流程分析

kobject/kset的相关代码比较简单，毕竟它只是作为一个结构体嵌入其他high-level的结构中，充当纽带的作用。不过，我还是简单的上一张图吧：

完成的工作基本就是分配结构体，初始化各个结构体字段，构建拓扑关系（主要是添加到kset的list中，parent的指向等）等，看懂了结构体的组织，这部分的代码理解起来就很轻松了；

示例

先上一个原理图：

代码

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


//自定义一个结构，包含了struct kobject子结构
struct test_kobj {
    int value;
    struct kobject kobj;
};


//自定义个属性结构体，包含了struct attribute结构
struct test_kobj_attribute {
    struct attribute attr;
    ssize_t (*show)(struct test_kobj *obj, struct test_kobj_attribute *attr, char *buf);
    ssize_t (*store)(struct test_kobj *obj, struct test_kobj_attribute *attr, const char *buf, size_t count);
};


//声明一个全局结构用于测试
struct test_kobj *obj;


//用于初始化sysfs_ops中的函数指针
static ssize_t test_kobj_attr_show(struct kobject *kobj, struct attribute *attr, char *buf)
{
    struct test_kobj_attribute *test_kobj_attr;
    ssize_t ret = -EIO;


    test_kobj_attr = container_of(attr, struct test_kobj_attribute, attr);

    //回调到具体的实现函数
    if (test_kobj_attr- >show)
        ret = test_kobj_attr- >show(container_of(kobj, struct test_kobj, kobj), test_kobj_attr, buf);

    return ret;
}


//用于初始化sysfs_ops中的函数指针
static ssize_t test_kobj_attr_store(struct kobject *kobj, struct attribute *attr, const char *buf, size_t count)
{
    struct test_kobj_attribute *test_kobj_attr;
    ssize_t ret = -EIO;


    test_kobj_attr = container_of(attr, struct test_kobj_attribute, attr);

    //回调到具体的实现函数
    if (test_kobj_attr- >store)
        ret = test_kobj_attr- >store(container_of(kobj, struct test_kobj, kobj), test_kobj_attr, buf, count);

    return ret;
}


//用于初始化kobj_ktype
const struct sysfs_ops test_kobj_sysfs_ops = {
    .show = test_kobj_attr_show,
    .store = test_kobj_attr_store,
};


//用于初始化kobj_ktype，最终用于释放kobject
void obj_release(struct kobject *kobj)
{
    struct test_kobj *obj = container_of(kobj, struct test_kobj, kobj);


    printk(KERN_INFO "test kobject release %sn", kobject_name(&obj- >kobj));

    kfree(obj);
}


//定义kobj_ktype，用于指定kobject的类型，初始化的时候使用
static struct kobj_type test_kobj_ktype = {
    .release = obj_release,
    .sysfs_ops = &test_kobj_sysfs_ops,
};


//show函数的具体实现
ssize_t name_show(struct test_kobj *obj, struct test_kobj_attribute *attr, char *buffer)
{
    return sprintf(buffer, "%sn", kobject_name(&obj- >kobj));
}


//show函数的具体实现
ssize_t value_show(struct test_kobj *obj, struct test_kobj_attribute *attr, char *buffer)
{
    return sprintf(buffer, "%dn", obj- >value);
}


//store函数的具体实现
ssize_t value_store(struct test_kobj *obj, struct test_kobj_attribute *attr, const char *buffer, size_t size)
{
    sscanf(buffer, "%d", &obj- >value);


    return size;
}


//定义属性，最终注册进sysfs系统
struct test_kobj_attribute name_attribute = __ATTR(name, 0664, name_show, NULL);
struct test_kobj_attribute value_attribute = __ATTR(value, 0664, value_show, value_store);
struct attribute *test_kobj_attrs[] = {
    &name_attribute.attr,
    &value_attribute.attr,
    NULL,
};


//定义组
struct attribute_group test_kobj_group = {
    .name = "test_kobj_group",
    .attrs = test_kobj_attrs,
};


//模块初始化函数
static int __init test_kobj_init(void)
{
    int retval;
    printk(KERN_INFO "test_kobj_initn");
    obj = kmalloc(sizeof(struct test_kobj), GFP_KERNEL);
    if (!obj) {
        return -ENOMEM;
    }

    obj- >value = 1;
    memset(&obj- >kobj, 0, sizeof(struct kobject));
    //添加进sysfs系统
    kobject_init_and_add(&obj- >kobj, &test_kobj_ktype, NULL, "test_kobj");


    //在sys文件夹下创建文件
    retval = sysfs_create_files(&obj- >kobj, (const struct attribute **)test_kobj_attrs);
    if (retval) {
        kobject_put(&obj- >kobj);
        return retval;
    }

    //在sys文件夹下创建group
    retval = sysfs_create_group(&obj- >kobj, &test_kobj_group);
    if (retval) {
        kobject_put(&obj- >kobj);
        return retval;
    }

    return 0;
}


//模块清理函数
static void __exit test_kobj_exit(void)
{
    printk(KERN_INFO "test_kobj_exitn");


    kobject_del(&obj- >kobj);
    kobject_put(&obj- >kobj);

    return;
}


module_init(test_kobj_init);
module_exit(test_kobj_exit);


MODULE_AUTHOR("LoyenWang");
MODULE_LICENSE("GPL");

Makefile

ifneq  ($(KERNELRELEASE),)
obj-m:=test_kobject.o
else
KERDIR := /lib/modules/$(shell uname -r)/build
PWD:=$(shell pwd)
all:
	make -C $(KERDIR) M=$(PWD) modules
clean:
	rm -f *.ko *.o *.symvers *.cmd *.cmd.o modules.* *.mod.c
endif