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From: ron@topaz.rutgers.edu.UUCP
Newsgroups: comp.periphs,comp.unix.wizards
Subject: Re: Filesystem/archive formats for WORM optical disks
Message-ID: <14040@topaz.rutgers.edu>
Date: Tue, 18-Aug-87 11:16:04 EDT
Article-I.D.: topaz.14040
Posted: Tue Aug 18 11:16:04 1987
Date-Received: Thu, 20-Aug-87 01:40:54 EDT
References: <1775@kontron.UUCP> <212@casemo.UUCP> <75@cipric.mn.org> <615@orcisi.UUCP>
Organization: Rutgers Univ., New Brunswick, N.J.
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Xref: utgpu comp.periphs:481 comp.unix.wizards:3492

No, There it is not supposed to write on the disk at all (hence the name).
There was a bug for a while in V6 (and hence early PWB kernels as well)
where if you had a sparse file the kernel bmap routine tried to allocate
a block from the free list (and hence update the superblock) when you
tried to read one of the empty blocks.  A slight fix to the bmap routine
to differentiate between reads and writes fixed the problem.  As a matter
of fact, only slight changes to the UNIX kernel (seperating pipedev from
rootdev) were required to allow UNIX to boot on a write-protected root
disk.  (4.2 actually would run for a few hours with the paging disk write
protected as well, everything was fine until memory filled up).

-Ron