#!/usr/bin/python
import os, time, struct, fcntl

# The following are from linux/if_tun.h
TUNSETIFF = 0x400454ca     # ioctl to configure a TUN/TAP interface
IFF_TAP = 0x0002           # Ethernet-level tunnel interface
IFF_NO_PI = 0x1000         # Protocol information header for tap interfaces

intf = 'tap0'

# Create a tap interface.
tapFd = os.open( '/dev/net/tun', os.O_RDWR )
ioctlData = struct.pack( '16s H 14x', intf, IFF_TAP | IFF_NO_PI )
fcntl.ioctl( tapFd, TUNSETIFF, ioctlData )

# Enable then disable the tap interface.
os.system( 'ip link set %s up' % intf )
print 'Enabled tap interface at', time.ctime( time.time() )
time.sleep( 1 )  # A delay here seems to be necessary to trigger the bug.
os.system( 'ip link set %s down' % intf )
print 'Disabled tap interface at', time.ctime( time.time() )
time.sleep( 17 ) # A delay here is not necessary, but illustrates that the 30 second
                 # interval starts when the interface is disabled, not when close is
                 # called.

# Destroy the tap interface.
print 'About to close tap FD at', time.ctime( time.time() )
os.close( tapFd )
print 'Closed tap FD at', time.ctime( time.time() )