最简单的模块

• hello.c

  #include <linux/module.h>
  
  int hello_init(void)
  {
      printk("Hello module init\n");
      return 0;
  }
  
  void hello_exit(void)
  {
      printk("Hello module exit\n");
  }
  
  module_init(hello_init);
  module_exit(hello_exit);
  
  MODULE_LICENSE("GPL");
  

• Makefile

  KDIR ?= /lib/modules/`uname -r`/build
  
  obj-m += hello.o
  
  module:
      make -C $(KDIR) M=$(PWD) modules
  
  clean:
      make -C $(KDIR) M=$(PWD) clean
  

• 运行

  $ make
  
  $ sudo insmod hello.ko
  $ lsmod | grep hello
  $ cat /proc/modules | grep hello
  
  $ sudo rmmod hello
  $ dmesg | tail
  

获取主设备号

• hello.c

  #include <linux/module.h>
  #include <linux/fs.h>
  
  /* 设置主设备号, 0 则由系统创建 */
  static int major = 0;
  
  static int hello_init(void)
  {
      int result;
      dev_t dev = MKDEV(major, 0);
  
      /* 配置主设备号 */
      if(major)
          result = register_chrdev_region(dev, 1, "hello");
      else        
      {
          /* major 为 0 则动态创建 */
          result = alloc_chrdev_region(&dev, 0, 1, "hello");
          major = MAJOR(dev);
      }
  
      if(result < 0)
      {
          printk("register device error\n");
          return result;
      }
  
      printk("register device major %d\n", major);
  
      return 0;
  }
  
  static void hello_exit(void)
  {
      dev_t dev = MKDEV(major, 0);
  
      unregister_chrdev_region(dev, 1);
  
      printk("unregister device major %d\n", major);
  }
  
  module_init(hello_init);
  module_exit(hello_exit);
  
  MODULE_LICENSE("GPL");
  

• 运行

  $ make 
  $ sudo insmod hello.ko
  $ dmesg | tail 
  $ cat  /proc/devices | grep hello
  
  $ sudo rmmod hello
  $ dmesg | tail 
  $ cat  /proc/devices | grep hello
  

添加字符设备

• hello.c

  #include <linux/module.h>
  #include <linux/fs.h>
  #include <linux/cdev.h>
  
  /* 填入希望绑定的主设备号, 0 则由系统决定 */
  static int major = 0;
  
  static struct cdev mycdev;
  
  #define MIN(a, b) (((a) < (b)) ? (a) : (b))
  
  static int hello_open(struct inode *node, struct file *file)
  {
      printk("open hello module\n");
  
      return 0;
  }
  
  static ssize_t hello_read(struct file *file, char __user *buf, size_t size, loff_t *ofs)
  {
      int n, m;
      char say[] = "Hello World\n";
      
      if(*ofs >= sizeof(say))
          return 0;
      
      m = MIN(sizeof(say) - *ofs, size);
  
      n = copy_to_user(buf, say + *ofs, m);
      *ofs += m - n;
      
      return m - n;
  }
  
  static struct file_operations fops = {
      .owner = THIS_MODULE,
      .open = hello_open,
      .read = hello_read,
  };
  
  static int hello_init(void)
  {
      int result;
      dev_t dev = MKDEV(major, 0);
  
      /* 配置主设备号 */
      if(major)
          result = register_chrdev_region(dev, 1, "hello");
      else        
      {
          /* major 为 0 则动态创建 */
          result = alloc_chrdev_region(&dev, 0, 1, "hello");
          major = MAJOR(dev);
      }
  
      if(result < 0)
      {
          printk("register device error\n");
          return result;
      }
  
      printk("register device major %d\n", major);
  
      /* 添加字符设备 */
      cdev_init(&mycdev, &fops);
      mycdev.owner = THIS_MODULE;
  
      cdev_add(&mycdev, dev, 1);
  
      return 0;
  }
  
  static void hello_exit(void)
  {
      cdev_del(&mycdev);
  
      unregister_chrdev_region(MKDEV(major, 0), 1);
  
      printk("unregister device major %d\n", major);
  }
  
  module_init(hello_init);
  module_exit(hello_exit);
  
  MODULE_LICENSE("GPL");
  

• 运行

  
  $ make 
  $ sudo insmod hello.ko
  $ cat  /proc/devices | grep hello
  # 填入获取的主设备号, 这里是 511
  $ sudo mknod /dev/hello c 511 0
  $ cat /dev/hello
  Hello World