linux-kernel - Re: [PATCH 6/8]i2c:i2c_core Fix warning: variable 'dummy' set but not used

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Date:	Mon, 14 Jun 2010 14:28:57 -0700
From:	David Daney <david.s.daney@...il.com>
To:	Jean Delvare <khali@...ux-fr.org>
CC:	"Justin P. Mattock" <justinmattock@...il.com>,
	linux-kernel@...r.kernel.org, reiserfs-devel@...r.kernel.org,
	linux-bluetooth@...r.kernel.org, clemens@...isch.de,
	debora@...ux.vnet.ibm.com, dri-devel@...ts.freedesktop.org,
	linux-i2c@...r.kernel.org, linux1394-devel@...ts.sourceforge.net,
	linux-media@...r.kernel.org
Subject: Re: [PATCH 6/8]i2c:i2c_core Fix warning: variable 'dummy' set but
 not used

On 06/14/2010 01:53 PM, Jean Delvare wrote:
> Hi Justin,
>
> On Mon, 14 Jun 2010 13:26:46 -0700, Justin P. Mattock wrote:
>> could be a right solution, could be wrong
>> here is the warning:
>>    CC      drivers/i2c/i2c-core.o
>> drivers/i2c/i2c-core.c: In function 'i2c_register_adapter':
>> drivers/i2c/i2c-core.c:757:15: warning: variable 'dummy' set but not used
>>
>>   Signed-off-by: Justin P. Mattock<justinmattock@...il.com>
>>
>> ---
>>   drivers/i2c/i2c-core.c |    2 ++
>>   1 files changed, 2 insertions(+), 0 deletions(-)
>>
>> diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
>> index 1cca263..79c6c26 100644
>> --- a/drivers/i2c/i2c-core.c
>> +++ b/drivers/i2c/i2c-core.c
>> @@ -794,6 +794,8 @@ static int i2c_register_adapter(struct i2c_adapter *adap)
>>   	mutex_lock(&core_lock);
>>   	dummy = bus_for_each_drv(&i2c_bus_type, NULL, adap,
>>   				 __process_new_adapter);
>> +	if(!dummy)
>> +		dummy = 0;
>
> One word: scripts/checkpatch.pl
>
> In other news, the above is just plain wrong. First we force people to
> read the result of bus_for_each_drv() and then when they do and don't
> need the value, gcc complains, so we add one more layer of useless
> code, which developers and possibly tools will later wonder and
> complain about? I can easily imagine that a static code analyzer would
> spot the above code as being a potential bug.
>
> Let's stop this madness now please.
>
> Either __must_check goes away from bus_for_each_drv() and from every
> other function which raises this problem, or we must disable that new
> type of warning gcc 4.6.0 generates. Depends which warnings we value
> more, as we can't sanely have both.
>

That is the crux of the whole thing.  Putting in crap to get rid of the 
__must_check warning someone obviously wanted to provoke is just plain 
wrong.

I don't know what the answer is, but in addition to your suggestion of 
removing the __must_check, you might try:

BUG_ON(dummy != WHAT_IT_SHOULD_BE);

or

if (dummy != WHAT_IT_SHOULD_BE)
	panic("nice message here);


or

static inline void i_really_know_what_i_am_doing(int arg)
{
	/*
	 * Trick the compiler because we don't want to
	 * handle error conditions.
	 */
	return;
}

.
.
.

	i_really_know_what_i_am_doing(dummy);



David Daney

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