Does the source tree include anything like a pseudo HBA 
driver?  Or does anyone know of one floating around?

I want to write a little driver that sits below the SCSI 
disk driver (sd.c) and receives SCSI commands but has no 
hardware below it.  It's fine that it's hardwired to 
sd.c. 

The idea is similar to a pseudo disk driver, such as a 
logical volume manager, but sits below sd.c, rather than 
above it.

If nothing like this exists already, do you have any 
documentation suggestions?

I'm wondering if it's as simple as adding a little piece 
of code to the kernel (either modloaded or statically 
linked) that dummys-up the arguments needed to call 
sdattach(), and then just call it.  Or is it a lot more 
complicated than that?

Thanks in advance for any help!
Larry