Linux 虚拟文件系统sysfs之属性文件attribute 整理（一）

sysfs接口函数到建立_DEVICE_ATTR

架构图：

 

 

 

 

最近在弄Sensor驱动，看过一个某厂家的成品驱动，里面实现的全都是sysfs接口，hal层利用sysfs生成的接口，对Sensor进行操作。

说道sysfs接口，就不得不提到函数宏 DEVICE_ATTR

原型是#define DEVICE_ATTR(_name, _mode, _show, _store) \

struct device_attribute dev_attr_##_name = __ATTR(_name, _mode, _show, _store)

函数宏DEVICE_ATTR内封装的是__ATTR(_name,_mode,_show,_stroe)方法，_show表示的是读方法，_stroe表示的是写方法。

当然_ATTR不是独生子女，他还有一系列的姊妹__ATTR_RO宏只有读方法，__ATTR_NULL等等

如 对设备的使用  DEVICE_ATTR  ，对总线使用  BUS_ATTR  ，对驱动使用 DRIVER_ATTR  ，对类 别 (class) 使用  CLASS_ATTR,  这四个高级的宏来自于<include/linux/device.h> 

DEVICE_ATTR  宏声明有四个参数，分别是名称、权限位、读函数、写函数。其中读函数和写函数是读写功能函数的函数名。

如果你完成了DEVICE_ATTR函数宏的填充，下面就需要创建接口了

例如：

    static DEVICE_ATTR(polling, S_IRUGO | S_IWUSR, show_polling, set_polling);
    static struct attribute *dev_attrs[] = {
            &dev_attr_polling.attr,
            NULL,
    };

当你想要实现的接口名字是polling的时候，需要实现结构体struct attribute *dev_attrs[]

其中成员变量的名字必须是&dev_attr_polling.attr

然后再封装

    static struct attribute_group dev_attr_grp = {
            .attrs = dev_attrs,
    };

 

在利用sysfs_create_group(&pdev->dev.kobj, &dev_attr_grp);创建接口

通 过以上简单的三个步骤，就可以在adb shell 终端查看到接口了。当我们将数据 echo 到接口中时，在上层实际上完成了一次 write 操 作，对应到 kernel ，调用了驱动中的 “store”。同理，当我们cat 一个 接口时则会调用 “show” 。到这里，只是简单的建立 了 android 层到 kernel 的桥梁，真正实现对硬件操作的，还是在 "show" 和 "store" 中完成的。

 

示例代码：

#include <linux/ctype.h>
#include <linux/device.h>
#include <linux/err.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/leds.h>
#include <linux/list.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/timer.h>
#include "leds.h"
#include <linux/init.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/of.h>
#include <linux/of_gpio.h>
#include <linux/gpio/consumer.h>
static struct class *leds_class;
static ssize_t brightness_show(struct device *dev,
		struct device_attribute *attr, char *buf)
{
	struct led_classdev *led_cdev = dev_get_drvdata(dev);
	/* no lock needed for this */
	led_update_brightness(led_cdev);
	return sprintf(buf, "%u\n", led_cdev->brightness);
}
static ssize_t brightness_store(struct device *dev,
		struct device_attribute *attr, const char *buf, size_t size)
{
	struct led_classdev *led_cdev = dev_get_drvdata(dev);
	unsigned long state;
	ssize_t ret;
	mutex_lock(&led_cdev->led_access);
	if (led_sysfs_is_disabled(led_cdev)) {
		ret = -EBUSY;
		goto unlock;
	}
	ret = kstrtoul(buf, 10, &state);
	if (ret)
		goto unlock;
	if (state == LED_OFF && !(led_cdev->flags & LED_KEEP_TRIGGER))
		led_trigger_remove(led_cdev);
	led_set_brightness(led_cdev, state);
	led_cdev->usr_brightness_req = state;
	ret = size;
unlock:
	mutex_unlock(&led_cdev->led_access);
	return ret;
}
static DEVICE_ATTR_RW(brightness);
static ssize_t max_brightness_show(struct device *dev,
		struct device_attribute *attr, char *buf)
{
	struct led_classdev *led_cdev = dev_get_drvdata(dev);
	return sprintf(buf, "%u\n", led_cdev->max_brightness);
}
static ssize_t max_brightness_store(struct device *dev,
		struct device_attribute *attr, const char *buf, size_t size)
{
	struct led_classdev *led_cdev = dev_get_drvdata(dev);
	unsigned long state;
	ssize_t ret = -EINVAL;
	ret = kstrtoul(buf, 10, &state);
	if (ret)
		return ret;
	led_cdev->max_brightness = state;
	led_set_brightness(led_cdev, led_cdev->usr_brightness_req);
	return size;
}
static DEVICE_ATTR_RW(max_brightness);
static ssize_t chenp_show(struct device *dev,
		struct device_attribute *attr, char *buf)
{	
	struct led_classdev *led_cdev = dev_get_drvdata(dev);
	/* no lock needed for this */
	led_update_brightness(led_cdev);
	return sprintf(buf, "%u\n", led_cdev->brightness);
}
static ssize_t chenp_store(struct device *dev,
		struct device_attribute *attr, const char *buf, size_t size)
{	
		struct led_classdev *led_cdev = dev_get_drvdata(dev);
		unsigned long state;
		ssize_t ret;
		struct lp8860_led *led = container_of(led_cdev, struct lp8860_led, led_dev);
	    led->brightness = 12;
		//if (led->enable_gpio)
		mutex_lock(&led_cdev->led_access);
		if (led_sysfs_is_disabled(led_cdev)) {
			ret = -EBUSY;
			goto unlock;
		}
		ret = kstrtoul(buf, 10, &state);
		printk("chenp %s(line%d) state=%lu \n",__FILE__,__LINE__,state);
		if (state)
			gpiod_direction_output(led->enable_gpio, 1);
		else
			gpiod_directiosn_output(led->enable_gpio, 0);
		if (ret)
			goto unlock;
		if (state == LED_OFF && !(led_cdev->flags & LED_KEEP_TRIGGER))
			led_trigger_remove(led_cdev);
		//led_set_brightness(led_cdev, state);
		led_cdev->usr_brightness_req = state;
		ret = size;
	unlock:
		mutex_unlock(&led_cdev->led_access);
		return ret;
}
static DEVICE_ATTR_RW(chenp);
#ifdef CONFIG_LEDS_TRIGGERS
static DEVICE_ATTR(trigger, 0644, led_trigger_show, led_trigger_store);
static struct attribute *led_trigger_attrs[] = {
	&dev_attr_trigger.attr,
	NULL,
};
static const struct attribute_group led_trigger_group = {
	.attrs = led_trigger_attrs,
};
#endif
static struct attribute *led_class_attrs[] = {
	&dev_attr_brightness.attr,
	&dev_attr_max_brightness.attr,
	&dev_attr_chenp.attr,
	NULL,
};
static const struct attribute_group led_group = {
	.attrs = led_class_attrs,
};
static const struct attribute_group *led_groups[] = {
	&led_group,
#ifdef CONFIG_LEDS_TRIGGERS
	&led_trigger_group,
#endif
	NULL,
};