linux-kernel - Re: [PATCH] xen: don't print error message in case of missing Xenstore entry

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Date:   Tue, 30 May 2017 09:25:33 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Juergen Gross <jgross@...e.com>, linux-kernel@...r.kernel.org,
        xen-devel@...ts.xenproject.org
Subject: Re: [PATCH] xen: don't print error message in case of missing
 Xenstore entry

On 05/29/2017 05:13 AM, Juergen Gross wrote:
> When registering for the Xenstore watch of the node control/sysrq the
> handler will be called at once. Don't issue an error message if the
> Xenstore node isn't there, as it will be created only when an event
> is being triggered.
>
> Signed-off-by: Juergen Gross <jgross@...e.com>
> ---
>  drivers/xen/manage.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/xen/manage.c b/drivers/xen/manage.c
> index c1ec8ee80924..7ddd0803da23 100644
> --- a/drivers/xen/manage.c
> +++ b/drivers/xen/manage.c
> @@ -277,8 +277,11 @@ static void sysrq_handler(struct xenbus_watch *watch, const char *path,
>  	err = xenbus_transaction_start(&xbt);
>  	if (err)
>  		return;
> -	if (xenbus_scanf(xbt, "control", "sysrq", "%c", &sysrq_key) < 0) {
> -		pr_err("Unable to read sysrq code in control/sysrq\n");
> +	err = xenbus_scanf(xbt, "control", "sysrq", "%c", &sysrq_key);
> +	if (err < 0) {
> +		if (err != -ENOENT)

Can we distinguish initialization invocation from actual watch firing?
E.g. '|| (system_state >= SYSTEM_RUNNING)'?

-boris

> +			pr_err("Error %d reading sysrq code in control/sysrq\n",
> +			       err);
>  		xenbus_transaction_end(xbt, 1);
>  		return;
>  	}