Initial implementation of the monitor modules and a simple mysql monitor to set

server up or down automatically.

Makefile

@@ -21,6 +21,7 @@
 # 					targets
 # 18/06/13	Mark Riddoch		Addition of install target
 # 21/06/13	Mark Riddoch		Addition of inih
+# 08/07/13	Mark Riddoch		Addition of monitor modules
 
 DEST=/usr/local/skysql
 
@@ -29,17 +30,20 @@ all:
 	(cd core; make)
 	(cd modules/routing; make)
 	(cd modules/protocol; make)
+	(cd modules/monitor; make)
 
 clean:
 	(cd Documentation; rm -rf html)
 	(cd core; make clean)
 	(cd modules/routing; make clean)
 	(cd modules/protocol; make clean)
+	(cd modules/monitor; make clean)
 
 depend:
 	(cd core; make depend)
 	(cd modules/routing; make depend)
 	(cd modules/protocol; make depend)
+	(cd modules/monitor; make depend)
 
 documentation:
 	doxygen doxygate
@@ -48,3 +52,4 @@ install:
 	(cd core; make DEST=$(DEST) install)
 	(cd modules/routing; make DEST=$(DEST) install)
 	(cd modules/protocol; make DEST=$(DEST) install)
+	(cd modules/moinitor; make DEST=$(DEST) install)

core/Makefile

@@ -55,7 +55,8 @@ LDFLAGS=-rdynamic -L$(LOGPATH) \
 
 SRCS= atomic.c buffer.c spinlock.c gateway.c gateway_mysql_protocol.c \
 	gw_utils.c utils.c dcb.c load_utils.c session.c service.c server.c \
-	poll.c config.c users.c hashtable.c dbusers.c thread.c gwbitmask.c
+	poll.c config.c users.c hashtable.c dbusers.c thread.c gwbitmask.c \
+	monitor.c
 
 HDRS= ../include/atomic.h ../include/buffer.h ../include/dcb.h \
 	../include/gateway_mysql.h ../include/gw.h ../include/mysql_protocol.h \

core/config.c

@@ -24,6 +24,7 @@
  *
  * Date		Who		Description
  * 21/06/13	Mark Riddoch	Initial implementation
+ * 08/07/13	mark Riddoch	Addition on monitor module support
  *
  * @endverbatim
  */
@@ -35,6 +36,7 @@
 #include <service.h>
 #include <server.h>
 #include <users.h>
+#include <monitor.h>
 
 static	int	process_config_context(CONFIG_CONTEXT	*);
 static	void	free_config_context(CONFIG_CONTEXT	*);
@@ -155,8 +157,12 @@ CONFIG_CONTEXT		*obj;
 			char *address = config_get_value(obj->parameters, "address");
 			char *port = config_get_value(obj->parameters, "port");
 			char *protocol = config_get_value(obj->parameters, "protocol");
+			char *monuser = config_get_value(obj->parameters, "monitoruser");
+			char *monpw = config_get_value(obj->parameters, "monitorpw");
 			if (address && port && protocol)
 				obj->element = server_alloc(address, protocol, atoi(port));
+			if (obj->element && monuser && monpw)
+				serverAddMonUser(obj->element, monuser, monpw);
 		}
 
 		obj = obj->next;
@@ -215,6 +221,30 @@ CONFIG_CONTEXT		*obj;
 					serviceAddProtocol(ptr->element, protocol, atoi(port));
 			}
 		}
+		else if (!strcmp(type, "monitor"))
+		{
+			char *module = config_get_value(obj->parameters, "module");
+			char *servers = config_get_value(obj->parameters, "servers");
+			if (module)
+			{
+				obj->element = monitor_alloc(obj->object, module);
+				if (servers && obj->element)
+				{
+					char *s = strtok(servers, ",");
+					while (s)
+					{
+						CONFIG_CONTEXT *obj1 = context;
+						while (obj1)
+						{
+							if (strcmp(s, obj1->object) == 0 && obj->element && obj1->element)
+								monitorAddServer(obj->element, obj1->element);
+							obj1 = obj1->next;
+						}
+						s = strtok(NULL, ",");
+					}
+				}
+			}
+		}
 
