--- block-iscsi.orig 2016-05-09 15:16:35.447480532 +1000
+++ block-iscsi    2016-05-05 15:43:58.222159351 +1000
@@ -37,8 +37,7 @@
 {
     # set multipath default value
     multipath="n"
-    for param in $(echo "$1" | tr "," "\n")
-    do
+    for param in $(echo "$1" | tr "," "\n"); do
         case $param in
         iqn=*)
             iqn=$(remove_label $param "iqn=")
@@ -55,6 +54,15 @@
                 fatal "Multipath selected, but no multipath tools found"
             fi
             ;;
+        locktarget=*)
+            locktarget=$(remove_label $param "locktarget=")
+            if ! command -v sg_persist > /dev/null 2>&1; then
+                fatal "Locking requested but no sg_persist found"
+            fi
+            if ! command -v gethostip > /dev/null 2>&1; then
+                fatal "Locking requested but no gethostip found for key generation"
+            fi
+            ;;
         esac
     done
     if [ -z "$iqn" ] || [ -z "$portal" ]; then
@@ -92,6 +100,31 @@
     fi
 }

+
+lock_device()
+{
+    ## Lock the iSCSI target as Exclusive Access.
+    key=$(gethostip -x $(uname -n))
+    if ! sg_persist -d ${dev} -o -G -S ${key} > /dev/null; then
+        unlock_device
+        iscsiadm -m node --targetname "$iqn" -p "$portal" --logout > /dev/null
+        fatal "iSCSI LOCK: Failed to register with target"
+    fi
+    if ! sg_persist -d ${dev} -o -R -K ${key} -T 6 > /dev/null; then
+        unlock_device
+        iscsiadm -m node --targetname "$iqn" -p "$portal" --logout > /dev/null
+        fatal "iSCSI LOCK: Failed to set persistent reservation"
+    fi
+}
+
+unlock_device()
+{
+    ## Unlock the iSCSI target.
+    key=$(gethostip -x $(uname -n))
+    sg_persist -d ${dev} -o -L -K ${key} -T 6 > /dev/null || true
+    sg_persist -d ${dev} -o -G -K ${key} -S 0 > /dev/null || true
+}
+
 command=$1
 target=$(xenstore-read $XENBUS_PATH/params || true)
 if [ -z "$target" ]; then
@@ -110,10 +143,17 @@

     ## Login to the iSCSI target.
     do_or_die iscsiadm -m node --targetname "$iqn" -p "$portal" --login > /dev/null
-
+    find_device
+    if [ "$locktarget" = "y" ]; then
+        lock_device
+    fi
     write_dev $dev
     ;;
 remove)
+    find_device
+    if [ "$locktarget" = "y" ]; then
+        unlock_device
+    fi
     do_or_die iscsiadm -m node --targetname "$iqn" -p "$portal" --logout > /dev/null
     ;;
 *)