[PATCH] xen: add error handling for xenbus_printf

[Zhouyang Jia <jiazhouyang09@gmail.com>]

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);
+			return err;
+		}
 	}
 
 	return 0;
-- 
2.7.4