Re: [PATCH v3 01/10] doc: Add settings storage documentation

[Johan Hedberg <johan.hedberg@gmail.com>]

Hi Marcel,

On Wed, Oct 10, 2012, Marcel Holtmann wrote:
> > +            ./keys
> 
> Not sure that I want the keys separated. That seems like a waste.

Agreed. Same file seems good.

> > +            ./attribute_db
> > +        ./<remote device address>/
> > +            ./settings
> > +            ./keys
> > +            ./attribute_db
> > +        ...
> 
> Why did we want directories for remote devices again? Can we not just
> put all in one big file with the name of the remote address?

For profile-specific storage this could be convenient (when removing the
device we just remove the entire directory and the core daemon doesn't
need to care about profiles details). OTOH the core needs to either way
provide some API so the plugins know to write to the right location
(be it a single file for the entire device or a single directory for the
device).

> > +Adapter directory files
> > +=======================
> > +
> > +Settings file contains 1 [General] group with adapter info:
> > +  [General]
> > +  Name=
> > +  Class=0x000000
> > +  Pairable=<true|false>
> > +  PairableTimeout=0
> > +  DiscoverableTimeout=0
> > +  Mode=<off|connectable|discoverable>
> > +  OnMode=<connectable|discoverable>
> 
> Actually with management interface now being used, we can be a bit
> smarter here. The mode can be programmed even if the controller is not
> powered.
> 
> So this might be better as Discoverable, Connectable, Pairable and
> Powered boolean options.
> 
> Also Pairable has no timeout in the kernel API anymore. Do we still need
> this?

We do have it currently as a documented adapter D-Bus property so that'd
need to be removed too. I don't personally have a great need for this
but I could imagine some device manufacturers deciding to have something
like this (especially those with very simple UI's with a single button
or so).

> > +The attribute_db file is a list of handles (group name) with UUID and Value as
> > +keys, for example:
> > +  [0x0001]
> > +  UUID=00002800-0000-1000-8000-00805f9b34fb
> > +  Value=0018
> > +
> > +  [0x0004]
> > +  UUID=00002803-0000-1000-8000-00805f9b34fb
> > +  Value=020600002A
> > +
> > +  [0x0006]
> > +  UUID=00002a00-0000-1000-8000-00805f9b34fb
> > +  Value=4578616D706C6520446576696365
> 
> Is this our primary key, the handle?

Yep, the reasoning was that you can easily have multiple
profiles/services with the same UUID with GATT, so the UUID is no good
as a unique identifier (not that GLib even supports multiple groups with
the same name - it merges their content together to a single logical
group).

> > +Names file contains 1 [Names] group with device address as key:
> > +  [Names]
> > +  <nn:nn:nn:nn:nn:nn>=device name a
> > +  <mm:mm:mm:mm:mm:mm>=device name b
> 
> I am not sure this is the best idea this way. Maybe just creating files
> for each address we ever see is a better idea. Details like LastSeen
> could be useful for unpaired devices.

So instead of a cache file we'd have a cache directory? I'd be fine with
that.

> > +  Features=0000000000000000
> > +  AddressType=<BR/EDR|LE>
> > +  LEAddressType=<public|random>
> 
> That is not needed. It is encoded in the address itself.

Not quite true. You cannot distinguish between public and random. But
once you do know that it's random you *can* figure out what kind of
random it is from the two most significant bits of the address.

What we discussed on #bluez was that this could simply be a reference to
what address is indicated by the directory (or filename, if that's what
we go with) for the device storage, e.g. AddressType=<static|public> and
for private resolvable addresses (for which we'd have the public address
in storage) we'd need to check if we have any IRK's to know if we need
to look for a private address to connect to them. Additionally we could
have a SupportedTechnologies list like "BR/EDR,LE", "LE", etc (feel free
to suggest a better name if you want).

Johan