BlueZ settings storage
**********************
Purpose
=======
The purpose of this document is to describe the directory structure of
BlueZ settings storage. In effect, this document will serve as the primary,
up to date source of BlueZ storage information.
It is intended as reference for developers. Direct access to the storage
outside from bluetoothd is highly discouraged.
Adapter and remote device info are read form the storage during object
initialization. Write to storage is performed immediately on every value
change.
Default storage directory is /var/lib/bluetooth. This can be adjusted
by the --localstatedir configure switch. Default is --localstatedir=/var.
When loading as a service the storage directory can be set via
StateDirectory environment variable:
https://www.freedesktop.org/software/systemd/man/systemd.exec.html
All files are in ini-file format.
Storage directory structure
===========================
The storage root directory contains an optional addresses file that's
used for managing adapters that come without a pre-allocated address.
The format of the addresses file is:
[Static]
<manufacturer id> = <array of addresses>
Each adapter with an assigned address has its own subdirectory under the
root, named based on the address, which contains:
- a settings file for the local adapter
- an attributes file containing attributes of supported LE services
- an admin policy file containing current values of admin policies
- a cache directory containing:
- one file per device, named by remote device address, which contains
device name
- one directory per remote device, named by remote device address, which
contains:
- an info file
- an attributes file containing attributes of remote LE services
- a ccc file containing persistent Client Characteristic Configuration
(CCC) descriptor information for GATT characteristics
So the directory structure is:
/var/lib/bluetooth/<adapter address>/
./settings
./attributes
./admin_policy_settings
./cache/
./<remote device address>
./<remote device address>
...
./<remote device address>/
./info
./attributes
./ccc
./<remote device address>/
./info
./attributes
...
Settings file format
====================
Settings file contains one [General] group with adapter info like:
Alias String Friendly user provided name advertised
for this adapter
This value overwrites the system
name (pretty hostname)
Discoverable Boolean Discoverability of the adapter
PairableTimeout Integer How long to stay in pairable mode
before going back to non-pairable.
The value is in seconds.
0 = disable timer, i.e. stay
pairable forever
DiscoverableTimeout Integer How long to stay in discoverable mode
before going back to non-discoverable.
The value is in seconds.
0 = disable timer, i.e. stay
discoverable forever
Sample:
[General]
Name=My PC
Discoverable=false
Pairable=true
DiscoverableTimeout=0
Identity file format
====================
Identity file contains one [General] group that holds identity information
such as keys and adresses:
IdentityResolvingKey String 128-bit value of the IRK
Sample:
[General]
IdentityResolvingKey=00112233445566778899aabbccddeeff
Attributes file format
======================
The attributes file lists all attributes supported by the local adapter or
remote device.
Attributes are stored using their handle as group name (decimal format).
Each group contains:
UUID String 128-bit UUID of the attribute
Value String Value of the attribute as hexadecimal encoded
string
EndGroupHandle Integer End group handle in decimal format
Sample:
[1]
UUID=00002800-0000-1000-8000-00805f9b34fb
Value=0018
[4]
UUID=00002803-0000-1000-8000-00805f9b34fb
Value=020600002A
[6]
UUID=00002a00-0000-1000-8000-00805f9b34fb
Value=4578616D706C6520446576696365
Admin Policy file format
======================
The admin policy file stores the current value of each admin policy.
[General] group contains:
ServiceAllowlist List of List of service UUID allowed by
strings adapter in 128-bits format, separated
by ','. Default is empty.
Sample:
[General]
ServiceAllowlist=
CCC file format
======================
The ccc file stores the current CCC descriptor values for GATT characteristics
which have notification/indication enabled by the remote device.
Information is stored using CCC attribute handle as group name (in decimal
format).
Each group contains:
Value String CCC descriptor value encoded in
hexadecimal
Cache directory file format
============================
Each file, named by remote device address, may includes multiple groups
(General, ServiceRecords, Attributes, Endpoints, NameResolving).
In ServiceRecords, SDP records are stored using their handle as key
(hexadecimal format).
