一。Kobject
每個在內核中註冊的kobject都對應於sysfs文件系統中的一個目錄。
kobject在文件include/linux/kobject中定義
- struct kobject {
- const char *name; //kobject的名稱
- struct list_head entry; //kobject結構鏈表
- struct kobject *parent; //父kobject結構體
- struct kset *kset; //kset集合
- struct kobj_type *ktype; //kobject的類型描述符
- struct sysfs_dirent *sd; //sysfs文件目錄
- struct kref kref; //kobject引用計數
- unsigned int state_initialized:1; //kobject是否初始化
- unsigned int state_in_sysfs:1; //是否已經加入sysfs
- unsigned int state_add_uevent_sent:1;
- unsigned int state_remove_uevent_sent:1;
- unsigned int uevent_suppress:1;
- };
sysfs組織結構,進入sysfs目錄中。有block bus class dev devices firmware fs kernel module power這些目錄。具體代表看名字差不多就可以看出。在層次結構上,假如有一個設備A。將有一個名稱爲A的目錄。A設備是在B總線上。那A設備應該在bus目錄下的B總線下。A設備肯定會有設備的屬性(ktype),例如是音頻設備則應該有音量屬性,則音量屬性將在A設備目錄下有個音量屬性文件。在使用設備時,如果要改變音量大小,則可以寫屬性文件入音量指。得到音量大小時,可以讀取屬性文件中的音量值。
二。Kobject初始化
初始化一個kobject結構體變量,kobject_init函數(lib/kobject.c),調用此函數前應先將kobject變量成員全部置0
- /**
- * kobject_init
- initialize a kobject structure
- * @kobj: pointerto the kobjectto initialize
- * @ktype: pointerto the ktypefor this kobject.
- *
- * This function will properly initialize a kobject such that it canthen
- * be passed to the kobject_add()call.
- *
- * After this
function is called, the kobject MUST be cleaned up by acall
- * to kobject_put(),not by acallto
kfree directlyto ensure that all of
- * the memory
is cleaned up properly.
- */
- void kobject_init(struct kobject
*kobj, struct kobj_type
*ktype)
- {
- char *err_str;
- if (!kobj){ //檢查kobj變量是否爲空
- err_str =
"invalid kobject pointer!";
- goto error;
- }
- if (!ktype){ //檢查ktype類型變量是否爲空
- err_str =
"must have a ktype to be initialized properly!\n";
- goto error;
- }
- if (kobj->state_initialized){ //是否已經初始化過
- /*donot
error out as sometimes we can recover*/
- printk(KERN_ERR
"kobject (%p): tried to init an initialized "
- "object, something is seriously wrong.\n", kobj);
- dump_stack();
- }
- kobject_init_internal(kobj); //進一步初始化kobj內部成員
- kobj->ktype= ktype; //將參數中傳來的ktype變量賦值給kobj的ktype變量。
- return;
- error:
- printk(KERN_ERR
"kobject (%p): %s\n", kobj, err_str);
- dump_stack();
- }
分析kobject_init_internal函數(lib/kobject.c),此函數主要設置一些kobj中的一些變量
- static void kobject_init_internal(struct kobject*kobj)
- {
- if (!kobj) //kobj是否爲空
- return;
- kref_init(&kobj->kref); //增加kobject的引用計數,kref_set(kref,
1);
- INIT_LIST_HEAD(&kobj->entry); //初始化kobj的鏈表
- kobj->state_in_sysfs= 0; //kobject還沒有註冊到sysfs中
- kobj->state_add_uevent_sent= 0; //
- kobj->state_remove_uevent_sent= 0;
- kobj->state_initialized= 1;
- }
三。kobj_type
對象的屬性結構體kobj_type(include/linux/kobject.h)
- struct kobj_type {
- void (*release)(struct kobject*kobj); //釋放函數(驅動編寫時提供),此函數會被kobject_put函數調用
- struct sysfs_ops *sysfs_ops; //屬性文件的操作函數(只有讀和寫操作)
- struct attribute **default_attrs; //屬性數組
- };
1.討論kobj_type和kobject的關係,就要先說說kobject的引用。引用一個kobject使用函數kobject_get()這個函數會增加kobject的引用並返回kobject的指針。增加其引用是通過其kobject中斷哦kref變量完成的。對kobject的引用管理主要是爲了知道被引用的情況,如引用不爲0就不能銷燬kobject對象,引用爲0時則調用相應的釋放函數等。
- struct kobject *kobject_get(struct kobject*kobj)
- {
- if (kobj)
- kref_get(&kobj->kref);
- return kobj;
- }
- void kref_get(struct kref
