在我的KVM书中，关于QEMU监控器（monitor）的使用还是讲了不少东西的，不过，翻看以前收藏的一篇文章，发现其中提到的通过网络访问QEMU monitor的方法是没有在书中提及的。所以，在这里简单介绍一下吧，也是给自己留个记忆。（如果–仅仅是如果，有再版的话，可以考虑加上一两页来讲个东东。）
1. QEMU monitor支持远程telnet访问：
[root@kvm-host ~]# qemu-system-x86_64 -enable-kvm -smp 2 -m 1024 vm2.img -monitor telnet:10.1.77.82:4444,server,nowait
关于这里-monitor的选项，做如下说明：
tcp – raw tcp sockets #下面第2点，我的举例是RAW TCP socket telnet – the telnet protocol is used instead of raw tcp sockets. This is the preferred option over tcp as you can break out of the monitor using Ctrl-] then typing quit. You can’t break out of the monitor like this after connecting with the raw socket option 10.1.77.82 – Listen on this host/IP only. You can use 127.0.0.1 if you want to only allow connections locally. If you want to listen on any ip address on the server, just leave this blank so you end up with two consecutive colons ie “::” . 4444 – port number to listen on. server – listening in server mode nowait – qemu will wait for a client socket application to connect to the port before continuing unless this option is used. In most cases you’ll want to use the nowait option.
通过telnet连接到远程的QEMU monitor上：
jay@jay-linux:~$ telnet 10.1.77.82 4444Trying 10.1.77.82...Connected to 10.1.77.82.Escape character is '^]'.QEMU 1.7.50 monitor - type 'help' for more information(qemu) info kvmkvm support: enabled(qemu) info statusVM status: running(qemu) help migratemigrate [-d] [-b] [-i] uri -- migrate to URI (using -d to not wait for completion) -b for migration without shared storage with full copy of disk -i for migration without shared storage with incremental copy of disk (base image shared between src and destination)(qemu) ctrl + ] （断掉telnet连接）telnet> quit （退出telnet）Connection closed.
2. QEMU monitor支持RAW socket的远程访问：
[root@kvm-host ~]# qemu-system-x86_64 -enable-kvm -smp 2 -m 1024 vm2.img -monitor tcp:10.1.77.82:4444,server,nowait
可以使用netcat去连接这个socket：
jay@jay-linux:~$ nc 10.1.77.82 4444QEMU 1.7.50 monitor - type 'help' for more information(qemu) info kvminfo kvmkvm support: enabled(qemu) ^C
自己写了个socket程序示例如连接monitor，效果如下：
jay@jay-linux:~/workspace/c-cpp.git/c2013$ ./monitor_clientsending command 'info kvm' to remote qemu monitoroutput from qemu monitor: QEMU 1.7.50 monitor - type 'help' for more information ??,?output from qemu monitor: (qemu) info kvmkvm support: enabled(qemu)
上面那个连接monitor的socket程序示例为：https://github.com/smilejay/c-cpp/blob/master/c2013/socket_qemu_monitor_client.c
/* socket_qemu_monitor_clinet.c* Connect to remote QEMU monitor socket and sending a command to the monitor.* author: Jay <smile665@gmail.com>*/#include <sys/types.h>#include <sys/socket.h>#include <stdio.h>#include <netinet/in.h>#include <arpa/inet.h>#include <unistd.h>#include <stdlib.h>#include <string.h>int main(int argc, char *argv[]){ int sockfd; int len; struct sockaddr_in address; int result; char *cmd = "info kvm\n"; char output[200]; /* Create a socket for the client. */ sockfd = socket(AF_INET, SOCK_STREAM, 0); /* Name the socket, as agreed with the server. */ address.sin_family = AF_INET; address.sin_addr.s_addr = inet_addr("10.1.77.82"); address.sin_port = htons(4444); len = sizeof(address); /* Now connect our socket to the server's socket. */ result = connect(sockfd, (struct sockaddr *)&address, len); if(result == -1) { perror("oops: socket connetion failed."); exit(1); } /* We can now read/write via sockfd. */ printf("sending command '%s' to remote qemu monitor\n", cmd); write(sockfd, cmd, strlen(cmd)); read(sockfd, output, sizeof(output)); printf("output from qemu monitor: %s\n", output); read(sockfd, output, sizeof(output)); printf("output from qemu monitor: %s\n", output); close(sockfd); exit(0);}
参考资料：
http://www.linux-kvm.com/content/two-ways-access-your-virtual-machine-monitor-across-network
Original article: 通过网络连接到QEMU monitor
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