Issue on ip_route_output_key() and ip_route_output_flow()

Hi,
  In /usr/src/linux/net/ipv4/route.c, there are two
functions, one is ip_route_output_key(), the other is
ip_route_output_flow(). Would you please tell me what
circumstances those two function are used for? and
What the difference between the two functions is? 
  As for ip_route_output_key() here, what is the
meaning of the "_key" in its name?

  Thank you.


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Best Regards,
Park Lee


		
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