[Bugs] #2460 UNSP: writing to data store broken due to permissions issue

[Sugar Labs Bugs]

#2460: writing to data store broken due to permissions issue
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    Reporter:  sascha_silbe               |          Owner:  silbe                      
        Type:  defect                     |         Status:  new                        
    Priority:  Unspecified by Maintainer  |      Milestone:  Unspecified by Release Team
   Component:  Rainbow                    |        Version:  Git as of bugdate          
    Severity:  Major                      |       Keywords:                             
Status_field:  New                        |   Distribution:                             
   Seeta_dev:                             |  
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 Writing data store entries fails inside the data store:

 {{{
 Traceback (most recent call last):
   File "/usr/lib/pymodules/python2.6/dbus/service.py", line 702, in
 _message_cb
     retval = candidate_method(self, *args, **keywords)
   File "/usr/lib/python2.6/dist-packages/carquinyol/datastore.py", line
 271, in get_filename
     return self._file_store.retrieve(uid, user_id, extension)
   File "/usr/lib/python2.6/dist-packages/carquinyol/filestore.py", line
 134, in retrieve
     os.chmod(file_path, 0440)
 OSError: [Errno 1] Operation not permitted:
 '/home/sascha.silbe/.sugar/default/datastore/2b/2bd396fa-ddb2-43e6-b8ae-
 680f475488ce/data'
 }}}

 That's because the submitted files are owned by the isolation user and
 moved (not copied) into the data store:

 {{{
 sascha.silbe at xo15-sascha:~/sugar-jhbuild/source/sugar-datastore$ ls -l
 /home/sascha.silbe/.sugar/default/datastore/2b/2bd396fa-ddb2-43e6-b8ae-
 680f475488ce/data
 -rw-rw-rw- 1 10046 sascha.silbe 232 Oct 17 22:22
 /home/sascha.silbe/.sugar/default/datastore/2b/2bd396fa-ddb2-43e6-b8ae-
 680f475488ce/data
 }}}

 Not sure what the best solution is:
 * Copying would be wasteful (especially for large entries)
 * For changing ownership after moving we'd need some helper running as
 root.
 * Leaving the permissions as-is would lead to the same issues I
 encountered with [http://activities.sugarlabs.org/en-US/sugar/addon/4326
 Backup] / [http://activities.sugarlabs.org/en-US/sugar/addon/4327
 Restore]: other activities cannot read or overwrite existing entries from
 an activity that set restrictive permissions.

 [http://dbus.freedesktop.org/doc/NEWS DBus 1.3.0] apparently has support
 for fd passing. Maybe the next generation of sugar-datastore and sugar-
 toolkit should use that to transfer the entries? Most activities wouldn't
 need to create an on-disk copy first.

-- 
Ticket URL: <http://bugs.sugarlabs.org/ticket/2460>
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