Re: Writing an out of the tree new GATT service (for Debian stable): plugin or DBus?

[Szymon Janc <ext.szymon.janc@tieto.com>]

Hi,

On Wednesday 02 of March 2016 16:18:22 Luiz Augusto von Dentz wrote:
> Hi Olivier,
> 
> On Wed, Mar 2, 2016 at 3:20 PM, Olivier Martin
> 
> <olivier.martin.fr@gmail.com> wrote:
> > Hello all,
> > I am looking at writing a new GATT (server) service for my Linux-based
> > bluetooth device using Bluez.
> > My device use Debian stable (Jessie) that uses Bluez v5.23.
> > Ideally, I would like to build my GATT service out of the Bluez tree.
> > As far as I understand I have two solutions:
> > 
> > Solution A) Stay with Bluez v5.23 and write a plugin. I managed to
> > build `plugins/gatt-example.c` out of the tree. But when `bluetoothd`
> > loads the plugin, it fails to find the symbol `attrib_db_update`. I am
> > wondering if it is due to the fact `shared/gatt-server` has not been
> > added to v5.23
> > (https://git.kernel.org/cgit/bluetooth/bluez.git/tree/src/shared?h=5.23).
> > And in this case it would not be possible to have a GATT service out of
> > the tree for this Bluez version.
> 
> It depends on the level of control you want to have, if you need extra
> permissions and low level of access than perhaps building as a plugin
> is probably a good idea. BlueZ daemon works kind similar to the
> kernel, the internal API may change so building out of the tree will
> never be very stable, and you still have to comply to GPL.
> 
> > Solution B) Moving to the latest Bluez version and use the GATT server
> > D-BUS API. But it means I need to remove and replace Bluez on my
> > stable Debian. I understand this solution is the long term solution
> > but it might take a while before the Linux distributions used this
> > version of Bluez.
> 
> If more people like you starting using this features it might become
> stable faster, thus we encourage people to go with this solution. Btw,
> you can disable the BlueZ from your distro and just run BlueZ from
> source without overwriting anything from your distro.
> 
> > So, is it possible to have an out of the tree plugin with v5.23? I saw
> > `sixaxis` plugin. But this plugin does not manipulate GATT services
> > and characteristics.
> 
> Possible, yes, but it is not recommended, but you can try to create a
> external plugin that is build within the source tree so that we keep
> it working as we change the internal APIs.

External plugins (like sixaxis) are able to use only btd_* (plus few
exceptions) functions. If you want to use other symbols you would have
to go with builtin plugin.

-- 
BR
Szymon Janc