Re: [PATCH 01/12] generic/757: fix various bugs in this test

[Christoph Hellwig <hch@lst.de>]

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.