The strncpy_from_user function copies a string from user space into a kernel buffer, given a user space source address and Max length.

strncpy _ from_user函数将一个字符串从用户空间复制到一个内核缓冲区，给定一个用户空间源地址和最大长度。

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The string passed into printk is then copied into the kernel log buffer using a special function that manages the bounds of the ring (emit_log_char).

这个字符串会被传递给printk，然后它会被一个管理缓冲边界(emit_log_char)的特殊函数复制到内核日志缓冲区中。

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