This repo contains demonstration programs for Linux networking.

1. python load test harness for wifi WPA network, change the device MAC and IP to hammer an openwrt router
2. epoll using combinations of edge/level triggers and blocking reads.

Use the pyroute2 python package to modify the IP and MAC of a wifi interface. pyroute2 uses the netlink interface.

this is a work in progress

There is a lot of mysterious code out there related to the epoll edge-triggered feature so I decided to write a simple TCP server using epoll to test out some of the concepts. See epoll_server.c for the code.

Start epoll_server in one window. It will start and listen either a static port you give it or a dynamic port assigned by the kernel. Either way, the port will be written to a temp file for the clients to connect on.

Use nc (or netcat) in other windows to generate traffic to the server. These can be interleavened, along with server standard in.

nc localhost $(cat /tmp/server.port)
... enter data 
^D to exit

nc localhost $(cat /tmp/server.port) < /tmp/dumpfile.log

If clients are configured for edge-triggered reads, epoll_wait will wait for only NEW data from the client. If there is un-read data from a previous stream, it will not be read. This is best illustrated by starting the server without putting the clients in non-blocking mode:

epoll_server -e

and entering some data either from stdin or nc. The (very small) buffer will be filled and written

If clients are configured for non-blocking reads, epoll_wait will wait for data and then it will all be read.

epoll_server -n

The edge-triggered epoll does not seem to be very helpful. If I set the clients to non-blocking and level-triggered it seems to have the same impact as edge-triggered.

However, if I set only edge-triggered epoll then it will not read the client streams correctly.