chardriver.c

reading a char driver

#include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h> /* printk() */
#include <linux/slab.h> /* kmalloc() */
#include <linux/fs.h> /* everything... */
#include <linux/errno.h> /* error codes */
#include <linux/types.h> /* size_t */
#include <linux/proc_fs.h>
#include <linux/fcntl.h> /* O_ACCMODE */
#include <asm/system.h> /* cli(), *_flags */
#include <asm/uaccess.h> /* copy_from/to_user */
MODULE_LICENSE("Dual BSD/GPL");
/* Declaration of memory.c functions */
int memory_open(struct inode *inode, struct file *filp);
int memory_release(struct inode *inode, struct file *filp);
ssize_t memory_read(struct file *filp, char *buf, size_t count, loff_t *f_pos);
ssize_t memory_write(struct file *filp, char *buf, size_t count, loff_t *f_pos);
void memory_exit(void);
int memory_init(void);
/* Structure that declares the usual file */
/* access functions */
struct file_operations memory_fops = {
  read: memory_read,
  write: memory_write,
  open: memory_open,
  release: memory_release
};
/* Declaration of the init and exit functions */
module_init(memory_init);
module_exit(memory_exit);
/* Global variables of the driver */
/* Major number */
int memory_major = 60;
/* Buffer to store data */
char *memory_buffer;

int memory_init(void) {
  int result;
  /* Registering device */
  result = register_chrdev(memory_major, "memory", &memory_fops);
  if (result < 0) {
    printk(
      "<1>memory: cannot obtain major number %d\n", memory_major);
    return result;
  }
  /* Allocating memory for the buffer */
  memory_buffer = kmalloc(1, GFP_KERNEL);
  if (!memory_buffer) {
    result = -ENOMEM;
    goto fail;
  }
  memset(memory_buffer, 0, 1);
  printk("<1>Inserting memory module\n");
  return 0;
  fail:
    memory_exit();
    return result;
}


void memory_exit(void) {
  /* Freeing the major number */
  unregister_chrdev(memory_major, "memory");
  /* Freeing buffer memory */
  if (memory_buffer) {
    kfree(memory_buffer);
  }
  printk("<1>Removing memory module\n");
}


int memory_open(struct inode *inode, struct file *filp) {
  /* Success */
  return 0;
}
int memory_release(struct inode *inode, struct file *filp) {
  /* Success */
  return 0;
}
ssize_t memory_read(struct file *filp, char *buf,
                      size_t count, loff_t *f_pos) {
  /* Transfering data to user space */
  copy_to_user(buf,memory_buffer,1);

  /* Changing reading position as best suits */
  if (*f_pos == 0) {
    *f_pos+=1;
    return 1;
  } else {
    return 0;
  }
}
ssize_t memory_write( struct file *filp, char *buf,
                      size_t count, loff_t *f_pos) {
  char *tmp;
  tmp=buf+count-1;
  copy_from_user(memory_buffer,tmp,1);
  return 1;
}