1 net_test v0.1 2 ============= 3 4 A simple framework for blackbox testing of kernel networking code. 5 6 7 Why use it? 8 =========== 9 10 - Fast test / boot cycle. 11 - Access to host filesystem and networking via L2 bridging. 12 - Full Linux userland including Python, etc. 13 - Kernel bugs don't crash the system. 14 15 16 How to use it 17 ============= 18 19 cd <kerneldir> 20 path/to/net_test/run_net_test.sh <test> 21 22 where <test> is the name of a test binary in the net_test directory. This can 23 be an x86 binary, a shell script, a Python script. etc. 24 25 26 How it works 27 ============ 28 29 net_test compiles the kernel to a user-mode linux binary, which runs as a 30 process on the host machine. It runs the binary to start a Linux "virtual 31 machine" whose root filesystem is the supplied Debian disk image. The machine 32 boots, mounts the root filesystem read-only, runs the specified test from init, and then drops to a shell. 33 34 35 Access to host filesystem 36 ========================= 37 38 The VM mounts the host filesystem at /host, so the test can be modified and 39 re-run without rebooting the VM. 40 41 42 Access to host networking 43 ========================= 44 45 Access to host networking is provided by tap interfaces. On the host, the 46 interfaces are named <user>TAP0, <user>TAP1, etc., where <user> is the first 47 10 characters of the username running net_test. (10 characters because 48 IFNAMSIZ = 16). On the guest, they are named eth0, eth1, etc. 49 50 net_test does not do any networking setup beyond creating the tap interfaces. 51 IP connectivity can be provided on the host side by setting up a DHCP server 52 and NAT, sending IPv6 router advertisements, etc. By default, the VM has IPv6 53 privacy addresses disabled, so its IPv6 addresses can be predicted using a tool 54 such as ipv6calc. 55 56 The provided filesystem contains a DHCPv4 client and simple networking 57 utilities such as ping[6], traceroute[6], and wget. 58 59 The number of tap interfaces is currently hardcoded to two. To change this 60 number, modify run_net_test.sh. 61 62 63 Logging into the VM, installing packages, etc. 64 ============================================== 65 66 net_test mounts the root filesystem read-only, and runs the test from init, but 67 since the filesystem contains a full Linux userland, it's possible to boot into 68 userland and modify the filesystem, for example to install packages using 69 apt-get install. Log in as root with no password. By default, the filesystem is 70 configured to perform DHCPv4 on eth0 and listen to RAs. 71 72 73 Bugs 74 ==== 75 76 Since the test mounts the filesystem read-only, tests cannot modify 77 /etc/resolv.conf and the system resolver is hardcoded to 8.8.8.8. 78