Path: utzoo!attcan!uunet!snorkelwacker!bloom-beacon!eru!luth!sunic!liuida!isy!dkm39
From: dkm39@isy.liu.se (Rickard Westman)
Newsgroups: comp.sys.amiga.tech
Subject: Info needed on FFS bitmap blocks
Keywords: AmigaDos, FFS
Message-ID: <1990Mar21.205448.3174@isy.liu.se>
Date: 21 Mar 90 20:54:48 GMT
Sender: dkm39@isy.liu.se
Reply-To: riw@linus.ida.liu.se (Rickard Westman)
Distribution: comp
Organization: Dept of EE, University of Linkoping
Lines: 30


I am working on some programs which need to access disk devices directly
for things like file system repair and file "undeletion".
However, there are some things I would need to know, which I haven't
seen documented anywhere.  (Perhaps this is mentioned in some issue of
AmigaMail, which is quite unknown in Europe.)

1. Where do I find the root block?

Under FFS and OFS it seems to be located at the exact middle,
rounded upwards if there is an even number of blocks.  Can I
rely on this?

2. Where are the bitmap pages located for large (>50 MB) partitions?

In the root block there are pointers to 26 bitmap blocks, each representing
4064 physical blocks.  This would limit the size of a partition to about
50 Mb, while I was under the impression that FFS supported disks of
"infinite" size.  So where do I find these extra bitmap blocks?  I
haven't been able to figure it out, since the size of my hard disk
is less than 50 MB.


I *do* want my programs to work on any disk device, so please enlighten me...


---------------------------------------------------------------------------
Richard Westman, University of Linkoping, Sweden   |   riw@linus.ida.liu.se
---------------------------------------------------------------------------
"Very few profound thoughts can be expressed in 80 characters."