From: Marko Mäkelä (marko.makela_at_hut.fi)
Date: 2003-06-26 01:16:59
Let's get back on topic:
On Fri, Jun 20, 2003 at 11:48:57PM +0200, Andre Fachat wrote:
> For my GeckOS/A65 I wrote a small ROM filesystem that is linked by
> storing the size of the next segment (file) at the start, so the file
> handler could jump from one to the next segment. Using an $FFFF as
> end marker gave me the possibility to expand the (EP)ROM by overburning
> just the next part from the empty EPROM $FF value to the data values :-)
How does your system keep track of available bytes? With a bitmap or by
traversing a pointer structure?
Currently, my directory entries have two 3-byte pointers to next and
previous entry, and a file name followed by the file contents. For
subdirectories, the contents is a 3-byte pointer into the first directory
entry. In this way, there can be multiple "hard links" into the same
directory, e.g., ".." for the parent directory.
It looks like I will have to add one more piece of data into file entries:
the length of the compressed data in bytes. Otherwise, finding the first
unused byte will require that the last file found is decompressed. Even
with this addition, allocating space for a new file requires traversal of
all "next" and "subdirectory" links, but it shouldn't be a problem, as
there will be at most a few thousand files.
Marko
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