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Date: Fri, 22 Nov 2024 13:31:33 +0100
From: Christoph Hellwig <hch@lst.de>
To: Brian Foster <bfoster@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>, Zorro Lang <zlang@redhat.com>,
	"Darrick J. Wong" <djwong@kernel.org>, linux-xfs@vger.kernel.org,
	fstests@vger.kernel.org
Subject: Re: [PATCH 01/12] generic/757: fix various bugs in this test
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References: <173197064408.904310.6784273927814845381.stgit@frogsfrogsfrogs> <173197064441.904310.18406008193922603782.stgit@frogsfrogsfrogs> <20241121095624.ecpo67lxtrqqdkyh@dell-per750-06-vm-08.rhts.eng.pek2.redhat.com> <20241121100555.GA4176@lst.de> <Zz8nWa1xGm7c2FHt@bfoster> <20241121131239.GA28064@lst.de> <Zz8_rFRio0vp07rd@bfoster>
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User-Agent: Mutt/1.5.17 (2007-11-01)

On Thu, Nov 21, 2024 at 09:11:56AM -0500, Brian Foster wrote:
> > I'm all for speeding up tests.  But relying on a unspecified side effect
> > of an operation and then requiring a driver that implements that side
> > effect without documenting that isn't really good practice.
> > 
> 
> It's a hack to facilitate test coverage. It would obviously need to be
> revisited if behavior changed sufficiently to break the test.
> 
> I'm not really sure what you're asking for wrt documentation. A quick
> scan of the git history shows the first such commit is 65cc9a235919
> ("generic/482: use thin volume as data device"), the commit log for
> which seems to explain the reasoning.

A comment on _log_writes_init that it must only be used by dm-thin
because it relies on the undocumented behavior that dm-trim zeroes
all blocks discarded.

Or even better my moving the dm-think setup boilerplate into the log
writes helpers, so that it gets done automatically.