 		obj = obj->next;
 	}

core/monitor.c

@@ -0,0 +1,116 @@
+/*
+ * This file is distributed as part of the SkySQL Gateway.  It is free
+ * software: you can redistribute it and/or modify it under the terms of the
+ * GNU General Public License as published by the Free Software Foundation,
+ * version 2.
+ *
+ * This program 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 General Public License for more
+ * details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program; if not, write to the Free Software Foundation, Inc., 51
+ * Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Copyright SkySQL Ab 2013
+ */
+
+/**
+ * @file monitor.c  - The monitor module management routines
+ *
+ * @verbatim
+ * Revision History
+ *
+ * Date		Who		Description
+ * 08/07/13	Mark Riddoch	Initial implementation
+ *
+ * @endverbatim
+ */
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <monitor.h>
+#include <spinlock.h>
+#include <modules.h>
+
+
+static MONITOR	*allMonitors = NULL;
+static SPINLOCK	monLock = SPINLOCK_INIT;
+
+/**
+ * Allocate a new monitor, load the associated module for the monitor
+ * and start execution on the monitor.
+ *
+ * @param name	The name of the monitor module to load
+ * @return 	The newly created monitor
+ */
+MONITOR *
+monitor_alloc(char *name, char *module)
+{
+MONITOR	*mon;
+
+	if ((mon = (MONITOR *)malloc(sizeof(MONITOR))) == NULL)
+	{
+		return NULL;
+	}
+
+	mon->name = strdup(name);
+	mon->module = strdup(module);
+	if ((mon->module = load_module(module, MODULE_MONITOR)) == NULL)
+	{
+		fprintf(stderr, "Unable to load monitor module '%s'\n", name);
+		free(mon->name);
+		free(mon);
+		return NULL;
+	}
+	mon->handle = (*mon->module->startMonitor)();
+
+	spinlock_acquire(&monLock);
+	mon->next = allMonitors;
+	allMonitors = mon;
+	spinlock_release(&monLock);
+
+	return mon;
+}
+
+/**
+ * Free a monitor, first stop the monitor and then remove the monitor from
+ * the chain of monitors and free the memory.
+ *
+ * @param mon	The monitor to free
+ */
+void
+monitor_free(MONITOR *mon)
+{
+MONITOR	*ptr;
+
+	mon->module->stopMonitor(mon->handle);
+	spinlock_acquire(&monLock);
+	if (allMonitors == mon)
+		allMonitors = mon->next;
+	else
+	{
+		ptr = allMonitors;
+		while (ptr->next && ptr->next != mon)
+			ptr = ptr->next;
+		if (ptr->next)
+			ptr->next = mon->next;
+	}
+	spinlock_release(&monLock);
+	free(mon->name);
+	free(mon);
+}
+
+/**
+ * Add a server to a monitor. Simply register the server that needs to be
+ * monitored to the running monitor module.
+ *
+ * @param mon		The Monitor instance
+ * @param server	The Server to add to the monitoring
+ */
+void
+monitorAddServer(MONITOR *mon, SERVER *server)
+{
+	mon->module->registerServer(mon->handle, server);
+}

core/server.c

@@ -238,3 +238,18 @@ server_clear_status(SERVER *server, int bit)
 {
 	server->status &= ~bit;
 }
+
+/**
+ * Add a user name and password to use for monitoring the
+ * state of the server.
+ *
+ * @param server	The server to update
+ * @param user		The user name to use
+ * @param passwd	The password of the user
+ */
+void
+serverAddMonUser(SERVER *server, char *user, char *passwd)
+{
+	server->monuser = strdup(user);
+	server->monpw = strdup(passwd);
+}

core/thread.c

@@ -61,3 +61,18 @@ void	*rval;
 
 	pthread_join((pthread_t)thd, &rval);
 }
+
+/**
+ * Put the thread to sleep for a number of milliseconds
+ *
+ * @param ms	Number of milliseconds to sleep
+ */
+void
+thread_millisleep(int ms)
+{
+struct timespec req;
+
+	req.tv_sec = ms / 1000;
+	req.tv_nsec = (ms % 1000) * 1000000;
+	nanosleep(&req, NULL);
+}

gateway.cnf

@@ -18,18 +18,24 @@ type=server
 address=127.0.0.1
 port=3306
 protocol=MySQLBackend
+monitoruser=massi
+monitorpw=massi
 
