Re: can we increase the send buffer size of rfcomm socket?

Hi Marcel,

2009/8/28 Marcel Holtmann [off-list ref]:

Hi Zhu,

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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,

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=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 msg->msg_=

flags & MSG_DONTWAIT, &err);

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=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

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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