linux-kernel - Re: [PATCH v2] drbd: Avoid Clang warning about pointless switch statment

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Message-ID: <20181217172401.GA30635@flashbox>
Date:   Mon, 17 Dec 2018 10:24:01 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Philipp Reisner <philipp.reisner@...bit.com>,
        Lars Ellenberg <lars.ellenberg@...bit.com>
Cc:     drbd-dev@...ts.linbit.com, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
        Jens Axboe <axboe@...nel.dk>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: [PATCH v2] drbd: Avoid Clang warning about pointless switch
 statment

On Thu, Oct 04, 2018 at 01:09:13PM -0700, Nathan Chancellor wrote:
> There are several warnings from Clang about no case statement matching
> the constant 0:
> 
> In file included from drivers/block/drbd/drbd_receiver.c:48:
> In file included from drivers/block/drbd/drbd_int.h:48:
> In file included from ./include/linux/drbd_genl_api.h:54:
> In file included from ./include/linux/genl_magic_struct.h:236:
> ./include/linux/drbd_genl.h:321:1: warning: no case matching constant
> switch condition '0'
> GENL_struct(DRBD_NLA_HELPER, 24, drbd_helper_info,
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> ./include/linux/genl_magic_struct.h:220:10: note: expanded from macro
> 'GENL_struct'
>         switch (0) {
>                 ^
> 
> Silence this warning by adding a 'case 0:' statement. Additionally,
> adjust the alignment of the statements in the ct_assert_unique macro to
> avoid a checkpatch warning.
> 
> This solution was originally sent by Arnd Bergmann with a default case
> statement: https://lore.kernel.org/patchwork/patch/756723/
> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/43
> Suggested-by: Lars Ellenberg <lars.ellenberg@...bit.com>
> Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
> ---
> 
> Since this is not the same as Arnd's patch, I took authorship for it
> while leaving a link to the original patch in the commit message. If
> this is not how it should have been done, please let me know.
> 
>  include/linux/genl_magic_struct.h | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/genl_magic_struct.h b/include/linux/genl_magic_struct.h
> index 5972e4969197..eeae59d3ceb7 100644
> --- a/include/linux/genl_magic_struct.h
> +++ b/include/linux/genl_magic_struct.h
> @@ -191,6 +191,7 @@ static inline void ct_assert_unique_operations(void)
>  {
>  	switch (0) {
>  #include GENL_MAGIC_INCLUDE_FILE
> +	case 0:
>  		;
>  	}
>  }
> @@ -209,6 +210,7 @@ static inline void ct_assert_unique_top_level_attributes(void)
>  {
>  	switch (0) {
>  #include GENL_MAGIC_INCLUDE_FILE
> +	case 0:
>  		;
>  	}
>  }
> @@ -218,7 +220,8 @@ static inline void ct_assert_unique_top_level_attributes(void)
>  static inline void ct_assert_unique_ ## s_name ## _attributes(void)	\
>  {									\
>  	switch (0) {							\
> -		s_fields						\
> +	s_fields							\
> +	case 0:								\
>  			;						\
>  	}								\
>  }
> -- 
> 2.19.0
> 

Hi Lars and Philipp,

Could you please make sure that this patch and the other one I sent make
it into 4.21/5.0? I am not sure when you were planning on sending the
pull request to Jens that you mentioned in the other thread but I've
noticed most maintainers typically send their requests for the impending
merge window around -rc7 or so and I wanted to make sure it was on your
radar.

Thank you,
Nathan