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

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Date:   Fri, 14 Jul 2017 03:08:56 -0700
From:   Joe Perches <joe@...ches.com>
To:     Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
        Karsten Keil <isdn@...ux-pingi.de>,
        "David S. Miller" <davem@...emloft.net>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Tejun Heo <tj@...nel.org>, Guenter Roeck <linux@...ck-us.net>,
        linux-ide@...r.kernel.org, linux-media@...r.kernel.org,
        akpm@...ux-foundation.org, dri-devel@...ts.freedesktop.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH 05/14] isdn: isdnloop: suppress a gcc-7 warning

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)))