Re: [PATCH 4/4] Bluetooth: Add support for Retransmission and Monitor Timers

[Marcel Holtmann <marcel@holtmann.org>]

Hi Gustavo,

> L2CAP uses rentransmission and monitor timers to inquiry the other side
> about unacked I-frames. After send each I-frame we (re)start the
> retransmission timer, if it expires, we start a monitor timer that send a
> S-frame with P bit set and wait for S-frame with F bit set.
> If monitor timer expires, it try again, at a maximum of
> L2CAP_DEFAULT_MAX_TX.
> 
> Signed-off-by: Gustavo F. Padovan <gustavo@las.ic.unicamp.br>
> ---
>  include/net/bluetooth/bluetooth.h |    1 +
>  include/net/bluetooth/l2cap.h     |   15 +++++-
>  net/bluetooth/l2cap.c             |   83 +++++++++++++++++++++++++++++++++++--
>  3 files changed, 92 insertions(+), 7 deletions(-)
> 
> diff --git a/include/net/bluetooth/bluetooth.h b/include/net/bluetooth/bluetooth.h
> index 65a5cf8..b8b9a84 100644
> --- a/include/net/bluetooth/bluetooth.h
> +++ b/include/net/bluetooth/bluetooth.h
> @@ -139,6 +139,7 @@ struct bt_skb_cb {
>  	__u8 pkt_type;
>  	__u8 incoming;
>  	__u8 tx_seq;
> +	__u8 retries;
>  };
>  #define bt_cb(skb) ((struct bt_skb_cb *)((skb)->cb))
>  
> diff --git a/include/net/bluetooth/l2cap.h b/include/net/bluetooth/l2cap.h
> index 653c313..02871df 100644
> --- a/include/net/bluetooth/l2cap.h
> +++ b/include/net/bluetooth/l2cap.h
> @@ -31,9 +31,9 @@
>  #define L2CAP_DEFAULT_FLUSH_TO		0xffff
>  #define L2CAP_DEFAULT_TX_WINDOW		63
>  #define L2CAP_DEFAULT_NUM_TO_ACK        (L2CAP_DEFAULT_TX_WINDOW/5)
> -#define L2CAP_DEFAULT_MAX_RECEIVE	1
> -#define L2CAP_DEFAULT_RETRANS_TO	300    /* 300 milliseconds */
> -#define L2CAP_DEFAULT_MONITOR_TO	1000   /* 1 second */
> +#define L2CAP_DEFAULT_MAX_TX		3
> +#define L2CAP_DEFAULT_RETRANS_TO	1000    /* 1 second */
> +#define L2CAP_DEFAULT_MONITOR_TO	12000   /* 12 seconds */
>  #define L2CAP_DEFAULT_MAX_PDU_SIZE	672
>  
>  #define L2CAP_CONN_TIMEOUT	(40000) /* 40 seconds */
> @@ -320,6 +320,7 @@ struct l2cap_pinfo {
>  	__u8		req_seq;
>  	__u8		expected_tx_seq;
>  	__u8		unacked_frames;
> +	__u8		retry_count;
>  	__u8		num_to_ack;
>  	__u16		sdu_len;
>  	__u16		partial_sdu_len;
> @@ -336,6 +337,8 @@ struct l2cap_pinfo {
>  
>  	__le16		sport;
>  
> +	struct timer_list	retrans_timer;
> +	struct timer_list	monitor_timer;
>  	struct sk_buff_head	tx_queue;
>  	struct l2cap_conn	*conn;
>  	struct sock		*next_c;
> @@ -355,6 +358,12 @@ struct l2cap_pinfo {
>  
>  #define L2CAP_CONN_SAR_SDU         0x01
>  #define L2CAP_CONN_UNDER_REJ       0x02
> +#define L2CAP_CONN_WAIT_ACK        0x04
> +
