Re: [PATCH v2 1/2] Bluetooth: Introduce HCI_CONN_FLAG_DEVICE_PRIVACY device flag

[Marcel Holtmann <marcel@holtmann.org>]

Hi Luiz,

>>>>> This introduces HCI_CONN_FLAG_DEVICE_PRIVACY which can be used by
>>>>> userspace to indicate to the controller to use Device Privacy Mode to a
>>>>> specific device.
>>>>> 
>>>>> Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
>>>>> ---
>>>>> v2: Fix marking Device Privacy Flag even when adapter is not capable of
>>>>> handling Set Privacy Mode.
>>>>> 
>>>>> include/net/bluetooth/hci_core.h |  4 ++++
>>>>> net/bluetooth/mgmt.c             | 24 ++++++++++++++++++++----
>>>>> 2 files changed, 24 insertions(+), 4 deletions(-)
>>>>> 
>>>>> diff --git a/include/net/bluetooth/hci_core.h b/include/net/bluetooth/hci_core.h
>>>>> index b5f061882c10..07d2d099dc2a 100644
>>>>> --- a/include/net/bluetooth/hci_core.h
>>>>> +++ b/include/net/bluetooth/hci_core.h
>>>>> @@ -160,6 +160,7 @@ struct bdaddr_list_with_flags {
>>>>> 
>>>>> enum hci_conn_flags {
>>>>>     HCI_CONN_FLAG_REMOTE_WAKEUP,
>>>>> +     HCI_CONN_FLAG_DEVICE_PRIVACY,
>>>>>     HCI_CONN_FLAG_MAX
>>>>> };
>>>>> 
>>>>> @@ -1468,6 +1469,9 @@ void hci_conn_del_sysfs(struct hci_conn *conn);
>>>>> #define use_ll_privacy(dev) (ll_privacy_capable(dev) && \
>>>>>                          hci_dev_test_flag(dev, HCI_ENABLE_LL_PRIVACY))
>>>>> 
>>>>> +#define privacy_mode_capable(dev) (use_ll_privacy(dev) && \
>>>>> +                                (hdev->commands[39] & 0x04))
>>>>> +
>>>>> /* Use enhanced synchronous connection if command is supported */
>>>>> #define enhanced_sco_capable(dev) ((dev)->commands[29] & 0x08)
>>>>> 
>>>>> diff --git a/net/bluetooth/mgmt.c b/net/bluetooth/mgmt.c
>>>>> index 06384d761928..8a8376d32be3 100644
>>>>> --- a/net/bluetooth/mgmt.c
>>>>> +++ b/net/bluetooth/mgmt.c
>>>>> @@ -4350,7 +4350,16 @@ static int set_exp_feature(struct sock *sk, struct hci_dev *hdev,
>>>>>                            MGMT_STATUS_NOT_SUPPORTED);
>>>>> }
>>>>> 
>>>>> -#define SUPPORTED_DEVICE_FLAGS() ((1U << HCI_CONN_FLAG_MAX) - 1)
>>>>> +static u32 supported_device_flags(struct hci_dev *hdev)
>>>>> +{
>>>>> +     u32 flags = BIT(HCI_CONN_FLAG_MAX) - 1;
>>>>> +
>>>>> +     /* Check if Privacy Mode can be set */
>>>>> +     if (!privacy_mode_capable(hdev))
>>>>> +             flags &= ~BIT(HCI_CONN_FLAG_DEVICE_PRIVACY);
>>>>> +
>>>>> +     return flags;
>>>>> +}
>>>> 
>>>> I am lost on what we are doing, I know that SUPPORTED_DEVICE_FLAGS was introduced by 4c54bf2b093bb from Abhishek, but I fail to reason now why it is correct.
>>> 
>>> But we don't set the HCI_CONN_FLAG_DEVICE_PRIVACY is hdev is not
>>> capable of setting it, anyway the general idea of the supported_flags
>>> is to indicate to userspace what flags the kernel is capable of
>>> settings, so yeah I would expected it to be capable of setting every
>>> flag except for those the controller don't have proper support for.
>>> Maybe you got confused by the logic of first enabling everything and
>>> then toggle back the bits that are not supported by the hdev.
>> 
>> and I think that is wrong. We should only set the bits that the hardware and/or kernel supports. I have no idea on how I missed this in the review back then. I am trying to figure it out, but I am failing to follow this logic.
> 
> There is only 1 flag currently though, HCI_CONN_FLAG_REMOTE_WAKEUP, so
> I wonder if that really requires a check? Or perhaps you want to
> change the way we supported_device_flags works to:
> 
> index fe52b7eefb56..3ad09ce6eaeb 100644
> --- a/net/bluetooth/mgmt.c
> +++ b/net/bluetooth/mgmt.c
> @@ -4351,11 +4351,15 @@ static int set_exp_feature(struct sock *sk,
> struct hci_dev *hdev,
> 
> static u32 supported_device_flags(struct hci_dev *hdev)
> {
> -       u32 flags = BIT(HCI_CONN_FLAG_MAX) - 1;
> +       u32 flags = 0;
> +
> +       /* Check if adapter can wakeup the system */
> +       if (hdev->wakeup && hdev->wakeup(hdev))
> +               flags |= HCI_CONN_FLAG_REMOTE_WAKEUP;
> 
>        /* Check if Privacy Mode can be set */
> -       if (!privacy_mode_capable(hdev))
> -               flags &= ~BIT(HCI_CONN_FLAG_DEVICE_PRIVACY);
> +       if (privacy_mode_capable(hdev))
> +               flags |= HCI_CONN_FLAG_DEVICE_PRIVACY;
> 
>        return flags;
> }

yes, that is how I would expected it to be.

Regards

Marcel