Project

General

Profile

Actions

DataPartition

/!\ Warning: Draft

This article is in draft form and is being written:
  • Everybody is welcome to contribute
  • Some things might not be accurate yet, so beware before using the information contained in it.

What does the data partition contain?

It probably depends on the devices and the Android versions.

On Replicant 6.0, it contains at least the application internal data: When various applications are installed, they have access to some storage where they can read and write data that is only visible to them and not to other applications. This is part of the Android security model that doesn't trust applications even if they are fully free software. This has serious usability consequences for users as it makes backuping and restoring the application data way more complicated than it should be: this data is tied to the application signatures, so because of that it's not easily portable across different Replicant versions. When application signatures changes (like between Replicant 6.0 0003 and 6.0 0004), the data needs to be migrated from the old signatures to the new ones.

In addition, on some devices it also contains the users data. This location and external microSD cards is where users typically their files like Music, photos, etc. This data is made accessible to the users in various location through a mechanism called fuse. In Replicant 6, this data is stored in the media directory in the data partition. Unlike application data, this data is not tied to any Android version or application signatures, so it can be moved, backed up, restored relatively easily across different devices and operating systems. It uses a similar file permission system than with GNU/Linux (unix DAC + Selinux).

Known data location:

Location Content
/data/app/<application name>/ Application apk, native libraries, java cache (base.odex)?
/data/data/<application name>/ Application internal data
/data/media/ User accessible storage to store music, photos, etc
Also mounted in /storage/emulated with fuse
/data/system/packages.xml Application and signing key, uid, etc mapping
/data/system/appops.xml Application permissions
For Silence:
Location Content
/data/data/org.smsecure.smssecure/ Silence data
/data/data/org.smsecure.smssecure/messages.db Silence (encrypted?) messages database (sqlite3)

TODO

Here's where the sdcard user accessible storage comes from:

/sdcard -> /storage/self/primary [1]
/storage/self/primary -> /mnt/user/0/primary [2]
/mnt/user/0/primary -> /storage/emulated/0 [3]

root@i9300:/ # readlink /sdcard                                                                                                                            
/mnt/user/0/primary
root@i9300:/ # readlink /storage/self/primary                                                                                                              
/mnt/user/0/primary
root@i9300:/ # readlink /mnt/user/0/primary                                                                                                                  
/storage/emulated/0
root@i9300:/ # mount | grep "/storage/emulated"                                                                                                              
/dev/fuse on /storage/emulated type fuse (rw,nosuid,nodev,noexec,noatime,user_id=1023,group_id=1023,default_permissions,allow_other)
TODO:
  • Explain that the user accessible storage is not always present
  • Explain that it depends on the devices (GTA04)

Concerns about the application internal data

TODO:
  • Explain the issue about the Replicant version <-> application data

Updated by Kurtis Hanna about 1 month ago · 21 revisions