Driver not found error when using examples with Qt 4.7 and QVFb?

I'm trying to get started with embedded linu开发者_如何学Cx Qt Development, and I've built Qt for embedded linux, and built QVFb but when I launch any of the example programs I get an error that a driver isn't found.

./analogclock -qws -display QVFb:0
QVFb: driver not found

Any idea what I've done wrong? Do I need to configure Qt for embedded and QVFb at the same time and rebuild everything?

have you qt configured with

-plugin-gfx-qvfb

option?