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.
> 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);
Which will never trigger.
> 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);
Which is adding a lot of lines, and might eventually fail when the
compiler becomes smarter (if it isn't already). Thanks but no thanks.
If I really have to chose one of these evils, I'll go for BUG_ON(), at
least the intent is clear and the bloat is minimum.
--
Jean Delvare
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