1、入口函数：do_migrate()

处理以下几件事：

(1) 判断当前migrate状态:active?

(2) 判断是否有block migrate设备存在

(3) 初始化

(4) 判断migrate协议:TCP/UNIX/EXEC/FD

(5) savevm state

(6) migrate state

2、函数调用

tcp_start_outgoing_migration()

migrate_fd_connect()

qemu_savevm_state_begin()

migrate_fd_put_ready()

qemu_savevm_state_iterate()

qemu_savevm_state_complete()

vm_start()