Re: [PATCH 17/23] proc: add a read_iter method to proc proc_ops

[Christoph Hellwig]

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.