linux-kernel - Re: [PATCHv3 0/8] direct-io: even more flexible io vectors

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Message-ID: <aK9amCpLYsxIweMk@kbusch-mbp>
Date: Wed, 27 Aug 2025 13:20:56 -0600
From: Keith Busch <kbusch@...nel.org>
To: Jan Kara <jack@...e.cz>
Cc: Ritesh Harjani <ritesh.list@...il.com>, Keith Busch <kbusch@...a.com>,
	linux-block@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-ext4@...r.kernel.org,
	snitzer@...nel.org, axboe@...nel.dk, dw@...idwei.uk,
	brauner@...nel.org, hch@....de, martin.petersen@...cle.com,
	djwong@...nel.org, linux-xfs@...r.kernel.org,
	viro@...iv.linux.org.uk, Jan Kara <jack@...e.com>,
	Brian Foster <bfoster@...hat.com>
Subject: Re: [PATCHv3 0/8] direct-io: even more flexible io vectors

On Wed, Aug 27, 2025 at 05:20:53PM +0200, Jan Kara wrote:
> Now both the old and new behavior make some sense so I won't argue that the
> new iomap_iter() behavior is wrong. But I think we should change ext4 back
> to the old behavior of failing unaligned dio writes instead of them falling
> back to buffered IO. I think something like the attached patch should do
> the trick - it makes unaligned dio writes fail again while writes to holes
> of indirect-block mapped files still correctly fall back to buffered IO.
> Once fstests run completes, I'll do a proper submission...

Your suggestion looks all well and good, but I have a general question
about fstests. I've written up some to test this series, and I have
filesystem specific expectations for what should error or succeed. If
you modify ext4 to fail direct-io as described, my test will have to be
kernel version specific too. Is there a best practice in fstests for
handling such scenarios?