1.设备号的获取

\qquad 设备号的获取方法：自动分配；指定设备号注册

2.自动分配函数

\qquad 函数：int alloc_chrdev_region(dev_t *dev, unsigned baseminor, unsigned count, const char *name)
\qquad 功能：分配设备号
\qquad 参数：第一个参数：dev_t类型定义的变量，取地址传入；第二个参数：次设备号，次设备号自己指定；第三个参数：设备个数；第四个参数：名字
\qquad 返回值：成功返回0；失败返回负数错误码

int alloc_chrdev_region(dev_t *dev, unsigned baseminor, unsigned count, const char *name)
{
	struct char_device_struct *cd;
	cd = __register_chrdev_region(0, baseminor, count, name);
	if (IS_ERR(cd))
		return PTR_ERR(cd);
	*dev = MKDEV(cd->major, cd->baseminor);
	return 0;
}

3.指定设备号注册

\qquad 函数：int register_chrdev_region(dev_t from, unsigned count, const char *name)
\qquad 功能：指定设备号注册
\qquad 参数：第一个参数：设备号（MKDEV(major,minor)）；第二个参数：设备个数；第三个参数：名字
\qquad 返回值：成功返回0；失败返回负数错误码

int register_chrdev_region(dev_t from, unsigned count, const char *name)
{
	struct char_device_struct *cd;
	dev_t to = from + count;
	dev_t n, next;

	for (n = from; n < to; n = next) {
		next = MKDEV(MAJOR(n)+1, 0);
		if (next > to)
			next = to;
		cd = __register_chrdev_region(MAJOR(n), MINOR(n),
			       next - n, name);
		if (IS_ERR(cd))
			goto fail;
	}
	return 0;
fail:
	to = n;
	for (n = from; n < to; n = next) {
		next = MKDEV(MAJOR(n)+1, 0);
		kfree(__unregister_chrdev_region(MAJOR(n), MINOR(n), next - n));
	}
	return PTR_ERR(cd);
}

4.注销设备号

\qquad 函数：void unregister_chrdev_region(dev_t from, unsigned count)
\qquad 功能：注销设备号
\qquad 参数：第一个参数：设备号；第二个参数：设备个数
\qquad 返回值：void

void unregister_chrdev_region(dev_t from, unsigned count)
{
	dev_t to = from + count;
	dev_t n, next;

	for (n = from; n < to; n = next) {
		next = MKDEV(MAJOR(n)+1, 0);
		if (next > to)
			next = to;
		kfree(__unregister_chrdev_region(MAJOR(n), MINOR(n), next - n));
	}
}