                                net_test v0.1
                                =============

A simple framework for blackbox testing of kernel networking code.


Why use it?
===========

- Fast test / boot cycle.
- Access to host filesystem and networking via L2 bridging.
- Full Linux userland including Python, etc.
- Kernel bugs don't crash the system.


How to use it
=============

cd <kerneldir>
path/to/net_test/run_net_test.sh <test>

where <test> is the name of a test binary in the net_test directory. This can
be an x86 binary, a shell script, a Python script. etc.


How it works
============

net_test compiles the kernel to a user-mode linux binary, which runs as a
process on the host machine. It runs the binary to start a Linux "virtual
machine" whose root filesystem is the supplied Debian disk image. The machine
boots, mounts the root filesystem read-only, runs the specified test from init, and then drops to a shell.


Access to host filesystem
=========================

The VM mounts the host filesystem at /host, so the test can be modified and
re-run without rebooting the VM.


Access to host networking
=========================

Access to host networking is provided by tap interfaces. On the host, the
interfaces are named <user>TAP0, <user>TAP1, etc., where <user> is the first
10 characters of the username running net_test. (10 characters because
IFNAMSIZ = 16). On the guest, they are named eth0, eth1, etc.

net_test does not do any networking setup beyond creating the tap interfaces.
IP connectivity can be provided on the host side by setting up a DHCP server
and NAT, sending IPv6 router advertisements, etc. By default, the VM has IPv6
privacy addresses disabled, so its IPv6 addresses can be predicted using a tool
such as ipv6calc.

The provided filesystem contains a DHCPv4 client and simple networking
utilities such as ping[6], traceroute[6], and wget.

The number of tap interfaces is currently hardcoded to two. To change this
number, modify run_net_test.sh.


Logging into the VM, installing packages, etc.
==============================================

net_test mounts the root filesystem read-only, and runs the test from init, but
since the filesystem contains a full Linux userland, it's possible to boot into
userland and modify the filesystem, for example to install packages using
apt-get install. Log in as root with no password. By default, the filesystem is
configured to perform DHCPv4 on eth0 and listen to RAs.


Bugs
====

Since the test mounts the filesystem read-only, tests cannot modify
/etc/resolv.conf and the system resolver is hardcoded to 8.8.8.8.