Re: [PATCH review for 4.9 31/50] xen/manage: correct return value check on xenbus_scanf()

[Boris Ostrovsky]

On 10/07/2017 06:36 PM, Levin, Alexander (Sasha Levin) wrote:
> From: Jan Beulich <JBeulich@xxxxxxxx>
>
> [ Upstream commit 4fed1b125eb6252bde478665fc05d4819f774fa8 ]
>
> A negative return value indicates an error; in fact the function at
> present won't ever return zero.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxx>

This patch will cause a warning to be printed. Please pull commit
4e93b64 ("xen: don't print error message in case of missing Xenstore
entry") as well.

Thanks.
-boris

> ---
>  drivers/xen/manage.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/xen/manage.c b/drivers/xen/manage.c
> index 26e5e8507f03..357a8db859c9 100644
> --- a/drivers/xen/manage.c
> +++ b/drivers/xen/manage.c
> @@ -277,7 +277,7 @@ static void sysrq_handler(struct xenbus_watch *watch, const char **vec,
>  	err = xenbus_transaction_start(&xbt);
>  	if (err)
>  		return;
> -	if (!xenbus_scanf(xbt, "control", "sysrq", "%c", &sysrq_key)) {
> +	if (xenbus_scanf(xbt, "control", "sysrq", "%c", &sysrq_key) < 0) {
>  		pr_err("Unable to read sysrq code in control/sysrq\n");
>  		xenbus_transaction_end(xbt, 1);
>  		return;