From mboxrd@z Thu Jan  1 00:00:00 1970
From: wkt@tuhs.org (Warren Toomey)
Date: Mon, 5 May 2008 00:33:43 +1000
Subject: [Unix-jun72] mkfs.c is now working
Message-ID: <20080504143343.GA39542@minnie.tuhs.org>

All, my mkfs.c $Revision: 1.17 $, $Date: 2008/05/04 14:20:12 $ now produces
mountable filesystem images, and it's now checked into the svn repository.
The problem was that the size of a directory is not the size of the blocks
allocated to it, but is in fact the number of bytes of the in-use directory
entries. For example, / was being allocated 1 block == 512 bytes. But 512
is not its size (as it would be in later UNIXes); in fact if / has entries

 41 sdrwr-  7 root     70 Jan  1 00:00:00 .
 41 sdrwr-  7 root     70 Jan  1 00:00:00 ..
 43 sdrwr-  2 root    570 Jan  1 00:00:00 bin
 42 sdrwr-  2 root    250 Jan  1 00:00:00 dev
 99 sdrwr-  2 root    100 Jan  1 00:00:00 etc
108 sdrwr-  2 root     70 Jan  1 00:00:00 tmp
114 sdrwr-  2 root     20 Jan  1 00:00:00 usr

then its size is 7 entries * 10 bytes each = 70 bytes.

Importantly, this also means that we can now make bootable root filesystems
without having to do a cold UNIX:

% tools/mkfs /usr/local/src/V1 rf0.dsk rf	# Make the / disk
% tools/mkfs /usr/local/src/V1 rk0.dsk rk	# Make the /usr disk, same stuff
% ./simh.cfg
PDP-11 simulator V3.7-3
./simh.cfg> #!tools/pdp11
Unknown command
Disabling CR
Disabling XQ
RF: buffering file in memory
TC0: 16b format, buffering file in memory
sim> g

:login: root
root
# /tmp/a.out
/dev/rk0# ls -l /usr/tmp
total    8
112 sxrwrw  1 root    156 Jan  1 00:00:00 a.out
110 sxrwrw  1 root   1664 Jan  1 00:00:00 etma
113 sxrwrw  1 root      6 Jan  1 00:00:00 hello
109 sxrwrw  1 root     26 Jan  1 00:00:00 ttmp
111 sxrwrw  1 root    142 Jan  1 00:00:00 utmp
# df
806+4602			# Number of free blocks on / and /usr

I added /usr/tmp/hello just to verify that I was getting files that
were not on the cold UNIX tape.

Cheers,
	Warren