*kref)
- {
- WARN_ON(!atomic_read(&kref->refcount));
- atomic_inc(&kref->refcount); //將kref中的這個原子變量加1
- smp_mb__after_atomic_inc();
- }
減少一個kobject對象的引用使用函數kobject_put()。當一個kobject對象的引用被減少到0時,程序就應該釋放這個kobject相關的資源。所以在減少引用的函數中就應該有調用釋放資源的相關代碼,在下面內核代碼中我們可以看到。
- void kobject_put(struct kobject
*kobj)
- {
- if (kobj){
- if (!kobj->state_initialized) //若kobj沒有初始化就不能減少其引用
- WARN(1, KERN_WARNING"kobject: '%s' (%p): is not "
- "initialized, yet kobject_put() is being "
- "called.\n", kobject_name(kobj), kobj);
- kref_put(&kobj->kref, kobject_release);//減少kref計數
- }
- }
- int kref_put(struct kref*kref, void(*release)(struct
kref*kref))
- {
- WARN_ON(release
== NULL); //爲空警告
- WARN_ON(release
== (void(*)(struct kref*))kfree);//如果release函數就是kfree,則警告(即release函數不能是簡單的kfree)
- if (atomic_dec_and_test(&kref->refcount)){ //遞減原子變量並檢查其值
- release(kref); //回調release函數
- return 1;
- }
- return 0;
- }
那這個release函數在哪裏保存呢,這就和kobj_type結構有關係了。上面我們可以看到kobj_type中有一個release函數指針,就是保存在這裏。每一個kobject的ktype都指向一個kobj_type,它保存了這個kobject類型的release函數指針。
四。Kset集合
1.Kset是具有相同類型的kobject集合。一個Kset集合可以表示在/sys/drivers/目錄下,表示一類驅動程序。kobject則表示一個具體的驅動目錄。這樣kset則可以將kobject組織成層次化結構。
- /**
- * struct kset
- a set of kobjects of a specific type, belongingto a specific subsystem.
- *
- * A kset defines a group of kobjects. They can be individually
- * different "types" but overall these kobjects all wantto be grouped
- * together and operatedonin the same manner. ksets are usedto
- * define the attribute callbacks
and other common events that happen to
- * a kobject.
- *
- * @list: the list of all kobjectsfor this kset
- * @list_lock: a lockfor iterating over the kobjects
- * @kobj: the embedded kobjectfor this kset(recursion, isn't
it fun...)
- * @uevent_ops: theset of uevent operationsfor this kset. These are
- * called whenever a kobject has something happento it so that the kset
- * can add new environment variables,orfilter out the ueventsif so
- * desired.
- */
- struct kset {
- struct list_head list; //這個鏈表存放這個kset關聯的所有kobject
- spinlock_t list_lock; //維護此鏈表的鎖
- struct kobject kobj; //內嵌的kobject。這樣kset本身也是一個kobject也被表現爲一個目錄
- struct kset_uevent_ops *uevent_ops; //支持熱插拔事件的函數集
- };
kset中的kobject對象,所有屬於這個kset集合的kobject對象的parent指針,均指向這個內嵌的kobject,也即表示在一個kset集合中的kobject是相同類型的他們有相同的parent對象。kset的引用計數也就是內嵌的kobject的引用計數。
所以kobject和kset的關係簡單來講,就是
1.kset是kobject的一個頂層容器,它包含了相同類型的kobject,kset中有鏈表成員保存所有的kobject指向。
2.kobject中的kset指針指向了一個kset
3.kset中有kobject對象,表明了kset也可以有kobject相關的操作。
4.kset鏈表中的kobject對象的parent指針一般都指向kset內嵌的kobject對象。
kset和kobject關係基本如下圖,
kset_uevent_ops熱插拔事件
熱插拔事件是用內核空間發送到用戶空間的通知。表明內核中的某些配置已經發生變化。用戶空間則會根據這些信息做相應的處理。例如,U盤插入USB系統時,會產生一個熱插拔事件,內核會捕捉到這個熱插拔事件,然後調用/sbin/hotplug程序,該程序通知加載驅動程序來相應U盤的插入動作。
熱插拔函數集的定義在include/linux/koject.h中
- struct kset_uevent_ops {
- int (*filter)(struct kset*kset,
struct kobject*kobj); //事件過濾函數
- const char
*(*name)(struct kset*kset, struct kobject*kobj); //事件名稱函數
- int (*uevent)(struct kset*kset,
struct kobject*kobj,struct kobj_uevent_env*env);
- //uevent函數可在熱插拔程序執行前,向環境變量寫值
- };
詳細的熱插拔事件先不在這裏分析。
2.註冊一個kset
- /**
- * kset_register
- initialize and add a kset.
