linux-kernel - Re: [PATCH] driver-core: use 'dev' argument in dev_dbg

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Date:	Thu, 31 Mar 2016 11:13:47 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Andrew Lunn <andrew@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Hiroshi Doyu <hdoyu@...dia.com>,
	Aaron Conole <aconole@...hat.com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] driver-core: use 'dev' argument in dev_dbg_ratelimited
 stub

On Thu, Mar 24, 2016 at 10:19:40PM +0100, Arnd Bergmann wrote:
> dev_dbg_ratelimited() is a macro that ignores its first argument when DEBUG is
> not set, which can lead to unused variable warnings:
> 
> ethernet/mellanox/mlxsw/pci.c: In function 'mlxsw_pci_cqe_sdq_handle':
> ethernet/mellanox/mlxsw/pci.c:646:18: warning: unused variable 'pdev' [-Wunused-variable]
> ethernet/mellanox/mlxsw/pci.c: In function 'mlxsw_pci_cqe_rdq_handle':
> ethernet/mellanox/mlxsw/pci.c:671:18: warning: unused variable 'pdev' [-Wunused-variable]
> 
> The macro already ensures that all its other arguments are silently
> ignored by the compiler without triggering a warning, through the
> use of the no_printk() macro, but the dev argument is not passed into
> that.
> 
> This changes the definition to use the same trick as no_printk() with
> an if(0) that leads the compiler to not evaluate the side-effects but
> still see that 'dev' might not be unused.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> Suggested-by: Andrew Lunn <andrew@...n.ch>
> Fixes: 6f586e663e3b ("driver-core: Shut up dev_dbg_reatelimited() without DEBUG")

Reviewed-by: Dmitry Torokhov <dmitry.torokhov@...il.com>

> ---
>  include/linux/device.h | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/device.h b/include/linux/device.h
> index 002c59728dbe..07f74c246cac 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -1293,8 +1293,11 @@ do {									\
>  		dev_printk(KERN_DEBUG, dev, fmt, ##__VA_ARGS__);	\
>  } while (0)
>  #else
> -#define dev_dbg_ratelimited(dev, fmt, ...)			\
> -	no_printk(KERN_DEBUG pr_fmt(fmt), ##__VA_ARGS__)
> +#define dev_dbg_ratelimited(dev, fmt, ...)				\
> +do {									\
> +	if (0)								\
> +		dev_printk(KERN_DEBUG, dev, fmt, ##__VA_ARGS__);	\
> +} while (0)
>  #endif
>  
>  #ifdef VERBOSE_DEBUG
> -- 
> 2.7.0
> 

-- 
Dmitry