 [server2]
 type=server
 address=127.0.0.1
 port=3307
 protocol=MySQLBackend
+monitoruser=massi
+monitorpw=massi
 
 [server3]
 type=server
 address=127.0.0.1
 port=3308
 protocol=MySQLBackend
+monitoruser=massi
+monitorpw=massi
 
 [Debug Service]
 type=service
@@ -46,3 +52,8 @@ type=listener
 service=Test Service
 protocol=MySQLClient
 port=4006
+
+[MySQL Monitor]
+type=monitor
+module=mysqlmon
+servers=server1,server2,server3

include/modules.h

@@ -29,6 +29,7 @@
  *
  * Date		Who		Description
  * 13/06/13	Mark Riddoch	Initial implementation
+ * 08/07/13	Mark Riddoch	Addition of monitor modules
  * @endverbatim
  */
 
@@ -47,6 +48,7 @@ typedef struct modules {
  */
 #define	MODULE_PROTOCOL	"Protocol"	/**< A protocol module type */
 #define	MODULE_ROUTER	"Router"	/**< A router module type */
+#define	MODULE_MONITOR	"Monitor"	/**< A database monitor module type */
 
 
 extern	void 	*load_module(const char *module, const char *type);

include/monitor.h

@@ -0,0 +1,79 @@
+#ifndef _MONITOR_H
+#define _MONITOR_H
+/*
+ * This file is distributed as part of the SkySQL Gateway.  It is free
+ * software: you can redistribute it and/or modify it under the terms of the
+ * GNU General Public License as published by the Free Software Foundation,
+ * version 2.
+ *
+ * This program 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 General Public License for more
+ * details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program; if not, write to the Free Software Foundation, Inc., 51
+ * Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Copyright SkySQL Ab 2013
+ */
+#include <server.h>
+
+/**
+ * @file monitor.h	The interface to the monitor module
+ *
+ * @verbatim
+ * Revision History
+ *
+ * Date		Who		Description
+ * 07/07/13	Mark Riddoch	Initial implementation
+ *
+ * @endverbatim
+ */
+
+/**
+ * The "Module Object" for a monitor module.
+ *
+ * The monitor modules are designed to monitor the backend databases that the gateway 
+ * connects to and provide information regarding the status of the databases that
+ * is used in the routing decisions.
+ *
+ * startMonitor is called to start the monitoring process, it is called on the main
+ * thread of the gateway and is responsible for creating a thread for the monitor
+ * itself to run on. This should use the entry points defined in the thread.h 
+ * header file rather than make direct calls to the operating system thrading libraries.
+ * The return from startMonitor is a void * handle that will be passed to all other monitor
+ * API calls.
+ *
+ * stopMonitor is responsible for shuting down and destroying a monitor, it is called 
+ * with the void * handle that was returned by startMonitor.
+ *
+ * registerServer is called to register a server that must be monitored with a running
+ * monitor. this will be called with the handle returned from the startMonitor call and
+ * the SERVER structure that the monitor must update and monitor. The SERVER structure
+ * contains the information required to connect to the monitored server.
+ *
+ * unregisterServer is called to remove a server from the set of servers that need to be
+ * monitored.
+ */
+typedef struct {
+	void 	*(*startMonitor)();
+	void	(*stopMonitor)(void *);
+	void	(*registerServer)(void *, SERVER *);
+	void	(*unregisterServer)(void *, SERVER *);
+} MONITOR_OBJECT;
+
+/**
+ * Representation of the running monitor.
+ */
+typedef struct monitor {
+	char		*name;		/**< The name of the monitor module */
+	MONITOR_OBJECT	*module;	/**< The "monitor object" */
+	void		*handle;	/**< Handle returned from startMonitor */
+	struct monitor	*next;		/**< Next monitor in the linked list */
+} MONITOR;
+
+extern MONITOR	*monitor_alloc(char *, char *);
+extern void	monitor_free(MONITOR *);
+extern void	monitorAddServer(MONITOR *, SERVER *);
+#endif

