>I swear I'm not stupid.  Really.  What's crazy is that back in November,
>I went through something like this, Wolfgang Solfrank explained to me
>how the i386 boot sequence works, and I was quite sure I understood.
>Certainly, I was able to fix the system last time.

If it makes you feel any better ... every time I have to do a new disklabel
on an i386 system from scratch, I _always_ fuck it up the first time.

>  - The above part zero bootcode reads the DOS partition table, finds the
>    active partition (in this case, the NetBSD partition) (or, if
>    bootselect, it may allow the user to select an alternative partition
>    using one of the function keys), then reads the first sector of that
>    and jumps to it.  This first sector of the NetBSD part of the disk
>    should contain part 1 of the NetBSD boot code (the "countdown");
>    the next sector contains the NetBSD disk label (including the NetBSD
>    partition table).

The magic here is that the I/O at this point is done via the BIOS,
and the DOS disklabel has to be _exactly_ correct.  By that I mean
that the beginning in C/H/S notation has to match ... which is my
experience is where the problems lie, because many times you're
using a "translated" geometry, and fdisk and the BIOS can get
confused as to which translated geometry you're using.

>The list of part 2 block locations appears to be hard-coded into part
>1, which suggests that part 1 does *not* read the filesystem to find
>the "/boot" file, but rather knows where the "rest of itself" is.  On
>the other hand, I can use a part 2 on sd0a from a part1 obtained from
>fd0a, which suggests that part 1 *can* read the filesystem (it can
>read it enough to do "ls", anyway!).  Confusion still reigns. :-(

When you've booted off of fd0a, you've already reached "part 2" (part 2
is what puts up the NetBSD Boot" mesasge).  Part 1 knows where part 2 is
because installboot patches in the sectors part 2 occupies.

>What I did
>----------
>
>(a) I used "fdisk -iua" to put an MBR on sd0.  "fdisk sd0" reports:
>
>|  NetBSD disklabel disk geometry:
>|  cylinders: 4826 heads: 4 sectors/track: 107 (428 sectors/cylinder)
>|  
>|  BIOS disk geometry:
>|  cylinders: 1023 heads: 255 sectors/track: 63 (16065 sectors/cylinder)
>|  
>|  Partition table:
>|  0: <UNUSED>
>|  1: <UNUSED>
>|  2: <UNUSED>
>|  3: sysid 169 (NetBSD)
>|      start 64, size 64 (0 MB), flag 0x80
>|          beg: cylinder    0, head   1, sector  2
>|          end: cylinder    0, head   2, sector  2

This seems ... way too small.  I think you want something like:

start 63, size 2065465
beg: cylinder 0, head 1, sector 1
end: cylinder 1022, head 254, sector 63

Just a guess.  If those numbers actually work, then I'll explain how
I got them :-)

--Ken