It is possible for mkdir(2) to return EINVAL in certain circumstances. However, the man page mkdir(2) doesn't mention that.

I am hitting it on overlayfs. Other instances reported: 

http://stackoverflow.com/questions/10015377/mkdir-pathname-with-symbol http://lists.opensuse.org/opensuse-bugs/2009-05/msg01771.html

So, it needs to be documented in man page for mkdir(2).

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Raghavendra