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Date: Tue, 27 Jul 2021 08:31:38 +0200
From: Christoph Hellwig <hch@lst.de>
To: "Darrick J. Wong" <djwong@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>, Dan Williams <dan.j.williams@intel.com>,
	Matthew Wilcox <willy@infradead.org>,
	Andreas Gruenbacher <agruenba@redhat.com>,
	Shiyang Ruan <ruansy.fnst@fujitsu.com>, linux-xfs@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, linux-btrfs@vger.kernel.org,
	nvdimm@lists.linux.dev, cluster-devel@redhat.com
Subject: Re: [PATCH 16/27] iomap: switch iomap_bmap to use iomap_iter
Message-ID: <20210727063138.GA10143@lst.de>
References: <20210719103520.495450-1-hch@lst.de> <20210719103520.495450-17-hch@lst.de> <20210719170545.GF22402@magnolia> <20210726081942.GD14853@lst.de> <20210726163922.GA559142@magnolia>
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User-Agent: Mutt/1.5.17 (2007-11-01)

On Mon, Jul 26, 2021 at 09:39:22AM -0700, Darrick J. Wong wrote:
> The documentation needs to be much more explicit about the fact that you
> cannot "break;" your way out of an iomap_iter loop.  I think the comment
> should be rewritten along these lines:
> 
> "Iterate over filesystem-provided space mappings for the provided file
> range.  This function handles cleanup of resources acquired for
> iteration when the filesystem indicates there are no more space
> mappings, which means that this function must be called in a loop that
> continues as long it returns a positive value.  If 0 or a negative value
> is returned, the caller must not return to the loop body.  Within a loop
> body, there are two ways to break out of the loop body: leave
> @iter.processed unchanged, or set it to the usual negative errno."
> 
> Hm.

Yes, I'll update the documentation.

> Clunky, for sure, but at least we still get to use break as the language
> designers intended.

I can't see any advantage there over just proper documentation.  If you
are totally attached to a working break we might have to come up with
a nasty for_each macro that ensures we have a final iomap_apply, but I
doubt it is worth the effort.