[Bluez-devel] Re: Disconnections are not being detected

[Bluez-devel] Re: Disconnections are not being detected

[andi.c]

ok, but how can my program be aware of this ? it has to do some tasks in =
response of
a link-fall.....


 >Hi Andrea,
 
 >> i am working on a=
 "pand" based that basically sets up bnep connections.
 > >For my tests,=
 i use simple usb bluetooth dongles (in particolar, some CSR
dongle).=0D
=
 > >My question is: how an endpoint (es a PANU) can detect a link lost ? =
I see
 > >w4_hup shuld
 > >handle this, but if i mnually remove the GN =
dongle, the PANU does"t signal
nothing.
 > >can someone help me ??
 =0D
=
 >the bnep0 ethernet device will disappear.
 
 >Regards
 
 >Marcel=0A=
=0A=0A=0A____________________________________________________________=0AR=
egala e regalati Libero ADSL: 3 mesi gratis, navighi veloce e scarichi a =
1.2 Mega. =0AAbbonati subito senza costi di attivazione su http://www.lib=
ero.it=0A=0A



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Re: [Bluez-devel] Re: Disconnections are not being detected

[Marcel Holtmann]

Hi Andrea,

> ok, but how can my program be aware of this ? it has to do some tasks in response of
> a link-fall.....

since I never needed it so far, I don't know. Check the source code of
some unix tools or look at netlink.

Regards

Marcel




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Re: [Bluez-devel] Re: Disconnections are not being detected.

[Marcel Holtmann]

Hi Vlad,

> But the official L2CAP specification.  (Version 1.1) says (page 288):
> 
> 	Result: 2 octets The result field indicates the outcome of
> 	the connection request. The result value of 0x0000 indicates
> 	success while a non-zero value indicates the connection request
> 	failed or is pending. A logical channel is established on the
> 	receipt of a successful result. Table 5.5 defines values for
> 	this field. If the result field is not zero. The DCID and SCID
> 	fields should be ignored when the result field indicates the
> 	connection was refused.
> 
> So although the BlueZ behavior is correct from common sense perspective,
> but it is not correct from the specification perspective. I am not sure
> what does version 1.2 of the spec say about this subject.

it is still the same for the 1.2 specification, but it is simply wrong
and stupid. You need at least the SCID to match the connect response to
a previous connect request. Otherwise this response is meaningless.

What we did wrong is sending the command reject for a response. I will
fix this, but this won't fix your problem. If we don't know for what
L2CAP channel we get a connection refused response, we can't do anything
else then waiting for a timeout event.

Check the bluetooth.org pages if they had an erratum for that and if not
ping them to correct it. Also write to SE about that.

Regards

Marcel




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[Bluez-devel] Re: Disconnections are not being detected.

[Vlad]

Marcel and Xavier,

Thank you for such a prompt response to my post.  Here are some
more details regarding this problem.

As Marcel pointed out:

  actually that is not quite right. The server (phone) sends back a
  connect response with PSM not supported error status. And we then send a
  command reject for that. This is really stupid. What kernel version do
  you use and what kind of hardware is this? Can you reproduce it with the
  latest 2.4 or 2.6 kernel?

You right ... I didn't pay close attention to the direction where the
command reject packet is being sent. The above log came from the laptop
that was running kernel version 2.4.24, but I believe that such behavior
can be repeated on the more recent versions. [see below]


and as Xavier wrote:
 
  I guess the command reject is due to scid and dcid being both set to 0 by
  the remote device. So bluez doesn't know who it's to talking to (as we can
  have several cid on one ACL link) ...

Marcel wrote:

  you are right. It should fill in dcid and scid. The remote device is
  broken. Blame SE about that. I still don't know where the command reject
  came from :(

You are both right, about why is this happening. Here is a link to the
linux kernel source.

    http://lxr.linux.no/source/net/bluetooth/l2cap.c?v=2.4.26#L1450 

But the official L2CAP specification.  (Version 1.1) says (page 288):

	Result: 2 octets The result field indicates the outcome of
	the connection request. The result value of 0x0000 indicates
	success while a non-zero value indicates the connection request
	failed or is pending. A logical channel is established on the
	receipt of a successful result. Table 5.5 defines values for
	this field. If the result field is not zero. The DCID and SCID
	fields should be ignored when the result field indicates the
	connection was refused.

So although the BlueZ behavior is correct from common sense perspective,
but it is not correct from the specification perspective. I am not sure
what does version 1.2 of the spec say about this subject.


So since my project requires this to be implemented corrected. I will 
come up with some kind of patch for this and post in on this mailing
list. (Within next couple of weeks). Meanwhile I would appreciate any
suggestions on how this could be implemented with the least pain for
everybody.


						Vlad











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