core-extra/docs/devguide.md

CORE Developer's Guide

• Table of Contents {:toc}

Repository Overview

The CORE source consists of several different programming languages for historical reasons. Current development focuses on the Python modules and daemon. Here is a brief description of the source directories.

Directory	Description
corefx	JavaFX based GUI using gRPC API to replace legacy GUI
daemon	Python CORE daemon code that handles receiving API calls and creating containers
docs	Markdown Documentation currently hosted on GitHub
gui	Tcl/Tk GUI
man	Template files for creating man pages for various CORE command line utilities
netns	Python C extension modules for creating CORE containers
ns3	Experimental python ns3 script support for running CORE
scripts	Template files used for running CORE as a service

Getting started

Overview for setting up the pipenv environment, building core, installing the GUI and netns, then running the core-daemon for development.

Setup Python Environment

To leverage the dev environment you need python 3.6+.

# change to daemon directory
cd $REPO/daemon

# install pipenv
pip3 install pipenv

# setup a virtual environment and install all required development dependencies
python3 -m pipenv install --dev

# setup python variable using pipenv created python
export PYTHON=$(python3 -m pipenv --py)

Setup pre-commit

Install pre-commit hooks to help automate running tool checks against code.

python3 -m pipenv run pre-commit install

Build CORE

# clone core
git clone https://github.com/coreemu/core.git
cd core

# build core
./bootstrap.sh
./configure --prefix=/usr
make

Install netns and GUI

Below commands assume your development will be focused on the daemon.

# install GUI
cd $REPO/gui
sudo make install

# install netns scripts
cd $REPO/netns
sudo make install

Running CORE

This will run the core-daemon server using the configuration files within the repo.

python3 -m pipenv run coredev

The CORE API

The CORE API is used between different components of CORE for communication. The GUI communicates with the CORE daemon using the API. One emulation server communicates with another using the API. The API also allows other systems to interact with the CORE emulation. The API allows another system to add, remove, or modify nodes and links, and enables executing commands on the emulated systems. Wireless link parameters are updated on-the-fly based on node positions.

CORE listens on a local TCP port for API messages. The other system could be software running locally or another machine accessible across the network.

The CORE API is currently specified in a separate document, available from the CORE website.

Linux Network Namespace Commands

Linux network namespace containers are often managed using the Linux Container Tools or lxc-tools package. The lxc-tools website is available here http://lxc.sourceforge.net/ for more information. CORE does not use these management utilities, but includes its own set of tools for instantiating and configuring network namespace containers. This section describes these tools.

vnoded

The vnoded daemon is the program used to create a new namespace, and listen on a control channel for commands that may instantiate other processes. This daemon runs as PID 1 in the container. It is launched automatically by the CORE daemon. The control channel is a UNIX domain socket usually named /tmp/pycore.23098/n3, for node 3 running on CORE session 23098, for example. Root privileges are required for creating a new namespace.

vcmd

The vcmd program is used to connect to the vnoded daemon in a Linux network namespace, for running commands in the namespace. The CORE daemon uses the same channel for setting up a node and running processes within it. This program has two required arguments, the control channel name, and the command line to be run within the namespace. This command does not need to run with root privileges.

When you double-click on a node in a running emulation, CORE will open a shell window for that node using a command such as:

gnome-terminal -e vcmd -c /tmp/pycore.50160/n1 -- bash

Similarly, the IPv4 routes Observer Widget will run a command to display the routing table using a command such as:

vcmd -c /tmp/pycore.50160/n1 -- /sbin/ip -4 ro

core-cleanup script

A script named core-cleanup is provided to clean up any running CORE emulations. It will attempt to kill any remaining vnoded processes, kill any EMANE processes, remove the :file:/tmp/pycore.* session directories, and remove any bridges or ebtables rules. With a -d option, it will also kill any running CORE daemon.

netns command

The netns command is not used by CORE directly. This utility can be used to run a command in a new network namespace for testing purposes. It does not open a control channel for receiving further commands.

Other Useful Commands

Here are some other Linux commands that are useful for managing the Linux network namespace emulation.

# view the Linux bridging setup
brctl show
# view the netem rules used for applying link effects
tc qdisc show
# view the rules that make the wireless LAN work
ebtables -L

Example Command Usage

Below is a transcript of creating two emulated nodes and connecting them together with a wired link:

# create node 1 namespace container
vnoded -c /tmp/n1.ctl -l /tmp/n1.log -p /tmp/n1.pid
# create a virtual Ethernet (veth) pair, installing one end into node 1
ip link add name n1.0.1 type veth peer name n1.0
ip link set n1.0 netns `cat /tmp/n1.pid`
vcmd -c /tmp/n1.ctl -- ip link set lo up
vcmd -c /tmp/n1.ctl -- ip link set n1.0 name eth0 up
vcmd -c /tmp/n1.ctl -- ip addr add 10.0.0.1/24 dev eth0

# create node 2 namespace container
vnoded -c /tmp/n2.ctl -l /tmp/n2.log -p /tmp/n2.pid
# create a virtual Ethernet (veth) pair, installing one end into node 2
ip link add name n2.0.1 type veth peer name n2.0
ip link set n2.0 netns `cat /tmp/n2.pid`
vcmd -c /tmp/n2.ctl -- ip link set lo up
vcmd -c /tmp/n2.ctl -- ip link set n2.0 name eth0 up
vcmd -c /tmp/n2.ctl -- ip addr add 10.0.0.2/24 eth0

# bridge together nodes 1 and 2 using the other end of each veth pair
brctl addbr b.1.1
brctl setfd b.1.1 0
brctl addif b.1.1 n1.0.1
brctl addif b.1.1 n2.0.1
ip link set n1.0.1 up
ip link set n2.0.1 up
ip link set b.1.1 up

# display connectivity and ping from node 1 to node 2
brctl show
vcmd -c /tmp/n1.ctl -- ping 10.0.0.2

The above example script can be found as twonodes.sh in the examples/netns directory. Use core-cleanup to clean up after the script.