int flags = fcntl(fd, F_GETFL, 0);
fcntl(fd, F_SETFL, flags | O_NONBLOCK);
The code snippet above will configure such a descriptor for non-blocking access. If data is not available when you call read, then the system call will fail with a return value of -1 and errno is set to EAGAIN. See the fcntl man pages for more information.
Alternatively, you can use select with a configurable timeout to check and/or wait a specified time interval for more data. This method is probably what you want and can be much more efficient.