT access
> (See Documentation/filesystems/ext4.txt) but open operations
> using O_CREAT|O_RDWR|O_DIRECT|O_SYNC have no warning in return and file is being
> created. This patch adds vfs super_operations compatibility flag function
> returning -EPERM in such a case.
> 
> Signed-off-by: Fabian Frederick <fabf@...net.be>

The general practice by most file systems in Linux (for better or for
worse) is to silently fall back to buffered I/O instead of failing the
O_DIRECT open.  Feel free to try to convince linux-fsdevel otherwise,
but that is the general and historical consensus of Linux file system
developers.

Cheers,

					- Ted