Question

我对char驱动程序示例感到困惑。在一些示例中，示例集中于创建字符设备并将其与file_operations连接。然后我们必须insmod驱动程序，使用mknod创建一个节点，然后我们的小应用程序才能使用此驱动程序读取或写入。这样一个简单的init_function：

static int char_init(void)
{
    alloc_chrdev_region(&mydev, 0, 1, "mydev");
    cdev = cdev_alloc();
    cdev->fops = &fops;
    cdev_add(cdev, mydev, 1);
    printk(KERN_ALERT "Major minor number available\n");
    printk(KERN_ALERT "major number = %d minor number = %d\n",MAJOR(mydev), MINOR(mydev));//Macros that extract the major and minor numbers from a device number.
    return 0;
}

在其他一些例子中，我们创建了一个类和一个设备。 Derek Molloy的char驱动程序的一个例子，

static int __init ebbchar_init(void){
   printk(KERN_INFO "EBBChar: Initializing the EBBChar LKM\n");

   // Try to dynamically allocate a major number for the device -- more difficult but worth it
   majorNumber = register_chrdev(0, DEVICE_NAME, &fops);
   if (majorNumber<0){
      printk(KERN_ALERT "EBBChar failed to register a major number\n");
      return majorNumber;
   }
   printk(KERN_INFO "EBBChar: registered correctly with major number %d\n", majorNumber);

   // Register the device class
   ebbcharClass = class_create(THIS_MODULE, CLASS_NAME);
   if (IS_ERR(ebbcharClass)){                // Check for error and clean up if there is
      unregister_chrdev(majorNumber, DEVICE_NAME);
      printk(KERN_ALERT "Failed to register device class\n");
      return PTR_ERR(ebbcharClass);          // Correct way to return an error on a pointer
   }
   printk(KERN_INFO "EBBChar: device class registered correctly\n");

   // Register the device driver
   ebbcharDevice = device_create(ebbcharClass, NULL, MKDEV(majorNumber, 0), NULL, DEVICE_NAME);
   if (IS_ERR(ebbcharDevice)){               // Clean up if there is an error
      class_destroy(ebbcharClass);           // Repeated code but the alternative is goto statements
      unregister_chrdev(majorNumber, DEVICE_NAME);
      printk(KERN_ALERT "Failed to create the device\n");
      return PTR_ERR(ebbcharDevice);
   }
   printk(KERN_INFO "EBBChar: device class created correctly\n"); // Made it! device was initialized
   return 0;
}

现在我可以用这两种策略得出什么结论？为什么不只使用第二个呢？另外，当我们使用cdev_add和cdev_init创建设备时，如果我必须使用mknod创建设备文件，该怎么办？

用char驱动程序示例理解什么

0 个答案: