Sure, you can use an ioctl for this. You could use some combination of ioctl()s to tunnel absolutely any API, just like you can wrap any text string in pointy brackets and call it XML.

The question is whether this is useful. In particular, once your interface requires ioctl(), you lose the benefit of easy interoperability with UNIX command-line tools.

Well, just below the Plan 9 sections comes this: http://catb.org/~esr/writings/taoup/html/ch20s03.html#id3016... And he's right, ioctl's can be quite tricky to operate sometimes.