Right after being pestered for a while I eventually got round to
fixing somethings in UnixFS. Looking through my old mail I found 2
distinct problems:

 o UnixFS can't access partitions that are over 2GB into the disk
 o attempting to write a file over a mode 444 file in a mode 777
   directory results in the file being truncated to the size of the
   new file, but the write of the data fails.

In reverse order, I fixed the file truncation bug (thanks Pete for
spotting it, and sorry about the file ;-) ), a new version of UnixFS
will be released sometime (I need to talk to Mark about some other
problems first).

The 2GB thing, well after a short amount of grubbing around I thought
I found the culprit. The internal partition table stores byte addresses
(a leftover from the pre-newfilecore days). I was about to rectify
this when I spotted another byte addressed int. Unfortunately this on
is in the disk record and holds the size of the disk in bytes !!! Now
unless something's changed recently I can't see how I can convince
filecore to let me access a >2GB disk (UnixFS accesses beyond the end
of the filecore disk by using an auxilary boot record with an enlarged
disk size).

There has been talk of a 2GB limit on partition sizes under RiscOS but
was this fixed by Acorn ? If so I need to buy some RiscOS 3 manuals,
if not then UnixFS won't be able to access partitions that aren't
completely below the 2GB boundary (partitions straddling the boundary
might mount, but might get corrupted when a data block is written
above 2GB).

Sorry for the bad news.

Cheers Scott

-- 
Scott Stevens, Network Services Group, Computer Centre, Imperial College
"I just don't trust that machine, man. Look, I know it's old-fashioned,
but I'm from the school that believes, "If God intended us to fly, he
wouldn't have invented Spanish air traffic control"." - Lister, Red Dwarf