general: find method to globally change shared data structures (shell commands, device parameters, network interfaces, ...)

[kaspar030]

We have many places where it would be really nice to add an entry to a shared array, from any file.

Think auto_init, shell_commands, device driver parameters, network interfaces, sensors, libc initializers, ...

I really appreciate that we haven't chosen to go libc's route of using the linker to sort these things out.
Still, I think that the current pile of hacks will get harder to maintain the more features RIOT gets.

I'm trying to come up with a nice way to be able to add entries to a global, shared array (per type).
I think all of the above can efficiently be modeled using const arrays of structs.

Something like:

in sys/random/sc_random.c:

SHELL_COMMAND { "random_init", function, ... }

in sys/gnrc/blah.c:

SHELL_COMMAND { "gnrc_print_blah", function, ... }

ends up as, e.g., bin/include/shell_commands_array.h:

shell_command_t shell_commands[] = {
  { "random_init", function, ... },
  { "gnrc_print_blah", function, ... },
}

IMHO, if we do this right, we can reuse it for all of the above "lists".
But:

• C can't do it by itself
• generated code sucks
• ...

Opinions?

[OlegHahm]

I guess linked lists are out of question because of memory overhead?

[kaspar030]

I guess linked lists are out of question because of memory overhead?

Well, yes. That would require run-time "register shell_command" for stuff that's available at runtime.
Also, that wouldn't work for auto-init.

[OlegHahm]

I'm not so sure I understand the auto_init problem. Where do we have arrays there?

[kaspar030]

I'm not so sure I understand the auto_init problem. Where do we have arrays there?

Well, currently we manually call void() auto init functions in auto_init.c.
That's no "problem", but needs manual maintanance of that file.

But that could be implemented as an iteration over a list of void(*)(void) function pointers.
That way, any auto-init module could specify in it's main .c file something like,

AUTO_INIT &xtimer_auto_init

... using the same global-shared-array method as shell commands and coap handlers.

auto_init.c could stay unmodified, just including the generated header with the list of function pointers.
(auto-init would need some kind of ordering, though)

[kaspar030]

Most project (e.g., Linux for modules) do this using linker sections. IMHO that gets clumsy and is limited (e.g., no configurable sorting). But it could be the way to go.

[haukepetersen]

It would indeed be very very nice to have this, and it would simplify things in many places quite significantly!

When keeping to the standard toolchain tools, I think using the linker script might be our only choice. I don't worry so much about being clumsy and the sorting, I think the bigger problem to solve regarding linker scripts are the platforms, where we use default ld scripts and have no means to add sections to them...

[kaspar030]

@haukepetersen While I love that you're able to change your mind, I hate that I listen to you too much. ;)

Agreed, linker scripts are the way to go. I'll close this.