char device

 /**
 * alloc_chrdev_region() - register a range of char device numbers
 * @dev: output parameter for first assigned number
 * @baseminor: first of the requested range of minor numbers
 * @count: the number of minor numbers required
 * @name: the name of the associated device or driver
 *
 * Allocates a range of char device numbers. The major number will be
 * chosen dynamically, and returned (along with the first minor number)
 * in @dev. Returns zero or a negative error code.
 */
 int alloc_chrdev_region(dev_t *dev, unsigned baseminor, unsigned count,
 const char *name)
 {//分配字符设备的次设备号范围，主设备号有系统动态分配，不需要主动指定
 struct char_device_struct *cd;
 cd = __register_chrdev_region(, baseminor, count, name);
 if (IS_ERR(cd))
 return PTR_ERR(cd);
 *dev = MKDEV(cd->major, cd->baseminor);
 return ;
 }

 static struct char_device_struct *
 __register_chrdev_region(unsigned int major, unsigned int baseminor,
                int minorct, const char *name)
 {
     struct char_device_struct *cd, **cp;
     int ret = ;
     int i;

     cd = kzalloc(sizeof(struct char_device_struct), GFP_KERNEL);
     if (cd == NULL)
         return ERR_PTR(-ENOMEM);

     mutex_lock(&chrdevs_lock);

     /* temporary */
     if (major == ) {
         for (i = ARRAY_SIZE(chrdevs)-; i > ; i--) {
             if (chrdevs[i] == NULL)
                 break;
         }

         if (i == ) {
             ret = -EBUSY;
             goto out;
         }
         major = i;
         ret = major;
     }

     cd->major = major;
     cd->baseminor = baseminor;
     cd->minorct = minorct;
     strlcpy(cd->name, name, sizeof(cd->name));

     i = major_to_index(major);

     for (cp = &chrdevs[i]; *cp; cp = &(*cp)->next)
         if ((*cp)->major > major ||
             ((*cp)->major == major &&
              (((*cp)->baseminor >= baseminor) ||
               ((*cp)->baseminor + (*cp)->minorct > baseminor))))
             break;

     /* Check for overlapping minor ranges.  */
     if (*cp && (*cp)->major == major) {
         int old_min = (*cp)->baseminor;
         int old_max = (*cp)->baseminor + (*cp)->minorct - ;
         int new_min = baseminor;
         int new_max = baseminor + minorct - ;

         /* New driver overlaps from the left.  */
         if (new_max >= old_min && new_max <= old_max) {
             ret = -EBUSY;
             goto out;
         }

         /* New driver overlaps from the right.  */
         if (new_min <= old_max && new_min >= old_min) {
             ret = -EBUSY;
             goto out;
         }
     }

     cd->next = *cp;
     *cp = cd;
     mutex_unlock(&chrdevs_lock);
     return cd;
 out:
     mutex_unlock(&chrdevs_lock);
     kfree(cd);
     return ERR_PTR(ret);
 }