Updating user policies please wait
ioctl Blocking I/O poll and select Asynchronous Notification Seeking a Device Access Control on a Device File Backward Compatibility Quick Reference In Chapter 3, "Char Drivers", we built a complete device driver that the user can write to and read from.But a real device usually offers more functionality than synchronous .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.Now that we're equipped with debugging tools should something go awry, we can safely go ahead and implement new operations.What is normally needed, in addition to reading and writing the device, is the ability to perform various types of hardware control via the device driver.
They have to: changing the command codes would break no end of binary programs.
Mary Jo Foley has covered the tech industry for 30 years for a variety of publications, including ZDNet, e Week and Baseline.
She is the author of Microsoft 2.0: How Microsoft plans to stay relevant in the post-Gates era (John Wiley & Sons, 2008).
The text file also lists the reasons why the convention should be used.
The old, and now deprecated, way of choosing an /* Use 'k' as magic number */ #define SCULL_IOC_MAGIC 'k' #define SCULL_IOCRESET _IO(SCULL_IOC_MAGIC, 0) /* * S means "Set" through a ptr * T means "Tell" directly with the argument value * G means "Get": reply by setting through a pointer * Q means "Query": response is on the return value * X means "e Xchange": G and S atomically * H means "s Hift": T and Q atomically */ #define SCULL_IOCSQUANTUM _IOW(SCULL_IOC_MAGIC, 1, scull_quantum) #define SCULL_IOCSQSET _IOW(SCULL_IOC_MAGIC, 2, scull_qset) #define SCULL_IOCTQUANTUM _IO(SCULL_IOC_MAGIC, 3) #define SCULL_IOCTQSET _IO(SCULL_IOC_MAGIC, 4) #define SCULL_IOCGQUANTUM _IOR(SCULL_IOC_MAGIC, 5, scull_quantum) #define SCULL_IOCGQSET _IOR(SCULL_IOC_MAGIC, 6, scull_qset) #define SCULL_IOCQQUANTUM _IO(SCULL_IOC_MAGIC, 7) #define SCULL_IOCQQSET _IO(SCULL_IOC_MAGIC, 8) #define SCULL_IOCXQUANTUM _IOWR(SCULL_IOC_MAGIC, 9, scull_quantum) #define SCULL_IOCXQSET _IOWR(SCULL_IOC_MAGIC,10, scull_qset) #define SCULL_IOCHQUANTUM _IO(SCULL_IOC_MAGIC, 11) #define SCULL_IOCHQSET _IO(SCULL_IOC_MAGIC, 12) #define SCULL_IOCHARDRESET _IO(SCULL_IOC_MAGIC, 15) /* debugging tool */ #define SCULL_IOC_MAXNR 15 should exchange values by pointer.