一些需要掌握的WMI类

原网页地址：http://www.codeproject.com/KB/server-management/Intro2WMI2.aspx

Msvm_ComputerSystem

是我们需要掌握的第一个类，这个类代表主机或者虚拟机系统。下面显示了这个类的属性以及方法RequestStateChange 这个方法对管理vm的多种状态非常有用。下面是这个类的定义，它与传统的类的定义方式不同， 因为它采用的是MOF（Managed Object Format）.

[Dynamic,
Provider
("VmmsWmiInstanceAndMethodProvider")]class Msvm_ComputerSystem : CIM_ComputerSystem
{
  string   Caption;
  string   Description;
  string   ElementName;
  datetime InstallDate;
  uint16   OperationalStatus[];
  string   StatusDescriptions[];
  string   Status;
  uint16   HealthState = 5;
  uint16   EnabledState;
  string   OtherEnabledState;
  uint16   RequestedState;
  uint16   EnabledDefault = 2;
  datetime TimeOfLastStateChange;
  string   CreationClassName;
  string   Name = "GUID";
  string   PrimaryOwnerName;
  string   PrimaryOwnerContact;
  string   Roles[];
  string   NameFormat;
  string   OtherIdentifyingInfo[];
  string   IdentifyingDescriptions[];
  uint16   Dedicated[];
  string   OtherDedicatedDescriptions[];
  uint16   ResetCapability = 1;
  uint16   PowerManagementCapabilities[];
  uint64   OnTimeInMilliseconds;
  datetime TimeOfLastConfigurationChange;
  uint32   ProcessID;
  uint16   AssignedNumaNodeList[];
};

 

现在，让我们获取一个Msvm_ComputerSystem类的对象，以便于我们能够执行方法RequestStateChange去改变vm的状态。首先让我们来定义一个 帮助程序，这个帮助程序会查询包含这个类的所有的属性和方法的命名空间，这个程序最终会返回一个ManagementObject对象，这个对象可以用来执行改变vm状态的方法。下面是Utility sample里的代码（默认之前已经定义了ManagementScope，此处省去了）：

public static ManagementObject GetTargetComputer
(string vmElementName, ManagementScope scope)
{
    string query = string.Format("select * from
    Msvm_ComputerSystem Where ElementName = '{0}'", vmElementName);

    ManagementObjectSearcher searcher = new
      ManagementObjectSearcher(scope, new ObjectQuery(query));

    ManagementObjectCollection computers = searcher.Get();

    ManagementObject computer = null;

    foreach (ManagementObject instance in computers)
    {
      computer = instance;
      break;
    }
return computer;
}

 

根据上面的方法，我们可以在程序里编写如下代码调用上面的方法获取Msvm_ComputerSystem 的一个实例：

ManagementObject vm = Utility.GetTargetComputer(vmName, scope);

vm就是我们获取到的Msvm_ComputerSystem实例，然后我们可以调用Msvm_ComputerSystem里的方法“RequestStateChange”，调用WMI类的方法需要用到GetMethodParameters，规则如下：

ManagementBaseObject inParams = vm.GetMethodParameters("RequestStateChange");

输入该方法需要的参数

inParams["RequestedState"] = Enabled;
ManagementBaseObject outParams =
vm.InvokeMethod("RequestStateChange", inParams, null);

if ((UInt32)outParams["ReturnValue"] == ReturnCode.Completed)
   {
     Console.WriteLine("{0} state was
           changed successfully.", vmName);
    }
    else
    {
      Console.WriteLine("Change virtual system
      state failed with error{0}", outParams["ReturnValue"]);
    }

}

 

至此我们已经成功改变了vm的状态，但是有一些问题需要注意，上面的例子里将vm的状态改为Enalbled，但是在这之前并没有检查当前vm是否就是这个状态。要在修改状态前检查vm状态，我们可以参考之前写的一边文章。

除此之外，我们还注意到InvokeMethod不能立即返回成功与否的状态。当vm正在启动的时候（starting），它不能返回已启动状态（started），所以我们应该做个方法等待状态修改完成并报告这个最终执行情况。我们在Utility里定义了一个JobCompleted（）方法，来跟踪InvokeMethod方法。

 

if ((UInt32)outParams["ReturnValue"]
          == ReturnCode.Started)
    {
     if (Utility.JobCompleted(outParams, scope))
      {
        Console.WriteLine("{0} state was changed
        successfully.",   vmName);
      }
      else
      {
        Console.WriteLine("Failed to change
            virtual system state");
      }
     }
    else if ((UInt32)outParams["ReturnValue"]
           == ReturnCode.Completed)
     {
        Console.WriteLine("{0} state was
            changed successfully.", vmName);
     }
     else
     {
      Console.WriteLine("Change virtual
        system state failed with error {0}",
        outParams ["ReturnValue"]);
     }

 

 

JobCompleted方法描述如下：

//This code demonstrates how the VM state change can be tracked

public static bool JobCompleted(ManagementBaseObject outParams,
                                ManagementScope scope)
{
    bool jobCompleted = true;

    //Retrieve msvc_StorageJob path. This is a full wmi path
    string JobPath = (string)outParams["Job"];
    ManagementObject Job = new ManagementObject(scope,
    new ManagementPath(JobPath), null);

    //Try to get storage job information
    Job.Get();
    while ((UInt16)Job["JobState"] == JobState.Starting
        || (UInt16)Job["JobState"] == JobState.Running)
    {
        Console.WriteLine("In progress... {0}% completed.",
            Job["PercentComplete"]);
        System.Threading.Thread.Sleep(1000);
        Job.Get();
    }

    //Figure out if job failed
    UInt16 jobState = (UInt16)Job["JobState"];
    if (jobState != JobState.Completed)
    {
        UInt16 jobErrorCode = (UInt16)Job["ErrorCode"];
        Console.WriteLine("Error Code:{0}", jobErrorCode);
        Console.WriteLine("ErrorDescription: {0}",
         (string)Job["ErrorDescription"]);
        jobCompleted = false;
    }
    return jobCompleted;
}