设备抽象层为上层应用程序提供了一套标准的、与设备无关的通信接口，并且通过文件描述表、设备描述表和驱动描述表建立了从通信接口到设备驱动的映射。

The device Abstract Layer provides a set of standard communication interface functions unrelated with specific device, which is mapped to device drivers by file table, device table and driver table.

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这里不需要让每个代理维护它自己的文件描述符表。

There is no need to have each agent maintain its own file descriptor table.

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表1描述了这些文件。

Table 1 describes these files.

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