Re: [kernel PATCH v1] Bluetooth: hci_sync: Resume adv with no RPA when active scan

Hi Luiz,

Where is that mentioned?

It is just below the command on "7.8.44 LE Set Address Resolution
Enable command".

On "4.7 RESOLVING LIST", there is another note:

Note: The Controller may generate Resolvable Private Addresses even when address resolution is disabled.

If this is the case, then the comment in the kernel
(hci_active_scan_sync) is not accurate.

/* Pause advertising since active scanning disables address resolution
* which advertising depend on in order to generate its RPAs.
*/

I think it may be related to the fact that it only affects the addr
resolution of remote devices, that said if you are active scanning
that probably means the user wants to setup a new device thus why we
don't enable any filtering like accept list, etc, so it is not really
useful to keep address resolution active either way.

That makes sense. When the local privacy is enabled, I assume the host
RPA will change
when advertising. I haven't tested that scenario, but if RPA
generation is not related to disable/enable
address resolution, why should the advertising be paused when active scan?

Thanks,
Zhengping

quoted

Thanks,
Zhengping

On Tue, Feb 14, 2023 at 4:09 PM Luiz Augusto von Dentz
[off-list ref] wrote:

quoted

Hi Zhengping,

On Tue, Feb 14, 2023 at 2:56 PM Zhengping Jiang [off-list ref] wrote:

quoted

The address resolution should be disabled during the active scan,
so all the advertisements can reach the host. The advertising
has to be paused before disabling the address resolution,
because the advertising will prevent any changes to the resolving
list and the address resolution status. Skipping this will cause
the hci error and the discovery failure.

It is probably a good idea to quote the spec saying:

7.8.44 LE Set Address Resolution Enable command

This command shall not be used when:
• Advertising (other than periodic advertising) is enabled,

quoted

If the host is using RPA, the controller needs to generate RPA for
the advertising, so the advertising must remain paused during the
active scan.

If the host is not using RPA, the advertising can be resumed after
disabling the address resolution.

Fixes: 9afc675edeeb ("Bluetooth: hci_sync: allow advertise when scan without RPA")
Signed-off-by: Zhengping Jiang <redacted>
---

Changes in v1:
- Always pause advertising when active scan, but resume the advertising if the host is not using RPA

 net/bluetooth/hci_sync.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/net/bluetooth/hci_sync.c b/net/bluetooth/hci_sync.c
index 117eedb6f709..edbf9faf7fa1 100644
--- a/net/bluetooth/hci_sync.c
+++ b/net/bluetooth/hci_sync.c

@@ -2402,7 +2402,7 @@ static u8 hci_update_accept_list_sync(struct hci_dev *hdev)
        u8 filter_policy;
        int err;

-       /* Pause advertising if resolving list can be used as controllers are
+       /* Pause advertising if resolving list can be used as controllers
         * cannot accept resolving list modifications while advertising.
         */
        if (use_ll_privacy(hdev)) {

@@ -5397,7 +5397,7 @@ static int hci_active_scan_sync(struct hci_dev *hdev, uint16_t interval)
        /* Pause advertising since active scanning disables address resolution
         * which advertising depend on in order to generate its RPAs.
         */
-       if (use_ll_privacy(hdev) && hci_dev_test_flag(hdev, HCI_PRIVACY)) {
+       if (use_ll_privacy(hdev)) {
                err = hci_pause_advertising_sync(hdev);
                if (err) {
                        bt_dev_err(hdev, "pause advertising failed: %d", err);

@@ -5416,6 +5416,10 @@ static int hci_active_scan_sync(struct hci_dev *hdev, uint16_t interval)
                goto failed;
        }

+       // Resume paused advertising if the host is not using RPA
+       if (use_ll_privacy(hdev) && !hci_dev_test_flag(hdev, HCI_PRIVACY))
+               hci_resume_advertising_sync(hdev);
+
        /* All active scans will be done with either a resolvable private
         * address (when privacy feature has been enabled) or non-resolvable
         * private address.
--

2.39.1.581.gbfd45094c4-goog

I think it is better that we add something like
hci_pause_addr_resolution so we can make it check all the conditions,
such as pausing advertising and resuming if needed. Btw, we do seem to
have proper checks for these conditions on the emulator:

https://git.kernel.org/pub/scm/bluetooth/bluez.git/tree/emulator/btdev.c#n4090

But perhaps there is no test which attempts to enable LL Privacy
without enabling Local Privacy, so it would be great if you could
update mgmt-tester adding a test that emulates such behavior.

--
Luiz Augusto von Dentz

--
Luiz Augusto von Dentz