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 path/to/net_test/run_net_test.sh where 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 TAP0, TAP1, etc., where 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.