linux-kernel - Re: [PATCH] media: cx18: Don't check for address of video

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Date:   Fri, 21 Sep 2018 13:40:08 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     awalls@...metrocast.net,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] media: cx18: Don't check for address of video_dev

On Fri, Sep 21, 2018 at 01:31:37PM -0700, Nick Desaulniers wrote:
> On Fri, Sep 21, 2018 at 1:03 PM Nathan Chancellor
> <natechancellor@...il.com> wrote:
> >
> > Clang warns that the address of a pointer will always evaluated as true
> > in a boolean context.
> >
> > drivers/media/pci/cx18/cx18-driver.c:1255:23: warning: address of
> > 'cx->streams[i].video_dev' will always evaluate to 'true'
> > [-Wpointer-bool-conversion]
> >                 if (&cx->streams[i].video_dev)
> >                 ~~   ~~~~~~~~~~~~~~~^~~~~~~~~
> > 1 warning generated.
> >
> > Presumably, the contents of video_dev should have been checked, not the
> > address. This check has been present since 2009, introduced by commit
> > 21a278b85d3c ("V4L/DVB (11619): cx18: Simplify the work handler for
> > outgoing mailbox commands")
> >
> > Reported-by: Nick Desaulniers <ndesaulniers@...gle.com>
> > Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
> > ---
> >
> > Alternatively, this if statement could just be removed since it has
> > evaluated to true since 2009 and I assume some issue with this would
> > have been discovered by now.
> >
> >  drivers/media/pci/cx18/cx18-driver.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/media/pci/cx18/cx18-driver.c b/drivers/media/pci/cx18/cx18-driver.c
> > index 56763c4ea1a7..753a37c7100a 100644
> > --- a/drivers/media/pci/cx18/cx18-driver.c
> > +++ b/drivers/media/pci/cx18/cx18-driver.c
> > @@ -1252,7 +1252,7 @@ static void cx18_cancel_out_work_orders(struct cx18 *cx)
> >  {
> >         int i;
> >         for (i = 0; i < CX18_MAX_STREAMS; i++)
> > -               if (&cx->streams[i].video_dev)
> > +               if (cx->streams[i].video_dev)
> 
> cx->streams[i].video_dev has the type `struct video_device video_dev`.
> So wouldn't this change always be true as well, since the struct is
> embedded?
> 

Guess I forgot to compile this with Clang before sending because I now
get a build error (sigh...)

drivers/media/pci/cx18/cx18-driver.c:1255:3: error: statement requires
expression of scalar type ('struct video_device' invalid)                                                                              
                if (cx->streams[i].video_dev)
                                ^   ~~~~~~~~~~~~~~~~~~~~~~~~
                                1 error generated.

I guess the whole if statement should go unless I'm missing something
else.

Thanks for the review!
Nathan

> >                         cancel_work_sync(&cx->streams[i].out_work_order);
> >  }
> >
> > --
> > 2.19.0
> >
> 
> 
> -- 
> Thanks,
> ~Nick Desaulniers