linux-kernel - Re: [PATCH] cgroup: add explicit cast and comment for return type conversion

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Date:	Mon, 25 May 2015 13:50:47 +0200
From:	Nicholas Mc Guire <der.herr@...r.at>
To:	Tejun Heo <tj@...nel.org>
Cc:	Nicholas Mc Guire <hofrat@...dl.org>,
	Li Zefan <lizefan@...wei.com>, cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cgroup: add explicit cast and comment for return type
	conversion

On Mon, 25 May 2015, Tejun Heo wrote:

> Hello, Nicholas.
> 
> On Mon, May 25, 2015 at 07:57:42AM +0200, Nicholas Mc Guire wrote:
> > nop not downward but signed/unsigned  if it were down it would not be
> > a problem but signed/unsigned can be - for those cases where it can't
> > be fixed up by changing the declarations or return variable types 
> > explicit cast might make sense - as noted in the patch Im not sure either
> > if this form of cleanups is helpful. 
> > 
> > In the kernel core there are about 400 signed/unsigned implicit 
> > conversions (about 3k in the entire kernel) which is what Im trying to 
> > remove or if that is not possible in a resonable way mark as false positive.
> 
> I still don't get it.  What does this buy us actually?  If we continue
> to do this, people would just learn to add explicit cast when doing
> sign conversions.  We just converge to a different behavior without
> actually gaining any protection.  What's the benefit of doing this?
>
that would be no benefit of course - the goal is not to simply put casts
in but to use casts as last resort if type cleanups are not doable or if
the type missmatch is intended - the cast then should document that it
is intentional and comments explain why it is justified. If that were the
result of type cleanup I think it would benefit the kernel code as I 
suspect that quite a few of the type missmatches simply happened.

thx!
hofrat
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