Diskdump / kdump format history

Hi Petr,

I wanted to ask you a bit about the history of the diskdump/kdump
format, since it seems like somebody who has written an entire library
for parsing it would have some interesting insights. I've CC'd the
linux-debuggers mailing list here, which I believe would be its
inaugural post! I think anybody interested in debugging kernel core
dumps could use any answers you have.

First, regarding naming. I guess I always assumed that "diskdump"
referred to some older utility which performed the same function that
makedumpfile now is commonly used for. Is that the case? Do you know the
origin of the diskdump format? Do you know where to find the code for
this older diskdump tool, if it existed?

Second, I have some confusion regarding headers. I've seen headers for
files with the content "DISKDUMP" and "KDUMP   " -- and according to
src/kdumpfile/diskdump.c, you have too. diskdump_probe() shows that you
check for these two headers and set a different description depending on
which is seen. Do you know why or where these two headers are set, and
which one is chose in which situation?

Third, sometimes I see an additional header with signature
"makedumpfile", and a few 64-bit integer fields, and then the
KDUMP/DISKDUMP header occurs at offset 4096/0x1000. I wonder if you're
familiar with that header, why or why not it occurs?

Finally, and this one is a long shot, do you know any good central
document describing the diskdump / kdump format? From everything I can
tell, it seems very much like a "living standard", one which lives in
code more than documentation. But I would be glad to be wrong here, if
there's a document which describes the format then I'd love to read it,
and if not, maybe I could be part of creating it to help everyone out.

Thanks,
Stephen