Linux tap device example code based on ljsyscall

tap-test.lua

-- tap-test.lua -- test program based on ljsyscall test code                                                                        
-- Reference example code for ljsyscall here:                                                                                       
-- https://github.com/justincormack/ljsyscall/blob/master/test/linux.lua     

-- Run via Snabb Switch like this:
--   sudo snabb snsh tap-test.lua

local syscall = require("syscall") -- ljsyscall                                                                                     

-- Create a new tap device                                                                                                          
local clonedev = "/dev/net/tun"
local fd = assert(syscall.open(clonedev, "rdwr"))
local ifr = syscall.t.ifreq()
ifr.flags = "tap"
assert(fd:ioctl("TUNSETIFF", ifr))

-- Print out the details we get                                                                                                     
local ifname = ifr.name
print("tunnel device: " .. ifname)                                                                                          
print()
print("netlink status:")
print(syscall.nl.interfaces()[ifname])

-- Echo packets e.g. while playing around with ip/tcpdump/ping/etc                                                                          
while true do
   local data = fd:read()
   print("Got packet:")
   print(core.lib.hexdump(data))
   fd:write(data)
   print("[Echoed packet back.]")
end

z-example-output

$ sudo src/snabb snsh ~/tap-test.lua
tunnel device: tap0

netlink status:
tap0      Link encap:Ethernet  HWaddr 86:a4:7d:ce:70:f1
          ALL VOLATILE MULTICAST BROADCAST  MTU: 1500
          RX packets:0 errors:0 dropped:0
          TX packets:0 errors:0 dropped:0

Got packet:
00 00 08 00 01 00 5E 00 00 16 86 A4 7D CE 70 F1 08 00 46 C0 00 28 00 00 40 00 01 02 F9 EF 0A 09 00 01 E0 00 00 16 94 04 00 00 22 00 
F9 02 00 00 00 01 04 00 00 00 E0 00 00 FB
[Echoed packet back.]
Got packet:
00 00 86 DD 33 33 00 00 00 16 86 A4 7D CE 70 F1 86 DD 60 00 00 00 00 24 00 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 FF 02 
00 00 00 00 00 00 00 00 00 00 00 00 00 16 3A 00 05 02 00 00 01 00 8F 00 FD CA 00 00 00 01 04 00 00 00 FF 02 00 00 00 00 00 00 00 00 
00 01 FF CE 70 F1
[Echoed packet back.]