IOCTL write crashing

Question

I am trying to implement ioctl in kernel space to write some date into the register, I am getting a crash in cmd of ioctl.

Below is my code:

Kernel side:

static struct file_operations fops = {
.compat_ioctl = device_ioctl
};

int device_ioctl(struct inode *inode, struct file *filep, 
                 unsigned int cmd, unsigned long arg)
{

    int len = 200;

    printk (KERN_INFO "In Device_ioctl !!\n");
    switch(cmd)
    {
    case IOCTL_WRITE_REG:
        write_ioctl((unsigned long *)arg);
        break;

    default:
        printk (KERN_INFO "default\n");
        return -ENOTTY;
    }
    printk (KERN_INFO "device_ioctl out\n");
    return len;
}

User Side

#define IOCTL_WRITE_REG _IOW(MAJOR_NUM, 1, int *)
void write_to_device(int write_fd)
{

    int retval;
    unsigned int to_write1 = 1;

    retval = ioctl(write_fd, IOCTL_WRITE_REG, &to_write1);
    if(retval < 0)
    {
        printf("fd: %d, write error: %d\n", write_fd, errno);
        exit(-1);
    }
}

It is not entering into device_ioctl function, Where am I going wrong ?

Answer 1

Few things I happen to notice:

• You need to use unlocked_ioctl instead of compat_ioctl. compat_ioctl is to allow 32-bit user space programs to invoke ioctl calls on a 64-bit kernel.

• The signature of your ioctl handler function is incorrect (for unlocked_ioctl). The expected signature is:

  long (*unlocked_ioctl) (struct file * filep, unsigned int, unsigned long);
  

I haven't tried really compiling this code, but I think this should work:

static struct file_operations fops = {
    .unlocked_ioctl = device_ioctl
};

long device_ioctl(struct file *filep, 
                  unsigned int cmd,
                  unsigned long arg)
{

    int len = 200;

    printk (KERN_INFO "In Device_ioctl !!\n");
    switch(cmd)
    {
    case IOCTL_WRITE_REG:
        write_ioctl((unsigned long *)arg);
        break;

    default:
        printk (KERN_INFO "default\n");
        return -ENOTTY;
    }
    printk (KERN_INFO "device_ioctl out\n");
    return len;
}