[Libguestfs] nbdkit: how to require use of filter

Hi, Is there a way for a nbdkit plugin to *require* use of a nbdkit filter (specifically the nbdkit-blocksize-filter) programmatically? Thanks! -Nikolaus -- GPG Fingerprint: ED31 791B 2C5C 1613 AF38 8B8A D113 FCAC 3C4E 599F »Time flies like an arrow, fruit flies like a Banana.«