+/*
+ * Any arbitrary string used as a key for locking the database.
+ * It doesn't matter what it is as long as all pppds use the same string.
+ */
+#define PPPD_LOCK_KEY "pppd lock"
+
+/*
+ * lock_db - get an exclusive lock on the TDB database.
+ * Used to ensure atomicity of various lookup/modify operations.
+ */
+void lock_db()
+{
+#ifdef USE_TDB
+ TDB_DATA key;
+
+ key.dptr = PPPD_LOCK_KEY;
+ key.dsize = strlen(key.dptr);
+ tdb_chainlock(pppdb, key);
+#endif
+}
+
+/*
+ * unlock_db - remove the exclusive lock obtained by lock_db.
+ */
+void unlock_db()
+{
+#ifdef USE_TDB
+ TDB_DATA key;
+
+ key.dptr = PPPD_LOCK_KEY;
+ key.dsize = strlen(key.dptr);
+ tdb_chainunlock(pppdb, key);
+#endif
+}
+