# 10.4 What comes next

_Peios / Developing for Peios / SDK Reference / rsi/source.h — Becoming a Source_

> Registration is the whole of this header — where the serve loop and the response helpers live.

Registration is the whole of this header. Once you hold the source fd, the serve loop lives in the other two:

- **[`<rsi/request.h>`](/peios/developing-for-peios/sdk-reference/sdk-rsi-request/rsi-request-h-decoding-requests.md)** — read and decode the requests the kernel sends.
- **[`<rsi/response.h>`](/peios/developing-for-peios/sdk-reference/sdk-rsi-response/rsi-response-h-building-responses.md)** — build and send the replies.

The [serving requests](/peios/developing-for-peios/registry-sources/serving-requests.md) guide ties them together into a working serve loop.