Having trouble with pseudodevice

[el16095 <el16095%mail.ntua.gr@localhost>]

I've been working on the Rumprun unikernel (which is based on NetBSD's 
rump kernels). In an attempt to enable MMIO for it, I've been trying to 
add a relevant pseudodevice. However, the process of adding such a 
device has had me somewhat confused. The intent is that the MMIO (glue) 
device always attaches and then based on some data it receives from the 
boot commandline (set by the hypervisor), it attaches VirtIO devices 
using MMIO.

However, after reading some relevant documentation and following some 
guides, I was unable to make it attach automatically by just 
configuration. I figured then, maybe I needed to add specific code that 
would cause the attachment. I tried to call config_found inside 
RUMP_COMPONENT(RUMP_COMPONENT_DEV_AFTERMAINBUS) to attach it to the 
mainbus, but this caused a panic: "kernel diagnostic assertion 
"!args->iattr || cfdriver_get_iattr(parent->dv_cfdriver, args->iattr)" 
failed, file "sys/kern/subr_autoconf.c", line 1147.

Is there something I need to do to make sure mainbus recognises the 
iattr I give it? Or is there a simpler way to achieve what I want? I'll 
admit I'm a little out of depth here, so any help is appreciated.

--
George Gkanas