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

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Date:	Tue, 26 May 2015 06:52:05 +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 01:50:47PM +0200, Nicholas Mc Guire wrote:
> > 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.
> 
> I'm having a bit of hard time agreeing with the utility of this.  If
> you can fix up the variable type to go away, sure, but adding
> unnecessary explicit cast and comment for something this trivial?  I'm
> not sure.  I mean, C is not a language which can propagate param
> constraints to the return types.  e.g. strnlen() will happily return
> size_t even when the maximum length is e.g. int.  We simply aren't
> writing in a language where these things are easily distinguished and
> I'm not sure shoehorning explicit constraints all over the source code
> brings enough benefit to justify the added noise.
> 
> If you can identify actual problem cases, awesome.  If some can easily
> be removed by tweaking types to match the actual usage, great too, but
> let's please not do this explicit version of implicit casts and
> pointless comments.
>
got it - not an issue for me - as noted I was not that sure how 
sensible it is either the point of this RFC was precisely to 
clarify this. Will mark those safe conversions as false-postives
then and leave it as is.

Thanks for the clarification!

thx!
hofrat
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