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

[David Daney]

On 06/15/2010 04:40 AM, Jean Delvare wrote:
> Hi David,
>
> On Mon, 14 Jun 2010 14:28:57 -0700, David Daney wrote:
> > 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@xxxxxxxxx>
> > > >
> > > > ---
> > > >    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.
>
> __process_new_adapter() calls i2c_do_add_adapter() which always returns
> 0. Why should I check the return value of bus_for_each_drv() when I
> know it will always be 0 by construction?
>
> Also note that the same function is also called through
> bus_for_each_dev() somewhere else in i2c-core, and there is no warning
> there because bus_for_each_dev() is not marked __must_check. How
> consistent is this? If bus_for_each_dev() is OK without __must_check,
> then I can't see why bus_for_each_drv() wouldn't be.

Well, I would advocate removing the __must_check then.


David Daney
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