Opening /tmp

[Dmitry Matveev <me%dmitrymatveev.co.uk@localhost>]

Hello,

When I am calling

  open("/tmp", O_RDONLY);

I am getting error EOPNOTSUPP ("Operation not supported"). Opening any 
file or directory with the same flags inside /tmp works fine. Opening 
any directory from / also works fine.
I have tried to ktruss some utils to find how they open /tmp, but it 
haven't helped.

Which flag should I pass to open(2) to make it work with /tmp?

Best regards,
Dmitry