linux-kernel - Re: [PATCH] Make is_signed

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Date:   Sun, 29 Sep 2019 17:16:27 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Alexey Dobriyan <adobriyan@...il.com>
Cc:     akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        jani.nikula@...ux.intel.com, joonas.lahtinen@...ux.intel.com,
        rodrigo.vivi@...el.com, intel-gfx@...ts.freedesktop.org,
        mingo@...hat.com, linux@...musvillemoes.dk
Subject: Re: [PATCH] Make is_signed_type() simpler

On Sun, 29 Sep 2019 23:44:24 +0300
Alexey Dobriyan <adobriyan@...il.com> wrote:

> On Sun, Sep 29, 2019 at 04:15:31PM -0400, Steven Rostedt wrote:
> > On Sun, 29 Sep 2019 23:06:19 +0300
> > Alexey Dobriyan <adobriyan@...il.com> wrote:
> >   
> > > * Simply compare -1 with 0,
> > > * Drop unnecessary parenthesis sets
> > > 
> > > New macro leaves pointer as "unsigned type" but gives a warning,
> > > which should be fine because asking whether a pointer is signed is
> > > strange question.
> > > 
> > > I'm not sure what's going on in the i915 driver, it is shipping kernel
> > > pointers to userspace.  
> > 
> > This tells us what the patch does, not why.  
> 
> Check the subject line.

I don't see how it's simpler.

-#define is_signed_type(type)	(((type)(-1)) < (type)1)
+#define is_signed_type(type)	((type)-1 < 0)
 

Requires more rational that "make it simpler". Rewriting futex or tty
layer code would be something I would love to see, but just replacing
"(type)1" with "0" isn't worth the churn.

-- Steve