The development of adaptive software systems is based on the adaptation requirements identification and analysis. It clarifies what changes the software will face during operation and how it needs to deal with them. However, the existing approaches pay little attention on the context analysis and lack of systematic process to identify the potential context changes. Moreover, they also lack of a framework to consider the adaptation requirements for both the known context changes and the unknown context changes. To address these issues, this paper provides an approach based on feedback control. Its basic idea is to model the adaptive software and its context as an adaptive control system, and to identify and analyze the adaptation requirements through identifying the feedback loops of such adaptive control system. By treating the context as the object to be controlled by software, it not only makes the context explicit, but also manages to define the context-aware feedback loops and the requirements-aware feedback loops to deal with the known context changes and the unknown context changes respectively. An example is used to illustrate the feasibility of the proposed approach.