A GPRS device, which resembles a modem with an extended at command set, must define a context using an at command before it enters data mode.

GPRS设备类似于拥有扩展AT命令集的调制解调器，在进入数据模式之前必须使用AT命令定义一个上下文。

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Step two: data is copied from the kernel buffer into the user buffer, and the read system call returns. The return from the call caused a context switch from kernel back to user mode.

步骤二：数据从内核空间缓冲区复制到用户空间缓冲区，之后系统调用read返回，这导致了从内核空间向用户空间的上下文切换。

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Code operating in this mode has read and write access to the global kernel address space and kernel data in the process region when executing within the context of a process.

当在某个进程的上下文中执行以此模式运行的代码时，它不仅对全局内核地址空间具有读写访问权限，还将对该进程中的内核数据也具有读写访问权限。

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