Re: [PATCHv2] Bluetooth: Fix registering hci with duplicate name

[Marcel Holtmann <marcel@holtmann.org>]

Hi Andrei,

> > > > > @@ -1755,16 +1756,17 @@ int hci_register_dev(struct hci_dev *hdev)
> > > > >  
> > > > >  	write_lock(&hci_dev_list_lock);
> > > > >  
> > > > > -	/* Find first available device id */
> > > > > -	list_for_each(p, &hci_dev_list) {
> > > > > -		if (list_entry(p, struct hci_dev, list)->id != id)
> > > > > -			break;
> > > > > -		head = p; id++;
> > > > > -	}
> > > > I am now a little bit confused. Is it not enough to just replace head
> > > > with &hci_dev_list to get this fixed? Or why is this failing in the
> > > > first place actually.
> > > 
> > > You can see actual code above. If you have hci0 and hci1 adding third AMP
> > > will fail since it just checks 0!=1 => break and trying to create hci1
> > > again.
> > 
> > I see a problem when you having only AMPs (no BR/EDR controller). Then
> > hci0 will be skipped and keep trying to create hci1 over and over again.
> > 
> > However in the case we have BR/EDR controller on hci0 and hci1 as AMP,
> > then this should just work.
> > 
> > So we need to fix the case where we have no BR/EDR controller on hci0
> > and trying to fix something else. Or did I get confused?
> 
> I think you got confused. 
> 
> We have hci0 (BREDR) and hci1 (AMP)
> 
> so list_for_each would give us first entry with id=0; Adding third (AMP)
> would compare 1 (as given by id = (hdev->dev_type == HCI_BREDR) ? 0 : 1)
> and 0 (id for BREDR) => break from the loop and tries to use id=1 again
> for third controller.
> 
> Actually I do not know how the current code works at all, it is really
> broken.

so it is broken on two levels actually. The case where we have no
BR/EDRI controller as hci0 is also broken.

Can you try to come up with a different solution that is not using a bit
mask. That one might overflow actually. Something like this:

	min_id = (hdev->dev_type == HCI_BREDR) ? 0 : 1)

	for each (...) {
		if (id >= min_id && hdev->id != id)
			break;

		...
	}

Regards

Marcel