linux-ext4 - Re: BLKZEROOUT + pread should return zeroes, right?

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Message-ID: <20141014092128.GA23656@infradead.org>
Date:	Tue, 14 Oct 2014 02:21:28 -0700
From:	Christoph Hellwig <hch@...radead.org>
To:	Dave Chinner <david@...morbit.com>
Cc:	"Darrick J. Wong" <darrick.wong@...cle.com>,
	Jens Axboe <axboe@...nel.dk>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	linux-fsdevel@...r.kernel.org, Theodore Ts'o <tytso@....edu>,
	linux-ext4 <linux-ext4@...r.kernel.org>
Subject: Re: BLKZEROOUT + pread should return zeroes, right?

On Tue, Oct 14, 2014 at 03:27:11PM +1100, Dave Chinner wrote:
> Broken usage, IMO. If you are going to use the block layer ioctls to
> manipulate data int eh block device, you should be using direct Io
> for all your data IO to the block device. Otherwise, coherency
> problems occur....

I'd say BLKZEROOUT semantics are broken.  Having an ioctl exposed
that maniulates on-disk data without cache coherence is a nightmare
that people trip over easily.  Even experienced people like Darrick.
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