Where is vpp code?

Some hack should be made to the vpp. Is this part of the code open source? Where can I find it?

Also recommend you join the Calico Slack and talk to the authors of the VPP code in #vpp-dataplane http://slack.projectcalico.org/

Based on your suggestion, I have also decided to join Calico Slack. Hopefully, it will be easier for me to find the required answers there.