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README
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.