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1995-11-04
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!CDFix (v1.00 4/11/95)
~~~~~~~~~~~~~~~~~~~~~~
This little application is designed to fix various flaws within Acorns CDFS
filing system. It works by ripping the exisitng CDFS module out of the RMA,
patching it, and writing it back. In the process of doing this, the module
grows by about 128 bytes.
The bugs fixed are:
* Filetypes:
CDFS contains a routine that maps file extensions to filetypes.
Unfortunately this routine is broken due to a typo. This program
reassembles working code over the top of the old version.
* Opaque Files:
CDs can contain "Opaque files". These are special files which are
usually associated with ordinary files on the CD. These are
explained below in more detail. This program patches CDFS so as to
allow them to be accessed by replacing occurences of "/" with "_".
Both of these bugs are to be fixed in a future release of CDFS by Acorn, but
this is intended as a stopgap measure.
A debt of Gratitude is owed to Martin Sperl and Mike Martin who wrote the
original Filetypes/CD_Type program on which this is based.
I will endeavour to keep the latest version of this software on-line as:
ftp://ftp.comlab.ox.ac.uk/tmp/Robin.Watts/CDFix.zip
Opaque Files:
~~~~~~~~~~~~~
In the mad mad world of apples, files are generally split into two sections
or "forks". One fork is known as the data fork and contains (for instance)
the compressed frames of a movie, or the image data for bitmaps. The other
is known as the resource fork, and contains information on how to interpret
the data fork, for instance where the frames start, what speed they should
be played back at, what compression type they use etc.
These are stored on CDs as separate files, with the same names. They are
differentiated by the resource fork having the "Opaque" bit set.
Unfortunately on RISC OS this means that the Filer window shows two
identically named files. As soon as you try to access one of them, it is
always the first of the pair that is actually accessed. Typically this means
you can only get to the resources for a file, and not the data itself (in
fact it can be ther other way round, but either way is useless).
As a blatent hack to get around this problem, CDFix patches CDFS to rewrite
any "/" in an opaque files filename as "_". Thus if you have a file
"FRED/MOV" on a CD, you will now see "FRED_MOV" and "FRED/MOV".
I wrote this application so as to allow MovieFS to run transparently from CD.
Future versions of MovieFS will automatically detect the dual files and use
them transparently.
Contact Addresses:
~~~~~~~~~~~~~~~~~~
I can be contacted at:
Robin Watts
Warm Silence Software,
St Catherine's College,
Oxford, OX1 3UJ
Tel: 0585 487642 (and yes, that is 0585, not 01585)
Email: Robin.Watts@comlab.ox.ac.uk
Martin Sperl (who wrote the original !Filetypes) can be contacted at:
Martin Sperl,
Nattergasse 12/32
A-1170 Vienna
Austria
Fido: 2:313/16.6
Email: Sperl@Astro1.auniw.ac.at
I do not have a contact address for Mike Martin other than "Softcorn".
History:
~~~~~~~~
Vesion 1.00: 4/11/95
Base release version.
[If this all scrolled past too fast, load an editor first. If the editor
displays TABs as [09] then get a copy of real editor like !Zap.]