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Subject: Re: [PATCHv2] Bluetooth: Fix registering hci with duplicate name
From: Marcel Holtmann <marcel@holtmann.org>
To: Andrei Emeltchenko <Andrei.Emeltchenko.news@gmail.com>
Cc: linux-bluetooth@vger.kernel.org
Date: Wed, 11 Apr 2012 17:33:13 +0200
In-Reply-To: <20120411110733.GG17779@aemeltch-MOBL1>
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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;
> > 
> > 		...
> > 	}
> 
> I think that would not work. If we have for example hci0,hci1,hci2 and
> adding another one would choose hci2 again since (2 > 1) && (hdev->id=1 !=
> 2)
> 
> otherwise I think this is a bit complex when compared to bitmask which is
> used in netdev in dev_alloc_name but they use a page:
> 
> /* Use one page as a bit array of possible slots */
> inuse = (unsigned long *) get_zeroed_page(GFP_ATOMIC);

I think we should not go over board with allocating a page.

> BTW: what is max number of controllers we support?

uint16 - 1 number of controllers can be handled.

Regards

Marcel