Re: [PATCH 0/6] HID: Add a stable method for retrieving the client MAC address of a HID device

[Frank Praznik <frank.praznik@gmail.com>]

On 1/31/2014 15:45, Benjamin Tissoires wrote:
> On Fri, Jan 31, 2014 at 3:04 PM, Frank Praznik <frank.praznik@oh.rr.com> wrote:
>> On 1/31/2014 14:10, Benjamin Tissoires wrote:
>>> Hi Frank,
>>>
>>> just a quick review:
>>>
>>> On Fri, Jan 31, 2014 at 12:32 PM, Frank Praznik <frank.praznik@oh.rr.com>
>>> wrote:
>>>> Currently there is no reliable way for a device module or hidraw
>>>> application to
>>>> retrieve the client MAC address of the associated wireless device.  This
>>>> series
>>>> of patches adds a stable way of retrieving this information.
>>> Well, if I look at the uevent of a Bluetooth mouse I have:
>>>
>>> $ cat
>>> /sys/devices/pci0000\:00/0000\:00\:14.0/usb3/3-2/3-2\:1.0/bluetooth/hci0/hci0\:43/0005\:046D\:B00D.001F/uevent
>>> DRIVER=hid-generic
>>> HID_ID=0005:0000046D:0000B00D
>>> HID_NAME=Ultrathin Touch Mouse
>>> HID_PHYS=00:10:60:ea:df:ae
>>> HID_UNIQ=00:1f:20:96:33:47
>>> MODALIAS=hid:b0005g0001v0000046Dp0000B00D
>>>
>>> I would say that HID_UNIQ is the client MAC address set by hidp, no?
>>> So you don't need to duplicate the info by adding a new field in
>>> hid_device.
>>>
>> In a patch I recently submitted I was using the UNIQ field for retrieving a
>> Bluetooth device MAC address and was warned against it because "UNIQ is a
>> way to provide unique identifiers for devices, but it's not guaranteed to
>> stay the same".  HIDP happens to store the MAC in the UNIQ data, but there
>> is no guarantee that it will always be there.  With these patches you can be
>> completely sure that the data in client_addr is the client device MAC
>> address.
> ok. But still, adding a transport-specific information to hid_device
> is IMO a bad idea. We fought to make HID agnostic of the transport
> layer enough.
>
> David, could you elaborate why you think that UNIQ may change in the
> future regarding BT?
> If the BT MAC address is the same principle of an ethernet MAC
> address, UNIQ seems to fit perfectly well.
>
> Otherwise, you may be able to retrieve the MAC address by using the
> parent of the current device.
>
> Cheers,
> Benjamin
Are you referring to using the hid_device::dev.parent pointer?  I know 
that hidp sets it to point to the hci_conn struct from which src address 
for the Bluetooth connection can be obtained, but making assumptions 
about an opaque pointer like that seems dangerous.  Is the parent 
pointer guaranteed to point to the hci_conn struct as long as the bus 
type is Bluetooth?