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Date: Wed, 22 Jun 2016 16:04:41 +0200
From: Christoph Hellwig <hch@lst.de>
To: "Martin K. Petersen" <martin.petersen@oracle.com>
Cc: Christoph Hellwig <hch@lst.de>, axboe@fb.com, shli@fb.com,
	snitzer@redhat.com, sitsofe@yahoo.com, linux-block@vger.kernel.org
Subject: Re: [PATCH] block: introduce BLKDEV_DISCARD_ZERO to fix zeroout
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On Wed, Jun 22, 2016 at 09:53:04AM -0400, Martin K. Petersen wrote:
> >>>>> "Christoph" == Christoph Hellwig <hch@lst.de> writes:
> 
> Christoph,
> 
> Christoph> Unlike discard outside the zeroout path, write same is a data
> Christoph> integrity operation.  Just like in the zero out case turning
> Christoph> an EOPNOTSUPP into 0 will get you data corruption, as the
> Christoph> caller will see a successful return for an operation that did
> Christoph> not actually write data to disk.
> 
> Exactly. So why add the dreaded -EOPNOTSUPP special casing to
> blkdev_issue_write_same()?

This is a leftover from bio_batch_end_io and not new behavior.  But
I agree that we should kill it.