From: Marcel Holtmann <marcel@holtmann.org>
To: BlueZ development <bluez-devel@lists.sourceforge.net>
In-Reply-To: <20070328152757.62286.qmail@web52302.mail.re2.yahoo.com>
References: <20070328152757.62286.qmail@web52302.mail.re2.yahoo.com>
Date: Sat, 31 Mar 2007 15:55:29 +0200
Message-Id: <1175349329.5815.271.camel@violet>
Mime-Version: 1.0
Subject: Re: [Bluez-devel] L2CAP: ECONNRESET is set for every
	l2cap	disconnect.
Reply-To: BlueZ development <bluez-devel@lists.sourceforge.net>
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Sender: bluez-devel-bounces@lists.sourceforge.net
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Hi Aarti,

> I am sure if this issue has been discussed before or
> not. 

it hasn't been discussed. I would remember it.

> Is it necessary to the set the struct sock->err value
> to ECONNRESET when l2cap disconnect request is
> received from remote device ?
> 
> l2cap_disconnect_req function sets the error value in
> sock structure by calling l2cap_chan_del(sk,
> ECONNRESET) every time l2cap connection is
> disconnected.

This is actually the correct behavior since the remote side is about to
terminate the connection. There is no more data pending. All data after
this command is invalid anyway.

> This might lead to some loss of data at receiver side
> in case of fast sender and slow receiver. 

This has been always a problem of L2CAP since flow control is missing.

> The sender will send l2cap packets and disconnects. 
> 
> The receiver side will read the packets, but once
> l2cap disconnect is received, even though there is
> data in sk_buff, the bt_sock_recvmsg will return 0 as
> skb_recv_datagram will return NULL. 
> 
> Can we set the value to ECONNRESET only in case of
> error condition and for the normal disconnect set it
> to 0 by calling l2cap_chan_del(sk,0) from
> l2cap_disconnect_req ?
> 
> So if error field is not set in sock structure,
> bt_sock_recvmsg will return data bytes till sk_buff is
> empty and which case 0 will be returned. This will
> prevent any data loss.
> 
> Also if the user wants to know when socket
> disconnected, POLLHUP will be set for sock fd so after
> disconnect happens and there is data to be read both
> POLLHUP and POLLIN will set.
> If we set sock err field then user will not be able to
> retrieve data from sk_buff, even if POLLLIN is set.

Provide a patch and a test program and I will have a look at it.

Regards

Marcel


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