RE: [Bluez-devel] Qualification Testing

[Marcel Holtmann <marcel@rvs.uni-bielefeld.de>]

Hi Max,

> >> Hmm, ok :). But after thinking more about this I think that we probably still need 
> >> some way to tell the apps that link became unreliable. I mean parsing syslogs is 
> >> not very elegant solution :). Also even though Cetecom accepted it as a solution 
> >> other BQBs might not.
> >> 
> >> Here is what I had in mind. We could add L2CAP socket option L2CAP_RELIABILITY,
> >> which will be used by the apps that are "paranoid" :) about link reliability.
> >> Then whenever we receive corrupted L2CAP frame we'd check connected sockets, attached
> >> to this connection, that have this option enabled and signal error condition on them. 
> >> i.e. read/recvmsg will return error. Application can then either clear that error with 
> >> getsockopt(SO_ERROR) and continue or close the socket.
> >
> >the idea itself sounds very good. But I see no advantage in implementing
> >such kind of extra functionality. We can not detect if a frame is
> >currupt or not, because we have no checksum mechanism. The only thing we
> >can detect is a length mismatch. What about a corrupted cid? 
> >If you notify the wrong socket and the application on that socket can't deal
> >with such an error.
> Definition of the L2CAP_RELAIBILITY option is rather broad :). In general it would mean
> "Notify me when you can no longer guaranty reliable transmission".
> You're right what we don't have checksum. But we can detect failures other than
> the wrong length. For example missing start frame or missing continuation frame.
> CID we're going to have to ignore because it doesn't necessarily mean that connection
> became unreliable.
> So there is no such thing as notifying the wrong socket in this case. If L2CAP detects
> that connection became unreliable it notifies all sockets on that connection (those 
> that explicitly requested notification of course).

so if we detect a failure in an ACL packet, we notify all L2CAP
connections on the ACL link that have this option set. This sounds a
little bit better to me. I understand you wrong at the first time and
now I think we should have such extra stuff.

But I don't like the name and your meaning of this options. It sounds
like something that it is not and will never be. For the description of
this option I think it should be something like

	"Notify me when you detect an error in the ACL payload"

And the option name can be L2CAP_CHECKACL. This is not very good, I
know, so any other proposals?

Regards

Marcel




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