linux - 主次设备号自动申请

alloc_chrdev_region 原型如下，该函数向内核申请一个空闲的主设备号。

alloc_chrdev_region(&g_aputriger_dev, 0, APUTRIGER_MAX_NUM, "aputriger0");

第四个参数是我们使用cat /proc/devices 看到的名称

/*** 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)
{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;
}

如果我们的设备不止一个，次设备号我们也希望是自动申请而不是人为指定的，那么可以使用ida_simple_get来申请，原型如下:

minor = ida_simple_get(&g_aputriger_dev, 0, APUTRIGER_MAX_NUM, GFP_KERNEL);

#define ida_simple_get(ida, start, end, gfp)	\ida_alloc_range(ida, start, (end) - 1, gfp)/*** ida_alloc_range() - Allocate an unused ID.* @ida: IDA handle.* @min: Lowest ID to allocate.* @max: Highest ID to allocate.* @gfp: Memory allocation flags.** Allocate an ID between @min and @max, inclusive.  The allocated ID will* not exceed %INT_MAX, even if @max is larger.** Context: Any context.* Return: The allocated ID, or %-ENOMEM if memory could not be allocated,* or %-ENOSPC if there are no free IDs.*/
int ida_alloc_range(struct ida *ida, unsigned int min, unsigned int max,gfp_t gfp)
{int id = 0;unsigned long flags;if ((int)min < 0)return -ENOSPC;if ((int)max < 0)max = INT_MAX;again:xa_lock_irqsave(&ida->ida_rt, flags);id = ida_get_new_above(ida, min);if (id > (int)max) {ida_remove(ida, id);id = -ENOSPC;}xa_unlock_irqrestore(&ida->ida_rt, flags);if (unlikely(id == -EAGAIN)) {if (!ida_pre_get(ida, gfp))return -ENOMEM;goto again;}return id;
}

创建设备示例：

	if (cdev_add(&cur_dev->cdev, MKDEV(g_aputriger_dev, minor), 1)) {pr_err("%s cdev add failed\n", cdev_name);goto err_class_destr;}/* devices create */cur_dev->dev = device_create(cur_dev->class, NULL, MKDEV(cur_dev->major, minor), NULL, cdev_name);