[ros-dev] FullFAT replacement for Fastfat.sys

[Steven Edwards]

On Thu, Jul 30, 2009 at 10:53 AM, James Walmsley<james at worm.me.uk> wrote:
> Actually thats just being developed into FullFAT already in
> preparation for the 1.0.0 release. I believe I already mentioned it,
> but here's a link the the linux kernel mailing list that explains how
> the patch works and why its legally valid.
>
> http://lkml.org/lkml/2009/6/26/314 -- A legal discussion about the patch.
> http://lkml.org/lkml/2009/6/26/313 -- Technical details of what the patch does.
>
> FAT stores a checksum in LFNs of the shortname, this can be used to
> verify the integrity of LFN entries in a directory. Of course using
> the linux patch, the short name can be used for other puposes. However
> its not really journaling because you still have to scan all the
> directories. This takes a long time.

Right. The set of patches I am thinking of is actually older than
Tridge's recent patent avoidance work. But I think the concept was the
same. If there is a performance hit then it would not worth it.

> Sarocet also makes a good point about the problem with a ReactOS
> journaling file. The journal should store some kind of hash or
> checksum value of the state of the FAT table (which is probably too
> big). Or atleast the directories affected by the journal changes. If
> this hash differs before journal transactions are committed to the FS
> then the journal should clear that transaction and not commit it.
>
> Really journaling should only be enabled for a ReactOS system
> partition, using journaling on removable media wouldn't bring any
> great benefit, because of the effect that Sarocet described.
>
> Still I think the journaling is something we won't add until the
> driver is working and stable.

I agree. It would be nice to have but that is way down the road but
for now, it would just be nice to have a bullet proof fat32
implementation although I suspect a lot of our problems are deeper
than the driver itself. If I recall there has been quite a bit of work
in the past to get our vfat driver to function on Windows.

Thanks
-- 
Steven Edwards

"There is one thing stronger than all the armies in the world, and
that is an idea whose time has come." - Victor Hugo