Linux 驱动开发2: IOCTL 操作

IOCTL 示例

• hello.c

  #include <linux/module.h>
  #include <linux/fs.h>
  #include <linux/cdev.h>
  
  static int major = 0;
  
  static struct cdev mycdev;
  
  #define HELLO_IOC_MAGIC 'W'
  #define HELLO_IOC_NUMMAX 12
  
  #define HELLO_IOC_GET _IO(HELLO_IOC_MAGIC, 1)
  
  long hello_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
  {
      int ret = 0;
  
      if(_IOC_TYPE(cmd) != HELLO_IOC_MAGIC) return -ENOTTY;
      if(_IOC_NR(cmd) >= HELLO_IOC_NUMMAX)  return -ENOTTY;
  
      switch (cmd)
      {
      case HELLO_IOC_GET:
          ret = __put_user(6666, (int __user *)arg);
          printk("HELLO_IOC_GET");
          break;
    
      default:
          break;
      }
    
      return ret;
  }
  
  static struct file_operations fops = {
      .owner = THIS_MODULE,
      .unlocked_ioctl = hello_ioctl
  };
  
  static int hello_init(void)
  {
      int result;
      dev_t dev;
  
      /* 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");
  

• Makefile

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

• test.c

  #include <stdio.h>
  #include <sys/ioctl.h>
  #include <fcntl.h>
  
  #define HELLO_IOC_MAGIC 'W'
  #define HELLO_IOC_NUMMAX 12
  
  #define HELLO_IOC_GET _IO(HELLO_IOC_MAGIC, 1)
   
  int main(int argc, char** argv)
  {
    if(argc != 2) 
    {
        printf("usage: %s device (example /dev/hello) \n", argv[0]);
        return -1;
    }
      
    int fd = open(argv[1], O_RDONLY);
    if(fd < 0)
      {
        perror("failed to open device");
        return -1;
    }
  
    int num = 0;
    if(ioctl(fd, HELLO_IOC_GET, &num))
    {
        perror("failed to get num");
        return -1;
    }
  
      printf("get num %d\n", num);
      
    return 0;
  }
  

• 运行

  $ make 
  $ gcc test.c
  $ sudo insmod 
  $ dmesg | tail
  # 获取主设备号
  $ sudo mknod /dev/hello c 244 0
  $ ./a.out /dev/hello
  get num 6666