Access is denied when updating drivers

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Using a pointer is the way to pass arbitrary data to the argument.Different commands have different numeric values, which are usually given symbolic names to simplify coding.

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For example, everything you write to a serial port is used as communication data, and you cannot change the baud rate by writing to the device.Therefore, the dots in the prototype represent not a variable number of arguments but a single optional argument, traditionally identified as .The dots are simply there to prevent type checking during compilation.In a real system, however, a system call can't actually have a variable number of arguments.System calls must have a well-defined number of arguments because user programs can access them only through hardware "gates,'' as outlined in "User Space and Kernel Space" in Chapter 2, "Building and Running Modules".

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