int ipc(unsigned int call, int first, int second, int third, void *ptr, long fifth);
描述ipc() is a common kernel entry point for the System V IPC calls for messages, semaphores, and shared memory. call determines which IPC function to invoke; the other arguments are passed through to the appropriate call.
User programs should call the appropriate functions by their usual names. Only standard library implementors and kernel hackers need to know about ipc().