[Click] Adding HEADROOM option to RawSocket and IPFlowRawSockets

[Michael Gellman]

I am using Click as an overlay router where I am receiving packets from
an application using the RawSocket and IPFlowRawSocket elements, then
adding a reasonably large overlay header, and then re-encapsulating into
a UDP-in-IP packet before it is sent out again.

In this scenario, I have found that I receive a number of warnings about
"expensive push operations" due to the fact that the packet received
from the RawSocket element has the default headroom assigned (currently
28 bytes) which isn't enough to accommodate the additional headers.

I've solved my problem using the attached patch, which adds a HEADROOM
keyword to both elements. Maybe this can be applied upstream?

Michael Gellman
-- 
Intelligent Systems & Networks Group
Dept of Electrical & Electronic Engineering
Imperial College London
London SW7 2BT
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