> +#define __mod_retrans_timer() mod_timer(&l2cap_pi(sk)->retrans_timer, \
> +		jiffies +  msecs_to_jiffies(L2CAP_DEFAULT_RETRANS_TO));
> +#define __mod_monitor_timer() mod_timer(&l2cap_pi(sk)->monitor_timer, \
> +		jiffies + msecs_to_jiffies(L2CAP_DEFAULT_MONITOR_TO));
>  
>  static inline int l2cap_tx_window_full(struct sock *sk)
>  {
> diff --git a/net/bluetooth/l2cap.c b/net/bluetooth/l2cap.c
> index 938d6db..bcfa9b9 100644
> --- a/net/bluetooth/l2cap.c
> +++ b/net/bluetooth/l2cap.c
> @@ -1179,6 +1179,37 @@ static int l2cap_sock_getname(struct socket *sock, struct sockaddr *addr, int *l
>  	return 0;
>  }
>  
> +static void l2cap_monitor_timeout(unsigned long arg)
> +{
> +	struct sock *sk = (void *) arg;
> +	u16 control;
> +
> +	if (l2cap_pi(sk)->retry_count >= l2cap_pi(sk)->remote_max_tx) {
> +		l2cap_send_disconn_req(l2cap_pi(sk)->conn, sk);
> +		return;
> +	}
> +
> +	l2cap_pi(sk)->retry_count++;
> +	__mod_monitor_timer();
> +
> +	control = L2CAP_CTRL_POLL;
> +	l2cap_send_sframe(l2cap_pi(sk), control);
> +}
> +
> +static void l2cap_retrans_timeout(unsigned long arg)
> +{
> +	struct sock *sk = (void *) arg;
> +	u16 control;
> +
> +	l2cap_pi(sk)->retry_count = 1;
> +	__mod_monitor_timer();
> +
> +	l2cap_pi(sk)->conn_state |= L2CAP_CONN_WAIT_ACK;
> +
> +	control = L2CAP_CTRL_POLL;
> +	l2cap_send_sframe(l2cap_pi(sk), control);
> +}
> +
>  static void l2cap_drop_acked_frames(struct sock *sk)
>  {
>  	struct sk_buff *skb;
> @@ -1193,6 +1224,9 @@ static void l2cap_drop_acked_frames(struct sock *sk)
>  		l2cap_pi(sk)->unacked_frames--;
>  	}
>  
> +	if (!l2cap_pi(sk)->unacked_frames)
> +		del_timer(&l2cap_pi(sk)->retrans_timer);
> +
>  	return;
>  }
>  
> @@ -1219,10 +1253,21 @@ static int l2cap_ertm_send(struct sock *sk)
>  	u16 *control;
>  	int err;
>  
> +	if (pi->conn_state & L2CAP_CONN_WAIT_ACK)
> +		return 0;
> +
>  	while ((skb = sk->sk_send_head) && (!l2cap_tx_window_full(sk))) {
>  		tx_seq = pi->next_tx_seq;
>  		tx_skb = skb_clone(skb, GFP_ATOMIC);
>  
> +		if (pi->remote_max_tx &&
> +				bt_cb(skb)->retries == pi->remote_max_tx) {
> +			l2cap_send_disconn_req(pi->conn, sk);
> +			break;
> +		}
> +
> +		bt_cb(skb)->retries++;
> +
>  		control = (u16 *)(skb->data + L2CAP_HDR_SIZE);
>  		*control |= cpu_to_le16(
>  				(pi->req_seq << L2CAP_CTRL_REQSEQ_SHIFT)
> @@ -1234,6 +1279,8 @@ static int l2cap_ertm_send(struct sock *sk)
>  			return err;
>  		}
>  
> +		__mod_retrans_timer();
> +
>  		L2CAP_SEQ_NUM_INC(pi->next_tx_seq);
>  		bt_cb(skb)->tx_seq = tx_seq;
>  
> @@ -1323,6 +1370,8 @@ static struct sk_buff *l2cap_create_pdu(struct sock *sk, struct msghdr *msg, siz
