[Bluez-devel] [RFC] HAL/Bluez integration

[Bluez-devel] [RFC] HAL/Bluez integration

[Matthew Garrett]

I've put a tarball up at 
http://www.codon.org.uk/~mjg59/tmp/hal-bluetooth.tar.gz as a first 
attempt at some degree of integration. The current interface is 
basically:

1) Bluetooth HCIs support a "Scan" method. Calling this will populate 
the tree with any located bluetooth devices.
2) Bluetooth devices support "Pair" and "Browse" methods. Calling the 
first will attempt to initiate a pairing interaction - the second will 
populate the tree with any services found on the device via SDP.

So it's fairly simple at the moment. The obvious next step is to allow 
services to provide rfcomm-binding methods and the like, and to ensure 
that relevant pieces of service information are provided via sdp.

Now, there's a couple of issues:

1) I'm not sure about the pairing interface. Right now, calling the pair 
method prompts hcid to attempt to send a message to a registered pairing 
agent via bluetooth. This strikes me as a mild security problem, since 
there's no mechanism for ensuring that it's the current user who has 
registered a pairing agent. The best that can be done is to attempt to 
register an agent, notice that the registration has failed and then bail 
before attempting to make the connection (setting an appropriate error). 
This isn't entirely ideal. David, can you see any way that PolicyKit can 
help us here?

2) The SDP interface in bluez is currently labelled "experimental" and 
is fairly limited in functionality. I tried going back through the 
mailing list archives, but the sourceforge interface makes me cry - has 
there been discussion of what this interface should look like and the 
technical problems involved?

Obligatory screenshot - http://www.codon.org.uk/~mjg59/tmp/bluetooth.png

-- 
Matthew Garrett | mjg59@srcf.ucam.org


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Re: [RFC] HAL/Bluez integration

[David Zeuthen]

On Sun, 2006-06-11 at 21:45 +0100, Matthew Garrett wrote:
> I've put a tarball up at 
> http://www.codon.org.uk/~mjg59/tmp/hal-bluetooth.tar.gz as a first 
> attempt at some degree of integration. 

Cool.

> The current interface is 
> basically:
> 
> 1) Bluetooth HCIs support a "Scan" method. Calling this will populate 
> the tree with any located bluetooth devices.
> 2) Bluetooth devices support "Pair" and "Browse" methods. Calling the 
> first will attempt to initiate a pairing interaction - the second will 
> populate the tree with any services found on the device via SDP.

Shouldn't Pair() take the pin?

> So it's fairly simple at the moment. The obvious next step is to allow 
> services to provide rfcomm-binding methods and the like, and to ensure 
> that relevant pieces of service information are provided via sdp.
> 
> Now, there's a couple of issues:
> 
> 1) I'm not sure about the pairing interface. Right now, calling the pair 
> method prompts hcid to attempt to send a message to a registered pairing 
> agent via bluetooth. This strikes me as a mild security problem, since 
> there's no mechanism for ensuring that it's the current user who has 
> registered a pairing agent. 

Right.

> The best that can be done is to attempt to 
> register an agent, notice that the registration has failed and then bail 
> before attempting to make the connection (setting an appropriate error). 
> This isn't entirely ideal. David, can you see any way that PolicyKit can 
> help us here?

Not really, sorry. 

It sounds like we want Pair() to take the pin and pass it on to hcid and
propagate errors back as appropriate. Intermittently we might want to
register a pairing agent with our hal stuff to pretend this just works.
But CreateBonding() on org.bluez.Adapter really ought to (optionally)
take the pincode too. Can Bluez be tweaked to support this?

Also, can we determine what devices are paired already? E.g. can we have
useful properties on the hal device objects such as
bluetooth_device.paired = TRUE|FALSE.

> 2) The SDP interface in bluez is currently labelled "experimental" and 
> is fairly limited in functionality. I tried going back through the 
> mailing list archives, but the sourceforge interface makes me cry - has 
> there been discussion of what this interface should look like and the 
> technical problems involved?

