[PATCH v2] staging: media: sunxi: Add bool cast to value

[Nishka Dasgupta]

On 22/07/19 5:54 PM, Paul Kocialkowski wrote:
> 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.linux at 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.

It's not a problem per se. I'm just working on a cleanup project for 
which I went through all of staging replacing single-line functions with 
what they were calling. In some cases that makes it easier to figure out 
what a particular function call does, since the called function actually 
does something itself instead of just calling a different function?
This function was also flagged as one such potentially-removable 
function by Coccinelle; but in order to do the same replacement that I'd 
done in other staging drivers, I thought I would do something about the 
type mismatch first, especially since find_format doesn't appear to be 
used anywhere else.
However, now I won't remove check_format and replace it with find_format 
as I'd originally planned, since you've said that isn't necessary here. 
That leaves the return type issue.


> So in the end, I think we should keep the !! and drop the (bool) cast if there's
> no particular warning about it.

Should I send a version 3 that does this?

Thanking you,
Nishka

> What do you think?
> 
> Cheers,
> 
> Paul
> 
>>>   static void cedrus_prepare_format(struct v4l2_pix_format *pix_fmt)
>>> --
>>> 2.19.1
>