使用DEVICE_ATTR宏，可以定义一个struct device_attribute设备属性，使用函数sysfs_create_group或sysfs_create_file便可以在设备目录下创建具有show和store方法的节点。能方便的进行调试。
一、使用DEVICE_ATTR构建device attribute下面将顺着我们直接使用的DEVICE_ATTR来分析一下，这个宏究竟都做了哪些事情。
DEVICE_ATTR的定义:
#define DEVICE_ATTR(_name, _mode, _show, _store) struct device_attribute dev_attr_##_name = __ATTR(_name, _mode, _show, _store)
而__ATTR宏的定义在include/linux/sysfs.h文件中，如下：
#define __ATTR(_name, _mode, _show, _store) { .attr = {.name = __stringify(_name), .mode = VERIFY_OCTAL_PERMISSIONS(_mode) }, .show = _show, .store = _store, }那么struct device_attribute的定义又是怎么样的呢？该结构体的定义在include /linux/device.h，其定义如下：
/* interface for exporting device attributes */struct device_attribute { struct attribute attr; ssize_t (*show)(struct device *dev, struct device_attribute *attr, char *buf); ssize_t (*store)(struct device *dev, struct device_attribute *attr, const char *buf, size_t count);}；而其中的struct attribute的定义在include/linux/device.h中，如下：
struct attribute { const char *name; umode_t mode;#ifdef CONFIG_DEBUG_LOCK_ALLOC bool ignore_lockdep:1; struct lock_class_key *key; struct lock_class_key skey;#endif};总结一下：
DEVICE_ATTR(_name, _mode, _show, _store)等价于：struct device_attribute dev_attr_##_name = { .attr = {.name = __stringify(_name), .mode = VERIFY_OCTAL_PERMISSIONS(_mode)}, .show = _show, .store = _store,}其中：.show和.store的类型定义如下：
show函数的详细描述：
ssize_t (*show)(struct device *dev, struct device_attribute *attr, char *buf); 入参buf是需要我们填充的string即我们cat属性节点时要显示的内容；函数的返回值是我们填充buf的长度，且长度应当小于一个页面的大小（4096字节）；其他参数一般不用关心。例如：
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 ", mybuf);}store函数的详细描述：
ssize_t (*store)(struct device *dev, struct device_attribute *attr, const char *buf, size_t count); 入参buf是用户传入的字符串，即echo到属性节点的内容；入参count是buf中字符串的长度。函数的返回值通常返回count即可。其他参数一般不用关心。例如：
static ssize_t store_my_device(struct device *dev, struct device_attribute *attr, const char *buf, size_t count) //echo命令时,将会调用该函数{ sprintf(mybuf, "%s", buf); return count;}mode的权限定义在kernel/include/uapi/linux/stat.h中。
#define S_IRWXU 00700 //用户可读写和执行#define S_IRUSR 00400//用户可读#define S_IWUSR 00200//用户可写#define S_IXUSR 00100//用户可执行#define S_IRWXG 00070//用户组可读写和执行#define S_IRGRP 00040//用户组可读#define S_IWGRP 00020//用户组可写#define S_IXGRP 00010//用户组可执行#define S_IRWXO 00007//其他可读写和执行#define S_IROTH 00004//其他可读#define S_IWOTH 00002//其他可写#define S_IXOTH 00001//其他可执行至此，我们已经定义好了.show和.store函数，那么就可以使用DEVICE_ATTR了。
static DEVICE_ATTR(my_device_test, S_IWUSR | S_IRUSR, show_my_device, store_my_device);二、将device attribute添加到sysfs中
上面我们已经创建好了所需要的device attribute，下面就要将这些attribute添加到sysfs中了，此处可用的函数由sysfs_create_file和sysfs_create_group。
1、只有一个节点的创建sysfs_create_file
此处在驱动的probe或module_init函数调用sysfs_create_file即可,在module_exit或remove函数中调用sysfs_remove_file来移除节点。
int __must_check sysfs_create_file(struct kobject *kobj, const struct attribute *attr);void sysfs_remove_file(struct kobject *kobj, const struct attribute *attr);以下是全部的代码：
