How to make nginx fail if it can't write to cache dir.

[unikron]

I can't think of any edge case that will happen to my nginx instances,
that's why I want it to die. 
I fail to see why it will keep on answering to new requests if it can't
fulfill any of them.

Posted at Nginx Forum: https://forum.nginx.org/read.php?2,293477,293484#msg-293484