Keeping reusable components under samples/ leads to build issues

[pfalcon]

Steps to reproduce:

1. Try to build samples/net/echo_server with BLE support:

make BOARD=96b_carbon CONF_FILE=prj_bt.conf

This will lead to following object layout:

$ find -name "*.o"
./bluetooth/gatt/ipss.o
./outdir/96b_carbon/arch/built-in.o
./outdir/96b_carbon/arch/common/built-in.o
./outdir/96b_carbon/arch/common/isr_tables.o
./outdir/96b_carbon/arch/arm/built-in.o

As can be seen, ipss.o goes outside the normal outdir/$(BOARD)/ hierarchy. This of course causes conflicts when building the same samples for other boards/archs (I don't see errors, but there're definitely spurious rebuilds).

Another issue trying to build a sample like samples/net/sockets/echo . As can be seen, this has 4 layers of hierarchy, while samples/net/common/Makefile.common refers to ipss.o as:

obj-y += ../../../bluetooth/gatt/ipss.o

so, it simply cannot find it for the samples like that.

[pfalcon]

@jukkar , @carlescufi, @Vudentz : Please let me know if you have an idea how best to fix this. My idea would be to introduce subsys/bluetooth/service/ , and start with moving ipss.o there, as that's truly reusable service as used in the codebase. Then other services from samples/bluetooth/gatt/ may follow, if needed.

[pfalcon]

Not that similar issue exists for other subsystems, e.g. recently similar was fixed for net, and this ticket talks about usb cases: #716

[carlescufi]

Agreed, I've never liked the samples/bluetooth/gatt folder. I do think that (standard) services belong in the subsys folder or, alternatively, in the lib folder. So as I see it either we move those to subsys/bluetooth/host/<gatt,services> or to lib/bluetooth/gatt

[pfalcon]

@carlescufi : Thanks for quick response. There's currently no lib/bluetooth/ , and the current content of lib/ is rather generic (libc/its adaptations, json). And having lib/bluetooth/ would mean that subsystem is split between 2 subtrees.

On the other hand, taking subsys/net/ as an example, it has net/ip/ for the "core" code, and net/lib/ for various protocols and helpers. So perhaps, keeping everything under subsys/bluetooth/ , in a suitable subdir, is possible.

[carlescufi]

@pfalcon right, I think subsys/bluetooth/gatt or subsys/bluetooth/services would be the right location for this

[nashif]

I talked about this with @jhedberg just recently, the idea is to move this to subsys/ as an application layer.

[jhedberg]

The way I see this code is that it's an extension of the application domain, or in other words a library that the application uses. One requirement of it is that it must only use public APIs. I'm therefore a little reluctant at putting it under subsys/bluetooth since it's not really on the same level as the Bluetooth subsystem, rather a layer above it (i.e. the application). Just like HCI drivers are a layer below the (host) stack, and therefore separately under drivers/bluetooth, I don't see anything wrong with putting this code under lib/bluetooth/