[Sugar-devel] Journal-like activities (was: Re: [ASLO] Release Read ETexts-19)

[Sascha Silbe]

On Wed, Mar 17, 2010 at 05:08:08PM -0500, James Simmons wrote:

> I was looking at the code for Leer Pen Drive and thinking how I could
> improve on it, and in the process I ended up looking at
> git.sugarlabs.org at the code for Journal.  Apparently that is not the
> most recent code,
I guess you were looking at the "journal" project (don't have internet 
access right now, so cannot check the exact name). That's indeed rather 
old code; the Journal has been integrated into the sugar package.

> That wouldn't be too surprising except that the Journal Activity can 
> write to a USB or thumb drive.  I couldn't figure out how or even 
> where it was doing it, [...]
The "journal" project is part of 0.82. Back then the data store handled 
removable media.
In 0.84+, the data store was rewritten from scratch [1] and only handles 
the on-disk, native Sugar objects. Handling of "traditional" (POSIX) 
file storage (USB sticks, hard disks, etc.) has been moved into the 
Journal.
The code you're looking for is sugar/src/jarabe/journal/model.py. In 
there, the classes DatastoreResultSet and InplaceResultSet form an 
abstraction layer over the data store and mounted (POSIX) file systems.

> but it does seem that you could write an Activity that does everything 
> the Journal does, from writing to mounted media to unmounting it.
Almost everything the Journal does can be done in an activity as well. 
It all boils down to permissions; usually the permissions are based on 
security considerations.
The following actions are implemented (source references are for 0.88):

- show item in Journal (D-Bus API)
    - sugar/src/jarabe/journal/journalactivity.py
    - D-Bus doesn't allow a second process with the same service name, so 
not overridable

- show object picker (D-Bus API)
    - sugar/src/jarabe/journal/journalactivity.py
    - again, D-Bus prevents activities from providing this

- mounting/unmounting file systems (e.g. USB sticks)
    - show new mount points: sugar/src/jarabe/journal/volumestoolbar.py
    - unmounting: sugar/src/jarabe/view/palettes.py:VolumePalette
    - mounting (Frame, not Journal): 
sugar/extensions/deviceicon/volume.py
    - without Rainbow:
      - activities are able to mount and umount file systems using gio 
(resp. gvfs for older systems)
    - with Rainbow:
      - gio/gvfs probably refuses to unmount file systems mounted by the 
Frame from within activities (because the user ids are different)

- browsing data store / file systems, reading all entries / files
    - sugar/src/jarabe/journal/model.py
    - without Rainbow:
      - unrestricted
    - with Rainbow:
      - currently:
        - data store access unrestricted
        - file system access prevented by gio/gvfs permission settings
      - future:
        - see P_DOCUMENT / P_DOCUMENT_RO Bitfrost [2] protections

- reading a single data store entry / file via Object Picker
    - sugar-toolkit/src/sugar/graphics/objectchooser.py
    - unrestricted

- writing a single data store entry / file (acquired via Object Picker)
    - without Rainbow:
      - unrestricted
    - with Rainbow:
      - currently:
        - data store access unrestricted
        - file system access prevented by gio/gvfs permission settings
      - future
        - unrestricted

- writing random data store entries / files
    - without Rainbow:
      - unrestricted
    - with Rainbow:
      - currently:
        - data store access unrestricted
        - file system access prevented by gio/gvfs permission settings
      - future
        - subject to P_DOCUMENT Bitfrost [2] protection


Bitfrost protections can be disabled, see the Bitfrost specs [2] for 
details.

Sorry for the long mail; it's not just an answer to your questions but 
also a Rainbow TODO list. :)


[1] http://wiki.sugarlabs.org/go/Development_Team/Datastore_Rewrite
[2] http://dev.laptop.org/git/security/tree/bitfrost.txt

CU Sascha

-- 
http://sascha.silbe.org/
http://www.infra-silbe.de/
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