Dxferp: a pointer to user memory of at least dxfer_len bytes in length for data transfer.

dxferp：指向数据传输时长度至少为dxfer_len字节的用户内存的指针。

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Larger data types are made by simply treating multiple bytes as a single unit (using two memory locations together for a 16-bit number, for instance).

较大的数据类型可以通过简单地将多个字节当作一个单位实现(例如，将两个内存位置放到一起作为一个16位的数字)。

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This request asks for sizeof(data) bytes of data copied from the address in main memory denoted by argp to be copied into the object data.

这个请求会要求将 sizeof(data) 字节的数据从 argp 所指向的主存地址处拷贝到 data 对象中。

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