include/server.h

@@ -54,6 +54,8 @@ typedef struct server {
 	unsigned short	port;		/**< Port to listen on */
 	char		*protocol;	/**< Protocol module to use */
 	unsigned int	status;		/**< Status flag bitmap for the server */
+	char		*monuser;	/**< User name to use to monitor the db */
+	char		*monpw;		/**< Password to use to monitor the db */
 	SERVER_STATS	stats;		/**< The server statistics */
 	struct	server	*next;		/**< Next server */
 	struct	server	*nextdb;	/**< Next server in list attached to a service */
@@ -100,4 +102,5 @@ extern void	dprintServer(DCB *, SERVER *);
 extern char	*server_status(SERVER *);
 extern void	server_set_status(SERVER *, int);
 extern void	server_clear_status(SERVER *, int);
+extern void	serverAddMonUser(SERVER *, char *, char *);
 #endif

include/thread.h

@@ -33,5 +33,6 @@
 
 extern void 	*thread_start(void (*entry)(void *), void *arg);
 extern void	thread_wait(void *thd);
+extern void	thread_millisleep(int ms);
 
 #endif

modules/monitor/Makefile

@@ -0,0 +1,59 @@
+# This file is distributed as part of the SkySQL Gateway.  It is free
+# software: you can redistribute it and/or modify it under the terms of the
+# GNU General Public License as published by the Free Software Foundation,
+# version 2.
+#
+# This program 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 General Public License for more
+# details.
+#
+# You should have received a copy of the GNU General Public License along with
+# this program; if not, write to the Free Software Foundation, Inc., 51
+# Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+#
+# Copyright SkySQL Ab 2013
+#
+# Revision History
+# Date		Who			Description
+# 08/07/13	Mark Riddoch		Initial implementation
+
+include ../../../build_gateway.inc
+LOGPATH := $(ROOT_PATH)/log_manager
+UTILSPATH := $(ROOT_PATH)/utils
+
+CC=cc
+CFLAGS=-c -fPIC -I. -I/usr/include -I../include -I../../include -I$(LOGPATH) \
+	-I$(UTILSPATH) -I/usr/include/mysql -Wall -g
+LDFLAGS=-shared  -L$(LOGPATH) -Wl,-rpath,$(LOGPATH) -Wl,-rpath,$(UTILSPATH)
+MYSQLSRCS=mysql_mon.c
+MYSQLOBJ=$(MYSQLSRCS:.c=.o)
+SRCS=$(MYSQLSRCS)
+OBJ=$(SRCS:.c=.o)
+LIBS=$(UTILSPATH)/skygw_utils.o -llog_manager \
+	-L/packages/mariadb-5.5.25/libmysql -lmysqlclient
+MODULES=libmysqlmon.so
+
+
+all:	$(MODULES)
+
+libmysqlmon.so: $(MYSQLOBJ)
+	$(CC) $(LDFLAGS) $(MYSQLOBJ) $(LIBS) -o $@
+
+.c.o:
+	$(CC) $(CFLAGS) $< -o $@
+
+clean:
+	rm -f $(OBJ) $(MODULES)
+
+tags:
+	ctags $(SRCS) $(HDRS)
+
+depend:
+	@rm -f depend.mk
+	cc -M $(CFLAGS) $(SRCS) > depend.mk
+
+install: $(MODULES)
+	install -D $< $(DEST)/gateway/modules
+
+include depend.mk

modules/monitor/depend.mk

@@ -0,0 +1,16 @@
+mysql_mon.o: mysql_mon.c /usr/include/stdio.h /usr/include/features.h \
+ /usr/include/sys/cdefs.h /usr/include/bits/wordsize.h \
+ /usr/include/gnu/stubs.h /usr/include/gnu/stubs-64.h \
+ /usr/lib/gcc/x86_64-redhat-linux/4.4.6/include/stddef.h \
+ /usr/include/bits/types.h /usr/include/bits/typesizes.h \
+ /usr/include/libio.h /usr/include/_G_config.h /usr/include/wchar.h \
+ /usr/lib/gcc/x86_64-redhat-linux/4.4.6/include/stdarg.h \
+ /usr/include/bits/stdio_lim.h /usr/include/bits/sys_errlist.h \
+ ../../include/monitor.h mysqlmon.h ../../include/server.h \
+ ../../include/dcb.h ../../include/spinlock.h ../../include/thread.h \
+ /usr/include/pthread.h /usr/include/endian.h /usr/include/bits/endian.h \
+ /usr/include/bits/byteswap.h /usr/include/sched.h /usr/include/time.h \
+ /usr/include/bits/sched.h /usr/include/bits/time.h \
+ /usr/include/xlocale.h /usr/include/bits/pthreadtypes.h \
+ /usr/include/bits/setjmp.h ../../include/buffer.h \
+ ../../include/gwbitmask.h

