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从我之前的问题：如何在 ubuntu 中构建外部模块？我以为我无法加载模块，因为loading out-of-treeor tainting kernel，但是我的scull_init_module（下面的来源）我已经添加了printk，所以我知道我是从内核日志加载的。但我没有（日志中没有输出——日志与链接中的相同）。

uname -a== 4.19.0-9-amd64 #1 SMP Debian 4.19.118-2 (2020-04-29) x86_64 GNU/Linux（不使用 ubuntu - 来自链接）。

scull_init_module：

#ifndef scull_major
#define scull_major 0
#endif

#ifndef scull_nr_devs
#define scull_nr_devs 4
#endif

struct scull_dev *scull_devices; /*array of active devices */
static void scull_setup_cdev(struct scull_dev *, int); /*helper function (internal) */  
int scull_minor = 0;


int scull_init_module(void) {
   int i;
   dev_t dev = 0; 
   /* register devices */
   int result = 1;
   result = alloc_chrdev_region(&dev, scull_minor, scull_nr_devs, "scull"); /**comment later**/
   printk(KERN_ALERT"Passed %s %d \n in scull_init_module\n", __FUNCTION__, __LINE__);

   if(result < 0){
      printk(KERN_WARNING "scull: can't get major %d\n", scull_major);
      return result;
   }

   /* allocate space for devices */ 
   scull_devices = kmalloc(sizeof(struct scull_dev) * scull_nr_devs, GFP_KERNEL);
   if(!scull_devices){
      result = -1;
      goto fail;
   }

   /*initilization of devices */
   for(i=0; i<scull_nr_devs;i++){
      scull_devices[i].quantum = scull_quantum;
      scull_devices[i].qset = scull_qset;
      scull_setup_cdev(&scull_devices[i], i);
   }

   return 0;
   fail:
      scull_cleanup_module();
      return result;
}

module_init(scull_init_module);

它基本上来自Linux 设备驱动程序，第三版，第 3 章。但我是手写的（没有复制/粘贴）。alloc_chrdev_region被正确调用，所以是scull_setup_cdev，那么哪里可能有问题？

编辑（dmesg 的输出）：dmesg看起来它确实加载了模块：

[ 2765.707018] scull: loading out-of-tree module taints kernel.
[ 2765.707106] scull: module verification failed: signature and/or required key missing - tainting kernel
[ 2765.707929] Passed scull_init_module 41 
                in scull_init_module

但是仍然/dev/scull0给出的节点No such device or address

#mknod /dev/scull0 c 241 0
#cat /dev/scull0
cat: /dev/scull0: No such device or address

因此，如果设备已正确注册（请参阅 dmesg）并且我在 /dev 层次结构中创建节点，那么意味着no device or address什么？为什么我会得到它？

EDIT2（函数 scull_setup_cdev）：

static void scull_setup_cdev(struct scull_dev *dev, int index){
    int err, devno=MKDEV(scull_major, scull_minor + index);

    cdev_init(&dev->cdev, &scull_fops);
    dev->cdev.owner = THIS_MODULE;
    dev->cdev.ops = &scull_fops; /**comment later**/
    err = cdev_add(&dev->cdev, devno, 1);   
    if (err) 
        printk(KERN_NOTICE "Error %d adding scull%d", err, index);
}
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