A more useful way to interact with the driver
Linux contains a syscall called ioctl, which is often used to communicate with a driver. ioctl() takes three parameters:
File Descriptor fd
an unsigned int
an unsigned long
The driver can be adapted to make the latter two virtually anything - perhaps a pointer to a struct or a string. In the driver source, the code looks along the lines of:
But if you want, you can interpret cmd and arg as pointers if that is how you wish your driver to work.
To communicate with the driver in this case, you would use the ioctl() function, which you can import in C:
And you would have to update the file_operations struct:
On modern Linux kernel versions, . The former is the replacement for .ioctl, with the latter allowing 32-bit processes to perform ioctl calls on 64-bit systems. As a result, the new file_operations is likely to look more like this:
static ssize_t ioctl_handler(struct file *file, unsigned int cmd, unsigned long arg) {
printk("Command: %d; Argument: %d", cmd, arg);
return 0;
}#include <sys/ioctl.h>
// [...]
ioctl(fd, 0x100, 0x12345678); // data is a stringstatic struct file_operations fops = {
.ioctl = ioctl_handler
};static struct file_operations fops = {
.compat_ioctl = ioctl_handler,
.unlocked_ioctl = ioctl_handler
};