I applied through a career fair and received an on-campus interview call after one week. The interview was scheduled three weeks after I got the email about being selected for the interview process. Facebook also hosted a dinner for all the candidates being interviewed.

Tell me about yourself, why Facebook, etc., etc.

Then he asked about my 'read' system call implementation. He provided me with a base file system interface which would always fetch 4k bytes from the current position. I had to make sure I read only as much bytes as specified in my system call.