[PATCH 2/3] erofs: convert to use kobject_is_added()

[Yangtao Li]

Hi Greg,

> just let it hang off as a separate structure (i.e. a pointer to something else.)

I have made some attempts. According to my understanding, the reason why the
filesystem needs to embed the kobj structure (not a pointer) is that the kobj_to_sbi
method is required in the attr_store/attr_show method for subsequent data processing.

130 static ssize_t erofs_attr_store(struct kobject *kobj, struct attribute *attr,
131                                                 const char *buf, size_t len)
132 {
133         struct erofs_sb_info *sbi = container_of(kobj, struct erofs_sb_info,
134                                                 s_kobj);

If we turn the kobject in sbi into a pointer, then we need to insert a pointer
to sbi in the kobject, or perform the following encapsulation.

struct filesystem_kobject {
        struct kobject kobject;
	void *private;
};

Later, I thought I could send some demo code that strips the kobject in sbi into a pointer.

BTW, Now sysfs.c in many file systems is full of a lot of repetitive code, maybe we can abstract the common part?
Like filesystem_attr、filesystem_kobject_ops、filesystem_kobject_ktype...

Thx,
Yangtao