From mboxrd@z Thu Jan  1 00:00:00 1970
From: Juergen Gross <jgross@suse.com>
Date: Thu, 07 Jul 2016 09:42:53 +0000
Subject: Re: [PATCH] xen-fbfront: correct return value checks on xenbus_scanf()
Message-Id: <577E241D.8040908@suse.com>
List-Id: <linux-fbdev.vger.kernel.org>
References: <577E258502000078000FBE6F@suse.com>
In-Reply-To: <577E258502000078000FBE6F@suse.com>
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
To: Jan Beulich <JBeulich@suse.com>, plagnioj@jcrosoft.com, tomi.valkeinen@ti.com
Cc: xen-devel <xen-devel@lists.xenproject.org>, Boris Ostrovsky <boris.ostrovsky@oracle.com>, David Vrabel <david.vrabel@citrix.com>, linux-fbdev <linux-fbdev@vger.kernel.org>

On 07/07/16 09:48, Jan Beulich wrote:
> Only a positive return value indicates success.

Hmm, I'm not convinced on this change (and the similar others as
well). From xenbus.h:

/* Single read and scanf: returns -errno or num scanned if > 0. */

There should be no case for xenbus_scanf() returning 0. And looking
into the functions proofs this is correct.


Juergen

> 
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> ---
>  drivers/video/fbdev/xen-fbfront.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> --- 4.7-rc6-xenbus_scanf.orig/drivers/video/fbdev/xen-fbfront.c
> +++ 4.7-rc6-xenbus_scanf/drivers/video/fbdev/xen-fbfront.c
> @@ -658,13 +658,13 @@ InitWait:
>  			goto InitWait; /* no InitWait seen yet, fudge it */
>  
>  		if (xenbus_scanf(XBT_NIL, info->xbdev->otherend,
> -				 "request-update", "%d", &val) < 0)
> +				 "request-update", "%d", &val) <= 0)
>  			val = 0;
>  		if (val)
>  			info->update_wanted = 1;
>  
>  		if (xenbus_scanf(XBT_NIL, dev->otherend,
> -				 "feature-resize", "%d", &val) < 0)
> +				 "feature-resize", "%d", &val) <= 0)
>  			val = 0;
>  		info->feature_resize = val;
>  		break;
> 
>