- * @k: kset.
- */
- int kset_register(struct kset*k)
- {
- int err;
- if (!k)
- return -EINVAL;
- kset_init(k);
- err = kobject_add_internal(&k->kobj); //將kset中的kobject添加進sysfs,函數將在後面講解
- if (err)
- return err;
- kobject_uevent(&k->kobj, KOBJ_ADD);
- return 0;
- }
- /**
- * kset_init - initialize a ksetfor use
- * @k: kset
- */
- void kset_init(struct kset
*k)
- {
- kobject_init_internal(&k->kobj);
- INIT_LIST_HEAD(&k->list);
- spin_lock_init(&k->list_lock);
- }
我們使用函數kset_create_and_add()還可以一次性將kset創建並註冊進sysyfs
- /**
- * kset_create_and_add
- create a struct kset dynamically and add itto sysfs
- *
- * @name: the namefor the kset
- * @uevent_ops: a struct kset_uevent_opsfor the kset
- * @parent_kobj: the parent kobject of this kset,if any.
- *
- * This function creates a kset structure dynamicallyand 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 wasnot ableto be created,NULL
will be returned.
- */
- struct kset *kset_create_and_add(const char*name,
- struct kset_uevent_ops *uevent_ops,
- struct kobject *parent_kobj)
- {
- struct kset *kset;
- int error;
- kset = kset_create(name, uevent_ops, parent_kobj); //根據參數創建一個kset
- if (!kset)
- return NULL;
- error = kset_register(kset); //將kset註冊進sysfs,函數在上面已經分析過
- if (error){
- kfree(kset);
- return NULL;
- }
- return kset;
- }
- /**
- * kset_create
- create a struct kset dynamically
- *
- * @name: the namefor the kset
- * @uevent_ops: a struct kset_uevent_opsfor 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 systemand show upin sysfs with acallto
- * 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 itis no longer being used.
- *
- * If the kset wasnot ableto be created,NULL
will be returned.
- */
- static struct kset *kset_create(const char*name,
- struct kset_uevent_ops *uevent_ops,
- struct kobject *parent_kobj)
- {
- struct kset *kset;
- int retval;
- kset = kzalloc(sizeof(*kset), GFP_KERNEL);
- if (!kset)
- return NULL;
- retval = kobject_set_name(&kset->kobj,
name); //設置kobject名稱
- if (retval){
- kfree(kset);
- return NULL;
- }
- kset->uevent_ops= uevent_ops;
- kset->kobj.parent= parent_kobj; //設置kset的kobject的父對象
- /*
- * The kobject of this kset will have a type of kset_ktypeand belongto
- * no kset itself. That way we can properly free it when itis
- * finished being used.
- */
- kset->kobj.ktype=&kset_ktype; //設置kset的kobject的默認屬性
- kset->kobj.kset=NULL;
- return kset;
- }
上面這些函數主要包含即調用關係如下,
kset_create_and_add
kset_create
kzalloc
kset_register
kset_init
kobject_add_internal
kset中嵌入了一個kobject,所以還有一些和kobject相似的函數如,
增加kset的引用,實際是調用kobject_get增加kset中的kobject的引用
- static inline struct kset *kset_get(struct kset*k)
- {
- return k ? to_kset(kobject_get(&k->kobj)):NULL;
- }
減少kset的引用,實際是調用kobject_put減少kset中的kobject的引用
- static inline void kset_put(struct kset
*k)
- {
- kobject_put(&k->kobj);
- }
順便提一下,子系統subsystem,在新的內核中已經沒有這個結構了。在原來的內核中它用來表示比kset更高一層的容器,kset應該屬於一個子系統,子系統幫助內核在分層結構中定位kset。內核子系統包括 block_subsys(/sys/block 塊設備)、 devices_subsys(/sys/devices 核心設備層)。現在subsystem已經被kset代替了。
五,將kobject註冊進sysfs系統
我們在看一下如何將kobject註冊進sysfs系統中。使用函數kobject_init_and_add()(lib/kobject.c)函數將一個kobject註冊進sysfs系統,在/sys中表現爲生成一個相應的目錄。
- /**
- * kobject_init_and_add
- initialize a kobject structure and add itto the kobject hierarchy
- * @kobj: pointerto the kobjectto initialize
- * @ktype: pointerto the ktypefor this kobject.
