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) {       //没有初始化的kobject，返回错误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);    //核心的实现代码va_end(args);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);         //设置kobject的nameif (retval) {printk(KERN_ERR "kobject: can not set name properly!\n");return retval;}kobj->parent = parent;                   //设置parent成员return kobject_add_internal(kobj);       //调用此函数进行进一步add操作
}

static int kobject_add_internal(struct kobject *kobj)
{int error = 0;struct kobject *parent;if (!kobj)return -ENOENT;if (!kobj->name || !kobj->name[0]) {                  //尝试注册一个name为空的kobjectWARN(1, "kobject: (%p): attempted to be registered with empty ""name!\n", kobj);return -EINVAL;}parent = kobject_get(kobj->parent);                  //kobj的parent的引用计数加1，返回parent/* join kset if set, use it as parent if we do not already have one */if (kobj->kset) {                            if (!parent)                                //在kset存在的前提下，如果kobj的parent节点为NULL，就将kobj的kset中的kobj设置为kobj的parentparent = kobject_get(&kobj->kset->kobj);kobj_kset_join(kobj);                       //添加kobj到kset的list链表中kobj->parent = parent;                      //设置kobj的parent}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);                          //在sys下创建目录if (error) {kobj_kset_leave(kobj);kobject_put(parent);kobj->parent = NULL;/* be noisy on error issues */if (error == -EEXIST)WARN(1, "%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));elseWARN(1, "%s failed for %s (error: %d parent: %s)\n",__func__, kobject_name(kobj), error,parent ? kobject_name(parent) : "'none'");} elsekobj->state_in_sysfs = 1;                  //设置state_in_sysfs为1，代表obj已经初始化在sys中return error;
}

下来大概看看create_dir的过程，也就是创建目录的过程。

static int create_dir(struct kobject *kobj)
{const struct kobj_ns_type_operations *ops;int error;error = sysfs_create_dir_ns(kobj, kobject_namespace(kobj));                     //为kobject创建目录if (error)return error;error = populate_dir(kobj);                                           //填充kobj的属性if (error) {sysfs_remove_dir(kobj);return error;}/** @kobj->sd may be deleted by an ancestor going away.  Hold an* extra reference so that it stays until @kobj is gone.*/sysfs_get(kobj->sd);                                             //kobj->sd引用计数加1/** If @kobj has ns_ops, its children need to be filtered based on* their namespace tags.  Enable namespace support on @kobj->sd.*/ops = kobj_child_ns_ops(kobj);                             //namespace的知识if (ops) {BUG_ON(ops->type <= KOBJ_NS_TYPE_NONE);BUG_ON(ops->type >= KOBJ_NS_TYPES);BUG_ON(!kobj_ns_type_registered(ops->type));sysfs_enable_ns(kobj->sd);}return 0;
}

主要是分析下sysfs_create_dir_ns函数的执行流程。

/*** sysfs_create_dir_ns - create a directory for an object with a namespace tag* @kobj: object we're creating directory for* @ns: the namespace tag to use*/
int sysfs_create_dir_ns(struct kobject *kobj, const void *ns)
{struct kernfs_node *parent, *kn;BUG_ON(!kobj);                            //如果执行到这里，kobj为NULL,就会panicif (kobj->parent)           parent = kobj->parent->sd;         //如果存在parent就在父目录下创建elseparent = sysfs_root_kn;            //如果不存在parent,就在sys目录下创建if (!parent)return -ENOENT;kn = kernfs_create_dir_ns(parent, kobject_name(kobj),        //正真的创建函数，不是此节的重点，不再分析。S_IRWXU | S_IRUGO | S_IXUGO, kobj, ns);if (IS_ERR(kn)) {if (PTR_ERR(kn) == -EEXIST)sysfs_warn_dup(parent, kobject_name(kobj));return PTR_ERR(kn);}kobj->sd = kn;return 0;
}

• kobject_init_and_add(kobject_init函数和kobject_add函数的合并)
• kobject_create(动态分析一个kobject)

struct kobject *kobject_create(void)
{struct kobject *kobj;kobj = kzalloc(sizeof(*kobj), GFP_KERNEL);            //分配一个kobject结构if (!kobj)return NULL;kobject_init(kobj, &dynamic_kobj_ktype);              //初始化kobject，kobj_type会在后面说到return kobj;
}

void kobject_del(struct kobject *kobj)
{struct kernfs_node *sd;if (!kobj)return;           //如果不存在，直接返回。sd = kobj->sd;sysfs_remove_dir(kobj);    //从sys目录下删除kobjsysfs_put(sd);             //sd的引用技术减去1kobj->state_in_sysfs = 0;   //表示没有在sys中初始化kobj_kset_leave(kobj);      //如果存在于kset中，从kset中删除kobject_put(kobj->parent);  //parent引用计数减1kobj->parent = NULL;
}

举例

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/kobject.h>
#include <linux/sysfs.h>
#include <linux/init.h>static struct kobject *kobj;static int kobject_test_init(void)
{kobj = kobject_create_and_add("123_test", NULL);return 0;
}static void kobject_test_exit(void)
{kobject_del(kobj);
}module_init(kobject_test_init);
module_exit(kobject_test_exit);
MODULE_LICENSE("GPL v2");

root@test:/sys # ls -l
drwxr-xr-x root     root              2012-01-02 09:31 123_test
drwxr-xr-x root     root              2012-01-02 07:13 bcm-dhd
drwxr-xr-x root     root              2012-01-02 05:02 block
drwxr-xr-x root     root              2012-01-02 05:02 bus
drwxr-xr-x root     root              2012-01-02 05:02 class
....

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/kobject.h>
#include <linux/sysfs.h>
#include <linux/init.h>static struct kobject *kobj;
static struct kobject *ckobj;static int kobject_test_init(void)
{kobj = kobject_create_and_add("123_test", NULL);ckobj = kobject_create_and_add("456_test", kobj);return 0;
}static void kobject_test_exit(void)
{kobject_del(ckobj);kobject_del(kobj);
}module_init(kobject_test_init);
module_exit(kobject_test_exit);
MODULE_LICENSE("GPL v2");

root@test:/sys/123_test # ls
456_test