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

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(...)
{
   ...
              skb = sock_alloc_send_skb(sk, size + RFCOMM_SKB_RESERVE,
                              msg->msg_flags & MSG_DONTWAIT, &err);
              if (!skb)
                      break;
   ...
}

Looks the send buffer is not adequate. Then I increased the send
buffer size in function rfcomm_sock_alloc(),  build 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/receive
buffer size, just like the usual  tcp/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 = RFCOMM_MAX_CREDITS * RFCOMM_DEFAULT_MTU * 10
to
sk->sk_sndbuf = 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 = 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?

no that is bluntly wrong. Why do you think the function has _old in its
name. It clearly shows that we are going to deprecate it soon. If you do
this for RFCOMM, then it should also be done for L2CAP. So make sure you
use SOL_BLUETOOTH. And make it similar to what TCP is doing.

Regards

Marcel