Linux kernel 之 kobject

总听有人说 Linux kernel 拥有一团无比巨大看似杂乱无章其实有迹可循的链表，今天参考一下其他大牛的相关资料记录一下。

• kset 结构体

    151 /**
    152  * struct kset - a set of kobjects of a specific type, belonging to a specific subsystem.
    153  *
    154  * A kset defines a group of kobjects.  They can be individually
    155  * different "types" but overall these kobjects all want to be grouped
    156  * together and operated on in the same manner.  ksets are used to
    157  * define the attribute callbacks and other common events that happen to
    158  * a kobject.
    159  *
    160  * @list: the list of all kobjects for this kset
    161  * @list_lock: a lock for iterating over the kobjects
    162  * @kobj: the embedded kobject for this kset (recursion, isn't it fun...)
    163  * @uevent_ops: the set of uevent operations for this kset.  These are
    164  * called whenever a kobject has something happen to it so that the kset
    165  * can add new environment variables, or filter out the uevents if so
    166  * desired.
    167  */
    168 struct kset {
    169     struct list_head list;       // 这里边包含了这个 kset 所有的 kobject
    170     spinlock_t list_lock;
    171     struct kobject kobj;         // 一个嵌入在里面的kobject
    172     const struct kset_uevent_ops *uevent_ops;     // 里面包含热拔插事件发生时的响应操作
    173 };

* #### kobject 结构体

    //  include/linux/kobject.h
     63 struct kobject {
     64     const char      *name;       // 名字
     65     struct list_head    entry;   // 连接到 kset 建立层次结构
     66     struct kobject      *parent;  // 上一个节点
     67     struct kset     *kset;        // 指向所属的 kset
     68     struct kobj_type    *ktype;   // 指向所属的 ktype
     69     struct kernfs_node  *sd; /* sysfs directory entry */     //  文件系统内的sysfs 的node
     70     struct kref     kref;         // 引用计数
     71 #ifdef CONFIG_DEBUG_KOBJECT_RELEASE
     72     struct delayed_work release;
     73 #endif
     74     unsigned int state_initialized:1;     //  初始化状态，只占 1 个位的空间，应用了位域
     75     unsigned int state_in_sysfs:1;
     76     unsigned int state_add_uevent_sent:1;
     77     unsigned int state_remove_uevent_sent:1;
     78     unsigned int uevent_suppress:1;
     79 };

* #### kobj_type 结构体

    116 struct kobj_type {
    117     void (*release)(struct kobject *kobj);
    118     const struct sysfs_ops *sysfs_ops;
    119     struct attribute **default_attrs;
    120     const struct kobj_ns_type_operations *(*child_ns_type)(struct kobject *kobj);
    121     const void *(*namespace)(struct kobject *kobj);
    122 };                                                                              

* #### kobject_init - initialize a kobject structure ： 初始化

    // lib/kobject.c
    // 318  * This function will properly initialize a kobject such that it can then
    // 319  * be passed to the kobject_add() call.   等下还有kobject_add()
    // 321  * After this function is called, the kobject MUST be cleaned up by a call
    // 322  * to kobject_put(), not by a call to kfree directly to ensure that all of
    // 323  * the memory is cleaned up properly.      必须用 kobject_put 去释放，而不是 kfree
     325 void kobject_init(struct kobject *kobj, struct kobj_type *ktype)
     326 {
     327     char *err_str;
     328
     329     if (!kobj) {
     330         err_str = "invalid kobject pointer!";
     331         goto error;
     332     }
     333     if (!ktype) {
     334         err_str = "must have a ktype to be initialized properly!\n";
     335         goto error;
     336     }
     337     if (kobj->state_initialized) {
     338         /* do not error out as sometimes we can recover */
     339         printk(KERN_ERR "kobject (%p): tried to init an initialized "
     340                "object, something is seriously wrong.\n", kobj);
     341         dump_stack();
     342     }
     343
     344     kobject_init_internal(kobj);       // 初始化有关的成员
     345     kobj->ktype = ktype;
     346     return;
     347
     348 error:
     349     printk(KERN_ERR "kobject (%p): %s\n", kobj, err_str);
     350     dump_stack();
     351 }
     352 EXPORT_SYMBOL(kobject_init);

