怎样判断句子主句和从句,比如 No sooner had he closedhis eyes than he fell asleep.

怎样判断句子主句和从句,比如 No sooner had he closedhis eyes than he fell asleep.
Not until he came back did I knew about it.
这种倒装句主倒从不倒,可我不知道哪个是主句啊