xen/scsiback: add error handling for xenbus_printf

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>
Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Juergen Gross <jgross@suse.com>

drivers/xen/xen-scsiback.c

@@ -1012,6 +1012,7 @@ static void scsiback_do_add_lun(struct vscsibk_info *info, const char *state,
 {
 	struct v2p_entry *entry;
 	unsigned long flags;
+	int err;
 
 	if (try) {
 		spin_lock_irqsave(&info->v2p_lock, flags);
@@ -1027,8 +1028,11 @@ static void scsiback_do_add_lun(struct vscsibk_info *info, const char *state,
 			scsiback_del_translation_entry(info, vir);
 		}
 	} else if (!try) {
-		xenbus_printf(XBT_NIL, info->dev->nodename, state,
+		err = xenbus_printf(XBT_NIL, info->dev->nodename, state,
 			      "%d", XenbusStateClosed);
+		if (err)
+			xenbus_dev_error(info->dev, err,
+				"%s: writing %s", __func__, state);
 	}
 }
 
@@ -1067,8 +1071,11 @@ static void scsiback_do_1lun_hotplug(struct vscsibk_info *info, int op,
 	snprintf(str, sizeof(str), "vscsi-devs/%s/p-dev", ent);
 	val = xenbus_read(XBT_NIL, dev->nodename, str, NULL);
 	if (IS_ERR(val)) {
-		xenbus_printf(XBT_NIL, dev->nodename, state,
+		err = xenbus_printf(XBT_NIL, dev->nodename, state,
 			      "%d", XenbusStateClosed);
+		if (err)
+			xenbus_dev_error(info->dev, err,
+				"%s: writing %s", __func__, state);
 		return;
 	}
 	strlcpy(phy, val, VSCSI_NAMELEN);
@@ -1079,8 +1086,11 @@ static void scsiback_do_1lun_hotplug(struct vscsibk_info *info, int op,
 	err = xenbus_scanf(XBT_NIL, dev->nodename, str, "%u:%u:%u:%u",
 			   &vir.hst, &vir.chn, &vir.tgt, &vir.lun);
 	if (XENBUS_EXIST_ERR(err)) {
-		xenbus_printf(XBT_NIL, dev->nodename, state,
+		err = xenbus_printf(XBT_NIL, dev->nodename, state,
 			      "%d", XenbusStateClosed);
+		if (err)
+			xenbus_dev_error(info->dev, err,
+				"%s: writing %s", __func__, state);
 		return;
 	}