Re: Problems with L2CAP: deferred setup and MTU

From: Ville Tervo <ville.tervo@nokia.com>
To: "ext Gustavo F. Padovan" <padovan@profusion.mobi>
Cc: "Elvis Pfützenreuter" <epx@signove.com>, linux-bluetooth@vger.kernel.org
Subject: Re: Problems with L2CAP: deferred setup and MTU
Date: Thu, 27 Jan 2011 10:03:49 +0200	[thread overview]
Message-ID: <20110127080349.GK874@null> (raw)
In-Reply-To: <20110124190913.GB4300@joana>

Hi Gustavo,

On Mon, Jan 24, 2011 at 05:09:13PM -0200, ext Gustavo F. Padovan wrote:
> Hi Elvis,
> 
> * Elvis Pfützenreuter <epx@signove.com> [2011-01-19 17:10:51 -0200]:
> 
> > I am currently investigating two problems with L2CAP sockets. Since I am not a kernel guy, I will take an indefinite amount of time to find and fix them; perhaps someone else can find and fix it in 5 minutes, so I think it is worth reporting.
> > 
> > First problem is ERTM x MTU, sockets configured with a MTU != 672. Normal sockets exchange MTU in initialization:
> > 
> > ./l2test -P 4099 -I 1000 -O 1000
> > l2test[3211]: Connect from 00:1B:DC:0F:C8:A9 [imtu 1000, omtu 1000, flush_to 65535, mode 0, handle 12, class 0x480100]
> > 
> > but ERTM sockets seem to ignore the setsockopt() value and exchange the default size (672):
> > 
> > ./l2test -P 4099 -I 1000 -O 1000 -X ERTM
> > l2test[3228]: Connect from 00:1B:DC:0F:C8:A9 [imtu 1000, omtu 672, flush_to 65535, mode 3, handle 11, class 0x480100]
> > 
> > (obviously the initiator side uses the same parameters)
> 
> I pushed I fix for this to bluetooth-next-2.6
> 
> Author: Gustavo F. Padovan <padovan@profusion.mobi>
> Date:   Mon Jan 24 16:01:43 2011 -0200
> 
>     Bluetooth: Fix setting of MTU for ERTM and Streaming Mode
>     
>     The desired MTU should be sent in an Config_Req for all modes.
>     
>     Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>
> 
> diff --git a/net/bluetooth/l2cap.c b/net/bluetooth/l2cap.c
> index ff191b9..1ee18c6 100644
> --- a/net/bluetooth/l2cap.c
> +++ b/net/bluetooth/l2cap.c
> @@ -2588,11 +2588,11 @@ static int l2cap_build_conf_req(struct sock *sk, void *data)
>         }
>  
>  done:
> +       if (pi->imtu != L4CAP_DEFAULT_MTU)
                          ^^^
Probably you noticed this typo already?

> +               l2cap_add_conf_opt(&ptr, L2CAP_CONF_MTU, 2, pi->imtu);
> +
>         switch (pi->mode) {
>         case L2CAP_MODE_BASIC:
> -               if (pi->imtu != L2CAP_DEFAULT_MTU)
> -                       l2cap_add_conf_opt(&ptr, L2CAP_CONF_MTU, 2, pi->imtu);
> -
>                 if (!(pi->conn->feat_mask & L2CAP_FEAT_ERTM) &&
>                                 !(pi->conn->feat_mask & L2CAP_FEAT_STREAMING))
>                         break;

-- 
Ville