modules/monitor/mysql_mon.c

@@ -0,0 +1,223 @@
+/*
+ * This file is distributed as part of the SkySQL Gateway.  It is free
+ * software: you can redistribute it and/or modify it under the terms of the
+ * GNU General Public License as published by the Free Software Foundation,
+ * version 2.
+ *
+ * This program 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 General Public License for more
+ * details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program; if not, write to the Free Software Foundation, Inc., 51
+ * Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Copyright SkySQL Ab 2013
+ */
+#include <stdio.h>
+#include <stdlib.h>
+#include <monitor.h>
+#include <mysqlmon.h>
+#include <thread.h>
+
+static	void	monitorMain(void *);
+
+static char *version_str = "V1.0.0";
+
+static	void 	*startMonitor();
+static	void	stopMonitor(void *);
+static	void	registerServer(void *, SERVER *);
+static	void	unregisterServer(void *, SERVER *);
+
+static MONITOR_OBJECT MyObject = { startMonitor, stopMonitor, registerServer, unregisterServer };
+
+/**
+ * Implementation of the mandatory version entry point
+ *
+ * @return version string of the module
+ */
+char *
+version()
+{
+	return version_str;
+}
+
+/**
+ * The module initialisation routine, called when the module
+ * is first loaded.
+ */
+void
+ModuleInit()
+{
+	fprintf(stderr, "Initialise the MySQL Monitor module.\n");
+}
+
+/**
+ * The module entry point routine. It is this routine that
+ * must populate the structure that is referred to as the
+ * "module object", this is a structure with the set of
+ * external entry points for this module.
+ *
+ * @return The module object
+ */
+MONITOR_OBJECT *
+GetModuleObject()
+{
+	return &MyObject;
+}
+
+/**
+ * Start the instance of the monitor, returning a handle on the monitor.
+ *
+ * This function creates a thread to execute the actual monitoring.
+ *
+ * @return A handle to use when interacting with the monitor
+ */
+static	void 	*
+startMonitor()
+{
+MYSQL_MONITOR *handle;
+
+	if ((handle = (MYSQL_MONITOR *)malloc(sizeof(MYSQL_MONITOR))) == NULL)
+		return NULL;
+	handle->databases = NULL;
+	handle->shutdown = 0;
+	spinlock_init(&handle->lock);
+	thread_start(monitorMain, handle);
+	return handle;
+}
+
+/**
+ * Stop a running monitor
+ *
+ * @param handle	Handle on thr running monior
+ */
+static	void	
+stopMonitor(void *arg)
+{
+MYSQL_MONITOR	*handle = (MYSQL_MONITOR *)arg;
+
+	handle->shutdown = 1;
+}
+
+/**
+ * Register a server that must be added to the monitored servers for
+ * a monitoring module.
+ *
+ * @param handle	A handle on the running monitor module
+ * @param server	The server to add
+ */
+static	void	
+registerServer(void *arg, SERVER *server)
+{
+MYSQL_MONITOR	*handle = (MYSQL_MONITOR *)arg;
+MONITOR_SERVERS	*ptr, *db;
+
+	if ((db = (MONITOR_SERVERS *)malloc(sizeof(MONITOR_SERVERS))) == NULL)
+		return;
+	db->server = server;
+	db->con = NULL;
+	db->next = NULL;
+	spinlock_acquire(&handle->lock);
+	if (handle->databases == NULL)
+		handle->databases = db;
+	else
+	{
+		ptr = handle->databases;
+		while (ptr->next != NULL)
+			ptr = ptr->next;
+		ptr->next = db;
+	}
+	spinlock_release(&handle->lock);
+}
+
+/**
+ * Remove a server from those being monitored by a monitoring module
+ *
+ * @param handle	A handle on the running monitor module
+ * @param server	The server to remove
+ */
+static	void	
+unregisterServer(void *arg, SERVER *server)
+{
+MYSQL_MONITOR	*handle = (MYSQL_MONITOR *)arg;
+MONITOR_SERVERS	*ptr, *lptr;
+
+	spinlock_acquire(&handle->lock);
+	if (handle->databases == NULL)
+	{
+		spinlock_release(&handle->lock);
+		return;
+	}
+	if (handle->databases->server == server)
+	{
+		ptr = handle->databases;
+		handle->databases = handle->databases->next;
+		free(ptr);
+	}
+	else
+	{
+		ptr = handle->databases;
+		while (ptr->next != NULL && ptr->next->server != server)
+			ptr = ptr->next;
+		if (ptr->next)
+		{
+			lptr = ptr->next;
+			ptr->next = ptr->next->next;
+			free(lptr);
+		}
+	}
+	spinlock_release(&handle->lock);
+}
+
+/**
+ * Monitor an individual server
+ *
+ * @param database	The database to probe
+ */
+static void
+monitorDatabase(MONITOR_SERVERS	*database)
+{
+	if (database->con == NULL || mysql_ping(database->con) != 0)
+	{
+		database->con = mysql_init(NULL);
+		if (mysql_real_connect(database->con, database->server->name,
+			database->server->monuser, database->server->monpw,
+				NULL, database->server->port, NULL, 0) == NULL)
+		{
+			server_clear_status(database->server, SERVER_RUNNING);
+			return;
+		}
+	}
+
+	// If we get this far then we have a workign connection
+	server_set_status(database->server, SERVER_RUNNING);
+	
+}
+
+/**
+ * The entry point for the monitoring module thread
+ *
+ * @param arg	The handle of the monitor
+ */
+static void
+monitorMain(void *arg)
+{
+MYSQL_MONITOR	*handle = (MYSQL_MONITOR *)arg;
+MONITOR_SERVERS	*ptr;
+
+	while (1)
+	{
+		thread_millisleep(1000);
+
+		if (handle->shutdown)
+			return;
+		ptr = handle->databases;
+		while (ptr)
+		{
+			monitorDatabase(ptr);
+			ptr = ptr->next;
+		}
+	}
+}

