Subject: Re: Another changer, another changer problem
To: Gandhi woulda smacked you <>
From: Bill Studenmund <>
List: current-users
Date: 10/04/1998 14:33:20
On Sun, 4 Oct 1998, Gandhi woulda smacked you wrote:

> I read it as "we have to support 32-bit aware devices AND 32-bit unaware
> devices", i.e. 8/8 splits AND 10/22 or whatever splits.
> if (I've misunderstood) {
>     exit(0);

Kinda. In an integer, the Major/minor split (M/m) is
for 16-bit node: 0000MMmm
for 32-bit node: mmmMMMmm

So for both major and minor numbers < 256, they are the same.

> }
> else {
>     WHY?  We're already running filesystems that, say, SunOS no longer
>     understands.  Why support the old device nodes any further?
>     i.e. if my system crashes, I cannot boot from a SunOS CD-ROM for
>     recovery.
> }

The difference is that, AFAICT, the differences between our fs's and sun's
are an upward-compatable thing. I.E. we've added new features. When we
change the unit/partition split, we aren't adding new information, we're
CHANGING how (existing) information is interpreted.

Because the transition, the "flag day in /dev" as der Mouse put it, has
too many ways to go wrong. If we f*ck up the device nodes, we're really
hosed. If ANYTHING goes wrong in the transition, we're hosed.

I think we need at least one full release, say 1.4 (.X) where both the 16
and 32-bit nodes co-exist (*) before we can abandon the older ones.

(*) really we're just fussing about the unit/partition split, or /8 vs. 
/32 or /64 device nodes co-existing. 

Plus, all we REALLY need is:

1) put some magic in DEVUNIT and DEVPART
2) add duplicate entries in the Xdevsw table
3) (probably) add some sort of canonicalization so that the buffer cache
and any lockings keep both ways at getting at the lower 8 partitions
consistent. I.e. if wd1f is mounted, accessing rwd1f behaves the same
regardless of using either the 8/5/3 or 12/12/6 (or 12/13/5) split device

Charles badgered a lot of us, correctly, that we must make the transition
from 8 partitions to more partitions correctly or else we'll royally screw
ourselves over.

Take care,