linux-kernel - [PATCH v2] xen: don't print error message in case of missing Xenstore entry

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Message-Id: <20170530185226.4666-1-jgross@suse.com>
Date:   Tue, 30 May 2017 20:52:26 +0200
From:   Juergen Gross <jgross@...e.com>
To:     linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org
Cc:     boris.ostrovsky@...cle.com, Juergen Gross <jgross@...e.com>
Subject: [PATCH v2] xen: don't print error message in case of missing Xenstore entry

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 | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/xen/manage.c b/drivers/xen/manage.c
index c1ec8ee80924..60cf71f1b256 100644
--- a/drivers/xen/manage.c
+++ b/drivers/xen/manage.c
@@ -277,8 +277,16 @@ 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) {
+		/*
+		 * 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;
 	}
-- 
2.12.3