- * @parent: pointerto the parent of this kobject.
- * @fmt: the name of the kobject.
- *
- * This function combines thecallto kobject_init()and
- * kobject_add(). The same type oferror handling after acall
to
- * kobject_add()and kobject lifetime rules are the same here.
- */
- int kobject_init_and_add(struct kobject*kobj, struct kobj_type*ktype,
- struct kobject *parent,const char*fmt,...)
- {
- va_list args;
- int retval;
- kobject_init(kobj, ktype); //調用初始化函數先初始化kobject變量
- va_start(args, fmt); //解析可變參數列表
- retval = kobject_add_varg(kobj, parent, fmt, args);//給kobject添加參數,並且將其添加到sysfs系統。
- va_end(args); //結束解析參數列表
- return retval;
- }
- static int kobject_add_varg(struct kobject*kobj, struct kobject*parent,const
char *fmt, va_list vargs)
- {
- int retval;
- retval = kobject_set_name_vargs(kobj, fmt, vargs); //設置kobject的名稱
- if (retval){
- printk(KERN_ERR
"kobject: can not set name properly!\n");
- return retval;
- }
- kobj->parent= parent; //設置kobject的父kobject
- return kobject_add_internal(kobj); //添加kobject
- }
- static int kobject_add_internal(struct kobject*kobj)
- {
- int error= 0;
- struct kobject *parent;
- if (!kobj) //檢查是否爲空
- return -ENOENT;
- if (!kobj->name||!kobj->name[0]){ //kobj是否有名稱,如果沒有則不能註冊,生成目錄。
- WARN(1,"kobject: (%p): attempted to be registered with empty "
- "name!\n", kobj);
- return -EINVAL;
- }
- parent = kobject_get(kobj->parent); //獲得父kobject,並增加父kobject的引用計數
- /*
join kset if
set, use it as parent
if we do not already have one*/
- if (kobj->kset){ //是否有kset集合
- if (!parent) //如果沒有父kobject則用kset中的kobject對象
- parent = kobject_get(&kobj->kset->kobj);
- kobj_kset_join(kobj); //將kobject添加進它關聯的kset的list鏈表中。
- kobj->parent= parent; //設置父koject
- }
- pr_debug("kobject: '%s' (%p): %s: parent: '%s', set: '%s'\n",
- kobject_name(kobj), kobj, __func__,
- parent ? kobject_name(parent):"<NULL>",
- kobj->kset? kobject_name(&kobj->kset->kobj):"<NULL>");
- error = create_dir(kobj); //創建kobject的相應目錄
-
- if (error){ //創建時出錯處理
- kobj_kset_leave(kobj);
- kobject_put(parent);
- kobj->parent=NULL;
- /* be noisyonerror issues*/
- if (error==-EEXIST)
- printk(KERN_ERR
"%s failed for %s with "
- "-EEXIST, don't try to register things with "
- "the same name in the same directory.\n",
- __func__, kobject_name(kobj));
- else
- printk(KERN_ERR
"%s failed for %s (%d)\n",
- __func__, kobject_name(kobj),error);
- dump_stack();
- } else
- kobj->state_in_sysfs= 1; //標記爲已經註冊進sysfs
- return error;
- }
sysfs創建目錄函數create_dir,在lib/kobject.c
- static int create_dir(struct kobject*kobj)
- {
- int error= 0;
- if (kobject_name(kobj)){
- error
= sysfs_create_dir(kobj); //在sysfs中創建目錄,將來有時間了可以分析下sysfs子系統。
- if (!error){
- error
= populate_dir(kobj);
- if
(error)
- sysfs_remove_dir(kobj);
- }
- }
- return error;
- }
以上函數的主要調用關係,如下
kobject_init_and_add
kobject_init
kobject_add_varg
kobject_add_internal
create_dir
還有一個函數kobject_add,也可以添加一個kobject,它只是沒有kobject_init這一步。
- int kobject_add(struct kobject*kobj, struct kobject*parent,
- const char
*fmt, ...)
- {
- va_list args;
- int retval;
- if (!kobj)
- return -EINVAL;
- if (!kobj->state_initialized){
- printk(KERN_ERR
"kobject '%s' (%p): tried to add an "
- "uninitialized object, something is seriously wrong.\n",
- kobject_name(kobj), kobj);
- dump_stack();
- return -EINVAL;
- }
- va_start(args, fmt);
- retval = kobject_add_varg(kobj, parent, fmt, args);
- va_end(args);
- return retval;
- }
轉自http://blog.chinaunix.net/uid-11319766-id-3253414.html