simplify procfs code for seq_file instances

[Christoph Hellwig]

On Tue, Apr 24, 2018 at 08:19:16AM -0700, Andrew Morton wrote:
> > > I want to ask if it is time to start using poorman function overloading
> > > with _b_c_e(). There are millions of allocation functions for example,
> > > all slightly difference, and people will add more. Seeing /proc interfaces
> > > doubled like this is painful.
> > 
> > Function overloading is totally unacceptable.
> > 
> > And I very much disagree with a tradeoff that keeps 5000 lines of 
> > code vs a few new helpers.
> 
> OK, the curiosity and suspense are killing me.  What the heck is
> "function overloading with _b_c_e()"?

The way I understood Alexey was to use have a proc_create macro
that can take different ops types.  Although the short cut for
__builtin_types_compatible_p would be _b_t_c or similar, so maybe
I misunderstood him.