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From: newsserv!stark!gene@cs.sunysb.edu (Gene Stark)
Newsgroups: comp.os.386bsd.questions
Subject: Re: FreeBSD - sio (com) and DOS HD problems
Date: 17 Sep 93 07:58:03
Organization: Gene Stark's home system
Lines: 58
Distribution: world
Message-ID: <NEWSSERV!STARK!GENE.93Sep17075803@stark.uucp>
References: <1993Sep16.201358.26183@doug.cae.wisc.edu>
Reply-To: stark@cs.sunysb.edu
NNTP-Posting-Host: stark.uucp
In-reply-to: tillemaj@cae.wisc.edu's message of 16 Sep 93 20:13:57 CDT
In article <1993Sep16.201358.26183@doug.cae.wisc.edu> tillemaj@cae.wisc.edu (John Edward Tillema) writes:
2. Is it possible to get info from a DOS hard disk partition
to FreeBSD? I tried creating a c device in mtools (2.0.7)
but that didn't work, I also tried creating a disklabel
(/dev/wd0h) for it (both are out of the FAQ), but again, that
didn't work. The changes I made were never present when I
would run disklabel again. It would say unused partition h
of size xxxx when I quit, then prompt if I wanted to overwrite
DOS parition table. Regardless of whether I answered y or n
it didn't save the changes. This is for a Conner 340 Meg IDE
drive.
The partitioning scheme used in 386BSD/FreeBSD is bizarre, to say the least.
To the best of my understanding, you will not be able to create a partition
for your DOS area, and then see that area from within FreeBSD, unless that
area lives on cylinders that are inside what has been declared to be the
BSD c partition. If you try to create a partition outside this area, you will
get the "unused partition" messages you describe.
So, I believe that if you expand the range of cylinders declared for the
BSD c partition, so that they cover the DOS area, you will then be able
also to define a new partition in the BSD disklabel that will allow you
access to the DOS area. But, this is not so easy as it might seem.
The disklabel program has the hard-coded default idea that the disklabel
should be written at the beginning of the "a" (root) partition of the BSD area.
If the beginning of your "a" partition does not coincide with the beginning
of your "c" area, then the disklabel will be written in the wrong spot
and you will not be able to boot your system.
I ran into this problem when I wanted to steal some cylinders from my DOS
area that was first on my disk, and give them to a new partition to be
included in the BSD area. The effect of this was to make a non-root
partition be the first one in the BSD area, and disklabel was not at all
happy. I eventually worked around the whole thing by using DOS fdisk
to delete all partitions on the disk, making a new primary DOS partition
of the size I wanted, booting the Tiny BSD install disk to get an initial
disklabel for the BSD area, then installing the disklabel I really wanted
after that. Once this was done, though, to redisklabel the BSD area
required specifying the partition that was first in the BSD area (e.g. wd0f)
rather than just using wd0 and letting the default (the "a" partition)
get labeled. I managed not to destroy any of the data that was in the
BSD area, so I was happy.
So, the moral of the story is this: You can try adding cylinders to your
BSD area ("c" partition) so that they include the area where the DOS partition
is. If your DOS partition occurs *after* the BSD area, then this should be
easy, and you should then be able to write a disklabel that contains a
partition you can mount as a PCFS. If your DOS partition occurs *before*
the BSD area, then you can probably do it too, but you have to be very careful,
because for the reasons explained above you might end up not being able to
boot your system. Make sure to keep around a fixit floppy with a copy of
your original disklabel (so you can go back) and facilities for editing
and writing new disklabels.
- Gene Stark
--
stark@cs.sunysb.edu