Linux-DEVICE_ATTR()參考

 1.介绍

使用DEVICE_ATTR，可以实现驱动在sys目录自动创建文件,我们只需要实现show和store函数即可.

然后在应用层就能通过cat和echo命令来对sys创建出来的文件进行读写驱动设备,实现交互.

2.DEVICE_ATTR()宏定义

DEVICE_ATTR()定义位于include/linux/device.h中,定义如下所示:

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

以下面DEVICE_ATTR()定义为例:

static ssize_t show_my_device(struct device *dev,
                  struct device_attribute *attr, char *buf)   //cat命令时,将会调用该函数
{
    return buf;
}

static ssize_t set_my_device(struct device *dev,
                 struct device_attribute *attr,
                 const char *buf, size_t len)   //echo命令时,将会调用该函数.
{
    return len;
}
static DEVICE_ATTR(my_device_test, S_IWUSR|S_IRUSR, show_my_device, set_my_device);   //定义一个名字为my_device_test的设备属性文件

最终将宏展开为:
struct device_attribute dev_attr_my_device_test ={  
    .attr = {.name = "my_device_test", .mode = S_IWUSR|S_IRUSR },     
    .show    = show_my_device,                 
    .store    = set_my_device,             
}

然后再通过device_create_file()或者sysfs_create_file()便来创建上面my_device_test设备文件.

3.使用示例
示例代码如下:
#include <board.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/platform_device.h>
#include <linux/gpio.h>
#include <linux/delay.h>
#include <linux/regulator/consumer.h>
#include <sound/soc.h>
#include <sound/jack.h>


static  char mybuf[100]="123";
static ssize_t show_my_device(struct device *dev,
                  struct device_attribute *attr, char *buf)        //cat命令时,将会调用该函数
{
    return sprintf(buf, "%s\n", mybuf);
}

static ssize_t set_my_device(struct device *dev,
                 struct device_attribute *attr,
                 const char *buf, size_t len)        //echo命令时,将会调用该函数
{
    sprintf(mybuf, "%s", buf);
    return len;
}
static DEVICE_ATTR(my_device_test, S_IWUSR|S_IRUSR, show_my_device, set_my_device);
                //定义一个名字为my_device_test的设备属性文件
                
struct file_operations mytest_ops={
         .owner  = THIS_MODULE,
};

static int major;
static struct class *cls;
static int mytest_init(void)
{
         struct device *mydev;   
         major=register_chrdev(0,"mytest", &mytest_ops);
         cls=class_create(THIS_MODULE, "mytest_class");
         mydev = device_create(cls, 0, MKDEV(major,0),NULL,"mytest_device");    //创建mytest_device设备    
    
    if(sysfs_create_file(&(mydev->kobj), &dev_attr_my_device_test.attr)){    //在mytest_device设备目录下创建一个my_device_test属性文件
            return -1;}
            
         return 0;
}

static void mytest_exit(void)
{
         device_destroy(cls, MKDEV(major,0));
         class_destroy(cls);
         unregister_chrdev(major, "mytest");
}

module_init(mytest_init);
module_exit(mytest_exit);
MODULE_LICENSE("GPL");
效果如下: