This chapter has described the traditional methods for device communication and control: sysctl and ioctl. Generally, sysctls are employed to adjust parameters, and ioctls are used for everything else—that’s why ioctls are the catchall of I/O operations. Note that if you find yourself creating a device node just for ioctl requests, you should probably use sysctls instead.

Incidentally, be aware that it’s fairly trivial to write user-mode programs that interact with drivers. Thus, your drivers—not your user-mode programs (for example, Example 3-2)—should always validate user input.