linux-kernel - Re: [PATCH V2] block: correctly fallback for zeroout

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Message-ID: <20160613082001.GA27508@infradead.org>
Date:	Mon, 13 Jun 2016 01:20:01 -0700
From:	Christoph Hellwig <hch@...radead.org>
To:	"Martin K. Petersen" <martin.petersen@...cle.com>
Cc:	Shaohua Li <shli@...com>, linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org, axboe@...com, sitsofe@...oo.com,
	snitzer@...hat.com, hch@...radead.org, Kernel-team@...com
Subject: Re: [PATCH V2] block: correctly fallback for zeroout

On Fri, Jun 10, 2016 at 09:49:44PM -0400, Martin K. Petersen wrote:
> >> What does the extra io_err buy us? Just have this function return an
> >> error. And then in blkdev_issue_discard if you get -EOPNOTSUPP you
> >> special case it there.
> 
> Shaohua> The __blkdev_issue_discard returns -EOPNOTSUPP if disk doesn't
> Shaohua> support discard.  in that case, blkdev_issue_discard doesn't
> Shaohua> return 0. blkdev_issue_discard only returns 0 if IO error is
> Shaohua> -EOPNOTSUPP.
> 
> Oh, I see. The sanity checks are now in __blkdev_issue_discard() so
> there is no way to distinguish between -EOPNOTSUPP and the other
> -EOPNOTSUPP. *sigh*

We can move the sanity checks out.  Or even better get rid of the
stupid behavior of ignoring the late -EOPNOTSUPP in this low level
helper and instead leaving it to the caller(s) that care.  So far
the DM test suite seems to be the only one that does.

> I am OK with your patch as a stable fix but this really needs to be
> fixed up properly.

And I'd much prefer to get this right now.  It's not like this is
recently introduced behavior.