linux-kernel - Re: [PATCH] drbd: avoid clang warning about pointless switch statement

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Message-ID: <20170206134323.GC16345@soda.linbit>
Date:   Mon, 6 Feb 2017 14:43:23 +0100
From:   Lars Ellenberg <lars.ellenberg@...bit.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Philipp Reisner <philipp.reisner@...bit.com>,
        drbd-dev@...ts.linbit.com,
        Nicolas Dichtel <nicolas.dichtel@...nd.com>,
        "David S. Miller" <davem@...emloft.net>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drbd: avoid clang warning about pointless switch
 statement

Ack.

Ok, not exactly "pintless", it's a valid compile time assert for uniq ids,
basically a BUILD_BUG_ON(duplicate-ids). But adding a default clause
there does not hurt.

Thanks,
    Lars


On Wed, Feb 01, 2017 at 05:55:02PM +0100, Arnd Bergmann wrote:
> The drbd code causes warnings that we cannot easily disable when building with clang:
> 
> In file included from drivers/block/drbd/drbd_debugfs.c:10:
> In file included from drivers/block/drbd/drbd_int.h:48:
> In file included from include/linux/drbd_genl_api.h:53:
> In file included from include/linux/genl_magic_struct.h:237:
> include/linux/drbd_genl.h:300:1: warning: no case matching constant switch condition '0'
> 
> There is nothing wrong with the code, and adding 'default:' labels
> in the right place is enough to let clang shut up about the warning.
> 
> Fixes: ec2c35ac1ea2 ("drbd: prepare the transition from connector to genetlink")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  include/linux/genl_magic_struct.h | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/include/linux/genl_magic_struct.h b/include/linux/genl_magic_struct.h
> index 6270a56e5edc..c6fbafb834f1 100644
> --- a/include/linux/genl_magic_struct.h
> +++ b/include/linux/genl_magic_struct.h
> @@ -190,6 +190,7 @@ static inline void ct_assert_unique_operations(void)
>  {
>  	switch (0) {
>  #include GENL_MAGIC_INCLUDE_FILE
> +	default:
>  		;
>  	}
>  }
> @@ -208,6 +209,7 @@ static inline void ct_assert_unique_top_level_attributes(void)
>  {
>  	switch (0) {
>  #include GENL_MAGIC_INCLUDE_FILE
> +	default:
>  		;
>  	}
>  }
> @@ -218,6 +220,7 @@ static inline void ct_assert_unique_ ## s_name ## _attributes(void)	\
>  {									\
>  	switch (0) {							\
>  		s_fields						\
> +		default:						\
>  			;						\
>  	}								\
>  }
> -- 
> 2.9.0