modules/monitor/mysqlmon.h

@@ -0,0 +1,55 @@
+#ifndef _MYSQLMON_H
+#define _MYSQLMON_H
+/*
+ * This file is distributed as part of the SkySQL Gateway.  It is free
+ * software: you can redistribute it and/or modify it under the terms of the
+ * GNU General Public License as published by the Free Software Foundation,
+ * version 2.
+ *
+ * This program 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 General Public License for more
+ * details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program; if not, write to the Free Software Foundation, Inc., 51
+ * Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Copyright SkySQL Ab 2013
+ */
+#include	<server.h>
+#include	<spinlock.h>
+#include	<mysql.h>
+
+/**
+ * @file mysqlmon.h - The MySQL monitor functionality within the gateway
+ *
+ * @verbatim
+ * Revision History
+ *
+ * Date		Who		Description
+ * 08/07/13	Mark Riddoch	Initial implementation
+ *
+ * @endverbatim
+ */
+
+/**
+ * The linked list of servers that are being monitored by the MySQL 
+ * Monitor module.
+ */
+typedef struct monitor_servers {
+	SERVER		*server;	/**< The server being monitored */
+	MYSQL		*con;		/**< The MySQL connection */
+	struct monitor_servers
+			*next;		/**< The next server in the list */
+} MONITOR_SERVERS;
+
+/**
+ * The handle for an instance of a MySQL Monitor module
+ */
+typedef struct {
+	SPINLOCK	lock;		/**< The monitor spinlock */
+	int		shutdown;	/**< Flag to shutdown the monitor thread */
+	MONITOR_SERVERS	*databases;	/**< Linked list of servers to monitor */
+} MYSQL_MONITOR;
+#endif