Re: [PATCH 5/6] Bluetooth: Use event-driven approach for handling ERTM receive buffer

["Gustavo F. Padovan" <padovan@profusion.mobi>]

Hi Mat,

* Mat Martineau <mathewm@codeaurora.org> [2011-06-29 14:35:23 -0700]:

> This change moves most L2CAP ERTM receive buffer handling out of the
> L2CAP core and in to the socket code.  It's up to the higher layer
> (the socket code, in this case) to tell the core when its buffer is
> full or has space available.  The recv op should always accept
> incoming ERTM data or else the connection will go down.
> 
> Within the socket layer, an skb that does not fit in the socket
> receive buffer will be temporarily stored.  When the socket is read
> from, that skb will be placed in the receive buffer if possible.  Once
> adequate buffer space becomes available, the L2CAP core is informed
> and the ERTM local busy state is cleared.
> 
> Receive buffer management for non-ERTM modes is unchanged.
> 
> Signed-off-by: Mat Martineau <mathewm@codeaurora.org>
> ---
>  include/net/bluetooth/l2cap.h |    3 ++
>  net/bluetooth/l2cap_core.c    |   41 ++++++++++++++++---------
>  net/bluetooth/l2cap_sock.c    |   67 +++++++++++++++++++++++++++++++++++++++--
>  3 files changed, 93 insertions(+), 18 deletions(-)
> 
> diff --git a/include/net/bluetooth/l2cap.h b/include/net/bluetooth/l2cap.h
> index 9c18e55..82387c5 100644
> --- a/include/net/bluetooth/l2cap.h
> +++ b/include/net/bluetooth/l2cap.h
> @@ -422,6 +422,8 @@ struct l2cap_conn {
>  struct l2cap_pinfo {
>  	struct bt_sock	bt;
>  	struct l2cap_chan	*chan;
> +	struct sk_buff	*rx_busy_skb;
> +	int rx_busy;
>  };
>  
>  enum {
> @@ -498,5 +500,6 @@ void l2cap_chan_close(struct l2cap_chan *chan, int reason);
>  void l2cap_chan_destroy(struct l2cap_chan *chan);
>  int l2cap_chan_connect(struct l2cap_chan *chan);
>  int l2cap_chan_send(struct l2cap_chan *chan, struct msghdr *msg, size_t len);
> +void l2cap_chan_busy(struct l2cap_chan *chan, int busy);
>  
>  #endif /* __L2CAP_H */
> diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
> index 4b764b1..f0e7ba7 100644
> --- a/net/bluetooth/l2cap_core.c
> +++ b/net/bluetooth/l2cap_core.c
> @@ -3350,21 +3350,21 @@ static int l2cap_push_rx_skb(struct l2cap_chan *chan, struct sk_buff *skb, u16 c
>  	}
>  
>  	err = l2cap_ertm_reassembly_sdu(chan, skb, control);
> -	if (err >= 0) {
> -		chan->buffer_seq = (chan->buffer_seq + 1) % 64;
> -		return err;
> -	}
> -
> -	l2cap_ertm_enter_local_busy(chan);
> -
> -	bt_cb(skb)->sar = control >> L2CAP_CTRL_SAR_SHIFT;
> -	__skb_queue_tail(&chan->busy_q, skb);
> -
> -	queue_work(_busy_wq, &chan->busy_work);
> +	chan->buffer_seq = (chan->buffer_seq + 1) % 64;
>  
>  	return err;
>  }
>  
> +void l2cap_chan_busy(struct l2cap_chan *chan, int busy)
> +{
> +	if (chan->mode == L2CAP_MODE_ERTM) {
> +		if (busy)
> +			l2cap_ertm_enter_local_busy(chan);
> +		else
> +			l2cap_ertm_exit_local_busy(chan);
> +	}
> +}
> +
>  static int l2cap_streaming_reassembly_sdu(struct l2cap_chan *chan, struct sk_buff *skb, u16 control)
>  {
>  	struct sk_buff *_skb;
> @@ -3463,13 +3463,22 @@ static void l2cap_check_srej_gap(struct l2cap_chan *chan, u8 tx_seq)
>  	struct sk_buff *skb;
>  	u16 control;
>  
> -	while ((skb = skb_peek(&chan->srej_q))) {
> +	while ((skb = skb_peek(&chan->srej_q)) &&
> +			!test_bit(CONN_LOCAL_BUSY, &chan->conn_state)) {
> +		int err;
> +
>  		if (bt_cb(skb)->tx_seq != tx_seq)
>  			break;
>  
>  		skb = skb_dequeue(&chan->srej_q);
>  		control = bt_cb(skb)->sar << L2CAP_CTRL_SAR_SHIFT;
> -		l2cap_ertm_reassembly_sdu(chan, skb, control);
> +		err = l2cap_ertm_reassembly_sdu(chan, skb, control);
> +
> +		if (err < 0) {
> +			l2cap_send_disconn_req(chan->conn, chan, ECONNRESET);
> +			break;
> +		}
> +
>  		chan->buffer_seq_srej =
>  			(chan->buffer_seq_srej + 1) % 64;
>  		tx_seq = (tx_seq + 1) % 64;
> @@ -3625,8 +3634,10 @@ expected:
>  	}
>  
>  	err = l2cap_push_rx_skb(chan, skb, rx_control);
> -	if (err < 0)
> -		return 0;
> +	if (err < 0) {
> +		l2cap_send_disconn_req(chan->conn, chan, ECONNRESET);
> +		return err;
> +	}
>  
>  	if (rx_control & L2CAP_CTRL_FINAL) {
>  		if (!test_and_clear_bit(CONN_REJ_ACT, &chan->conn_state))
> diff --git a/net/bluetooth/l2cap_sock.c b/net/bluetooth/l2cap_sock.c
> index 39082d4..ab0494b 100644
> --- a/net/bluetooth/l2cap_sock.c
> +++ b/net/bluetooth/l2cap_sock.c
> @@ -711,6 +711,8 @@ static int l2cap_sock_sendmsg(struct kiocb *iocb, struct socket *sock, struct ms
>  static int l2cap_sock_recvmsg(struct kiocb *iocb, struct socket *sock, struct msghdr *msg, size_t len, int flags)
>  {
>  	struct sock *sk = sock->sk;
> +	struct l2cap_pinfo *pi = l2cap_pi(sk);
> +	int err;
>  
>  	lock_sock(sk);
>  
> @@ -725,9 +727,40 @@ static int l2cap_sock_recvmsg(struct kiocb *iocb, struct socket *sock, struct ms
>  	release_sock(sk);
>  
>  	if (sock->type == SOCK_STREAM)
> -		return bt_sock_stream_recvmsg(iocb, sock, msg, len, flags);
> +		err = bt_sock_stream_recvmsg(iocb, sock, msg, len, flags);
> +	else
> +		err = bt_sock_recvmsg(iocb, sock, msg, len, flags);
> +
> +	if (pi->chan->mode == L2CAP_MODE_ERTM) {
> +		int queue_err;
> +		int threshold;
> +
> +		/* Attempt to put pending rx data in the socket buffer */
> +
> +		lock_sock(sk);
> +		if (pi->rx_busy_skb) {
> +			queue_err = sock_queue_rcv_skb(sk, pi->rx_busy_skb);
> +
> +			if (!queue_err)
> +				pi->rx_busy_skb = NULL;
> +		}
> +
> +		/* Restore data flow when half of the receive buffer is
> +		 * available.  This avoids resending large numbers of
> +		 * frames.
> +		 */
> +		threshold = sk->sk_rcvbuf >> 1;
> +		if (pi->rx_busy && !pi->rx_busy_skb &&
> +				atomic_read(&sk->sk_rmem_alloc) <= threshold) {
> +
> +			pi->rx_busy = 0;
> +			l2cap_chan_busy(l2cap_pi(sk)->chan, pi->rx_busy);
> +		}
> +
> +		release_sock(sk);

