[sugar] clarification of SUGAR_ACTIVITY_ROOT

[Michael Stone]

Paul,

>> Paul Fox
>> - what if my activity might have larger data needs than
>> can be accomodated on the root fs?  what if i'd like to
>> use space on a removeable device?  is there a way to

> Bert
> This is not possible in the current datastore design AFAIK. Removable  
> devices are supported as "mount-points" in the datastore but cannot  
> currently be used to create files there without an intermediate copy  
> in the root fs.

Due to this infelicity of design, activities can directly manipulate
mounted removable storage (i.e. /media/*) with the usual Unix filesystem
API. However, there are two things you need to remember:

 * you'll need to take extra care with error-handling - the user can and
   will yank out the removable storage at any time!

 * data confidentiality cannot be correctly enforced by Unix permissions, 
   because the filesystem on the removable storage might not record them
   (e.g. FAT) or because the filesystem on the storage does record them
   and your next activity instance will be unable to manipulate
   restricted files created by the present instance (without using the
   DS to mediate)!
 
Michael