一、摘要

构建一个kobject对象
构建一个sysfs中的目录项（kernfs_node）
把他们关联起来

二、重点

关注sysfs目录项与kobject对象的关联过程
关注kobject对象默认的属性文件接口

三、驱动结构模型

四、关键函数分析

kobject_create_and_add()函数

/home/geralt/linux_driver/kernel/ebf_linux_kernel_6ull_depth1/lib/kobject.c

struct kobject *kobject_create_and_add(const char *name, struct kobject *parent)
{
	struct kobject *kobj;
	int retval;
    
    // 创建并初始化
	kobj = kobject_create();
	if (!kobj)
		return NULL;

    // sysfs创建一个目录项并与kobject对象关联
	retval = kobject_add(kobj, parent, "%s", name);
	if (retval) {
		pr_warn("%s: kobject_add error: %d\n", __func__, retval);
		kobject_put(kobj);
		kobj = NULL;
	}
	return kobj;
}

kobject_create()函数

/home/geralt/linux_driver/kernel/ebf_linux_kernel_6ull_depth1/lib/kobject.c

struct kobject *kobject_create(void)
{
	struct kobject *kobj;
    
    // 动态申请内存，存放kobject对象
	kobj = kzalloc(sizeof(*kobj), GFP_KERNEL);
	if (!kobj)
		return NULL;

	kobject_init(kobj, &dynamic_kobj_ktype);
	return kobj;
}

static struct kobj_type dynamic_kobj_ktype = {
	.release	= dynamic_kobj_release,
	.sysfs_ops	= &kobj_sysfs_ops,
};

const struct sysfs_ops kobj_sysfs_ops = {
	.show	= kobj_attr_show,
	.store	= kobj_attr_store,
};

kobject_init（）函数

/home/geralt/linux_driver/kernel/ebf_linux_kernel_6ull_depth1/lib/kobject.c

void kobject_init(struct kobject *kobj, struct kobj_type *ktype)
{
	char *err_str;

	if (!kobj) {
		err_str = "invalid kobject pointer!";
		goto error;
	}
	if (!ktype) {
		err_str = "must have a ktype to be initialized properly!\n";
		goto error;
	}
	if (kobj->state_initialized) {
		/* do not error out as sometimes we can recover */
		pr_err("kobject (%p): tried to init an initialized object, something is seriously wrong.\n",
		       kobj);
		dump_stack();
	}

	kobject_init_internal(kobj);
	kobj->ktype = ktype;
	return;

error:
	pr_err("kobject (%p): %s\n", kobj, err_str);
	dump_stack();
}

kobject_init_internal(）函数

home/geralt/linux_driver/kernel/ebf_linux_kernel_6ull_depth1/lib/kobject.c

static void kobject_init_internal(struct kobject *kobj)
{
	if (!kobj)
		return;
    // 将kobject的引用计数设置为1
	kref_init(&kobj->kref);
    // 初始化链表节点
	INIT_LIST_HEAD(&kobj->entry);
    // 该kobject对象还没和sysfs目录项关联
	kobj->state_in_sysfs = 0;
	kobj->state_add_uevent_sent = 0;
	kobj->state_remove_uevent_sent = 0;
    // kobject对象的初始化标志
	kobj->state_initialized = 1;
}

kobject_add（）函数

home/geralt/linux_driver/kernel/ebf_linux_kernel_6ull_depth1/lib/kobject.c

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) {
		pr_err("kobject '%s' (%p): tried to add an uninitialized object, something is seriously wrong.\n",
		       kobject_name(kobj), kobj);
		dump_stack();
		return -EINVAL;
	}
    // 获取第一个可变参数，可变参数函数的实现与函数传参的栈结构有关
	va_start(args, fmt);
	retval = kobject_add_varg(kobj, parent, fmt, args);
	va_end(args);

	return retval;
}

kobject_add_varg（）函数

home/geralt/linux_driver/kernel/ebf_linux_kernel_6ull_depth1/lib/kobject.c

static __printf(3, 0) 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);
	if (retval) {
		pr_err("kobject: can not set name properly!\n");
		return retval;
	}
    // 第一次设置的kobj的parent指针
	kobj->parent = parent;
	return kobject_add_internal(kobj);
}

kobject_set_name_vargs()函数

int kobject_set_name_vargs(struct kobject *kobj, const char *fmt,
				  va_list vargs)`
{
	const char *s;

	if (kobj->name && !fmt)
		return 0;
    
    // 参数格式化打印到s字符串中
	s = kvasprintf_const(GFP_KERNEL, fmt, vargs);
	if (!s)
		return -ENOMEM;

	/*
	 * ewww... some of these buggers have '/' in the name ... If
	 * that's the case, we need to make sure we have an actual
	 * allocated copy to modify, since kvasprintf_const may have
	 * returned something from .rodata.
	 */
	if (strchr(s, '/')) {
		char *t;

		t = kstrdup(s, GFP_KERNEL);
		kfree_const(s);
		if (!t)
			return -ENOMEM;
		strreplace(t, '/', '!');
		s = t;
	}
	kfree_const(kobj->name);
    // 设置kobject对象的名称
	kobj->name = s;

	return 0;
}

kobject_add_internal()函数

static int kobject_add_internal(struct kobject *kobj)
{
	int error = 0;
	struct kobject *parent;

	if (!kobj)
		return -ENOENT;

	if (!kobj->name || !kobj->name[0]) {
		WARN(1,
		     "kobject: (%p): attempted to be registered with empty name!\n",
		     kobj);
		return -EINVAL;
	}

	parent = kobject_get(kobj->parent);

	/* join kset if set, use it as parent if we do not already have one */
	if (kobj->kset) {
		if (!parent)
			parent = kobject_get(&kobj->kset->kobj);
		kobj_kset_join(kobj);
		kobj->parent = 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);
	if (error) {
		kobj_kset_leave(kobj);
		kobject_put(parent);
		kobj->parent = NULL;

		/* be noisy on error issues */
		if (error == -EEXIST)
			pr_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
			pr_err("%s failed for %s (error: %d parent: %s)\n",
			       __func__, kobject_name(kobj), error,
			       parent ? kobject_name(parent) : "'none'");
	} else
		kobj->state_in_sysfs = 1;

	return error;
}

create_dir(）函数

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));
	if (error)
		return error;

	error = populate_dir(kobj);
	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);

	/*
	 * 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);
	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;
}

sysfs_create_dir_ns()函数

文件：/home/geralt/linux_driver/kernel/ebf_linux_kernel_6ull_depth1/fs/sysfs

int sysfs_create_dir_ns(struct kobject *kobj, const void *ns)
{
	struct kernfs_node *parent, *kn;
	kuid_t uid;
	kgid_t gid;

	BUG_ON(!kobj);

	if (kobj->parent)
        // 获取上一层节点的目录项
		parent = kobj->parent->sd;
	else
        // 设置上一层节点的目录项sysfs
		parent = sysfs_root_kn;

	if (!parent)
		return -ENOENT;

	kobject_get_ownership(kobj, &uid, &gid);

	kn = kernfs_create_dir_ns(parent, kobject_name(kobj),
				  S_IRWXU | S_IRUGO | S_IXUGO, uid, gid,
				  kobj, ns);
	if (IS_ERR(kn)) {
		if (PTR_ERR(kn) == -EEXIST)
			sysfs_warn_dup(parent, kobject_name(kobj));
		return PTR_ERR(kn);
	}
    
    // kobj对象关联sysfs目录项
	kobj->sd = kn;
	return 0;
}

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