Finding out names of mountable devices

[Juho Vuori]

Tried on freebsd-questions without an answer. I suppose this is not 
doable, but I'll ask here anyway.

If I plug in e.g. a USB thumb drive, which becomes, say, umass0. 
Normally something like /dev/da0 will also be created and slices of that 
device may be mounted. But is there a API for finding out what is the 
corresponding block device for umass devices? The device driver writes 
that to syslog, but reading logs for something like that is quite clumsy. 

Juho Vuori