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Date:   Thu, 2 Jul 2020 07:18:11 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Al Viro <viro@zeniv.linux.org.uk>
Cc:     Christoph Hellwig <hch@lst.de>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Luis Chamberlain <mcgrof@kernel.org>,
        Matthew Wilcox <willy@infradead.org>,
        Kees Cook <keescook@chromium.org>,
        Iurii Zaikin <yzaikin@google.com>,
        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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References: <20200701200951.3603160-1-hch@lst.de> <20200701200951.3603160-18-hch@lst.de> <20200701212751.GL2786714@ZenIV.linux.org.uk>
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On Wed, Jul 01, 2020 at 10:27:51PM +0100, Al Viro wrote:
> 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 looked at that initially.  We'd need to more instances as there
already are two due to compat stuff.  If that is preferably I can
switch to that version.

> 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.

The other user of it is seq_file, which as-is should go away, but
will probably keep the occasional version of it in the caller.  I just
got really tired of reimplementing it a few times.