The PIPE_BUF POSIX requirement is about guaranteeing that when multiple processes write less than PIPE_BUF to the same pipe, the reader will not see its input i

The PIPE_BUF POSIX requirement is about guaranteeing that when multiple processes write less than PIPE_BUF to the same pipe, the reader will not see its input intermingled from different processes. It is often wrongly interpreted as "a single write() of less than PIPE_BUF will be retrieved via a single read() on the other side".