csci3753

CSCI3753 Coursework
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char_driver.c (3467B)

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// Jack Sangdahl
// CSCI3753 SP24
// PA3 Device Driver
#include <linux/fs.h>
#include <linux/module.h>
#include <linux/slab.h>

MODULE_AUTHOR("jasa7131");
MODULE_LICENSE("GPL");

#define BUFFER_SIZE 900
#define MAJOR_NUM 510
#define DEVICE_NAME "char_dev"
static int major, counter = 0;
static char *data;

int char_driver_open(struct inode *, struct file *);
int char_driver_close(struct inode *, struct file *);
ssize_t char_driver_read(struct file *, char *, size_t, loff_t *);
ssize_t char_driver_write(struct file *, const char *, size_t, loff_t *);
loff_t char_driver_seek(struct file *, loff_t, int);

struct file_operations char_fops = {.owner = THIS_MODULE,
                                    .open = char_driver_open,
                                    .release = char_driver_close,
                                    .read = char_driver_read,
                                    .write = char_driver_write,
                                    .llseek = char_driver_seek};

int char_driver_open(struct inode *pinode, struct file *pfile) {
  counter++;
  printk("Device opened %d times\n", counter);
  return 0;
}

int char_driver_close(struct inode *pinode, struct file *pfile) {
  printk("Device closed %d times\n", counter);
  return 0;
}

ssize_t char_driver_read(struct file *pfile, char __user *buffer, size_t length,
                         loff_t *offset) {
  size_t data_avail = BUFFER_SIZE - *offset, bytes_read = length;
  if (*offset >= BUFFER_SIZE || !length)
    return 0;
  if (length > data_avail)
    bytes_read = data_avail;
  printk("Requested data size: %zd bytes\n", length);
  long res = copy_to_user(buffer, data + *offset, bytes_read);
  printk("Read %zd bytes from device\n", bytes_read);
  length -= res;
  *offset += length;
  return length;
}

ssize_t char_driver_write(struct file *pfile, const char __user *buffer,
                          size_t length, loff_t *offset) {
  size_t data_avail = BUFFER_SIZE - *offset, bytes_written = length;
  if (*offset >= BUFFER_SIZE || !length)
    return 0;
  if (length > data_avail)
    bytes_written = data_avail;
  printk("Requested data size: %zd bytes\n", length);
  long res = copy_from_user(data + *offset, buffer, bytes_written);
  printk("Wrote %zd bytes to device\n", bytes_written);
  length -= res;
  *offset += bytes_written;
  return length;
}

loff_t char_driver_seek(struct file *pfile, loff_t offset, int whence) {
  loff_t new_pos = 0;
  switch (whence) {
  case SEEK_SET:
    new_pos = offset;
    break;
  case SEEK_CUR:
    new_pos = pfile->f_pos + offset;
    break;
  case SEEK_END:
    new_pos = BUFFER_SIZE - offset;
    break;
  }
  if (new_pos > BUFFER_SIZE)
    new_pos = BUFFER_SIZE;
  if (new_pos < 0)
    new_pos = 0;
  pfile->f_pos = new_pos;
  return new_pos;
}

static int char_driver_init(void) {
  printk("Registering device %s\n", DEVICE_NAME);
  data = (char *)kmalloc(BUFFER_SIZE * sizeof(char), GFP_KERNEL);
  major = register_chrdev(MAJOR_NUM, DEVICE_NAME, &char_fops);
  if (major < 0) {
    printk(KERN_ALERT "REGISTRATION FAILED: %s could not be reigstered.\n",
           DEVICE_NAME);
    return -EFAULT;
  }
  printk("REGISTRATION SUCCESS: %s successfully registered.\n", DEVICE_NAME);
  return 0;
}

static void char_driver_exit(void) {
  kfree(data);
  unregister_chrdev(major, DEVICE_NAME);
  printk("UNREGISTER SUCCESS: %s successfully unregistered\n", DEVICE_NAME);
}

module_init(char_driver_init);
module_exit(char_driver_exit);