linux-kernel - Re: [PATCH v3] err.h: allow IS_ERR_VALUE to handle properly more types

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Date:	Thu, 11 Feb 2016 17:39:49 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Andrzej Hajda <a.hajda@...sung.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	open list <linux-kernel@...r.kernel.org>,
	Bob Peterson <rpeterso@...hat.com>, linux@...musvillemoes.dk
Subject: Re: [PATCH v3] err.h: allow IS_ERR_VALUE to handle properly more types

On Thursday 11 February 2016 08:00:54 Andrzej Hajda wrote:
> > I think the easiest way to express this would be to ensure that the argument
> > is 'unsigned long', like:
> >
> > #define IS_ERR_VALUE(x) ((unsigned long*)NULL == (typeof (x)*)NULL && \
> >        unlikely((unsigned long long)(x) >= (unsigned long long)(typeof(x))-MAX_ERRNO))
> 
> This way you will limit it only to unsigned long type, which seems too
> strict to me.
> I think the macro should accept all long enough unsigned types, otherwise we
> could end up with bunch of macros IS_ERR_VALUE_U32, IS_ERR_VALUE_ULL...

I think in practice we only care about 'int' and 'unsigned long', which are
the ones that 90% of the existing users pass in today. u32 has never worked
on 64-bit architectures so far, so we don't necessarily have to make it work.
As Al mentioned, most users of IS_ERR_VALUE are wrong anyway and should
just use 'if (err < 0)' or 'if (err)'.

We could also consider making just 'int' and 'unsigned long' allowed types
for the moment, and then change all users passing 'int' before forbidding them.

	Arnd