No root filesystem

I just tried to update my box, but the new kernel wouldn't find a
root device.  This is a rather vanilla amd64 box, no zfs, one SATA
disk, no other operating systems.

It tried to mount ufs:/dev/ad6s1a, which is correct, but somehow
came up empty.  At the "Manual root filesystem specification" prompt,
"?" did not list any devices.

My previous good kernel is about 48 hours old, so this must have
been introduced very recently.

(I'm a bit short on details because I had to boot a good kernel to write
this message.)
-- 
Christian "naddy" Weisgerber                          naddy_at_mips.inka.de