[PATCH 1/4] gpiolib: introduce descriptor-based GPIO interface
nicolas.pitre at linaro.org
Wed Jan 9 09:44:16 EST 2013
On Wed, 9 Jan 2013, Russell King - ARM Linux wrote:
> On Wed, Jan 09, 2013 at 10:44:14AM +0000, Russell King - ARM Linux wrote:
> > On Wed, Jan 09, 2013 at 10:35:22AM +0000, Arnd Bergmann wrote:
> > > On Wednesday 09 January 2013, Alexandre Courbot wrote:
> > > > On Tue, Jan 8, 2013 at 9:59 PM, Arnd Bergmann <arnd at arndb.de> wrote:
> > > > > Please avoid the use of IS_ERR_OR_NULL(), especially on interfaces you
> > > > > introduce yourself. AFAICT, gpiod_get cannot return NULL, so you
> > > > > should not check for that.
> > > >
> > > > Sure - you sound like IS_ERR_OR_NULL() is generally considered evil,
> > >
> > > Correct.
> > >
> > > > may I ask why this is the case?
> > >
> > > It's very hard to get right: either you are interested in the error code,
> > > and then you don't have one in some cases, or you don't care but have
> > > to check for it anyway. When you define a function, just make it clear
> > > what the expected return values are, either NULL for error or a negative
> > > ERR_PTR value, but not both.
> > Indeed, and any code which does this:
> > if (IS_ERR_OR_NULL(ptr))
> > return PTR_ERR(ptr);
> > is buggy because on NULL it returns 0, which is generally accepted as being
> > "success".
[ examples of broken code skipped ]
> These are just a few of the issues I've picked out at random from grepping
> the kernel source for IS_ERR_OR_NULL(). Yes, there's some valid use cases
> but the above are all horrid, buggy or down right wrong, and I wouldn't be
> at all surprised if that was all too common.
I do agree with Russell here. Despite the original intentions behind
IS_ERR_OR_NULL() which were certainly legitimate, the end result in
practice is less reliable code with increased maintenance costs. Unlike
other convenience macros in the kernel, this one is giving a false sense
of correctness with too many people falling in the trap of using it just
because it is available.
I strongly think this macro should simply be removed from the source
tree entirely and the code reverted to explicit tests against NULL when
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