how to hardcode kernel dump device in kernel

[Johan A. van Zanten]

 I'm trying to get a crash dump of a ZFS-related kernel crash, but it
happens before "dumpon" has run, so i think i need to hardcode the device
in the kernel.  However, i can't find the syntax for this.  Anyone have
any ideas?

 All i've found in the docs is this:

 "Alternatively, the dump device can be hard-coded via the dump clause in
 the config(5) line of a kernel configuration file. This approach is
 deprecated and should be used only if a kernel is crashing before
 dumpon(8) can be executed."

http://www.freebsd.org/doc/en_US.ISO8859-1/books/developers-handbook/kerneldebug.html#KERNELDEBUG-OBTAIN

 I've also looked at config(5).

 Thanks, johan