Since Linux 2.6.27, it's possible to set SOCK_NONBLOCK directly at the
creation of the socket (using socket() and accept4()). So you don't
need any extra call.
I implemented something similar for SOCK_CLOEXEC flag to implement the
PEP 433. See for example:
http://hg.python.org/features/pep-433/fil
FWIW, looking into Python's Lib/socket.py module, it would seem that the
dup() method of a _sockobject() just transfers the underlying fd, not
performing a new socket create. So a caller could know about that behavior
and work to call setblocking(0) only when it has a socket not seen before.
In ev
