add a web-based Ip Allocator:

In external-ip mode, management server can get user VM's ip from
direct.attach.network.externalIpAllocator.url.
This simple tool provides such kind of ip allocator service.

How to:
1. setup the dnsmasq:
	add the following in dnsmasq.conf:
		dhcp-range=starting-ip-allocate-to-vm,end-ip,netmask,static
    		dhcp-option=option:router,gateway
2. run cloud-web-ipallocator,
	The default listing port is 8080, if it's used by others, change the port by:
		cloud-web-ipallocator other-port
3. set the following in direct.attach.network.externalIpAllocator.url:
	http://your-host-ip:listening-port/ipallocator

python/bindir/cloud-web-ipallocator.in

@@ -0,0 +1,136 @@
+#! /usr/bin/python
+import web
+import socket, struct
+import cloud_utils
+from cloud_utils import Command
+urls = ("/ipallocator", "ipallocator")
+app = web.application(urls, globals())
+
+augtool = Command("augtool")
+service = Command("service")
+class dhcp:
+	_instance = None
+	def __init__(self):
+		self.availIP=[]
+		self.router=None
+		self.netmask=None
+		self.initialized=False
+
+		options = augtool.match("/files/etc/dnsmasq.conf/dhcp-option").stdout.strip()
+		for option in options.splitlines():
+			if option.find("option:router") != -1:
+				self.router = option.split("=")[1].strip().split(",")[1]
+				print self.router
+
+		dhcp_range = augtool.get("/files/etc/dnsmasq.conf/dhcp-range").stdout.strip()
+		dhcp_start = dhcp_range.split("=")[1].strip().split(",")[0]
+		dhcp_end = dhcp_range.split("=")[1].strip().split(",")[1]
+		self.netmask = dhcp_range.split("=")[1].strip().split(",")[2]
+		print dhcp_start, dhcp_end, self.netmask
+
+ 		start_ip_num = self.ipToNum(dhcp_start);
+		end_ip_num =  self.ipToNum(dhcp_end)
+		print start_ip_num, end_ip_num
+	
+		for ip in range(start_ip_num, end_ip_num + 1):
+			self.availIP.append(ip)	
+		print self.availIP[0], self.availIP[len(self.availIP) - 1]	
+		
+		#load the ip already allocated
+		self.reloadAllocatedIP()
+
+	def ipToNum(self, ip):
+		return struct.unpack("!I", socket.inet_aton(ip))[0]
+
+	def numToIp(self, num):
+		return socket.inet_ntoa(struct.pack('!I', num))
+
+	def getFreeIP(self):
+		if len(self.availIP) > 0:
+			ip = self.numToIp(self.availIP[0])
+			self.availIP.remove(self.availIP[0])	
+			return ip
+		else:
+			return None
+
+	def getNetmask(self):
+		return self.netmask
+
+	def getRouter(self):
+		return self.router
+
+	def getInstance():
+		if not dhcp._instance:
+			dhcp._instance = dhcp()
+		return dhcp._instance
+	getInstance = staticmethod(getInstance)
+
+	def reloadAllocatedIP(self):
+		dhcp_hosts = augtool.match("/files/etc/dnsmasq.conf/dhcp-host").stdout.strip().splitlines()
+		
+		for host in dhcp_hosts:
+			if host.find("dhcp-host") != -1:
+				allocatedIP = self.ipToNum(host.split("=")[1].strip().split(",")[1])
+				if allocatedIP in self.availIP:	
+					self.availIP.remove(allocatedIP)
+		
+	def allocateIP(self, mac):
+		newIP = self.getFreeIP()
+		dhcp_host = augtool.match("/files/etc/dnsmasq.conf/dhcp-host").stdout.strip()
+		cnt = len(dhcp_host.splitlines()) + 1
+		script = """set %s %s
+			    save"""%("/files/etc/dnsmasq.conf/dhcp-host[" + str(cnt) + "]", str(mac) + "," + newIP)
+		augtool < script
+		#reset dnsmasq
+		service("dnsmasq", "restart", stdout=None, stderr=None)
+		return newIP
+
+	def releaseIP(self, ip):
+		dhcp_host = augtool.match("/files/etc/dnsmasq.conf/dhcp-host").stdout.strip()
+		path = None
+		for host in dhcp_host.splitlines():
+			if host.find(ip) != -1:
+				path = host.split("=")[0].strip()
+				
+		if path == None:
+			print "Can't find " + str(ip) + " in conf file"
+			return None
+
+		print path
+		script = """rm %s
+			    save"""%(path)
+		augtool < script
+		
+		#reset dnsmasq
+		service("dnsmasq", "restart", stdout=None, stderr=None)
+
+class ipallocator:
+	def GET(self):
+		try:
+			user_data = web.input()
+			command = user_data.command
+			print "Processing: " + command
+
+			dhcpInit = dhcp.getInstance()
+
+			if command == "getIpAddr":
+				mac = user_data.mac
+				zone_id = user_data.dc
+				pod_id = user_data.pod
+				print mac, zone_id, pod_id
+				freeIP = dhcpInit.allocateIP(mac)
+				if not freeIP:
+					return "0,0,0"
+				print "Find an available IP: " + freeIP
+		
+				return freeIP + "," + dhcpInit.getNetmask() + "," + dhcpInit.getRouter()
+			elif command == "releaseIpAddr":
+				ip = user_data.ip
+				zone_id = user_data.dc
+				pod_id = user_data.pod
+				dhcpInit.releaseIP(ip)
+		except:
+			return None
+
+if __name__ == "__main__":
+	app.run()