Some questions:

 1. What other API do we need? I suspect that we want

  1a. Some way of setting the device ID of an adapter (equiv to device {
      name "foo"} in hcid.conf)

  1b. Some way of setting the pin of the adapter

    I guess both 1a and 1b falls under replacing hcid.conf (<insert rant
    about why text-based configuration files are bad>)

  1c. A way to pair well-known devices that are not yet in your
      vicinity?

    This is just thinking out loud, I suspect you have a much better
    idea about this than I do. I guess it naturally falls out once one
    starts thinking about the UI.

 2. We probably need a way to make hal device objects disappear when the
    parent disappears. Would setting info.reap_when_parent_dies=TRUE be
    sufficient? If so, I can quickly implement this.

 3. Probably need to delete devices not being reported when doing a
    Scan()

> Obligatory screenshot - http://www.codon.org.uk/~mjg59/tmp/bluetooth.png

Cool.

    David

Re: [Bluez-devel] [RFC] HAL/Bluez integration

[Marcel Holtmann]

Hi David,

> > 2) Bluetooth devices support "Pair" and "Browse" methods. Calling the 
> > first will attempt to initiate a pairing interaction - the second will 
> > populate the tree with any services found on the device via SDP.
> 
> Shouldn't Pair() take the pin?

be careful with this. The new Simple Pairing will come at some point and
then alternate authentication methods like NFC and other OOB stuff might
have to be considered.

The application should take by itself to register a passkey agent if the
default one is not the preferred one. For example in case of a wizard.

> > 1) I'm not sure about the pairing interface. Right now, calling the pair 
> > method prompts hcid to attempt to send a message to a registered pairing 
> > agent via bluetooth. This strikes me as a mild security problem, since 
> > there's no mechanism for ensuring that it's the current user who has 
> > registered a pairing agent. 
> 
> Right.

We left out the multiple user interaction consideration out of it for
now. The reason was to establish a usable API first. All user specific
checks (and settings) should be done by hcid and they should be fully
transparent for the actual user. For the next releases we need to
integrate this kind of checking.

> It sounds like we want Pair() to take the pin and pass it on to hcid and
> propagate errors back as appropriate. Intermittently we might want to
> register a pairing agent with our hal stuff to pretend this just works.
> But CreateBonding() on org.bluez.Adapter really ought to (optionally)
> take the pincode too. Can Bluez be tweaked to support this?

Because of upcoming Simple Pairing this is not an option. See comment
above.

> Some questions:
> 
>  1. What other API do we need? I suspect that we want
> 
>   1a. Some way of setting the device ID of an adapter (equiv to device {
>       name "foo"} in hcid.conf)
> 
>   1b. Some way of setting the pin of the adapter
> 
>     I guess both 1a and 1b falls under replacing hcid.conf (<insert rant
>     about why text-based configuration files are bad>)

It is possible to have a presistent storage for the device name. The
value in hcid.conf is only the default value. It will be overwritten by
the saved value. Set the name through the BlueZ D-Bus API and your
device will use it next time.

>   1c. A way to pair well-known devices that are not yet in your
>       vicinity?
> 
>     This is just thinking out loud, I suspect you have a much better
>     idea about this than I do. I guess it naturally falls out once one
>     starts thinking about the UI.

Not a good idea. Pair them once needed. Otherwise don't even care.

>  2. We probably need a way to make hal device objects disappear when the
>     parent disappears. Would setting info.reap_when_parent_dies=TRUE be
>     sufficient? If so, I can quickly implement this.

Sounds enough too me.

>  3. Probably need to delete devices not being reported when doing a
>     Scan()

Not a good idea. A device can become invisible, but still in range. You
need to keep track of last seen and last used. And paired or trusted
device should always be available.

Regards

Marcel




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Re: [Bluez-devel] [RFC] HAL/Bluez integration

[Marcel Holtmann]

Hi Matthew,

> 2) The SDP interface in bluez is currently labelled "experimental" and 
> is fairly limited in functionality. I tried going back through the 
> mailing list archives, but the sourceforge interface makes me cry - has 
> there been discussion of what this interface should look like and the 
> technical problems involved?

we need to add an asynchronous SDP API to bluez-libs and integrate
working caching of SDP objects. This is not a simple task and there was
no enough time for it.

Regards

Marcel




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