Re: Ultrix and SunOS FFS compatibility?

[Thor Lancelot Simon <tls%panix.com@localhost>]

On Sat, Nov 22, 2025 at 09:59:10AM -0000, Michael van Elst wrote:
> cmhanson%eschatologist.net@localhost (Chris Hanson) writes:
> 
> >Should FFS on NetBSD be automatically compatible with FFS on Ultrix and =
> >SunOS?
> 
> The various FFS flavours are not compatible. Partially because details
> have deviated, partially because validation routines don't handle
> legacy defaults or previosly undefined values.

Our code was definitely able to mount Ultrix filesystems on little
endian 32-bit hosts.  I don't know if it was ever tested on a little
endian 64-bit host.  Finding the filesystem could be a bit of pain
because we never to my knowledge had a kernel option to enable Ultrix
disklabel support on any platform other than pmax.

So if this doesn't work now, it's a regression.  It even reliably worked
read/write without corruption for many, many years.  Ultrix filesystems
are essentially just 4.2BSD; if we can't mount theirs, we probably
can't safely mount "our own" from that era either.

-- 
Thor Lancelot Simon	                                     tls%panix.com@localhost
  "The liberties...lose much of their value whenever those who have greater
   private means are permitted to use their advantages to control the course
   of public debate."					-John Rawls