1 files changed, 98 insertions, 0 deletions
diff --git a/os-plugins/plugins/xen/files/xen.examples/scripts/locking.sh b/os-plugins/plugins/xen/files/xen.examples/scripts/locking.sh
new file mode 100644
index 00000000..6ff58e7e
--- /dev/null
+++ b/os-plugins/plugins/xen/files/xen.examples/scripts/locking.sh
@@ -0,0 +1,98 @@
+#
+# Copyright (c) 2005 XenSource Ltd.
+#
+# This library is free software; you can redistribute it and/or
+# modify it under the terms of version 2.1 of the GNU Lesser General Public
+# License as published by the Free Software Foundation.
+#
+# This library is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+# Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public
+# License along with this library; if not, write to the Free Software
+# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+#
+
+#
+# Serialisation
+#
+
+LOCK_SLEEPTIME=1
+LOCK_SPINNING_RETRIES=5
+LOCK_RETRIES=100
+LOCK_BASEDIR=/var/run/xen-hotplug
+
+
+claim_lock()
+{
+  local lockdir="$LOCK_BASEDIR/$1"
+  mkdir -p "$LOCK_BASEDIR"
+  _claim_lock "$lockdir"
+}
+
+
+release_lock()
+{
+  _release_lock "$LOCK_BASEDIR/$1"
+}
+
+
+_claim_lock()
+{
+  local lockdir="$1"
+  local owner=$(_lock_owner "$lockdir")
+  local retries=0
+
+  while [ $retries -lt $LOCK_RETRIES ]
+  do
+    mkdir "$lockdir" 2>/dev/null && trap "release_lock $1; sigerr" ERR &&
+      _update_lock_info "$lockdir" && return
+
+    local new_owner=$(_lock_owner "$lockdir")
+    if [ "$new_owner" != "$owner" ]
+    then
+      owner="$new_owner"
+      retries=0
+    fi
+
+    if [ $retries -gt $LOCK_SPINNING_RETRIES ]
+    then
+      sleep $LOCK_SLEEPTIME
+    else
+      sleep 0
+    fi
+    retries=$(($retries + 1))
+  done
+  _steal_lock "$lockdir"
+}
+
+
+_release_lock()
+{
+  trap sigerr ERR
+  rm -rf "$1" 2>/dev/null || true
+}
+
+
+_steal_lock()
+{
+  local lockdir="$1"
+  local owner=$(cat "$lockdir/owner" 2>/dev/null || echo "unknown")
+  log err "Forced to steal lock on $lockdir from $owner!"
+  _release_lock "$lockdir"
+  _claim_lock "$lockdir"
+}
+
+
+_lock_owner()
+{
+  cat "$1/owner" 2>/dev/null || echo "unknown"
+}
+
+
+_update_lock_info()
+{
+  echo "$$: $0" >"$1/owner"
+}