help with "dumpdev"

[Cedric Berger]

I've a diskless box that panics with the following message
(OpenBSD current, 3 weeks old)

...
fdc0 at isa0 port 0x3f0/6 irq 6 drq 2
fd0 at fdc0 drive 0: 1.44 MB 80 cyl, 2 head, 18 sec
biomask 4040 netmask c840 ttymask d8c2
pctr: 686-class user-level performance sounters enabled
mtrr: Pentium Pro MTRR support
panic: dumpconf: bad dumpdev=0xff00
Stopped at - Debugger +0x4: leave
ddb>

Unfortunately, I've no direct access to the box.
I'm trying to follow the source, but I don't know yet:

- What is "dumpdev" exactly (I know about rootdev & swapdev)
- Where is it used in the code?
- What should be the right value for a diskless box?
- Where is this value initialized from?

Thanks a lot,
Cedric