使用libvirt技术监控虚拟机资源利用情况

（一）计算资源与内存资源的监控

libvirt中提供virDomainGetInfo方法可以将一个domain的计算资源和内存资源的使用情况封装在一个结构体中，如下：

struct virDomainInfo{
unsigned char state : //the running state, one of virDomainState
unsigned long maxMem :// the maximum memory in KBytes allowed
unsigned long memory :// the memory in KBytes used by the domain
unsigned short nrVirtCpu :// the number of virtual CPUs for the domain
unsigned long long cpuTime : //the CPU time used in nanoseconds
}

  

获取内存资源和计算资源监控信息并打印的方法如下：

virDomainInfoPtr domaininfo;
domaininfo = malloc(sizeof(virDomainInfo)* 1);
m = virDomainGetInfo(allDomains[numOfDom] , domaininfo);
printf("状态:%d    ",(*domaininfo).state);
printf("最大内存:%ld    ",((*domaininfo).maxMem)/1024);
printf("内存:%ld   ",((*domaininfo).memory)/1024);
printf("虚拟cpu个数:%d   ",(*domaininfo).nrVirtCpu);
printf("cpu时间:%lld   ",(*domaininfo).cpuTime);

  

libvirt中并不能直接获取到虚拟机的CPU使用率，但是可以通过CPUTIME来计算出实际使用率。计算的公式为：

首先得到一个周期差：cpu_time_diff = cpuTime_now — cpuTime_{t seconds ago}

然后根据这个差值计算实际使用率：%CPU = 100 × cpu_time_diff / (t × nr_cores × 10⁹)

 

cpuTime可以通过virDomainGetInfo(C)和virDomain::info()(Python)获得

#include <stdio.h>
#include <sys/time.h>
#include <libvirt/libvirt.h>
#include <libvirt/virterror.h>

int main(int argc, char ** argv) {
    virConnectPtr conn = virConnectOpen("qemu:///system");
    if(conn == NULL) {
        printf("error connecting qemu driver\n");
        exit(1);
    }
    virDomainPtr vm_ptr = virDomainLookupByName(conn, "1");
    if(vm_ptr == NULL) {
        printf("error finding domain\n");
        virConnectClose(conn);
        exit(1);
    }
    virDomainInfo info_s,info_e;
    struct timeval real_time_s, real_time_e;
    int cpu_diff, real_diff;
    float usage;
    while(true){
        if(virDomainGetInfo(vm_ptr, &info_s) !=0) {
            printf("error get domain info\n");
            virDomainFree(vm_ptr);
            virConnectClose(conn);
            exit(1);
        }

        if(gettimeofday(&real_time_s, NULL) == -1) {
            printf("error get time of day\n");
            virDomainFree(vm_ptr);
            virConnectClose(conn);
            exit(1);
        }

        sleep(1);
        
        if(virDomainGetInfo(vm_ptr, &info_e) !=0) {
            printf("error get domain info\n");
            virDomainFree(vm_ptr);
            virConnectClose(conn);
            exit(1);
        }

        if(gettimeofday(&real_time_e, NULL) == -1) {
            printf("error get time of day\n");
            virDomainFree(vm_ptr);
            virConnectClose(conn);
            exit(1);
        }//转换成微秒
        cpu_diff = (info_e.cpuTime - info_s.cpuTime) / 1000;
        //转换成微秒
        real_diff = 1000000 * (real_time_e.tv_sec - real_time_s.tv_sec) +
                    (real_time_e.tv_usec - real_time_s.tv_usec);
        //是否要考虑多核的情况？

        usage = cpu_diff / (float) (real_diff);
        printf("cpu_diff:%d, real_diff:%d, cpu usage:%f\n", cpu_diff, real_diff, usage);
    }
    virDomainFree(vm_ptr);
    virConnectClose(conn);
    return 0;

        
        

    

 

 

#include <stdio.h>
#include <sys/time.h>
#include <libvirt/libvirt.h>
#include <libvirt/virterror.h>

int main(int argc, char ** argv) {
    virConnectPtr conn = virConnectOpen("qemu:///system");
    if(conn == NULL) {
        printf("error connecting qemu driver\n");
        exit(1);
    }
    virDomainPtr vm_ptr = virDomainLookupByName(conn, "1");
    if(vm_ptr == NULL) {
        printf("error finding domain\n");
        virConnectClose(conn);
        exit(1);
    }

    virTypedParameter par_s, par_e;
    struct timeval real_time_s, real_time_e;

    int cpu_diff, real_diff;
    float usage;

    while(true){
        if(gettimeofday(&real_time_s, NULL) == -1) {
            printf("error get time of day\n");
            virDomainFree(vm_ptr);
            virConnectClose(conn);
            exit(1);
        }
        virDomainGetCPUStats(vm_ptr, &par_s, 1, -1, 1, 0);
        sleep(1);
        if(gettimeofday(&real_time_e, NULL) == -1) {
            printf("error get time of day\n");
            virDomainFree(vm_ptr);
            virConnectClose(conn);
            exit(1);
        virDomainGetCPUStats(vm_ptr, &par_e, 1, -1, 1, 0);
        cpu_diff = (par_e.value.ul - par_s.value.ul) / 1000;
        real_diff = 1000000 * (real_time_e.tv_sec - real_time_s.tv_sec) +
                    (real_time_e.tv_usec - real_time_s.tv_usec);
        usage = cpu_diff / (float)(real_diff);
        printf("cpu_diff:%d, real_diff:%d, cpu usage:%f\n", cpu_diff, real_diff, usage);

    }
    virDomainFree(vm_ptr);
    virConnectClose(conn);
    return 0;
}

这两个接口的结果差不多，利用率与top命令输出一致，但是与虚拟机内部使用率不一致。如将结果除以vcpu个数，则cpu利用率更接近虚拟机内部的虚拟机使用率。

 对于memory利用率，windows需要安装 virtio memory balloon drivers for Windows guests，这样 memory/MaxMemory就是正确的内存利用率。如果不安装，那么这个比例始终为1。

（二）获得网络流量信息

    可以使用 virDomainInterfaceStats方法，将一个domain的网络流量信息封装在一个virDomainInterfaceStatsStruct结构体中，该方法需要传递一个虚拟网卡接口的参数，这个参数可以通过XML文件取得：

<interface type='bridge'>
      <mac address='00:16:3e:74:03:53'/>
      <source bridge='xenbr0'/>
      <script path='vif-bridge'/>
      <target dev='vif1.0 '/>          /*这个就是需要的参数*/
    </interface>

具体代码如下：

virDomainInterfaceStatsPtr interfacestats;

interfacestats = malloc(sizeof(virDomainInterfaceStatsStruct)* 10);
m = virDomainInterfaceStats(allDomains[numOfDom], i_path, interfacestats, 10);
 printf("rx字节数:%ld    ",(*interfacestats).rx_bytes);
 printf("tx字节数:%ld    ",(*interfacestats).tx_bytes);
 printf("rx丢包:%ld    ",(*interfacestats).rx_drop);
 printf("tx丢包:%ld\n",(*interfacestats).tx_drop);