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SubjectRe: devfs
  Date: Fri, 16 Jan 1998 09:53:07 +1100
From: Richard Gooch <rgooch@atnf.CSIRO.AU>

What does *BSD/Intel have as it's naming scheme for partitions and for
slices?

Pre-emptive proposal: it we have to deal with partitions *and* slices,
one possibility is to munge the partition ID and slice ID
together. The first N "subdevices" (s) would be real partitions, the
remaining subdevices would be slices within partitions.
However, this I consider messy. You would have to know how many real
partitions you have and which ones have how many slices.
So, it would be more logical to have a naming scheme for
controller,bus,target,device(lun),partition thus:
/dev/sd/c0b0t0d0p1 a whole partition

Then, if any slices are found in partitions, you would also have:
/dev/sd/c0b0t0d0p1s3 a single Solaris slice within a partition

and of course:
/dev/sd/c0b0t0d0 a whole disc

Leonard: what do you think of this? I don't think we can ignore the
fact that partitions and slices are different. Munging them together
only partially hides it.
Also, if we were to go back to "p" for partition, how about "u" for
LUN?

To some extent, we already have this situation with "normal" PC style
partitions. The "extended" partition is split into "slices" called logical
partitions similarly. In Linux we number those from 5..N after the four
primary partitions, but I don't believe this is universal with other PC
operating systems; I seem to recall that DOS calls these Logical Partition 1,
and so on. If we're going to be consistent with using a new letter for
subdivisions, then we really should allow for only 4 primary partitions, some
of which may be divided further. Now, do Solaris slices live within both
primary and logical partitions, or only within a primary partition? How about
BSD? Is it legal to have multiple extended partitions each containing logical
partitions, or only a single one?

Perhaps I've missed something, but I still don't feel that we've seen a
complete description of how BSD and Solaris present these subdivided partitions
to the user. It doesn't bother me terribly much to have slices just using
higher numbers as we do now for logical partitions, but I don't know if the
structure is simple enough to allow for that. This is getting complicated
fast... we really need to know the full structure we need to address if we
want an all-encompassing solution. What would a multi-boot system with Linux,
BSD, Solaris, and Win 95 or NT look like?

If we can get away with "d" (device) and "s" (subdevice) without building a
complicated and fully general tree, I'm still in favor of that.

Leonard

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