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

[Yangtao Li]

> > Meta-comment, we need to come up with a "filesystem kobject type" to get
> > rid of lots of the boilerplate filesystem kobject logic as it's
> > duplicated in every filesystem in tiny different ways and lots of times
> > (like here), it's wrong.
> 
> Can we add the following structure?
> 
> struct filesystem_kobject {
>         struct kobject kobject;
>         struct completion unregister;
> };
> 
> w/ it, we can simplify something:
> 
> 1. merge init_completion and kobject_init_and_add
>
> 2. merge kobject_put and wait_for_completion
>
> 3. we can have a common release func for kobj_type release

It seems that the above ideas are not crazy enough, maybe we should do more.
Any ideas and suggestions are very welcome.

MBR,
Yangtao