Re: dump to cgdNb device

[Taylor R Campbell <campbell+netbsd-tech-kern%mumble.net@localhost>]

   Date: Thu, 16 Jun 2016 20:20:14 +0100
   From: Alexander Nasonov <alnsn%yandex.ru@localhost>

   Taylor R Campbell wrote:
   > Slightly simpler version attached -- device_private is not
   > device_lookup; device_private never fails.  (If the device_lookup in
   > cgddump failed, we wouldn't have gotten to cgd_dumpblocks anyway.)

   It dumped succesfully but savecore doesn't see any valid core. If I
   run savecore -f, it prints gibberish.

Just to double-check (since I am likely to make this mistake myself!),
you're not using a random-keyed cgd, right?  Random-keyed cgd is great
for swap while the key is in memory but not so great for dump after
rebooting!

Does strings(1) on /dev/rcgd1b show anything vaguely meaningful?

Failing that, I might start sprinkling debug prints in everywhere.

Hmm...  I might have caused your dump to scribble all over another
part of the disk, by not adjusting the blkno before passing it along
to bdev_dump.  I'm not sure about this -- but the blkno adjustments
certainly need to be reviewed.