#+Title: AF_XDP socket multi-threaded forwarding sample application

This sample code could originally be found in the Linux source code
tree under samples/bpf. It illustrates the packet forwarding between
multiple AF_XDP sockets in multi-threading environment. All the
threads and sockets are sharing a common buffer pool, with each socket
having its own private buffer cache. The sockets are created with the
xsk_socket__create_shared() function, which allows multiple AF_XDP
sockets to share the same UMEM object.

Example 1: Single thread handling two sockets. Packets received from
socket A (on top of interface IFA, queue QA) are forwarded to socket B
(on top of interface IFB, queue QB) and vice-versa.  The thread is
affinitized to CPU core C:

#+BEGIN_SRC sh
./xsk_fwd -i IFA -q QA -i IFB -q QB -c C
#+END_SRC

Example 2: Two threads, each handling two sockets. Packets from socket
A are sent to socket B (by thread X), packets from socket B are sent
to socket A (by thread X); packets from socket C are sent to socket D
(by thread Y), packets from socket D are sent to socket C (by thread
Y). The two threads are bound to CPU cores CX and CY:

#+BEGIN_SRC sh
./xdp_fwd -i IFA -q QA -i IFB -q QB -i IFC -q QC -i IFD -q QD -c CX -c CY
#+END_SRC