Patch "xen: don't print error message in case of missing Xenstore entry" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

xen: don't print error message in case of missing Xenstore entry

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
xen-don-t-print-error-message-in-case-of-missing-xenstore-entry.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Juergen Gross <[email protected]>
Date: Tue, 30 May 2017 20:52:26 +0200
Subject: xen: don't print error message in case of missing Xenstore entry

From: Juergen Gross <[email protected]>

[ Upstream commit 4e93b6481c87ea5afde944a32b4908357ec58992 ]

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.

---
 drivers/xen/manage.c |   12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

@@ -277,8 +277,16 @@ static void sysrq_handler(struct xenbus_
 	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) {
+		/*
+		 * The Xenstore watch fires directly after registering it and
+		 * after a suspend/resume cycle. So ENOENT is no error but
+		 * might happen in those cases.
+		 */
+		if (err != -ENOENT)
+			pr_err("Error %d reading sysrq code in control/sysrq\n",
+			       err);
 		xenbus_transaction_end(xbt, 1);
 		return;
 	}

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/xen-don-t-print-error-message-in-case-of-missing-xenstore-entry.patch queue-4.9/xen-manage-correct-return-value-check-on-xenbus_scanf.patch