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NAMEioctl - control device
int ioctl(int fd, unsigned long request, ...);
DESCRIPTIONThe ioctl() function manipulates the underlying device parameters of special files. In particular, many operating characteristics of character special files (e.g., terminals) may be controlled with ioctl() requests. The argument fd must be an open file descriptor.
The second argument is a device-dependent request code. The third argument is an untyped pointer to memory. It's traditionally char *argp (from the days before void * was valid C), and will be so named for this discussion.
An ioctl() request has encoded in it whether the argument is an in parameter or out parameter, and the size of the argument argp in bytes. Macros and defines used in specifying an ioctl() request are located in the file <sys/ioctl.h>.
RETURN VALUEUsually, on success zero is returned. A few ioctl() requests use the return value as an output parameter and return a nonnegative value on success. On error, -1 is returned, and errno is set appropriately.
- fd is not a valid descriptor.
- argp references an inaccessible memory area.
- request or argp is not valid.
- fd is not associated with a character special device.
- The specified request does not apply to the kind of object that the descriptor fd references.