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

Hi Luiz,

Thanks for the comment. I will submit a new patch to address that.

I notice in the spec, it is mentioned

Note: This command does not affect the generation of Resolvable Private Addresses.

How should I understand this note? Does it mean even if the address
resolution is disabled, the controller can still generate RPA for
advertising?  Does it mean the advertising can always be resumed
during active scan?

Thanks,
Zhengping

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

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