字符驱动（按键）初始化函数分析：
int charDrvInit(void)
{
devNum = MKDEV(reg_major, reg_minor);
printk(KERN_EMERG"devNum is %d\r\n", devNum);
if(OK == register_chrdev_region(devNum, subDevNum, DEVICE_NAME))//subdevnum：要申请的第一个次设备号
{
printk(KERN_EMERG"register_chrdev_region ok\r\n");
}
else
{
printk(KERN_EMERG"register_chrdev_region error\r\n");
return ERROR;
}
16
/**
* register_chrdev_region() - register a range of device numbers
* @from: the first in the desired range of device numbers; must include
* the major number.
* @count: the number of consecutive device numbers required
* @name: the name of the device or driver.
*
* Return value is zero on success, a negative error code on failure.
*/
int register_chrdev_region(dev_t from, unsigned count, const char *name) //count = 1
{
struct char_device_struct *cd;
static struct char_device_struct {
struct char_device_struct *next;
unsigned int major;
unsigned int baseminor;
int minorct;
];
struct cdev *cdev; /* will die */
} *chrdevs[CHRDEV_MAJOR_HASH_SIZE];
struct char_device_struct
dev_t to = from + count;
dev_t n, next;
for (n = from; n < to; n = next) {
next = MKDEV(MAJOR(n)+, );/*先得到下一个设备号（其实也是一个设备号，只不过此时的次设备号为0）并存储于next中*/
18 if (next > to) /*溢出的情况*/ /*判断在from的基础上再追加count个设备(dev_t to = from+count)是否已经溢出到下一个主设备号*/
next = to;
/* 如果没有溢出（next小于to），那么整个for语句就只执行个一次__register_chrdev_region函数；
否则当设备号溢出时，会把当前溢出的设备号范围划分为几个小范围，分别调用__register_chrdev_region函数。 */
/*
* Register a single major with a specified minor range.
*
* If major == 0 this functions will dynamically allocate a major and return
* its number.
*
* If major > 0 this function will attempt to reserve the passed range of
* minors and will return zero on success.
*
* Returns a -ve errno on failure.
*/
static struct char_device_struct *
13 __register_chrdev_region(unsigned int major, unsigned int baseminor,
14 int minorct, const char *name)
{
struct char_device_struct *cd, **cp;
;
int i;
cd = kzalloc(sizeof(struct char_device_struct), GFP_KERNEL);
if (cd == NULL)
return ERR_PTR(-ENOMEM);
mutex_lock(&chrdevs_lock);
/* temporary */
//此if语句目的在于如果主设备号为零，则自动分配主设备号（寻找设备号列表中的空的位置（从大到小））并返回
) {
; i > ; i--) {
if (chrdevs[i] == NULL)
break;
}
) {
ret = -EBUSY;
goto out;
}
major = i;
ret = major;
}
//新元素赋值
cd->major = major;
cd->baseminor = baseminor;
cd->minorct = minorct;
strlcpy(cd->name, name, sizeof(cd->name));
i = major_to_index(major);
/* index in the above */
static inline int major_to_index(unsigned major)
{
return major % CHRDEV_MAJOR_HASH_SIZE;
}
//寻找新元素插入的位置
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) {//如果当前元素存在并且主设备号和要添加的主设备号一致
int old_min = (*cp)->baseminor;//更新旧的最小值，值为当前元素的次设备号
;////更新旧的最大值，值为当前次设备号+要申请号的设备个数-1,-1是因为从0开始的次设备号
int new_min = baseminor;//新的最小值为要添加的次设备号
;
//新的最大值为要添加的次设备号+要申请号的设备个数-1,-1是因为次设备号从0开始
/* New driver overlaps from the left. */
//显然生成的新的值必须要大于旧的最大值或者小于旧的最小值
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);
}
if (IS_ERR(cd))
goto fail;
}
;
fail:
to = n;
for (n = from; n < to; n = next) {
next = MKDEV(MAJOR(n)+, );
kfree(__unregister_chrdev_region(MAJOR(n), MINOR(n), next - n));
}
return PTR_ERR(cd);
}
gDev = kzalloc(sizeof(struct cdev), GFP_KERNEL);
gFile = kzalloc(sizeof(struct file_operations), GFP_KERNEL);
gFile->open = butsOpen;
//注册设备函数到file_operations结构体gFile
//gDev->owner = THIS_MODULE;
gFile->owner = THIS_MODULE;
cdev_init(gDev, gFile);
//在cdev结构体中添加指针指向file_operations结构体gFile
cdev_add(gDev, devNum, );
//建立设备号与cdev结构体联系
printk(KERN_EMERG"button driver initial done...\r\n");
;
}