设备模型的基础---kobject,kset

设备模型的基础是kobject,kset,kobj_type。
kobject本身并没有什么意义，真正有用的地方在于嵌入了kobject的结构体(对象)，kobject可以看成是一个最小单元，sysfs的层次结构中的元素都是由kobject构成。

kset与kobject的关系：
kset会包含一类的kobject对象(内核链表串起来)，而这些对象对应在sysfs中就是同一级的各个子目录，每一个kobject对象有自己的属性，这些属性就对应于各自子目录的文件。
如此，就会构成一个有层次的组织结构。
kset本身也包含一个kobject，但这个kobject与kset内核链表list中的kobjects并没有什么关系。

kobject的两个主要作用：

1.引用计数

2.事件上报(kobject不加入某个kset是不会上报uevent的 http://www.cnblogs.com/black-mamba/p/5055683.html)

相关文档：
linux/Documentation/kobject.txt
Documentation/filesystems/sysfs.txt
Documentation/filesystems/sysfs-pci.txt

linux/include/linux/kobject.h
struct kset {
struct list_head list;//所有属于当前集合的kobject对象的链表
spinlock_t list_lock;
struct kobject kobj; //与集合中包含的各个kobject无关，只是用来管理kset对象本身
const struct kset_uevent_ops *uevent_ops;//用于将集合的状态信息传递给用户层。该机制有驱动程序的核心使用。
};

//描述内核对象的共同特性
struct kobj_type {
void (*release)(struct kobject *kobj);
const struct sysfs_ops *sysfs_ops;
struct attribute **default_attrs;
const struct kobj_ns_type_operations *(*child_ns_type)(struct kobject *kobj);
const void *(*namespace)(struct kobject *kobj);
};

//kobject直接嵌入到其他数据结构中，通过管理kobject即可以对包含kobject的对象进行管理。
//kobject包含在一个层次化的组织中。
struct kobject {
const char *name;//对象名称
struct list_head entry;
struct kobject *parent; //决定kobject出现在sysfs层次结构中的位置:如果存在父对象,那么需要在父对象对应的目录中新建一项;否则，将其放置到kobject所在的kset所属的kobject对应的目录中
struct kset *kset;//集合指针
struct kobj_type *ktype;
struct sysfs_dirent *sd;
struct kref kref; //引用计数
unsigned int state_initialized:1;
unsigned int state_in_sysfs:1;
unsigned int state_add_uevent_sent:1;
unsigned int state_remove_uevent_sent:1;
unsigned int uevent_suppress:1;
};

struct kobj_attribute {
struct attribute attr;
ssize_t (*show)(struct kobject *kobj, struct kobj_attribute *attr,//用户空间读属性时，内核会调用该函数
char *buf);
ssize_t (*store)(struct kobject *kobj, struct kobj_attribute *attr,//用户空间写属性时，内核会调用该函数
const char *buf, size_t count);
};

/disk/A9/linux-3.5/include/linux/sysfs.h
struct attribute {
const char *name;//显示的文件名
umode_t mode;//文件的权限
#ifdef CONFIG_DEBUG_LOCK_ALLOC
bool ignore_lockdep:1;
struct lock_class_key *key;
struct lock_class_key skey;
#endif
};

#define __ATTR(_name,_mode,_show,_store) { \
.attr = {.name = __stringify(_name), .mode = _mode }, \
.show = _show, \
.store = _store, }

struct attribute_group {
const char *name;
umode_t (*is_visible)(struct kobject *,
struct attribute *, int);
struct attribute **attrs;
};

struct kobject *kobject_get(struct kobject *kobj) //引用+1
void kobject_put(struct kobject *kobj)//引用-1

void kobject_init(struct kobject *kobj, struct kobj_type *ktype)
初始化kobeject结构体

struct kobject *kobject_create(void)//非导出函数
创建一个kobject结构体，并用kobject_init初始化

int kobject_add(struct kobject *kobj, struct kobject *parent,
const char *fmt, ...)
注册一个kobject,在sysfs中生成相应的目录。
如果parent为空，则kobject的parent指向其kset的kobject;如果kset也没有分配，则kobject位于/sys下

struct kobject *kobject_create_and_add(const char *name, struct kobject *parent)
创建一个kobject并注册到sysfs，失败返回空。

int kobject_init_and_add(struct kobject *kobj, struct kobj_type *ktype,
struct kobject *parent, const char *fmt, ...)
初始化一个kobject并注册到sysfs,属性文件会自动生成。

Q1：用户空间调用什么接口是与show、store是相对应的？

linux/include/linux/kobject.h
 /**
* struct kset - a set of kobjects of a specific type, belonging to a specific subsystem.
*
* A kset defines a group of kobjects.  They can be individually
* different "types" but overall these kobjects all want to be grouped
* together and operated on in the same manner.  ksets are used to
* define the attribute callbacks and other common events that happen to
* a kobject.
*
* @list: the list of all kobjects for this kset
* @list_lock: a lock for iterating over the kobjects
* @kobj: the embedded kobject for this kset (recursion, isn‘t it fun...)
* @uevent_ops: the set of uevent operations for this kset.  These are
* called whenever a kobject has something happen to it so that the kset
* can add new environment variables, or filter out the uevents if so
* desired.
*/
struct kset {
    struct list_head list;//所有属于当前集合的kobject对象的链表
    spinlock_t list_lock;
    struct kobject kobj;  //与集合中包含的各个kobject无关，只是用来管理kset对象本身
    const struct kset_uevent_ops *uevent_ops;//用于将集合的状态信息传递给用户层。该机制由驱动程序的核心使用。
}; 

/**
 * kset_create - create a struct kset dynamically
 *
 * @name: the name for the kset
 * @uevent_ops: a struct kset_uevent_ops for the kset
 * @parent_kobj: the parent kobject of this kset, if any.
 *
 * This function creates a kset structure dynamically.  This structure can
 * then be registered with the system and show up in sysfs with a call to
 * kset_register().  When you are finished with this structure, if
 * kset_register() has been called, call kset_unregister() and the
 * structure will be dynamically freed when it is no longer being used.
 *
 * If the kset was not able to be created, NULL will be returned.
 */
 //非导出函数
static struct kset *kset_create(const char *name,
                const struct kset_uevent_ops *uevent_ops,
                struct kobject *parent_kobj)
/**
 * kset_init - initialize a kset for use
 * @k: kset
 */
void kset_init(struct kset *k)

/**
 * kset_register - initialize and add a kset.
 * @k: kset.
 */
int kset_register(struct kset *k)

/**
 * kset_unregister - remove a kset.
 * @k: kset.
 */
void kset_unregister(struct kset *k)

/**
 * kobject_uevent - notify userspace by sending an uevent
 *
 * @action: action that is happening
 * @kobj: struct kobject that the action is happening to
 *
 * Returns 0 if kobject_uevent() is completed with success or the
 * corresponding error when it fails.
 */
int kobject_uevent(struct kobject *kobj, enum kobject_action action)

/**
 * kset_create_and_add - create a struct kset dynamically and add it to sysfs
 *
 * @name: the name for the kset
 * @uevent_ops: a struct kset_uevent_ops for the kset
 * @parent_kobj: the parent kobject of this kset, if any.
 *
 * This function creates a kset structure dynamically and registers it
 * with sysfs.  When you are finished with this structure, call
 * kset_unregister() and the structure will be dynamically freed when it
 * is no longer being used.
 *
 * If the kset was not able to be created, NULL will be returned.
 */
struct kset *kset_create_and_add(const char *name,
                 const struct kset_uevent_ops *uevent_ops,
                 struct kobject *parent_kobj)