linux sys节点属性

从底层把值传给上层有很多种方法,sysfs就是很简单的一个:

提到sysfs,就不得不提函数宏 DEVICE_ATTR

DEVICE_ATTR的原型:

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

struct device_atttribute dev_attr_##_name = __ATTR(_name,_mode,_show,_store) //名称,权限位,读函数,写函数

其中_show表示读方法 --- 对应于adb的cat

_store表示写方法 --- 对应于adb的echo.

 

_ATTR宏有很多,例如设备使用的是DEVICE_ATTR,总线使用的是BUS_ATTR,驱动使用的是DRIVER_ATTR,类别(class)使用的是CLASS_ATTR, 这四个宏定义在<inlude/linux/device.h>中.

#include <linux/module.h>
#include <linux/slab.h>
#include <linux/kobject.h>
#include <linux/platform_device.h>

struct att_dev{
	struct platform_device *pdev;
	struct kobject *kobj;
};

static ssize_t att_store(struct device *dev, 
					struct device_attribute *attr, 
					const char *buf, size_t count) 
{
	printk("echo debug buf\n");

	return count;
}

static ssize_t att_show(struct device *dev,
                 struct device_attribute *attr,
                 char *buf)
{
	printk("cat debug buf\n");
	return 0;
}
static DEVICE_ATTR(test,0777,att_show,att_store);

static struct att_dev *dev = NULL;

static __devinit int att_probe(struct platform_device *ppdev){
	int ret;
	
	dev->kobj = kobject_create_and_add("attkobj", NULL); 
	if(dev->kobj == NULL){
		ret = -ENOMEM;
		goto kobj_err;
	}

	ret = sysfs_create_file(&dev->pdev->dev.kobj,&dev_attr_test.attr);
	if(ret < 0){
		goto file_err;
	}
	return 0;

file_err:
	 kobject_del(dev->kobj);  
kobj_err:
	return ret;
}

static struct platform_driver att_driver = {
	.probe = att_probe,
	.driver = {
		.owner = THIS_MODULE,
		.name = "att_test",
	},
};

static int __init att_init(void)
{
	int ret;

	dev = kzalloc(sizeof(struct att_dev),GFP_KERNEL);
	if(dev == NULL){
		printk("%s get dev memory error\n",__func__);
		return -ENOMEM;
	}
	
	dev->pdev = platform_device_register_simple("att_test", -1, NULL, 0);  
	if(IS_ERR(dev->pdev)){
		PTR_ERR(dev->pdev); 
		printk("%s pdev error\n",__func__);
		return -1;
	}

    ret = platform_driver_register(&att_driver);
    if(ret < 0){
        printk("%s register driver error\n",__func__);
        return ret;
    }

	return 0;
}

static void __exit att_exit(void)
{
    sysfs_remove_file(&dev->pdev->dev.kobj,&dev_attr_test.attr);
    kobject_del(dev->kobj);
    platform_device_unregister(dev->pdev);
    platform_driver_unregister(&att_driver);
    if(dev != NULL)
        kfree(dev);
}

module_init(att_init);
module_exit(att_exit);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("driverSir");

安装之后/sys/devices/platform/att_test/test

echo 1 > test 

cat test

dmesg之后会看到内核打印出

[  424.793357] echo debug buf
[  427.122139] cat debug buf

说明在echo 1 > test 时调用了att_store,cat test 的时候调用了att_show

 

具体例子:

 

static DEVICE_ATTR(delay, S_IRUGO|S_IWUSR|S_IWGRP, sensor_delay_show, sensor_delay_store);
static DEVICE_ATTR(enable, S_IRUGO|S_IWUSR|S_IWGRP, sensor_enable_show, sensor_enable_store);
static DEVICE_ATTR(data, S_IRUGO, sensor_data_show, NULL);
static DEVICE_ATTR(status, S_IRUGO, sensor_status_show, NULL);

 

 static struct attribute *sensor_attributes[] = {
 &dev_attr_delay.attr,
 &dev_attr_enable.attr,
 &dev_attr_data.attr,
 &dev_attr_status.attr,
 NULL
};

 

如果你想实现的接口名字是data的时候,需要实现static struct attribute *sensor_attribute[] = { &dev_attr_data.attr}

 

将sensor_attribute封装为:static struct attribute_group sensor_attribute_group = {
 .attrs = sensor_attributes
};

 

只要利用sysfs_create_group(&input_data->dev.kobj, &sensor_attribute_group);创建接口.

通过以上三个步骤,就可以在adb shell终端查看到接口了.

当我们在shell中输入:echo "1" > enable时,在上层实际上完成了一次写操作,对应到kernel,就会调用驱动中的sensor_enable_store.

当我们在shell中输入:cat enable时,在上层实际上完成了一次读操作,对应到kernel,就会调用驱动中的sensor_enable_show.

