[luatex] Loading PK fonts in Lua

[David Shourabi Porcel]

Hello,

I am dealing with a TFM-PK font pair which I would like to load in
Lua. The following code doesn't work, however:

function define_font(name, size)
    metrics = font.read_tfm("font.tfm", size)

    metrics.type = "real"
    metrics.format = "type3"
    metrics.fullname = "font.600pk"
    metrics.filename = "font.600pk"
    metrics.embedding = "full"

    return metrics
end
callback.register("define_font", define_font)

LuaTeX complains:
   warning  (file font) (type 3): font font at 216 not found

That is, the metrics file is found and loaded, but the bitmap file is
not. What am I doing wrong?

As far as I could understand from the manual, map files should not be
needed (support for them might be removed in the future, anyway).

Thank you,

David