>  		kfree_skb(skb);
>  		return ERR_PTR(err);
>  	}
> +
> +	bt_cb(skb)->retries = 0;
>  	return skb;
>  }
>  
> @@ -2011,7 +2060,7 @@ done:
>  	case L2CAP_MODE_ERTM:
>  		rfc.mode            = L2CAP_MODE_ERTM;
>  		rfc.txwin_size      = L2CAP_DEFAULT_TX_WINDOW;
> -		rfc.max_transmit    = L2CAP_DEFAULT_MAX_RECEIVE;
> +		rfc.max_transmit    = L2CAP_DEFAULT_MAX_TX;
>  		rfc.retrans_timeout = 0;
>  		rfc.monitor_timeout = 0;
>  		rfc.max_pdu_size    = cpu_to_le16(L2CAP_DEFAULT_MAX_PDU_SIZE);
> @@ -2506,6 +2555,12 @@ static inline int l2cap_config_req(struct l2cap_conn *conn, struct l2cap_cmd_hdr
>  		l2cap_pi(sk)->next_tx_seq = 0;
>  		l2cap_pi(sk)->expected_ack_seq = 0;
>  		l2cap_pi(sk)->unacked_frames = 0;
> +
> +		setup_timer(&l2cap_pi(sk)->retrans_timer,
> +				l2cap_retrans_timeout, (unsigned long) sk);
> +		setup_timer(&l2cap_pi(sk)->monitor_timer,
> +				l2cap_monitor_timeout, (unsigned long) sk);
> +
>  		__skb_queue_head_init(TX_QUEUE(sk));
>  		l2cap_chan_ready(sk);
>  		goto unlock;
> @@ -2615,6 +2670,8 @@ static inline int l2cap_disconnect_req(struct l2cap_conn *conn, struct l2cap_cmd
>  	sk->sk_shutdown = SHUTDOWN_MASK;
>  
>  	skb_queue_purge(TX_QUEUE(sk));
> +	del_timer(&l2cap_pi(sk)->retrans_timer);
> +	del_timer(&l2cap_pi(sk)->monitor_timer);
>  
>  	l2cap_chan_del(sk, ECONNRESET);
>  	bh_unlock_sock(sk);
> @@ -2639,6 +2696,8 @@ static inline int l2cap_disconnect_rsp(struct l2cap_conn *conn, struct l2cap_cmd
>  		return 0;
>  
>  	skb_queue_purge(TX_QUEUE(sk));
> +	del_timer(&l2cap_pi(sk)->retrans_timer);
> +	del_timer(&l2cap_pi(sk)->monitor_timer);
>  
>  	l2cap_chan_del(sk, 0);
>  	bh_unlock_sock(sk);
> @@ -2944,9 +3003,25 @@ static inline int l2cap_data_channel_sframe(struct sock *sk, u16 rx_control, str
>  
>  	switch (rx_control & L2CAP_CTRL_SUPERVISE) {
>  	case L2CAP_SUPER_RCV_READY:
> -		pi->expected_ack_seq = __get_reqseq(rx_control);
> -		l2cap_drop_acked_frames(sk);
> -		l2cap_ertm_send(sk);
> +		if (rx_control & L2CAP_CTRL_POLL) {
> +			u16 control = L2CAP_CTRL_FINAL;
> +			l2cap_send_sframe(l2cap_pi(sk), control);
> +		}
> +		else if (rx_control & L2CAP_CTRL_FINAL) {

Coding style is } else if.

> +			if (pi->conn_state & L2CAP_CONN_WAIT_ACK)
> +				break;
> +
> +			pi->conn_state &= !L2CAP_CONN_WAIT_ACK;
> +			del_timer(&pi->monitor_timer);
> +
> +			if (pi->unacked_frames > 0)
> +				__mod_retrans_timer();
> +		}
> +		else {

Same here.

> +			pi->expected_ack_seq = __get_reqseq(rx_control);
> +			l2cap_drop_acked_frames(sk);
> +			l2cap_ertm_send(sk);
> +		}
>  		break;
>  
>  	case L2CAP_SUPER_REJECT:

Regards

Marcel