Hi, On Mon 22 Jul 19, 12:12, Jeremy Sowden wrote: > On 2019-07-22, at 11:36:51 +0530, Nishka Dasgupta wrote: > > Typecast as bool the return value of cedrus_find_format in > > cedrus_check_format as the return value of cedrus_check_format is > > always treated like a boolean value. > > > > Signed-off-by: Nishka Dasgupta <nishkadg.li...@gmail.com> > > --- > > Changes in v2: > > - Add !! to the returned pointer to ensure that the return value is > > always either true or false, and never a non-zero value other than > > true. > > > > drivers/staging/media/sunxi/cedrus/cedrus_video.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/drivers/staging/media/sunxi/cedrus/cedrus_video.c > > b/drivers/staging/media/sunxi/cedrus/cedrus_video.c > > index e2b530b1a956..b731745f21f8 100644 > > --- a/drivers/staging/media/sunxi/cedrus/cedrus_video.c > > +++ b/drivers/staging/media/sunxi/cedrus/cedrus_video.c > > @@ -86,7 +86,7 @@ static struct cedrus_format *cedrus_find_format(u32 > > pixelformat, u32 directions, > > static bool cedrus_check_format(u32 pixelformat, u32 directions, > > unsigned int capabilities) > > { > > - return cedrus_find_format(pixelformat, directions, capabilities); > > + return !!(bool)cedrus_find_format(pixelformat, directions, > > capabilities); > > } > > I think the original was fine. The return value of cedrus_find_format > will be automatically converted to bool before being returned from > cedrus_check_format since that is the return-type of the function, and > the result of converting any non-zero value to bool is 1.
Okay I was a bit unsure about that and wanted to play it on the safe side without really looking it up, but that gave me the occasion to verify. >From what I could find (from my GNU system's /usr/include/unistring/stdbool.h): Limitations of this substitute, when used in a C89 environment: - In C99, casts and automatic conversions to '_Bool' or 'bool' are performed in such a way that every nonzero value gets converted to 'true', and zero gets converted to 'false'. This doesn't work with this substitute. With this substitute, only the values 0 and 1 give the expected result when converted to _Bool' or 'bool'. So since the kernel is built for C89 (unless I'm mistaken), I don't think the compiler provides any guarantee about bool values being converted to 1 when they are non-zero. As a result, I think it's best to be careful. However, I'm not sure I really see what cocinelle was unhappy about. You mentionned single-line functions, but I don't see how that can be a problem. So in the end, I think we should keep the !! and drop the (bool) cast if there's no particular warning about it. What do you think? Cheers, Paul > > static void cedrus_prepare_format(struct v4l2_pix_format *pix_fmt) > > -- > > 2.19.1 -- Paul Kocialkowski, Bootlin Embedded Linux and kernel engineering https://bootlin.com _______________________________________________ devel mailing list de...@linuxdriverproject.org http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel