Question

I am writing a device driver for Linux. It creates a device with 4 minor numbers. Whenever we attempt to write to the device at minor number 3, we are suppose to kill the device and currently it isn’t suppose to do anything else except print it is writing to the booga device. Here is some of my current code and I can post more code if necessary:

Write method:

static ssize_t booga_write (struct file *filp, const char *buf, size_t count, loff_t *f_pose) {
    printk("Attempting to write to booga device\n");
    /* need to protect this with a semaphore if multiple processes
       will invoke this driver to prevent a race condition */

    if (down_interruptible (&booga_device_stats->sem))
        return (-ERESTARTSYS);
    booga_device_stats->num_bytes_written += count; 
    up(&booga_device_stats->sem);
    return count; // pretend that count bytes were written

}

How it is tested:

static void run_write_test(char *device, int bufsize)
{
    char *buf;
    int src;
    int out;

    src = open(device, O_WRONLY);
    if (src < 0) {
        perror("Open for write failed:");
        exit(1);
    }
    buf = (char *) malloc(sizeof(char)*(bufsize+1));
    fprintf(stderr, "Attempting to write to booga device\n");
    out = write(src, buf, bufsize);
    fprintf(stderr, "Wrote %d bytes.\n", out);
    free(buf);
    close(src);

}

I am wondering if there is a way to get the minor number. I looked in linux/fs.h and saw that the file struct has a member called private_data but whenever I attempt to call this, it will crash my system as it is currently set to null.

Or should I not be trying to get the minor number from the struct file at all and should attempt to keep track of it when I first open the device?

Answer 1

You can get the minor number like so:

iminor(filp->f_path.dentry->d_inode)