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Date:      Tue, 21 Feb 1995 17:55:53 +1100
From:      Bruce Evans <bde@zeta.org.au>
To:        obiwan!bob@uudell.us.dell.com, roberto@blaise.ibp.fr
Cc:        current@FreeBSD.org, phk@ref.tfs.com
Subject:   Re: ATTENTION
Message-ID:  <199502210655.RAA08777@godzilla.zeta.org.au>

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>>[slices]
>1. what will it change  ?

Mainly sd.c and wd.c.  The specialness of the 'd' partition will go
away and you will have to use (e.g.) /dev/sd0 instead of /dev/sd0d.
Almost nothing used /dev/sd0d (fdisk, sysinstall and benchmarks are
the only things that should have used it), so you won't notice in
normal operation.

>2. how do we convert from the old system ?

Simply compiling the new version should be enough to get ordinary
ufs partitions working.  The bootstrap will probably complain about
'd' partitions and may complain about MSDOS partitions and delete
them from the in-core disklabel (partitions not within the BSD slice
are not allowed).  You can delete the bogus partitions to get rid of
the warnings.  I keep them for testing.  To get at (primary) MSDOS
slices that are no longer in the label, you have to edit
/etc/fstab to give the new name of the slice, e.g., /dev/sd0s1
(DOSpartition 1).  If you want new features such as more than one
BSD slices, then you have to edit /etc/fstab some more and
/dev/MAKEDEV to create the new devices (there are too many possible
devices to create by default and I haven't added nonstandard cases
yet).  If the second BSD slice is /dev/sd0s3, then you would need
devices /dev/[r]sd0s3[a-h].  Booting from BSD slices after the first
is currently not supported.

>3. if someone wants to stay as is it now, will it be possible or
>  will slices be mandatory  ?

The slice code will be mandatory but you won't see much evidence of
it.  However, there is a lot of compatibility cruft to make the old
devices work transparently.  I'd like this to go away soon.  Devices
would have to be named differently in /etc/fstab and in config files,
e.g., /dev/sd0s2a instead of /dev/sd0a if /dev/sd0s2 is the first BSD
slice.  (The partitions on the first BSD slice in the DOSpartition
table are aliased to /dev/[r]sd0[a-h].  This requires confusing
minor numbering:

	name		slice bits in minor	DOSpartition number
	[r]sd0[a-h]	0 << 21			aliased
	[r]sd0[c]	1 << 21			none
	[r]sd0s1[a-h]	2 << 21			1
	....
	[r]sd0s4[a-h]	5 << 21			4).

>4. will it require to have a DOS partition or not. ?

Not necessary.  The case BSD on the whole disk hasn't been tested
much.  I think it works with a correct DOSpartition table (covering
the whole disk) or no DOSpartition table (no 0xAA55 signature).
Unfortunately, the standard bootstrap creates an incorrect
DOSpartition table.  This case will probably work too, by throwing
out the table.

Bruce



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