FreeBSD Device Drivers

Invoking ioctl

To invoke a d_ioctl function, you’d use the ioctl(2) system call.

#include <sys/ioctl.h>

int
ioctl(int d, unsigned long request, ...);

The d argument, which stands for descriptor, expects a file descriptor for a device node. The request argument is the ioctl command to be issued (for example, ECHO_CLEAR_BUFFER). The remaining argument (...) is a pointer to the data that’ll be passed to the d_ioctl function.

Example 3-2 presents a command-line utility designed to invoke the echo_ioctl function in Example 3-1:

Example 3-2. echo_config.c

#include <sys/types.h>
  #include <sys/ioctl.h>

  #include <err.h>
  #include <fcntl.h>
  #include <limits.h>
  #include <stdio.h>
  #include <stdlib.h>
  #include <unistd.h>

 #define ECHO_CLEAR_BUFFER       _IO('E', 1)