linux-kernel - Re: [PATCH] bitfield.h: annotate type_replace_bits functions with __must

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Date:   Wed, 16 Sep 2020 17:20:59 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
Cc:     davem@...emloft.net, vkoul@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] bitfield.h: annotate type_replace_bits functions with
 __must_check

On Wed, Sep 16, 2020 at 04:03:33PM +0100, Srinivas Kandagatla wrote:
> usage of apis like u32_replace_bits() without actually catching the return
> value could hide problems without any warning!
> 
> Found this with recent usage of this api in SoundWire!
> Having __must_check annotation would really catch this issues in future!
> 
> Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
> ---
>  include/linux/bitfield.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/bitfield.h b/include/linux/bitfield.h
> index 4e035aca6f7e..eb4f69253946 100644
> --- a/include/linux/bitfield.h
> +++ b/include/linux/bitfield.h
> @@ -131,7 +131,7 @@ static __always_inline __##type type##_encode_bits(base v, base field)	\
>  		__field_overflow();					\
>  	return to((v & field_mask(field)) * field_multiplier(field));	\
>  }									\
> -static __always_inline __##type type##_replace_bits(__##type old,	\
> +static __always_inline __must_check __##type type##_replace_bits(__##type old, \
>  					base val, base field)		\
>  {									\
>  	return (old & ~to(field)) | type##_encode_bits(val, field);	\
> -- 
> 2.21.0
> 

Don't add __must_check to things that if merged will instantly cause
build warnings to the system, that's just rude :(

Fix up everything first, and then try to make this type of change.

But why does this function have to be checked?

thanks,

greg k-h