Re: [PATCH] bluetoothd: add option to automatically power on the first adapter found

[Marcel Holtmann <marcel@holtmann.org>]

Hi Alexander,

>>> Your race power on vs keys and known devices programmed into the
>>> kernel. It needs to be done in the right order.
>> 
>> Hmm, I still seem to function, no sign of races, besides that I'm
>> happily working without a Linux kernel.
>> 
>> But in regard to the patch. Maybe. No idea. It works for me (tm) and is
>> faster and more reliable here than other stuff.
> 
> To pick up that thread again, if you want that I remove a race in that patch I don't see by looking at it, you have to be a bit more verbose about the race.

it is pretty simple, you want to configure the list of known devices and its keys before you turn on your device for general operation. If you don't do that, you have a race condition.

> For me it currently reads like you're more talking about an existing problem in the kernel. If the kernel doesn't like it that a bt-device will be turned on before something like keys and known devices have been setup, then the kernel should throw an error back to userspace.

The kernel is not enforcing policy. We can not require to have keys loaded first. There might be no keys or you want to use the Bluetooth subsystem for something else. The kernel mgmt interface provides a flexible way into the general procedures that Bluetooth requires. With bluetoothd we enforce profiles and other behaviors to be consistent. That is not the kernel's job.

And even if we wanted to restrict this heavily, we can not easily do that without potentially breaking existing userspace.

> But that's just an assumption from me, I haven't read through all the source in bluetoothd or the kernel, but instead just turned on a knob like it would be turned on by issuing "power on" in bluetoothctl.

With bluetoothctl you talk over the D-Bus interface to bluetoothd. So when you turn power on there, then it is ensured that everything happens in the right order. That is what bluetoothd enforces. It is not the kernels job to do that.

Regards

Marcel