linux内核 简化版kset-example.c解析

/**********************************************
 * Author: lewiyon@hotmail.com
 * File name: kset_sample.c
 * Description: kset example
 * Date: 2011-12-10
 *********************************************/

#include <linux/kobject.h>
#include <linux/string.h>
#include <linux/sysfs.h>
#include <linux/slab.h>
#include <linux/module.h>
#include <linux/init.h>

/*
 * 将要创建的文件foo对应的kobj.
 */
struct foo_obj {
	struct kobject kobj;
	int foo;
	int baz;
	int bar;
};
/* 通过域成员返回结构体的指针 */
#define to_foo_obj(x) container_of(x, struct foo_obj, kobj)

/* 属性 */
struct foo_attribute {
	struct attribute attr;
	ssize_t (*show)(struct foo_obj *foo, struct foo_attribute *attr, char *buf);
	ssize_t (*store)(struct foo_obj *foo, struct foo_attribute *attr, const char *buf, size_t count);
};
#define to_foo_attr(x) container_of(x, struct foo_attribute, attr)

/*
 * 属性foo信息显示函数 (涉及文件目录foo/)
 */
static ssize_t foo_attr_show(struct kobject *kobj,
			     struct attribute *attr,
			     char *buf)
{
	struct foo_attribute *attribute;
	struct foo_obj *foo;

	attribute = to_foo_attr(attr);
	foo = to_foo_obj(kobj);

	if (!attribute->show)
		return -EIO;

	return attribute->show(foo, attribute, buf);
}

/*
 * 属性foo存储函数(涉及文件目录foo/) (when a value is written to a file.)
 */
static ssize_t foo_attr_store(struct kobject *kobj,
			      struct attribute *attr,
			      const char *buf, size_t len)
{
	struct foo_attribute *attribute;
	struct foo_obj *foo;

	attribute = to_foo_attr(attr);
	foo = to_foo_obj(kobj);

	if (!attribute->store)
		return -EIO;

	return attribute->store(foo, attribute, buf, len);
}

/* 
 * foo的show/store列表
 */
static const struct sysfs_ops foo_sysfs_ops = {
	.show = foo_attr_show,
	.store = foo_attr_store,
};

/*
 * The release function for our object.  This is REQUIRED by the kernel to
 * have.  We free the memory held in our object here.
 */
static void foo_release(struct kobject *kobj)
{
	struct foo_obj *foo;

	foo = to_foo_obj(kobj);
	kfree(foo);
}

/*
 * 当需要从foo文件中读取信息时，调用此函数
 */
static ssize_t foo_show(struct foo_obj *foo_obj, struct foo_attribute *attr,
			char *buf)
{
	return sprintf(buf, "%d\n", foo_obj->foo);
}

/*
 * 当往foo文件写入信息时，调用此函数
 */
static ssize_t foo_store(struct foo_obj *foo_obj, struct foo_attribute *attr,
			 const char *buf, size_t count)
{
	sscanf(buf, "%du", &foo_obj->foo);
	return count;
}

static struct foo_attribute foo_attribute =
	__ATTR(foo, 0666, foo_show, foo_store);

/*
 * foo_ktype的属性列表
 */
static struct attribute *foo_default_attrs[] = {
	&foo_attribute.attr,
	NULL,	/* need to NULL terminate the list of attributes */
};

/*
 * 定义kobj_type结构体
 * 指定sysfs_ops,release函数, 属性列表foo_default_attrs
 */
static struct kobj_type foo_ktype = {
	.sysfs_ops = &foo_sysfs_ops,
	.release = foo_release,
	.default_attrs = foo_default_attrs,
};

static struct kset *example_kset;
static struct foo_obj *foo_obj;

static struct foo_obj *create_foo_obj(const char *name)
{
	struct foo_obj *foo;
	int retval;

	/* allocate the memory for the whole object */
	foo = kzalloc(sizeof(*foo), GFP_KERNEL);
	if (!foo)
		return NULL;

	foo->kobj.kset = example_kset;

    /*
     * 初始化kobject数据结结构foo->lobj,
     * 即 在foo->kobj的层次组织kset中创建个名为name的文件foo/foo
     * 成功返回0
     */
	retval = kobject_init_and_add(&foo->kobj, &foo_ktype, NULL, "%s", name);
	if (retval) {
        /* 减小kobj的引用计数 */
		kobject_put(&foo->kobj);
		return NULL;
	}

	/*
     * 发送 KOBJ_ADD / KOBJ_REMOVE 等事件
	 * We are always responsible for sending the uevent that the kobject
	 * was added to the system.
	 */
	kobject_uevent(&foo->kobj, KOBJ_ADD);

	return foo;
}

static void destroy_foo_obj(struct foo_obj *foo)
{
    /* 减小kobj的引用计数 */
	kobject_put(&foo->kobj);
}

static int __init example_init(void)
{
	/* 
     * 动态地在kernel_kobj所对应的目录/sys/kernel/下创建一个目录kset_example
     * 并返回kset_example对应的kset
     */
	example_kset = kset_create_and_add("kset_example", NULL, kernel_kobj);
	if (!example_kset)
		return -ENOMEM;

	foo_obj = create_foo_obj("foo");
	if (!foo_obj)
		goto foo_error;

	return 0;

foo_error:
	return -EINVAL;
}

static void __exit example_exit(void)
{
	destroy_foo_obj(foo_obj);
	kset_unregister(example_kset);
}

module_init(example_init);
module_exit(example_exit);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("lewiyon <lewiyon@hotmail.com>");