[PATCH 05/14] isdn: isdnloop: suppress a gcc-7 warning

[PATCH 05/14] isdn: isdnloop: suppress a gcc-7 warning

[Arnd Bergmann]

We test whether a bit is set in a mask here, which is correct
but gcc warns about it as it thinks it might be confusing:

drivers/isdn/isdnloop/isdnloop.c:412:37: error: ?: using integer constants in boolean context, the expression will always evaluate to 'true' [-Werror=int-in-bool-context]

This replaces the negation of an integer with an equivalent
comparison to zero, which gets rid of the warning.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 drivers/isdn/isdnloop/isdnloop.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/isdn/isdnloop/isdnloop.c b/drivers/isdn/isdnloop/isdnloop.c
index 6ffd13466b8c..5792928b944d 100644
--- a/drivers/isdn/isdnloop/isdnloop.c
+++ b/drivers/isdn/isdnloop/isdnloop.c
@@ -409,7 +409,7 @@ isdnloop_sendbuf(int channel, struct sk_buff *skb, isdnloop_card *card)
 		return -EINVAL;
 	}
 	if (len) {
-		if (!(card->flags & (channel) ? ISDNLOOP_FLAGS_B2ACTIVE : ISDNLOOP_FLAGS_B1ACTIVE))
+		if ((card->flags & (channel) ? ISDNLOOP_FLAGS_B2ACTIVE : ISDNLOOP_FLAGS_B1ACTIVE) == 0)
 			return 0;
 		if (card->sndcount[channel] > ISDNLOOP_MAX_SQUEUE)
 			return 0;
-- 
2.9.0

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Re: [PATCH 05/14] isdn: isdnloop: suppress a gcc-7 warning

[Joe Perches]

On Fri, 2017-07-14 at 11:25 +0200, Arnd Bergmann wrote:
> We test whether a bit is set in a mask here, which is correct
> but gcc warns about it as it thinks it might be confusing:
> 
> drivers/isdn/isdnloop/isdnloop.c:412:37: error: ?: using integer constants in boolean context, the expression will always evaluate to 'true' [-Werror=int-in-bool-context]
> 
> This replaces the negation of an integer with an equivalent
> comparison to zero, which gets rid of the warning.
[]
> diff --git a/drivers/isdn/isdnloop/isdnloop.c b/drivers/isdn/isdnloop/isdnloop.c
[]
> @@ -409,7 +409,7 @@ isdnloop_sendbuf(int channel, struct sk_buff *skb, isdnloop_card *card)
>  		return -EINVAL;
>  	}
>  	if (len) {
> -		if (!(card->flags & (channel) ? ISDNLOOP_FLAGS_B2ACTIVE : ISDNLOOP_FLAGS_B1ACTIVE))
> +		if ((card->flags & (channel) ? ISDNLOOP_FLAGS_B2ACTIVE : ISDNLOOP_FLAGS_B1ACTIVE) == 0)
>  			return 0;
>  		if (card->sndcount[channel] > ISDNLOOP_MAX_SQUEUE)
>  			return 0;

The if as written can not be zero.

drivers/isdn/isdnloop/isdnloop.h:#define ISDNLOOP_FLAGS_B1ACTIVE 1      /* B-Channel-1 is open           */
drivers/isdn/isdnloop/isdnloop.h:#define ISDNLOOP_FLAGS_B2ACTIVE 2      /* B-Channel-2 is open           */

Perhaps this is a logic defect and should be:

		if (!(card->flags & ((channel) ? ISDNLOOP_FLAGS_B2ACTIVE : ISDNLOOP_FLAGS_B1ACTIVE)))

Re: [PATCH 05/14] isdn: isdnloop: suppress a gcc-7 warning

[Arnd Bergmann]

