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From:   Kenny Bian <kennybian@gmail.com>
Date:   Tue, 13 Apr 2021 10:17:40 -0700
Message-ID: <CAC9s0NYCJD58F4iWb2JZhcy-X1Ax-5U9Pphc_SXQKYV9BkdmjA@mail.gmail.com>
Subject: Re: Disabled bluetooth cache. But the app still getting wrong data?
To:     Jamie Mccrae <Jamie.Mccrae@lairdconnect.com>
Cc:     "linux-bluetooth@vger.kernel.org" <linux-bluetooth@vger.kernel.org>
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Hi Jamie,

Thank you for your email. Do you know how to add "Service Changed
Indication"? We would like to support that. But we don't know how to
do it.

In fact, I posted the question before:
https://www.spinics.net/lists/linux-bluetooth/msg89959.html. It seems
"If you are registering the services with Bluetoothd then it should
generate the service change". Our GATT server is based on
https://git.kernel.org/pub/scm/bluetooth/bluez.git/tree/test/example-gatt-s=
erver.
By saying "registering the services", does it mean our code should
call "RegisterApplication()"? We did call RegisterApplication(). But
we never saw the "[ServiceChanged]"
section(https://git.kernel.org/pub/scm/bluetooth/bluez.git/tree/doc/setting=
s-storage.txt#n321).
Please let us know if you know how to add "Service Changed
Indication".

Thanks!
Kenny

Kenny

On Mon, Apr 12, 2021 at 11:39 PM Jamie Mccrae
<Jamie.Mccrae@lairdconnect.com> wrote:
>
> Hi Kenny,
> Why not just add the service changed indication as you refer to below? It=
 was purposely designed for this specific purpose, you're trying to work ar=
ound an issue created because you don't want to use the feature that preven=
ts this issue. Any workaround is just that, a workaround, and might not wor=
k as intended.
> Thanks,
> Jamie
>
> -----Original Message-----
> From: Kenny Bian <kennybian@gmail.com>
> Sent: 13 April 2021 06:59
> To: linux-bluetooth@vger.kernel.org
> Subject: Disabled bluetooth cache. But the app still getting wrong data?
>
> EXTERNAL EMAIL: Be careful with attachments and links.
>
> Previously we had an issue: if there is a change of characteristics in th=
e new build of our firmware, then the app will get the wrong data.
> By saying changed characteristics, it can be an added or removed characte=
ristic, or adding notification to an existing characteristic.
> In order to keep the pairing information, the "/var/lib/bluetooth"
> folder is copied over to the new build's partition. We realized that ther=
e is no "service changed indication". The app can't handle the changed serv=
ices. So we disabled the bluetooth cache by set this in
> "/etc/bluetooth/main.conf":
> [GATT]
> Cache =3D no
>
> But recently, we saw the problem again even if the bluetooth cache is
> disabled: in the build number 101, a characteristic is removed. But when =
we upgrade the build from 100 to 101, the app gets the wrong data. We looke=
d at the log. When the app tries to read temperature by using the temperatu=
re UUID, somehow the bluetooth service we created received the request to r=
ead the "device name"(device name UUID). So the "device name" is returned t=
o the app as the temperature. This looks like the same behavior as the blue=
tooth cache is not disabled. I looked at the "/var/lib/bluetooth/[BT_MAC]/c=
ache" folder. There is no "[Attributes]" section in the files in the folder=
. That means the disabled cache seems working.
>
> The only way to fix this issue is to force exit the mobile app on the pho=
ne and "Forget This Device" in iOS or "Unpair" in Android.
>
> I looked at the btmon(see attached). For the working btmon log, there is =
"Attribute group list: XX entries" under "ACL Data TX". But there is no "At=
tribute group list: XX entries" under "ACL Data TX" in the attached problem=
atic btmon log.
>
> Questions:
> 1. How is it possible that this still happens even if the bluetooth cache=
 is disabled?
> 2. Is this the problem on the Linux side which runs the GATT server or on=
 the mobile side?
> 3. Is there anything else we should look into?
>
> We're going to release our product soon. This is a critical issue for us.=
 Please help if you have any suggestions.
>
> Thanks!
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