Peter De Wachter has created a Debian source code search engine for developers. It lets them find out quickly what files contain, for example, the usb_device structure required for accessing USB devices. More here
This not only enables programmers to search for the correct header file, it also lets the developers of the libusb USB library see what other Debian packages would be affected by any changes in the structure. The OpenGrok search engine used by the project allows both full-text searches and special searches, such as for definitions or external symbols. Searching can be restricted to a specific file path.