On Fri, Jul 14, 2017 at 12:08 PM, Joe Perches [off-list ref] wrote:

On Fri, 2017-07-14 at 11:25 +0200, Arnd Bergmann wrote:

quoted

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.

[]

quoted

diff --git a/drivers/isdn/isdnloop/isdnloop.c b/drivers/isdn/isdnloop/isdnloop.c

[]

quoted

@@ -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