Re: [Xen-devel] [PATCH] xen-fbfront: correct return value checks on xenbus_scanf()

[Juergen Gross <jgross@xxxxxxxx>]

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@xxxxxxxx>
> ---
>  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;
> 
> 


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