instance-name.monitor的用途
首先我们注意到openstack中创建的每台KVM虚拟机，都会在/var/lib/libvirt/qemu/目录下生成一个instance-name.monitor socket文件
这个文件的用途是什么？
libvirt.xml里面以及用virsh dumpxml命令都看不到这个文件的配置，它是怎么创建出来的？
wangpan@xx–yy–zz–8:~$ sudo ls /var/lib/libvirt/qemu/ –l
srwxr–xr–x 1 libvirt–qemu kvm 0 Aug 30 2012 instance–000000a4.monitor
srwxr–xr–x 1 libvirt–qemu kvm 0 Sep 17 2012 instance–000001ec.monitor
srwxr–xr–x 1 libvirt–qemu kvm 0 Oct 9 2012 instance–00000217.monitor
用途：用来查看qemu运行状态以及与qemu进行交互，管理虚拟机，提供类似qemu命令行方式启动虚拟机的与虚拟机的交互操作
怎么创建的：可以查看libvirt的运行时配置文件/var/run/libvirt/qemu/instance-name.xml，打开可以看到如下内容：
<monitor path=’/var/lib/libvirt/qemu/instance-00000611.monitor’ json=’1′ type=’unix’/>
但是我们在openstack生成的libvirt.xml中又看不到这项配置，那它到底是怎么生成的？
普通列表项目看了libvirt的源码，在创建虚拟机的qemuProcessstart()的时候会先准备qemu监控字符设备‘MonitorChr’：
VIR_DEBUG(“Preparing monitor state”);
if (qemuProcessPrepareMonitorChr(driver, priv->monConfig, vm->def->name) < 0)
goto cleanup;
这里就会增加monitor字符设备，类型为unix domain socket，文件路径为libvirt libdir+vm-name+.monitor，具体代码如下：
int
qemuProcessPrepareMonitorChr(struct qemud_driver *driver,
virDomainChrSourceDefPtr monConfig,
const char *vm)
{
monConfig->type = VIR_DOMAIN_CHR_TYPE_UNIX;
monConfig->data.nix.listen = true;
if (virAsprintf(&monConfig->data.nix.path, “%s/%s.monitor”,
driver->libDir, vm) < 0) {
virReportOOMError();
return –1;
}
return 0;
}
最后libvirt生成qemu命令行参数的时候会把这个配置加进去：
VIR_DEBUG(“Building emulator command line”);
if (!(cmd = qemuBuildCommandLine(conn, driver, vm->def, priv->monConfig,
priv->monJSON != 0, priv->qemuCaps,
migrateFrom, stdin_fd, snapshot, vmop)))
goto cleanup;
qemuBuildCommandLine():
……
if (monitor_chr) { /*monitor_chr就是priv->monConfig，所以这里走if分支*/
char *chrdev;
/* Use -chardev if it’s available */
if (qemuCapsGet(qemuCaps, QEMU_CAPS_CHARDEV)) {
virCommandAddArg(cmd, “-chardev”);
if (!(chrdev = qemuBuildChrChardevStr(monitor_chr, “monitor”,
qemuCaps)))
goto error;
virCommandAddArg(cmd, chrdev);
VIR_FREE(chrdev);
virCommandAddArg(cmd, “-mon”);
virCommandAddArgFormat(cmd,
“chardev=charmonitor,id=monitor,mode=%s”,
monitor_json ? “control” : “readline”);
} else {
const char *prefix = NULL;
if (monitor_json)
prefix = “control,”;
virCommandAddArg(cmd, “-monitor”);
if (!(chrdev = qemuBuildChrArgStr(monitor_chr, prefix)))
goto error;
virCommandAddArg(cmd, chrdev);
VIR_FREE(chrdev);
}
}
最终生成的qemu命令行信息为：
-chardev socket,id=charmonitor,path=/var/lib/libvirt/qemu/instance-00000611.monitor,server,nowait -mon chardev=charmonitor,id=monitor,mode=control
使用qemu-monitor-command查询、管理虚拟机
libvirt提供了qemu-monitor-command命令行及API，下面以命令行方式为例进行介绍：
$ sudo virsh help qemu–monitor–command
NAME
qemu–monitor–command – QEMU Monitor Command
SYNOPSIS
qemu–monitor–command <domain> [–hmp] {[–cmd] <string>}…
DESCRIPTION
QEMU Monitor Command
OPTIONS
[–domain] <string> domain name, id or uuid
—hmp command is in human monitor protocol
[–cmd] <string> command
$ sudo virsh qemu–monitor–command ${instance–name} —hmp ‘info commands’
info balloon — show balloon information
info block — show the block devices
info block–jobs — show progress of ongoing block device operations
info blockstats — show block device statistics
info capture — show capture information
info chardev — show the character devices
info cpus — show infos for each CPU
info history — show the command line history
info irq — show the interrupts statistics (if available)
info jit — show dynamic compiler info
info kvm — show KVM information
info mem — show the active virtual memory mappings
info mice — show which guest mouse is receiving events
info migrate — show migration status
info mtree — show memory tree
info name — show the current VM name
info network — show the network state
info numa — show NUMA information
info pci — show PCI info
info pcmcia — show guest PCMCIA status
info pic — show i8259 (PIC) state
info profile — show profiling information
info qdm — show qdev device model list
info qtree — show device tree
info registers — show the cpu registers
info roms — show roms
info snapshots — show the currently saved VM snapshots
info spice — show the spice server status
info status — show the current VM status (running|paused)
info tlb — show virtual to physical memory mappings
info trace–events — show available trace–events & their state
info usb — show guest USB devices
info usbhost — show host USB devices
info usernet — show user network stack connection states
info uuid — show the current VM UUID
info version — show the version of QEMU
info vnc — show the vnc server status
$ sudo virsh qemu–monitor–command instance–00000611 —hmp ‘info vnc’
Server:
address: 114.113.199.8:5900
auth: none
Client: none
还有一些其他的管理类的操作，这里不一一列举，可参考：
另外在openstack Folsom版本中没有看到有用到这个monitor，没有看到这个Libvirt API被调用，不知道后续会不会有用处？个人感觉应该不会用到，因为这个monitor是libvirt自己生成的，跟openstack其实没有关系。
