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Subject: Re: Status report
From: perterm (perterm_at_vce.de)
Date: 2002-05-08


Björn Stenberg wrote:

> And finally, the disk i/o code is now ready. The ATA driver, FAT32 driver,
> directory handling layer and file layer are tested and green-flagged for
> use.

Excellent news!
But when reading about FAT some issues come up to my mind: splitting mp3
files. Does FAT provide easy ways for splitting files?
I haven't done anything with filesystems so all this brainstorm is based
on my wild assumptions.
Probably it's easy to truncate a file at the end. Maybe it's just
adjusting the file size and marking the remaining space as free.
But I wonder if there's a way for real splitting without having to copy
the all the remainder to a whole new file.

The usual case would be that we want to split a file somewhere right in
the middle of a sector of the disc. Assume the situation that we want to
split a file that uses sector 1 - 3 and we want to split the file within
sector 2.

              splitpoint
                  V
|xxxxxxxxxx|xxxxxxxxxx|xxxxxxx---|----------|
   sector 1 sector 2 sector 3 sector 4

x : used by the file
- : free space
| : sector boundaries

Our goal is to obtain two files: FileA and FileB.
This probably means that the content of sector 2 has to be duplicated to
be used in both files. In this example we copy the content of sector 2
to sector 4. FileA consists of sector 1;2 and FileB of sector 4;3.

        endpoint FileA startpoint FileB
                  V V
|xxxxxxxxxx|xxxxx-----|xxxxxxx---|-----xxxxx|
   sector 1 sector 2 sector 3 sector 4

But now the startpoint of FileB is in the middle of sector 4. Is
somehting like this possible with FAT? Or must each file start at a
sector boundary? And if so - does the mp3 file format allow to fill the
empty space with dummy data?

Still wished I had time to do more than questions...

Phil



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