This is to much core logic outside of the core. I didn't think hard on this
but this can be simplified to just read the threshold and report core if we
are not busy anymore, and then get rid of rx_busy and rx_busy_skb.

> +	}
>  
> -	return bt_sock_recvmsg(iocb, sock, msg, len, flags);
> +	return err;
>  }
>  
>  /* Kill socket (only if zapped and orphan)
> @@ -811,9 +844,32 @@ static struct l2cap_chan *l2cap_sock_new_connection_cb(void *data)
>  
>  static int l2cap_sock_recv_cb(void *data, struct sk_buff *skb)
>  {
> +	int err;
>  	struct sock *sk = data;
> +	struct l2cap_pinfo *pi = l2cap_pi(sk);
> +
> +	if (pi->rx_busy_skb)
> +		return -ENOMEM;
> +
> +	err = sock_queue_rcv_skb(sk, skb);
> +
> +	/* For ERTM, handle one skb that doesn't fit into the recv
> +	 * buffer.  This is important to do because the data frames
> +	 * have already been acked, so the skb cannot be discarded.
> +	 *
> +	 * Notify the l2cap core that the buffer is full, so the
> +	 * LOCAL_BUSY state is entered and no more frames are
> +	 * acked and reassembled until there is buffer space
> +	 * available.
> +	 */
> +	if (err < 0 && pi->chan->mode == L2CAP_MODE_ERTM) {
> +		pi->rx_busy = 1;
> +		pi->rx_busy_skb = skb;
> +		l2cap_chan_busy(pi->chan, pi->rx_busy);
> +		err = 0;
> +	}

This can totally be in l2cap_core.c. The idea is move Core stuff to
l2cap_core.c and not let the L2CAP users handle this. Just enter in LOCAL_BUSY
when recv_cb returns returns less than 0.

	Gustavo