I don't agree with this assumption:

When select comes back to you it means that some data is available; it doesn't say how much. Then you try to read 1024 bytes. If there isn't that much data available, and you're in blocking mode, it'll try to wait.

read() and/or sysread() will read whatever is there without waiting on the remainder of the 1024 bytes. They will block if there's no data to read, but select() says there is data.