In "Attributes" group GATT database is stored using attribute handle as key
(hexadecimal format). Value associated with this handle is serialized form of
all data required to re-create given attribute. ":" is used to separate fields.
In "Endpoints" group A2DP remote endpoints are stored using the seid as key
(hexadecimal format) and ":" is used to separate fields. It may also contain
an entry which key is set to "LastUsed" which represented the last endpoint
used.
In "NameResolving", information regarding remote name resolving are stored to
prevent wasting time resolving name for unresponsive devices.
[General] group contains:
Name String Remote device friendly name
ShortName String Remote device shortened name
[ServiceRecords] group contains
<0x...> String SDP record as hexadecimal encoded
string
In [Attributes] group value always starts with attribute type, that determines
how to interpret rest of value:
Primary service:
2800:end_handle:uuid
Secondary service:
2801:end_handle:uuid
Included service:
2802:start_handle:end_handle:uuid
Characteristic:
2803:value_handle:properties:uuid
Descriptor:
value:uuid
uuid
Sample Attributes section:
[Attributes]
0001=2800:0005:1801
0002=2803:0003:20:2a05
0014=2800:001c:1800
0015=2803:0016:02:2a00
0017=2803:0018:02:2a01
0019=2803:001a:02:2aa6
0028=2800:ffff:0000180d-0000-1000-8000-00805f9b34fb
0029=2803:002a:10:00002a37-0000-1000-8000-00805f9b34fb
002b=2803:002c:02:00002a38-0000-1000-8000-00805f9b34fb
002d=2803:002e:08:00002a39-0000-1000-8000-00805f9b34fb
[Endpoints] group contains:
<xx>:<xx>:<xx>::<xx...> String First field is the endpoint type,
followed by codec type and delay
reporting and its
capabilities as hexadecimal encoded
string.
LastUsed:<xx>:<xx> String LastUsed has two fields which are the
local and remote seids as hexadecimal
encoded string.
[NameResolving] group contains:
FailedTime Integer The last time we failed to complete name
resolving procedure, measured from an
arbitrary, fixed point in the past.
Info file format
================
Info file may includes multiple groups (General, Device ID, Link key and
Long term key) related to a remote device.
[General] group contains:
Name String Remote device friendly name
Alias String Alias name
Class String Device class in hexadecimal,
i.e. 0x000000
Appearance String Device appearance in hexadecimal,
i.e. 0x0000
SupportedTechnologies List of List of technologies supported by
strings device, separated by ";"
Technologies can be BR/EDR or LE
AddressType String An address can be "static" or "public"
Trusted Boolean True if the remote device is trusted
Blocked Boolean True if the remote device is blocked
Services List of List of service UUIDs advertised by
strings remote in 128-bits UUID format,
separated by ";"
[DeviceID] group contains:
Source Integer Assigner of Device ID
Vendor Integer Device vendor
Product Integer Device product
Version Integer Device version
[LinkKey] group contains:
Key String Key in hexadecimal format
Type Integer Type of link key
PINLength Integer Length of PIN
[LongTermKey] group contains:
Key String Long term key in hexadecimal format
Authenticated Boolean True if remote device has been
authenticated
EncSize Integer Encrypted size
EDiv Integer Encrypted diversifier
Rand Integer Randomizer
[PeripheralLongTermKey] group contains:
Same as the [LongTermKey] group, except for peripheral keys.
[ConnectionParameters] group contains:
MinInterval Integer Minimum Connection Interval
MaxInterval Integer Maximum Connection Interval
Latency Integer Connection Latency
Timeout Integer Supervision Timeout
[LocalSignatureKey] and [RemoteSignatureKey] groups contain:
Key String Key in hexadecimal format
Counter Integer Signing counter
Authenticated Boolean True if the key is authenticated
[ServiceChanged]
This section holds information related to Service Changed characteristic
of GATT core service.
CCC_LE Integer CCC value for LE transport
CCC_BR/EDR Integer CCC value for BR/EDR transport
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