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原帖由 ktrudger 于 2006-9-1 16:57 发表
ioctl是一个设备驱动程序的提供给用户态传递设备控制信息接口，很多设备都会提供给用户态程序相应的ioctl接口的，所以要看你到底想知道哪个ioctl的内部实现。
The implementation of the ioctl system call is broken into two major levels. The upper level handles the system call itself. The ioctl call includes a descriptor, a command, and pointer to a data area. The command argument encodes what the size is of the data area for the parameters and whether the parameters are input, output, or both input and output. The upper level is responsible for decoding the command argument, allocating a buffer, and copying in any input data. If a return value is to be generated and there is no input, the buffer is zeroed. Finally, the ioctl is dispatched through the file-entry ioctl function, along with the I/O buffer, to the lower-level routine that implements the requested operation.
The lower level does the requested operation. Along with the command argument, it receives a pointer to the I/O buffer. The upper level has already checked for valid memory references, but the lower level may do more precise argument validation because it knows more about the expected nature of the arguments. However, it does not need to copy the arguments in or out of the user process. If the command is successful and produces output, the lower level places the results in the buffer provided by the top level. When the lower level returns, the upper level copies the results to the process.
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发表于 2006-09-01 15:57
