linux-kernel - Re: [PATCH 17/23] proc: add a read_iter method to proc proc

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Message-ID: <20200701212751.GL2786714@ZenIV.linux.org.uk>
Date:   Wed, 1 Jul 2020 22:27:51 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Christoph Hellwig <hch@....de>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Kees Cook <keescook@...omium.org>,
        Iurii Zaikin <yzaikin@...gle.com>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 17/23] proc: add a read_iter method to proc proc_ops

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.