    // kobject_init_internal 一些属性的初始化
     187 static void kobject_init_internal(struct kobject *kobj)
     188 {
     189     if (!kobj)
     190         return;
     191     kref_init(&kobj->kref);     // 设置计数为1
     192     INIT_LIST_HEAD(&kobj->entry);
     193     kobj->state_in_sysfs = 0;
     194     kobj->state_add_uevent_sent = 0;
     195     kobj->state_remove_uevent_sent = 0;
     196     kobj->state_initialized = 1;        // 设置初始化状态                                        

* #### 通过总线注册函数解析 kset , kobjectd , ktype 这些结构体的关系。

    // drivers/base/bus.c
    // 这里先将 两个变量作为全局变量
      25 /* /sys/devices/system */
      26 static struct kset *system_kset;
     178 static struct kset *bus_kset;
    // 入口函数
    1278 int __init buses_init(void)
    1279 {            // kset 创建和添加  , 名字为"bus"  "bus事件操作" “父project 为空”
    1280     bus_kset = kset_create_and_add("bus", &bus_uevent_ops, NULL);
    1281     if (!bus_kset)
    1282         return -ENOMEM;
    1283
    1284     system_kset = kset_create_and_add("system", NULL, &devices_kset->kobj);
    1285     if (!system_kset)
    1286         return -ENOMEM;
    1287
    1288     return 0;
    1289 }

    // kset_create_and_add
    // 头文件 include/linux/kobject.h
    178 extern struct kset * __must_check kset_create_and_add(const char *name,
    179                         const struct kset_uevent_ops *u,
    180                         struct kobject *parent_kobj);   

    // 源代码  lib/kobject.c
     936 struct kset *kset_create_and_add(const char *name,
     937                  const struct kset_uevent_ops *uevent_ops,
     938                  struct kobject *parent_kobj)
     939 {
     940     struct kset *kset;
     941     int error;
     942                   // 名字为"bus" ，申请一段空间并初始化相关kset 属性
     943     kset = kset_create(name, uevent_ops, parent_kobj);
     944     if (!kset)
     945         return NULL;
     946     error = kset_register(kset);  // 注册
     947     if (error) {
     948         kfree(kset);
     949         return NULL;
     950     }
     951     return kset;
     952 }

    //  lib/kobject.c
    //  kset_register
     809 int kset_register(struct kset *k)
     810 {
     811     int err;
     812
     813     if (!k)
     814         return -EINVAL;
     815     // 初始化
     816     kset_init(k);
     817     err = kobject_add_internal(&k->kobj);   // 接下
     818     if (err)
     819         return err;
     820     kobject_uevent(&k->kobj, KOBJ_ADD);
     821     return 0;
     822 }
     823 EXPORT_SYMBOL(kset_register);

    // kset 初始化
     767 void kset_init(struct kset *k)
     768 {   // 这个在上面已经跟过了
      // 最主要是初始化了 state_initialized = 1
     769     kobject_init_internal(&k->kobj);
     770     INIT_LIST_HEAD(&k->list); // 设置为链表头
     771     spin_lock_init(&k->list_lock);
     772 }

    // kobject_add_internal
     200 static int kobject_add_internal(struct kobject *kobj)
     201 {
     202     int error = 0;
     203     struct kobject *parent;
     204
     205     if (!kobj)
     206         return -ENOENT;
     207
     208     if (!kobj->name || !kobj->name[0]) {
     209         WARN(1, "kobject: (%p): attempted to be registered with empty "
     210              "name!\n", kobj);
     211         return -EINVAL;
     212     }
     213
     214     parent = kobject_get(kobj->parent);
     215
     216     /* join kset if set, use it as parent if we do not already have one */
     217     if (kobj->kset) {
     218         if (!parent)
     219             parent = kobject_get(&kobj->kset->kobj);
     220         kobj_kset_join(kobj);
     221         kobj->parent = parent;
     222     }