That sounds like the 'standard' model of several threads calling accept(), after all if you are multi-threaded you don't need to pass a file descriptor around,

That sounds like the 'standard' model of several threads calling accept(), after all if you are multi-threaded you don't need to pass a file descriptor around, each thread will already have it. With FD passing, you can have multiple processes, related or unrelated, pulling incoming connections from the same socket. You use the FD passing to share the listening socket.