Shameless plug, searchco.de allows you to search over github,

http://searchco.de/?q=irq_create_mapping+url%3Agithub

You just need to add the url:github portion to any search. You can do the same over bitbucket, codeplex, google code, sourceforge and the fedora source tree too. See, http://searchco.de/blog/view/variety-of-updates