 

这样android和kernel就建立起了桥梁,可以根据不同的操作,在store和show函数中完成对应的硬件操作

driver例子：

#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/slab.h>
#include <linux/input.h>
#include <linux/kthread.h>
#include <linux/semaphore.h>

struct v_dev{
	struct platform_device *p_dev;	
	struct input_dev *input;
	int x;
	int y;
	struct task_struct *run_thread;
	struct semaphore sem;
};

struct v_dev *vmouse_dev = NULL;

static ssize_t write_pos(struct device *dev, struct device_attribute *attr,
             const char *buf, size_t count)
{
	int x,y;
	sscanf(buf,"%d%d",&x,&y);
	vmouse_dev->x = x;
	vmouse_dev->y =y;

	//post 信号量
	up(&vmouse_dev->sem);	

	return count;
}

static ssize_t show_pos(struct device *dev, struct device_attribute *attr,
            char *buf){
	return sprintf(buf,"(%d,%d)\n",vmouse_dev->x,vmouse_dev->y);
}

DEVICE_ATTR(pos,0644,show_pos,write_pos);

static int vmouse_thread(void *data)
{
	int x,y;
	struct v_dev *vmouse_dev = (struct v_dev*)data;
	struct semaphore *sema = &(vmouse_dev->sem);
	
	printk(KERN_INFO "vmouse thread running\n");
	
	while(1){
		//等待信号量
		while((down_interruptible(sema)) == -EINTR){} ;
			
		x = vmouse_dev->x;
		y = vmouse_dev->y;
		input_report_abs(vmouse_dev->input,ABS_X,x);
		input_report_abs(vmouse_dev->input,ABS_Y,y);
		input_sync(vmouse_dev->input);

		printk("vmouse thread report\n");
	}

	return 0;
}	

static int vmouse_probe(struct platform_device *pdev)
{
	int ret = -1;
	printk("%s debug \n",__func__);
	
	if(vmouse_dev->p_dev == pdev){
		printk("platform device is same\n");
	}
	
	vmouse_dev->input = input_allocate_device();
	if(!(vmouse_dev->input)){
		printk("%s request input deivce error\n",__func__);
		goto alloc_input;
	}
	
	vmouse_dev->input->name = "vmouse";
	set_bit(EV_ABS,vmouse_dev->input->evbit);
	input_set_abs_params(vmouse_dev->input, ABS_X, -1024, 1024, 0, 0);
	input_set_abs_params(vmouse_dev->input, ABS_Y, -1024, 1024, 0, 0);

	ret = input_register_device(vmouse_dev->input);
	if(ret < 0){
		printk("%s register input device error\n",__func__);
		goto input_register;
	}
	
	device_create_file(&pdev->dev,&dev_attr_pos);
//初始化信号量，在线程中要用到
	sema_init(&(vmouse_dev->sem),0);	

	vmouse_dev->run_thread = kthread_run(vmouse_thread,vmouse_dev,"vmouse_thread");
	
	return 0;

input_register:
	input_free_device(vmouse_dev->input);
alloc_input:
	kfree(vmouse_dev);
	return ret;
}

static struct platform_driver vmouse_driver = {
	.probe = vmouse_probe,
	.driver = {
		.owner = THIS_MODULE,
		.name = "v_mouse",
	},
};

static int __init vmouse_init(void)
{
	int ret =-1;
	
	printk("%s\n", __func__);
	
	vmouse_dev = kzalloc(sizeof(struct v_dev),GFP_KERNEL);
	if(vmouse_dev == NULL){
		printk("%s alloc memory  error\n",__func__);
		return -ENOMEM;
	}

	vmouse_dev->p_dev= platform_device_register_simple("v_mouse",-1,NULL,0);	
	if(!(vmouse_dev->p_dev)){
		printk("%s register platform device error\n",__func__);
		return ret;
	}
	
	ret = platform_driver_register(&vmouse_driver);
	if(ret < 0){
		printk("%s register driver error\n",__func__);
		return ret;
	}

	return 0;
}

static void __exit vmouse_exit(void)
{
	printk("%s\n", __func__);
	if(vmouse_dev->input != NULL){
		input_unregister_device(vmouse_dev->input);
	}
	printk("%s debug__1\n",__func__);
	
	if(vmouse_dev != NULL){
	platform_device_unregister(vmouse_dev->p_dev);
	}
	printk("%s debug__2\n",__func__);
	
	platform_driver_unregister(&vmouse_driver);
	printk("%s debug__3\n",__func__);
	
	kfree(vmouse_dev);
	printk("%s debug__4\n",__func__);
}

module_init(vmouse_init);
module_exit(vmouse_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("WEED<[email protected]>");

应用层例子：

#include <fcntl.h>
#include <linux/input.h>
#include <stdio.h>
//要看自己的节点了
#define EVENT_DEV "/dev/input/event5"

int main(void)
{
	struct input_event ev;
	int count,x,y;

	int fd = open(EVENT_DEV, O_RDWR);
	if(fd < 0){
		printf("open %s failed\n",EVENT_DEV);
		return 0;
	}

	while(1){
		count = read(fd, &ev,sizeof(struct input_event));
		if(EV_ABS == ev.type){
			if(ev.code == ABS_X){
				x = ev.value;
			}else if(ev.code == ABS_Y){
				y = ev.value;
			}
			printf("position: x=%d, y=%d\n",x,y);
		}else if(EV_SYN == ev.type){
				puts("sync!");
		}
	}

	return 0;	
}

先运行应用程序：./test_sys  
在另一个终端执行：echo "90 90" >/sys/devices/platform/v_mouse/pos

你就会看到你input设备上报的坐标，打印信息如下：

position: x=90, y=0
position: x=90, y=90
sync!