Question

I have written a device driver and need to pass an int value to it. Am using copy_from_user() for this. Here is what I have done so far,

#define MY_MAGIC 'G'
#define TEST_IOCTL _IO(MY_MAGIC, 0)
#define PASS_STRUCT_ARRAY_SIZE _IOW(MY_MAGIC, 1, int )
#define TEST_IOCTL_ONE _IO(MY_MAGIC, 2)


int major;

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

int ret, SIZE;

switch(cmd){

    case TEST_IOCTL:
        printk("NO argument IOCTL called\n");
        break;

    case PASS_STRUCT_ARRAY_SIZE:
            printk("Inside PASS_STRUCT_ARRAY_SIZE\n");
        ret = copy_from_user(SIZE, arg, sizeof(int));
        if(ret < 0){
            printk("Error in PASS_STRUCT_ARRAY_SIZE\n");
            return -1;  
        }
        printk("Struct Array Size : %d\n",SIZE);
        break;

    case TEST_IOCTL_ONE:
        printk("NO argument IOCTL_ONE called\n");
        break;

    default :
        return -ENOTTY;
}

return 0;

}

When I call the TEST_IOCTL & TEST_IOCTL_ONE the module works properly. However when I call PASS_STRUCT_ARRAY_SIZE the system freezes.

Userspace code is this,

if(ioctl(fd, PASS_STRUCT_ARRAY_SIZE, 10) < 0){
    perror("PASS_STRUCT_ARRAY_SIZE : ");
        return -1;
}

What can I be doing wrong?

Answer 1

Sorry, my previous answer was wrong. Since the argument is an integer you should just use it without copy_from_user:

SIZE = arg;

You only need copy_from_user when the argument is a pointer.