> sendfile() is file-to-socket (zero-copy as well), and has very high performance as well, for both Linux and BSDs. It only supports file-to-socket, however, and well, to stay relevant, sendmsg() can't be used with pipes in the general case, it is for UNIX domain sockets, INET sockets, and other socket types.

On Linux, sendfile supports more than just file to socket, as it's implemented using splice. I've used it for file-to-block-device in the past.