Basic Linux Char Device Example #chardevice #linux #kernel #driver

chardev-ex.c

#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/cdev.h>
#include <linux/device.h>

MODULE_DESCRIPTION("");
MODULE_AUTHOR("Talha Can Havadar <[email protected]>");
MODULE_LICENSE("GPL");

typedef struct
{
  dev_t devno;
  struct cdev cdev;
  struct class class;
  struct file_operations fops;
} ExampleDriverStc;

static int example_open(struct inode *, struct file *);

static ExampleDriverStc exampleDriver = {
  .fops = {
    .owner = THIS_MODULE,
    .llseek         = NULL,
    .read           = NULL,
    .write          = NULL,
    .unlocked_ioctl = NULL,
    .open           = example_open,
    .flush          = NULL,
    .release        = NULL,
  },
  .class = {
    .owner = THIS_MODULE,
    .name = "chardev-ex",
  }
};

static int example_open(struct inode* inode, struct file* filp)
{
  ExampleDriverStc* pDriver;
  pDriver = container_of(inode->i_cdev, ExampleDriverStc, cdev);

  filp->private_data = pDriver;

  return 0;
}

static int __init example_init(void)
{
  printk(KERN_INFO "Hello from the char device example.\n");

  if (alloc_chrdev_region(&exampleDriver.devno, 0, 1, "chardev-ex") < 0)
  {
    printk(KERN_INFO "chardev-ex: not able to allocate char device");
    return -1;
  }

  // Create sysfs class
  if (class_register(&exampleDriver.class) < 0)
  {
    printk(KERN_INFO "chardev-ex: not able to register sysfs class.\n");
    unregister_chrdev_region(exampleDriver.devno, 1);
    return -1;
  }

  cdev_init(&exampleDriver.cdev, &exampleDriver.fops);
  exampleDriver.cdev.owner = THIS_MODULE;
  cdev_add(&exampleDriver.cdev, exampleDriver.devno, 1);
  device_create(&exampleDriver.class, NULL, exampleDriver.devno, NULL, "chardev-ex-%d", 0);

  return 0;
}

static void __exit example_exit(void)
{
  printk(KERN_INFO "Bye from the char device example.\n");
  device_destroy(&exampleDriver.class, exampleDriver.devno);
  cdev_del(&exampleDriver.cdev);
  class_unregister(&exampleDriver.class);
  unregister_chrdev_region(exampleDriver.devno, 1);
}

module_init(example_init);
module_exit(example_exit);

Makefile

obj-m += chardev-ex.o

CROSS_COMPILE=
LINUX_DIR=/lib/modules/$(shell uname -r)/build
PWD=$(shell pwd)

all:
	make -C $(LINUX_DIR) M=$(PWD) modules

clean:
	make -C $(LINUX_DIR) M=$(PWD) clean