Subject: Re: [Bluez-devel] Zero length L2CAP packets
From: Marcel Holtmann <marcel@holtmann.org>
To: BlueZ Mailing List <bluez-devel@lists.sourceforge.net>
Cc: Moritz Gmelin <moritz.gmelin@avetana.de>
In-Reply-To: <200502101112.09602.harbaum@beecon.de>
References: <200502101112.09602.harbaum@beecon.de>
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Date: Thu, 10 Feb 2005 15:04:48 +0100

Hi Till,

> while working on the avetana jsr82 implementation we discovered, that the bt 
> spec as well as jsr82 allow to transmit zero length l2cap packets. IMHO the 
> linux socket interface does not support zero length packets and a read 
> returning zero indicates an end of file (in this case meaning that the 
> connection has been closed).
> 
> What happens if the other side actually sends a zero length packet? Is this 
> dropped inside the kernel? Or will read return zero which i'll misinterpret 
> as the eof marker? How can i distinguish between eof and a zero length 
> packet?

actually I see no problem with zero length L2CAP packets. I modified the
l2test program to actually be able to send and receive them, but there
is no problem at all. This is a socket and not a file and so you might
use poll() or select() to detect the hangup of the connection and not
some weird zero length magic.

The kernel btw is dropping no packets. I see all of these zero packets
flying from one end to the other.

Regards

Marcel


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