Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753867AbdGNKhL (ORCPT ); Fri, 14 Jul 2017 06:37:11 -0400 Received: from mail-oi0-f54.google.com ([209.85.218.54]:35972 "EHLO mail-oi0-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753479AbdGNKhH (ORCPT ); Fri, 14 Jul 2017 06:37:07 -0400 MIME-Version: 1.0 In-Reply-To: <1500026936.4457.68.camel@perches.com> References: <20170714092540.1217397-1-arnd@arndb.de> <20170714092540.1217397-6-arnd@arndb.de> <1500026936.4457.68.camel@perches.com> From: Arnd Bergmann Date: Fri, 14 Jul 2017 12:37:05 +0200 X-Google-Sender-Auth: laB12S0gmTimK1Bvz2uJrJBL5eA Message-ID: Subject: Re: [PATCH 05/14] isdn: isdnloop: suppress a gcc-7 warning To: Joe Perches Cc: Linux Kernel Mailing List , Karsten Keil , "David S. Miller" , Greg Kroah-Hartman , Linus Torvalds , Tejun Heo , Guenter Roeck , IDE-ML , Linux Media Mailing List , Andrew Morton , dri-devel , Networking Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2190 Lines: 50 On Fri, Jul 14, 2017 at 12:08 PM, Joe Perches 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