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Date:   Wed, 1 Jul 2020 22:27:51 +0100
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Christoph Hellwig <hch@lst.de>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Luis Chamberlain <mcgrof@kernel.org>,
        Matthew Wilcox <willy@infradead.org>,
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        linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 17/23] proc: add a read_iter method to proc proc_ops
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 <20200701200951.3603160-18-hch@lst.de>
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On Wed, Jul 01, 2020 at 10:09:45PM +0200, Christoph Hellwig wrote:
> This will allow proc files to implement iter read semantics.

*UGH*

You are introducing file_operations with both ->read() and ->read_iter();
worse, in some cases they are not equivalent.  Sure, ->read() takes
precedence right now, but...  why not a separate file_operations for
->read_iter-capable files?

I really hate the fallbacks of that sort - they tend to be brittle
as hell.  And while we are at it, I'm not sure that your iter_read() 
has good cause to be non-static.