Messages in this thread | | | Date | Wed, 10 Feb 2016 07:16:47 -0800 | From | Guenter Roeck <> | Subject | Re: [PATCH v3] err.h: allow IS_ERR_VALUE to handle properly more types |
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On Fri, Feb 05, 2016 at 12:37:00AM +0100, Rasmus Villemoes wrote: > On Wed, Feb 03 2016, Andrzej Hajda <a.hajda@samsung.com> wrote: > > > Current implementation of IS_ERR_VALUE works correctly only with > > following types: > > - unsigned long, > > - short, int, long. > > Other types are handled incorrectly either on 32-bit either on 64-bit > > either on both architectures. > > The patch fixes it by comparing argument with MAX_ERRNO casted > > to argument's type for unsigned types and comparing with zero for signed > > types. As a result all integer types bigger than char are handled properly. > > > > > > Signed-off-by: Andrzej Hajda <a.hajda@samsung.com> > > --- > > v3: > > - use '<= -1' instead of '< 0' to silence verbose warnings for gcc > > older than 4.8, > > v2: > > - use '<= 0' instead of '< 0' to silence gcc verbose warnings, > > - expand commit message. > > --- > > include/linux/err.h | 4 +++- > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > diff --git a/include/linux/err.h b/include/linux/err.h > > index 56762ab..b7d4a9f 100644 > > --- a/include/linux/err.h > > +++ b/include/linux/err.h > > @@ -18,7 +18,9 @@ > > > > #ifndef __ASSEMBLY__ > > > > -#define IS_ERR_VALUE(x) unlikely((x) >= (unsigned long)-MAX_ERRNO) > > +#define IS_ERR_VALUE(x) ((typeof(x))(-1) <= 0 \ > > + ? unlikely((x) <= -1) \ > > + : unlikely((x) >= (typeof(x))-MAX_ERRNO)) > > > > I'm a bit worried that you consider any negative value an error when x > is signed - at least that's a change which deserves some comment why > that's ok. For example, I could imagine someone using e.g. INT_MIN as a > sentinel return value meaning 'not an error, but something special > still'. > Theoretically maybe, but I think that is quite unlikely in the real world.
It turns out that
if (-22 >= (unsigned long)-MAX_ERRNO) printf("This is odd\n");
actually does print "This is odd" (because -22 is promoted to unsigned long).
Instead of relying on such behavior, I think it would be better to convert uses of IS_ERR_VALUE() on integer values to direct comparisons. A coccinelle script to do that conversion that is already available for pm functions (scripts/coccinelle/api/pm_runtime.cocci). Such a conversion would make the code easier to read, and reduce code size instead of (at least potentially) increasing it.
Guenter
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