因為公司需要做這方面的介面所以自己在網上查了好久才發現方法做了出來，其中遇到了不少的坑寫一下以便以後再次遇到。

1、首先在xenAPI給的一些介面中雖然有關於這方面的介面但是現在的版本不能直接得到，如果直接呼叫VM_guest_metrics中的方法返回的資料是空的。

3、說一下獲得的過程：

大致分三步 1、首先登陸要獲取的伺服器 2、得到RRD中的資料 3、解析資料

剛開始遇到最大的坑 就是登入認證不通過 原因在獲取登入伺服器 session_id是用session.handle處理一下就OK了基本上就沒什麼問題了。 

python的參考程式碼

#!/usr/bin/python
# Example code for reading RRDs
# Contact: Jon Ludlam (
 
[email protected])
#
# Mostly this script is taken from perfmon, by Alex Zeffert
#
import XenAPI
import urllib
from xml.dom import minidom
from xml.parsers.expat import ExpatError
import time
# Per VM dictionary (used by RRDUpdates to look up column numbers by variable names)
class VMReport(dict):
    """Used internally by RRDUpdates"""
    def __init__(self, uuid):
        self.uuid = uuid
# Per Host dictionary (used by RRDUpdates to look up column numbers by variable names)
class HostReport(dict):
    """Used internally by RRDUpdates"""
    def __init__(self, uuid):
        self.uuid = uuid
class RRDUpdates:
    """ Object used to get and parse the output the http://localhost/rrd_udpates?...
    """
    def __init__(self):
        # params are what get passed to the CGI executable in the URL
        self.params = dict()
        self.params['start'] = int(time.time()) - 1000 # For demo purposes!#開始獲取資料的時間
        self.params['host'] = 'true'   # include data for host (as well as for VMs)
        self.params['cf'] = 'AVERAGE'  # consolidation function, each sample averages 12 from the 5 second RRD #可以獲取max average min 型別的資料
        self.params['interval'] = '60'#獲取資料的間隔
    def get_nrows(self):
        return self.rows
    def get_vm_list(self):
        return self.vm_reports.keys()
    def get_vm_param_list(self, uuid):
        report = self.vm_reports[uuid]
        if not report:
            return []
        return report.keys()
    def get_vm_data(self, uuid, param, row):
        report = self.vm_reports[uuid]
        col = report[param]
        return self.__lookup_data(col, row)
    def get_host_uuid(self):
        report = self.host_report
        if not report:
            return None
        return report.uuid
    def get_host_param_list(self):
        report = self.host_report
        if not report:
            return []
        return report.keys()
    def get_host_data(self, param, row):
        report = self.host_report
        col = report[param]
        return self.__lookup_data(col, row)
    def get_row_time(self,row):
        return self.__lookup_timestamp(row)
    # extract float from value (<v>) node by col,row
    def __lookup_data(self, col, row):
        # Note: the <rows> nodes are in reverse chronological order, and comprise
        # a timestamp <t> node, followed by self.columns data <v> nodes
        node = self.data_node.childNodes[self.rows - 1 - row].childNodes[col+1]
        return float(node.firstChild.toxml()) # node.firstChild should have nodeType TEXT_NODE
    # extract int from value (<t>) node by row
    def __lookup_timestamp(self, row):
        # Note: the <rows> nodes are in reverse chronological order, and comprise
        # a timestamp <t> node, followed by self.columns data <v> nodes
        node = self.data_node.childNodes[self.rows - 1 - row].childNodes[0]
        return int(node.firstChild.toxml()) # node.firstChild should have nodeType TEXT_NODE
    def refresh(self, session, override_params = {}):
        params = override_params
        params['session_id'] = session
        params.update(self.params)
        paramstr = "&".join(["%s=%s"  % (k,params[k]) for k in params])
        # this is better than urllib.urlopen() as it raises an Exception on http 401 'Unauthorised' error
        # rather than drop into interactive mode
        sock = urllib.URLopener().open("http://localhost/rrd_updates?%s" % paramstr)
        xmlsource = sock.read()
        sock.close()
        xmldoc = minidom.parseString(xmlsource)
        self.__parse_xmldoc(xmldoc)
        # Update the time used on the next run
        self.params['start'] = self.end_time + 1 # avoid retrieving same data twice
    def __parse_xmldoc(self, xmldoc):
        # The 1st node contains meta data (description of the data)
        # The 2nd node contains the data
        self.meta_node = xmldoc.firstChild.childNodes[0]
        self.data_node = xmldoc.firstChild.childNodes[1]
        def lookup_metadata_bytag(name):
            return int (self.meta_node.getElementsByTagName(name)[0].firstChild.toxml())
        # rows = number of samples per variable
        # columns = number of variables
        self.rows = lookup_metadata_bytag('rows')
        self.columns = lookup_metadata_bytag('columns')
        # These indicate the period covered by the data
        self.start_time = lookup_metadata_bytag('start')
        self.step_time  = lookup_metadata_bytag('step')
        self.end_time   = lookup_metadata_bytag('end')
        # the <legend> Node describes the variables
        self.legend = self.meta_node.getElementsByTagName('legend')[0]
        # vm_reports matches uuid to per VM report
        self.vm_reports = {}
        # There is just one host_report and its uuid should not change!
        self.host_report = None
        # Handle each column.  (I.e. each variable)
        for col in range(self.columns):
            self.__handle_col(col)
    def __handle_col(self, col):
        # work out how to interpret col from the legend
        col_meta_data = self.legend.childNodes[col].firstChild.toxml()
        # vm_or_host will be 'vm' or 'host'.  Note that the Control domain counts as a VM!
        (cf, vm_or_host, uuid, param) = col_meta_data.split(':')
        if vm_or_host == 'vm':
            # Create a report for this VM if it doesn't exist
            if not self.vm_reports.has_key(uuid):
                self.vm_reports[uuid] = VMReport(uuid)
            # Update the VMReport with the col data and meta data
            vm_report = self.vm_reports[uuid]
            vm_report[param] = col
        elif vm_or_host == 'host':
            # Create a report for the host if it doesn't exist
            if not self.host_report:
                self.host_report = HostReport(uuid)
            elif self.host_report.uuid != uuid:
                raise PerfMonException, "Host UUID changed: (was %s, is %s)" % (self.host_report.uuid, uuid)
            # Update the HostReport with the col data and meta data
            self.host_report[param] = col
        else:
            raise PerfMonException, "Invalid string in <legend>: %s" % col_meta_data
def main():
    xapi = XenAPI.xapi_local();
    xapi.login_with_password("","")
    session=xapi._session
    rrd_updates = RRDUpdates()
    rrd_updates.refresh(session,{})
    for uuid in rrd_updates.get_vm_list():
        print "Got values for VM: "+uuid
        for param in rrd_updates.get_vm_param_list(uuid):
            print "param: "+param
            data=""
            for row in range(rrd_updates.get_nrows()):
                data=data+"(%d,%f) " % (rrd_updates.get_row_time(row),
                                        rrd_updates.get_vm_data(uuid,param,row))
            print data
main()