句子:Harry, whose thoughts had been upstairs with the Broom-stick Servicing Kit, was brought back to earth with an unpleasant bump.
问题:whose thoughts had been upstairs with the Broom-stick Servicing Kit 这句话是修饰Harry, Harry, whose thoughts had been upstairs with the Broom-stick Servicing Kit,这个一整个句子是句子主语吗?