linux-kernel - Re: [PATCH v6 00/10] block atomic writes

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Date: Mon, 15 Apr 2024 22:18:30 +0100
From: Matthew Wilcox <willy@...radead.org>
To: Luis Chamberlain <mcgrof@...nel.org>
Cc: John Garry <john.g.garry@...cle.com>,
	Pankaj Raghav <p.raghav@...sung.com>,
	Daniel Gomez <da.gomez@...sung.com>,
	Javier González <javier.gonz@...sung.com>,
	axboe@...nel.dk, kbusch@...nel.org, hch@....de, sagi@...mberg.me,
	jejb@...ux.ibm.com, martin.petersen@...cle.com, djwong@...nel.org,
	viro@...iv.linux.org.uk, brauner@...nel.org, dchinner@...hat.com,
	jack@...e.cz, linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org,
	linux-fsdevel@...r.kernel.org, tytso@....edu, jbongio@...gle.com,
	linux-scsi@...r.kernel.org, ojaswin@...ux.ibm.com,
	linux-aio@...ck.org, linux-btrfs@...r.kernel.org,
	io-uring@...r.kernel.org, nilay@...ux.ibm.com,
	ritesh.list@...il.com
Subject: Re: [PATCH v6 00/10] block atomic writes

On Sun, Apr 14, 2024 at 01:50:16PM -0700, Luis Chamberlain wrote:
> On Wed, Apr 10, 2024 at 05:05:20AM +0100, Matthew Wilcox wrote:
> > Have you tried just using the buffer_head code?  I think you heard bad
> > advice at last LSFMM.  Since then I've landed a bunch of patches which
> > remove PAGE_SIZE assumptions throughout the buffer_head code, and while
> > I haven't tried it, it might work.  And it might be easier to make work
> > than adding more BH hacks to the iomap code.
> 
> I have considered it but the issue is that *may work* isn't good enough and
> without a test plan for buffer-heads on a real filesystem this may never
> suffice. Addressing a buffere-head iomap compat for the block device cache
> is less error prone here for now.

Is it really your position that testing the code I already wrote is
harder than writing and testing some entirely new code?  Surely the
tests are the same for both.

Besides, we aren't talking about a filesystem on top of the bdev here.
We're talking about accessing the bdev's page cache directly.