查了好多资料，发现还是不全，干脆自己整理吧，至少保证在我的做法正确的，以免误导读者，也是给自己做个记录吧！
backing
*
Information about the backing of this virtual device presented in the context of the virtual machine's environment. Not all devices are required to have backing information.
See
connectable
*
controllerKey
*
deviceInfo
*
A unique key that distinguishes this device from other devices in the same virtual machine. Keys are immutable but may be recycled; that is, a key does not change as long as the device is associated with a particular virtual machine. However, once a device is removed, its key may be used when another device is added.
This property is not read-only, but the client cannot control its value. Persistent device keys are always assigned and managed by the server, which guarantees that all devices will have non-negative key values.
When adding new devices, it may be necessary for a client to assign keys temporarily in order to associate controllers with devices in configuring a virtual machine. However, the server does not allow a client to reassign a device key, and the server may assign a different value from the one passed during configuration. Clients should ensure that existing device keys are not reused as temporary key values for the new device to be added (for example, by using unique negative integers as temporary keys).
When editing or deleting a device, clients must use the server-provided key to refer to an existing device.
unitNumber
*
文章结束给大家分享下程序员的一些笑话语录：
人工智能今天的发展水平：8乘8的国际象棋盘其实是一个体现思维与创意的强大媒介。象棋里蕴含了天文数字般的变化。卡斯帕罗夫指出，国际象棋的合法棋步共有1040。在棋局里每算度八步棋，里面蕴含的变化就已经超过银河系里的繁星总数。而地球上很少有任何数量达到这个级别。在金融危机之前，全世界的财富总和大约是1014人民币，而地球人口只有1010。棋盘上，所有可能的棋局总数达到10120，这超过了宇宙里所有原子的总数！经典语录网