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Date: Fri, 28 Aug 2009 17:34:31 +0800
Message-ID: <113d36d80908280234m34473a05n45654ab37a484ed0@mail.gmail.com>
Subject: Re: can we increase the send buffer size of rfcomm socket?
From: Lan Zhu <zhu.lan.cn@gmail.com>
To: Marcel Holtmann <marcel@holtmann.org>
Cc: linux-bluetooth@vger.kernel.org
Content-Type: text/plain; charset=ISO-8859-1
List-ID: <linux-bluetooth.vger.kernel.org>

Hi Marcel,

2009/8/28 Marcel Holtmann <marcel@holtmann.org>:
> Hi Zhu,
>
>> >> We tried to write a 64k data to rfcomm socket, but it will break
>> >> before sending all of the data out. The problem is in function
>> >> rfcomm_sock_sendmsg() in net/bluetooth/rfcomm/sock.c, it breaks after
>> >> calling sock_alloc_send_skb().
>> >>
>> >> static int rfcomm_sock_sendmsg(...)
>> >> {
>> >> =A0 =A0...
>> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 skb =3D sock_alloc_send_skb(sk, size + RF=
COMM_SKB_RESERVE,
>> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 msg->msg_=
flags & MSG_DONTWAIT, &err);
>> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 if (!skb)
>> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 break;
>> >> =A0 =A0...
>> >> }
>> >>
>> >> Looks the send buffer is not adequate. Then I increased the send
>> >> buffer size in function rfcomm_sock_alloc(), =A0build kernel and try
>> >> again, this time the sendmsg can complete sending all the data.
>> >>
>> >> Can we use the setsockopt() method to change the socket's send/receiv=
e
>> >> buffer size, just like the usual =A0tcp/ip socket?
>> >
>> > yes we can. Send a patch for it and I am going to review it.
>> >
>> > Regards
>> >
>> > Marcel
>> >
>> >
>> >
>>
>> Today I changed the send buffer size but found kernel become very
>> unstable. It usually crash during sending rfcomm data. Do you know
>> what's the reason?
>>
>> Below is what I changed in net/bluetooth/rfcomm/sock.c.
>>
>> in function rfcomm_sock_alloc(),
>>
>> change sk->sndbuf
>> from
>> sk->sk_sndbuf =3D RFCOMM_MAX_CREDITS * RFCOMM_DEFAULT_MTU * 10
>> to
>> sk->sk_sndbuf =3D RFCOMM_MAX_CREDITS * RFCOMM_DEFAULT_MTU * 20
>
> which kernel is this? There have been some fixes in the network stack
> for this. Also I need oopses to see what might happen here.
>
> Regards
>
> Marcel
>
>
>

Yes, it's our kernel's problem. We used another version and it worked
fine. Here the change in rfcomm_sock_alloc() is only for testing. What
I'm doing now is adding a case for RFCOMM_SNDBUF in the function
rfcomm_sock_setsockopt_old(), as below.

	case RFCOMM_SNDBUF:
		sk->sk_sndbuf =3D opt;
		break;

I'm thinking to add a limitation for a maximum buffer size, but don't
know what maximum size is appropriate here. Do you have any idea?

Thanks,
Zhu Lan