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 13:08:25 -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 05/30/2017 11:03 AM, Juergen Gross wrote:
> On 30/05/17 15:25, Boris Ostrovsky wrote:
>> 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)'?
> The watch will fire again after suspend/resume (e.g. live migration).


That's unfortunate. (And system_state check would also not be a good
solution btw since the watch might be processed by the watch thread
after we enter SYSTEM_RUNNING).

Can you add a comment explaining why we are ignoring ENOENT?

-boris



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