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Date: Mon, 6 Jun 2016 23:38:42 -0700
From: Christoph Hellwig <hch@infradead.org>
To: "Martin K. Petersen" <martin.petersen@oracle.com>
Cc: Mike Snitzer <snitzer@redhat.com>,
	Christoph Hellwig <hch@infradead.org>,
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Subject: Re: block: correctly fallback for zeroout
Message-ID: <20160607063842.GA21032@infradead.org>
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On Mon, Jun 06, 2016 at 10:32:38PM -0400, Martin K. Petersen wrote:
> >>>>> "Mike" == Mike Snitzer <snitzer@redhat.com> writes:
> 
> Mike> But hch was originally in favor of _always_ dropping EOPNOTSUPP on
> Mike> the floor (that is what his commit 38f25255330 did).  Then he said
> Mike> he disagrees with these interfaces playing games with masking
> Mike> EOPNOTSUPP -- to which you seemingly really don't agree.  Unless
> Mike> I'm completely misreading you.
> 
> Userland apps rely on EOPNOTSUPP, we can't break that.

Rely on what exactly?  Current we return EOPNOTSUPP if the device
doesn't claim to support discards, but it returns 0 if the device first
claims to support it but then fails the I/O.