The curious case of O_DIRECTORY|O_CREAT

opendir(3) is implemented on top of open(2), and the man page for open(2) on my Linux system says:

>O_DIRECTORY
>
>If pathname is not a directory, cause the open to fail. This flag was added in kernel version 2.1.126, to avoid denial-of-service problems if opendir(3) is called on a FIFO or tape device.