On Fri, Jul 14, 2017 at 12:08 PM, Joe Perches <joe@perches.com> wrote:
> On Fri, 2017-07-14 at 11:25 +0200, Arnd Bergmann wrote:
>> We test whether a bit is set in a mask here, which is correct
>> but gcc warns about it as it thinks it might be confusing:
>>
>> drivers/isdn/isdnloop/isdnloop.c:412:37: error: ?: using integer constants in boolean context, the expression will always evaluate to 'true' [-Werror=int-in-bool-context]
>>
>> This replaces the negation of an integer with an equivalent
>> comparison to zero, which gets rid of the warning.
> []
>> diff --git a/drivers/isdn/isdnloop/isdnloop.c b/drivers/isdn/isdnloop/isdnloop.c
> []
>> @@ -409,7 +409,7 @@ isdnloop_sendbuf(int channel, struct sk_buff *skb, isdnloop_card *card)
>>               return -EINVAL;
>>       }
>>       if (len) {
>> -             if (!(card->flags & (channel) ? ISDNLOOP_FLAGS_B2ACTIVE : ISDNLOOP_FLAGS_B1ACTIVE))
>> +             if ((card->flags & (channel) ? ISDNLOOP_FLAGS_B2ACTIVE : ISDNLOOP_FLAGS_B1ACTIVE) == 0)
>>                       return 0;
>>               if (card->sndcount[channel] > ISDNLOOP_MAX_SQUEUE)
>>                       return 0;
>
> The if as written can not be zero.
>
> drivers/isdn/isdnloop/isdnloop.h:#define ISDNLOOP_FLAGS_B1ACTIVE 1      /* B-Channel-1 is open           */
> drivers/isdn/isdnloop/isdnloop.h:#define ISDNLOOP_FLAGS_B2ACTIVE 2      /* B-Channel-2 is open           */
>
> Perhaps this is a logic defect and should be:
>
>                 if (!(card->flags & ((channel) ? ISDNLOOP_FLAGS_B2ACTIVE : ISDNLOOP_FLAGS_B1ACTIVE)))

Yes, good catch. I had thought about it for a bit whether that would be
the answer, but come to the wrong conclusion on my own.

Note that the version you suggested will still have the warning, so I think
it needs to be

                 if (card->flags &
                    ((channel) ? ISDNLOOP_FLAGS_B2ACTIVE :
ISDNLOOP_FLAGS_B1ACTIVE)
                     == 0)

or something like that, probably having a temporary flag variable would be best:

          int flag =  channel ? ISDNLOOP_FLAGS_B2ACTIVE :
ISDNLOOP_FLAGS_B1ACTIVE;
          if ((card->flags & flag) == 0)
                       return 0;

         Arnd

Re: [PATCH 05/14] isdn: isdnloop: suppress a gcc-7 warning

[Kevin Easton]

On Fri, Jul 14, 2017 at 12:37:05PM +0200, Arnd Bergmann wrote:
> On Fri, Jul 14, 2017 at 12:08 PM, Joe Perches <joe@perches.com> wrote:
> > On Fri, 2017-07-14 at 11:25 +0200, Arnd Bergmann wrote:
> >> We test whether a bit is set in a mask here, which is correct
> >> but gcc warns about it as it thinks it might be confusing:
> >>
> >> drivers/isdn/isdnloop/isdnloop.c:412:37: error: ?: using integer constants in boolean context, the expression will always evaluate to 'true' [-Werror=int-in-bool-context]

...

> > Perhaps this is a logic defect and should be:
> >
> >                 if (!(card->flags & ((channel) ? ISDNLOOP_FLAGS_B2ACTIVE : ISDNLOOP_FLAGS_B1ACTIVE)))
> 
> Yes, good catch. I had thought about it for a bit whether that would be
> the answer, but come to the wrong conclusion on my own.
> 
> Note that the version you suggested will still have the warning, so I think
> it needs to be

It shouldn't - the warning is for using an integer *constant* in boolean
context, but the result of & isn't a constant and should be fine.

!(flags & mask) is a very common idiom.

    - Kevin