linux-kernel - Re: [PATCH] Fix cpuset sched_relax_domain

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Date:	Wed, 7 May 2008 12:48:09 +0300
From:	Adrian Bunk <bunk@...nel.org>
To:	Paul Menage <menage@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>,
	Paul Jackson <pj@....com>, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Fix cpuset sched_relax_domain_level control file

On Tue, May 06, 2008 at 06:41:39PM -0700, Paul Menage wrote:
> On Tue, May 6, 2008 at 6:38 PM, Andrew Morton <akpm@...ux-foundation.org> wrote:
> > On Tue, 06 May 2008 18:08:17 -0700 Paul Menage <menage@...gle.com> wrote:
> >
> >  > -static int update_relax_domain_level(struct cpuset *cs, char *buf)
> >  > +static int update_relax_domain_level(struct cpuset *cs, s64 val)
> >  >  {
> >  > -     int val = simple_strtol(buf, NULL, 10);
> >  > -
> >  > -     if (val < 0)
> >  > +     if ((int)val < 0)
> >  >               val = -1;
> >  >
> >
> >  Are you sure about the typecast here?  If `val' has a value of say
> >  0x0000_ffff_ffff_ffff then I assume the casted value will be negative, only
> >  it wasn't?
> 
> It seems like the simplest approach - if it's outside the range of a
> positive int, set it to -1.

That's very hard to understand for someone who looks at the code - and 
being able to understand the code is much more important than the 
number of characters in the source code.

If you'd write something like

  if ((val < 0) || (val > INT_MAX))

instead it would be obvious for the reader what's happening here, and 
that this was intended.

> Paul

cu
Adrian

BTW: I have seen that even further restrictions are discussed in this 
     case, my comment is more about the general readability of this
     "simplest approach".

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed

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