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Subject: Re: [PATCH] xen: add error handling for xenbus_printf
To:     Zhouyang Jia <jiazhouyang09@gmail.com>
Cc:     Juergen Gross <jgross@suse.com>, xen-devel@lists.xenproject.org,
        linux-kernel@vger.kernel.org
References: <1528775073-39322-1-git-send-email-jiazhouyang09@gmail.com>
From:   Boris Ostrovsky <boris.ostrovsky@oracle.com>
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Date:   Thu, 14 Jun 2018 17:57:39 -0400
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On 06/11/2018 11:44 PM, Zhouyang Jia wrote:
> When xenbus_printf fails, the lack of error-handling code may
> cause unexpected results.
>
> This patch adds error-handling code after calling xenbus_printf.
>
> Signed-off-by: Zhouyang Jia <jiazhouyang09@gmail.com>
> ---
>  drivers/xen/manage.c | 17 ++++++++++++++---
>  1 file changed, 14 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/xen/manage.c b/drivers/xen/manage.c
> index 8835065..159694d 100644
> --- a/drivers/xen/manage.c
> +++ b/drivers/xen/manage.c
> @@ -289,8 +289,15 @@ static void sysrq_handler(struct xenbus_watch *watch, const char *path,
>  		return;
>  	}
>  
> -	if (sysrq_key != '\0')
> -		xenbus_printf(xbt, "control", "sysrq", "%c", '\0');
> +	if (sysrq_key != '\0') {
> +		err = xenbus_printf(xbt, "control", "sysrq", "%c", '\0');
> +		if (err) {
> +			pr_err("Error %d writing sysrq code in control/sysrq\n",
> +			       err);
> +			xenbus_transaction_end(xbt, 1);
> +			return;
> +		}
> +	}
>  
>  	err = xenbus_transaction_end(xbt, 0);
>  	if (err == -EAGAIN)
> @@ -342,7 +349,11 @@ static int setup_shutdown_watcher(void)
>  			continue;
>  		snprintf(node, FEATURE_PATH_SIZE, "feature-%s",
>  			 shutdown_handlers[idx].command);
> -		xenbus_printf(XBT_NIL, "control", node, "%u", 1);
> +		err = xenbus_printf(XBT_NIL, "control", node, "%u", 1);
> +		if (err) {
> +			pr_err("Error %d writing %s\n", err, node);


Adding __func__ will make it it easier trying to understand where the
error is coming from. And for consistency, I'd add it to the one above
as well.


-boris