plugins/lua/example.lua

   1 -- Example Lua plugin.
   2 --
   3 -- This example can be freely used for any purpose.
   4
   5 -- Run it from the build directory like this:
   6 --
   7 --   ./nbdkit -f -v lua ./plugins/lua/example.lua file=disk.img
   8 --
   9 -- Or run it after installing nbdkit like this:
  10 --
  11 --   nbdkit -f -v lua ./plugins/lua/example.lua file=disk.img
  12 --
  13 -- The -f -v arguments are optional.  They cause the server to stay in
  14 -- the foreground and print debugging, which is useful when testing.
  15 --
  16 -- You can connect to the server using guestfish or qemu, eg:
  17 --
  18 --   guestfish --format=raw -a nbd://localhost
  19 --   ><fs> run
  20 --   ><fs> part-disk /dev/sda mbr
  21 --   ><fs> mkfs ext2 /dev/sda1
  22 --   ><fs> list-filesystems
  23 --   ><fs> mount /dev/sda1 /
  24 --   ><fs> [etc]
  25
  26 -- This is called from: nbdkit lua example.lua --dump-plugin
  27 function dump_plugin ()
  28    print ("example_lua=1")
  29 end
  30
  31 -- We expect a file=... parameter pointing to the file to serve.
  32 function config (key, value)
  33    if key == "file" then
  34       file = value
  35    else
  36       error ("unknown parameter " .. key .. "=" .. value)
  37    end
  38 end
  39
  40 -- Check the file parameter was passed.
  41 function config_complete ()
  42    if not file then
  43       error ("file parameter missing")
  44    end
  45 end
  46
  47 -- Open a new client connection.
  48 function open (readonly)
  49    -- Open the file.
  50    local flags
  51    if readonly then
  52       flags="rb"
  53    else
  54       flags="r+b"
  55    end
  56    local fh = assert (io.open (file, flags))
  57
  58     -- We can return any Lua object as the handle.  In this
  59     -- plugin it's convenient to return the file handle.
  60    return fh
  61 end
  62
  63 -- Close a client connection.
  64 function close (fh)
  65    assert (fh:close())
  66 end
  67
  68 function get_size (fh)
  69    local size = assert (fh:seek ("end"))
  70    return size
  71 end
  72
  73 function pread (fh, count, offset)
  74    assert (fh:seek ("set", offset))
  75    local data = assert (fh:read (count))
  76    return data
  77 end
  78
  79 function pwrite (fh, buf, offset)
  80    assert (fh:seek ("set", offset))
  81    assert (fh:write (buf))
  82 end