linux-kernel - Re: [PATCH 51/56] drivers/char/mem: support compiling out splice

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Message-ID: <20141114001948.GA30946@cloud>
Date:	Thu, 13 Nov 2014 16:19:48 -0800
From:	josh@...htriplett.org
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Pieter Smith <pieter@...sman.nl>, Arnd Bergmann <arnd@...db.de>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 51/56] drivers/char/mem: support compiling out splice

On Thu, Nov 13, 2014 at 03:34:16PM -0800, Greg Kroah-Hartman wrote:
> On Thu, Nov 13, 2014 at 02:31:50PM -0800, josh@...htriplett.org wrote:
> > [Please don't top-post.]
> > 
> > On Thu, Nov 13, 2014 at 11:23:46PM +0100, Pieter Smith wrote:
> > > Okay with moving the relevant functions to a new translation unit and
> > > squashing it out in the Makefile
> > 
> > No, you don't need to do that either.  Mark pipe_to_null and
> > splice_write_null as __maybe_unused, then wrap the initialization of
> > .splice_write = splice_write_null to make it .splice_write =
> > splice_p(splice_write_null).  That will avoid adding a single ifdef.
> 
> Again, ick, no.  You aren't saving anything "real" at all, just take out
> the splice core code, leave the file pointer alone, and never do that
> horrid "splice_p" stuff, ick ick ick.

Without doing the splice_p change (which should add zero lines of code,
total diffstat of -3+3 in this case, just a couple of __maybe_unused
tokens and a splice_p() in the initializer), the actual splice
implementations for filesystems and drivers won't get thrown away.  I
certainly agree that #ifdefs for those would be painful and not worth
it.  However, what problem would the proposed __maybe_unused / splice_p
cause?

On the other hand, I can *definitely* understand not bothering with
changing filesystems that nobody will use on a space-constrained system
(e.g.  cluster filesystems); the patch series could likely be narrowed
to just a half-dozen likely filesystems and drivers, all of which could
be done separately from the initial series removing the core splice
code.  Would that be more appealing?

- Josh Triplett
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