https://www.unitedbsd.com/d/590-testing-the-lua-kernel-interpreter

UnitedBSD

Loading...
This site is best viewed in a modern browser with JavaScript enabled.
Something went wrong while trying to load the full version of this
site. Try hard-refreshing this page to fix the error.

Testing the Lua kernel interpreter

JuvenalUrbino

I was curious to see lua(4) in action, so I decided to perform some
quick test.

printing a "hello, world!" script

First of all, load the relevant kernel modules:

$ modload lua
$ modload luasystm


To have them loaded automatically at boot:

printf '%s\n%s\n' 'lua' 'luasystm' >> /etc/modules.conf

If everything's right the kernel buffer will show:

[     6.176500] lua0: Lua 5.3.5  Copyright (C) 1994-2018 Lua.org, PUC-Rio

And modstat will return:

NAME                    CLASS    SOURCE   FLAG  REFS    SIZE REQUIRES
lua                     misc     filesys  -        1       - -
luasystm                misc     filesys  -        0       - lua

Let's enhance the verbosity of the lua(4) module:

$ sysctl -w kern.lua.verbose=1
kern.lua.verbose: 0 -> 1

Without further ado, we can now proceed to test the built-in kernel
parser, using luactl(8):

 1. create a state to load our scripts

    $ luactl create s1 testing
    s1 created
    $ luactl
    Name             Creator  Description
    s1               user     testing

 2. load luasystm bindings on state s1 (required for print())

    $ luactl require s1 systm
    systm required by s1

 3. Write a sample 'hello world' script:

    $ cat << eof > hello.lua
    -- hello world!
    systm.print("hello world!\n")
    eof
    $ luactl load s1 ./hello.lua
    ./hello.lua loaded into s1
    $ dmesg | tail -1
    [  2769.687618] hello world!

    Notice that the absolute path is required for luactl to read the
    script


    more testing

    1) parsing simple functions

    -- sum func
    function add(x, y)
      return x + y
    end
    systm.print("the sum of 16 and 32 is:\n")
    systm.print (add(16, 32))

    systm.print ("\n")

    -- factorial func
    function fact (n)
      if n == 0 then
        return 1
      else
        return n * fact(n-1)
      end
    end
    systm.print("the factorial of 7 is:\n")
    systm.print (fact(7))


    $ luactl load s1 ./sample.lua
    ./sample.lua loaded into s1
     $ dmesg | grep -A 5 sample
    [  4283.160428] lua0: loading ./sample.lua into state s1
    [  4283.170432] the sum of 16 and 32 is:
    [  4283.170432] 48
    [  4283.170432] the factorial of 7 is:
    [  4283.180433] 5040

    2) displaying OS info

    -- print system info
    function uname()
      tbl = {"copyright", "cpu_model", "machine", "machine_arch", "osrelease", "os
    type", "kernel_ident", "version"}
      for i = 1, #tbl do
        systm.print(systm[tbl[i]] .. "\n")
      end
    end

    uname()

    Which produces:

    [  5519.710421] lua0: loading ./sys.lua into state s1
    [  5519.720425] Copyright (c) 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005,
    [  5519.730424]     2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017,
    [  5519.730424]     2018, 2019, 2020 The NetBSD Foundation, Inc.  All rights reserved.
    [  5519.740424] Copyright (c) 1982, 1986, 1989, 1991, 1993
    [  5519.750425]     The Regents of the University of California.  All rights reserved.

    [  5519.760427] raspberrypi,3-model-b
    [  5519.760427] evbarm
    [  5519.760427] aarch64
    [  5519.760427] 9.2_STABLE
    [  5519.770428] NetBSD
    [  5519.770428] GENERIC64
    [  5519.770428] NetBSD 9.2_STABLE (GENERIC64) #0: Fri Aug 20 19:33:44 UTC 2021
    [  5519.780428] mkrepro@mkrepro.NetBSD.org:/usr/src/sys/arch/evbarm/compile/GENERIC64

    3) display hostname

    function hostname()
      local f = io.popen ("/bin/hostname")
      local host = f:read("*a") or ""
      f:close()
      host =string.gsub(host, "\n$", "")
      systm.print (host)
    end
    systm.print("Welcome to:\n")
    hostname()

    This is not going to work:

    $ luactl load s1 ./host.lua
    luactl: LUALOAD: Invalid argument

---------------------------------------------------------------------