Re: [ros-dev] FullFAT replacement for Fastfat.sys

[Steven Edwards]

On Thu, Jul 30, 2009 at 10:53 AM, James Walmsley<james(a)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