Several ways of registering differences chrdev character device

data structure

#define CHRDEV_MAJOR_HASH_SIZE  255

static struct char_device_struct {
 struct char_device_struct *next;
 unsigned int major;
 unsigned int baseminor;
 int minorct;
 char name[64];
 struct file_operations *fops;
 struct cdev *cdev; /* will die */
} *chrdevs[CHRDEV_MAJOR_HASH_SIZE];

/* index in the above */
static inline int major_to_index(int major)
{
 return major % CHRDEV_MAJOR_HASH_SIZE;
}

Chrdevs global variables, all the characters is a backup array device, by converting the primary index values in ascending order;
each char_device_struct element is a linked list of elements per-view device numbers in ascending order.
Relationship between the master device of the index number: major% CHRDEV_MAJOR_HASH_SIZE, namely: major = 1 major = 256 and use the same index value, index = 1;

Differences in the way the application equipment

-----------------------------------------------  支持多设备 -----------------------------------------------
    int alloc_chrdev_region(dev_t *dev, unsigned baseminor, unsigned count, const char *name)
        dev = 0 时，为动态申请设备，申请到的设备号保存到dev；
        baseminor，次设备号起始编号；
        count，申请连续设备号的数量；
        name，设备名称；
    -----------------------------------------------  只支持静态申请 -----------------------------------------------
    int register_chrdev_region(dev_t from, unsigned count, const char *name)
        from，申请的设备号起始编号；
        count，申请连续设备号的数量；
        name，设备名称；
-----------------------------------------------  单设备 -----------------------------------------------
    int register_chrdev(unsigned int major, const char *name, const struct file_operations *fops)
        major = 0 时，为动态申请设备，申请到的主设备号保存到major；
        name，设备名称；
        fops，关联设备的文件操作符；

NOTE: For sequential application device number, using reverse application. Eventually return to the starting device number.

Functional Differences

Complete the registration process

    register_chrdev = { alloc_chrdev_region + cdev_init + cdev_add }