#include #include #include #include #include static char sysfs_buff[100] = "my_sysfs_test_string";static ssize_t show_sys_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 ", sysfs_buff);}static ssize_t store_sys_device(struct device *dev, struct device_attribute *attr, const char *buf, size_t count) //echo命令时,将会调用该函数{ sprintf(sysfs_buff, "%s", buf); return count;}static DEVICE_ATTR(sys_device_file, S_IWUSR | S_IRUSR, show_sys_device, store_sys_device);//定义一个名字为sys_device_file的设备属性文件struct file_operations mytest_ops = { .owner = THIS_MODULE,};static int major;static struct class *cls;struct device *mydev;static int mytest_init(void){ 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_sys_device_file.attr)) { //在mytest_device设备目录下创建一个sys_device_file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"); sysfs_remove_file(&(mydev->kobj), &dev_attr_sys_device_file.attr);}module_init(mytest_init);module_exit(mytest_exit);MODULE_LICENSE("GPL");
2、多个节点的创建sysfs_create_group
定义attribute属性结构体数组到属性组中：
static DEVICE_ATTR(sys_device_file, S_IWUSR | S_IRUSR, show_sys_device, store_sys_device);static DEVICE_ATTR(sys_device_file0, S_IWUSR | S_IRUSR, show_sys_device, store_sys_device);static DEVICE_ATTR(sys_device_file1, S_IWUSR | S_IRUSR, show_sys_device, store_sys_device);static DEVICE_ATTR(sys_device_file2, S_IWUSR | S_IRUSR, show_sys_device, store_sys_device);static struct attribute *sys_device_attributes[] = { &dev_attr_sys_device_file.attr, &dev_attr_sys_device_file0.attr, &dev_attr_sys_device_file1.attr, &dev_attr_sys_device_file2.attr, NULL////属性结构体数组最后一项必须以NULL结尾。};static const struct attribute_group sys_device_attr_group = { .attrs = sys_device_attributes,};下面就可以利用sysfs_create_group和sysfs_create_group来添加、移除属性节点组了。
定义如下：
int sysfs_create_group(struct kobject *kobj, const struct attribute_group *grp)void sysfs_remove_group(struct kobject *kobj, const struct attribute_group *grp)
全部代码如下：
#include #include #include #include #include static char sysfs_buff[100] = "my_sysfs_test_string";static ssize_t show_sys_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 ", sysfs_buff);}static ssize_t store_sys_device(struct device *dev, struct device_attribute *attr, const char *buf, size_t count) //echo命令时,将会调用该函数{ sprintf(sysfs_buff, "%s", buf); return count;}//定义多个sys_device_file的设备属性文件static DEVICE_ATTR(sys_device_file, S_IWUSR | S_IRUSR, show_sys_device, store_sys_device);static DEVICE_ATTR(sys_device_file0, S_IWUSR | S_IRUSR, show_sys_device, store_sys_device);static DEVICE_ATTR(sys_device_file1, S_IWUSR | S_IRUSR, show_sys_device, store_sys_device);static DEVICE_ATTR(sys_device_file2, S_IWUSR | S_IRUSR, show_sys_device, store_sys_device);static struct attribute *sys_device_attributes[] = { &dev_attr_sys_device_file.attr, &dev_attr_sys_device_file0.attr, &dev_attr_sys_device_file1.attr, &dev_attr_sys_device_file2.attr, NULL////属性结构体数组最后一项必须以NULL结尾。};static const struct attribute_group sys_device_attr_group = { .attrs = sys_device_attributes,};struct file_operations mytest_ops = { .owner = THIS_MODULE,};static int major;static struct class *cls;struct device *mydev;static int mytest_init(void){ 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_group(&(mydev->kobj), &sys_device_attr_group)) { //在mytest_device设备目录下创建多个sys_device_file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"); sysfs_remove_group(&(mydev->kobj), &sys_device_attr_group);}module_init(mytest_init);module_exit(mytest_exit);MODULE_LICENSE("GPL");