Driver for a different view of a filesystem

Paul Tomlin (paul_tomlin@life01.com)
Fri, 04 Jun 1999 22:12:40 +0100


I'm rattling out an idea to do a driver which will present
the data on a drive in a different format. Specifically I
am thinking about graphics files but there is no reason the
idea can't be extended to other data types.

Essentially the aim is to produce a driver which presents
the files in a fashion similar to that used by the DPS
Perception driver for NT. The Perception is a video disk
recorder for PC's which has its own SCSI bus and MJPEG
compressor. The files are stored on the drive in some
proprietary format but the drive (as seen by NT) has a
directory structure similar to this...

P: --> Project --> TGA --> PROJECT0001.TGA
| PROJECT0002.TGA
| ....
| PROJECT9999.TGA
|
|-> BMP --> PROJECT0001.BMP
| PROJECT0002.BMP
| ...
| PROJECT9999.BMP
|
|-> JPG blah
|
|-> TIFF blah

You get the jist. Basically the driver, with some help from the
HW was able to convert the video format into individual frames
in various file formats on request.

My thoughts are..

Use an existing fs for the real disk work. It may be possible
to create an fs which is ideal for video (large files) but that
would weaken any possibiliy of extending the idea to other data
types. It is also possible to tune existing fs types to perform
better for various, dedicated media types. No point duplicating
work.

Creae a new fs type which can be mounted. The driver would then
mount the drive using ext2, for example, and present the altered
image.

Things troubling me include implementation (I haven't written
a driver, bar 'Hello world', before), the data conversion may
well be extremely CPU intensive (and does that make it best
suited to user/kernel space?), potential tie-ins with other
drivers for real HW (say an MPEG card) which could reduce the
CPU load, the list goes on.

I am basically looking for some response about the idea. I'm at the
point where I am trying to work out if this is a char or block
driver so please go easy if this is a *REAL* dumb idea..

Paul

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