Lpc2000

--- In lpc2000@yahoogroups.com, "Dan Beadle" <dan.beadle@i...> wrote:
>
> When you delete an entry in the DIR by writing E5 to the first 
byte, you
> must first deallocate all used sectors. 

I don't think so.  If you deallocate at that point, you can never 
recover the file and an entire aftermarket software industry would 
crash and burn.  I gotta think about this...  Perhaps the sectors 
are unallocated when the directory entry is used for a new file.

Anyway, deallocating a used cluster would be done by writing 
0x00000000 to the cluster entry in the FAT?

>  
> 
> (If you don't, you have to old DOS problem of lost clusters)
> 
>  
> 
> Delete File:
> 
>             Starting at First Cluster,  (from Dir entry)
> 
>                         Walk through the cluster allocation table,
> unlinking each cluster from the file (returning to free)

Again, by writing 0x00000000?  Or is there a linked list of free 
clusters?  If so, I missed that somehow!  Or do I just wander around 
in the FAT looking for a 0x00000000 entry?  Maybe the closest one 
above the current cluster?

> 
>             Then mark first byte of file name to E5.
> 
>  
> 
>  
> 
> As for writing, it is just the reverse...
> 
>  
> 
> Make sure the files does not exist, if it does, delete it per 
above.
> 
>  
> 
> Search the directory for an entry starting in NULL or 0xE5 
(previously
> deleted)
> 
> Fill in your information in that structure. (File names are fixed 
size,
> not null terminated. Pad with blanks)
> 
> Find a free cluster from the Cluster Allocation Table. 
> 
> Put that entry into the Dir. 
> 
> Mark that cluster as EOF (FFFF) in the CAT
> 
> Write the first cluster of information. 

Dealing with sectors per cluster along the way...
 
> 
> If there is more, find another free cluster
> 
>             Mark the new cluster as EOF in the Cat
> 
>             Change the EOF on the prior cluster from EOF to point 
to
> this cluster
> 
>  
> 
> Repeat till end of file...

No questions here...

> 
> Update the directory structure with file size, time (if desired).
> 
>

Yes, do this in close();  So, what do you do with the remaining 
bytes in a partially filled sector and the remaining sectors in a 
partially filled cluster?  My tendency from a security point of view 
would be to fill them with 0's, or my personal favorite 0x5A.
  
Richard