Bluetooth: Initial support for retransmission of packets with REJ frames

When receiving an I-frame with unexpected txSeq, receiver side start the
recovery procedure by sending a REJ S-frame to the transmitter side. So
the transmitter can re-send the lost I-frame.

This patch just adds a basic support for retransmission, it doesn't
mean that ERTM now has full support for packet retransmission.

Signed-off-by: Gustavo F. Padovan <gustavo@las.ic.unicamp.br>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

2 files changed, 44 insertions, 14 deletions

diff --git a/include/net/bluetooth/l2cap.h b/include/net/bluetooth/l2cap.h
index 0afde8d22b56..a1d8ec468ef3 100644
--- a/include/net/bluetooth/l2cap.h
+++ b/include/net/bluetooth/l2cap.h
@@ -351,6 +351,7 @@ struct l2cap_pinfo {
 #define L2CAP_CONF_MAX_CONF_RSP 2
 
 #define L2CAP_CONN_SAR_SDU         0x01
+#define L2CAP_CONN_UNDER_REJ       0x02
 
 static inline int l2cap_tx_window_full(struct sock *sk)
 {
diff --git a/net/bluetooth/l2cap.c b/net/bluetooth/l2cap.c
index 167e02532697..35e9f5b80545 100644
--- a/net/bluetooth/l2cap.c
+++ b/net/bluetooth/l2cap.c
@@ -2951,22 +2951,36 @@ static inline int l2cap_data_channel_iframe(struct sock *sk, u16 rx_control, str
 
         BT_DBG("sk %p rx_control 0x%4.4x len %d", sk, rx_control, skb->len);
 
-        if (tx_seq != pi->expected_tx_seq)
-                return -EINVAL;
+        if (tx_seq == pi->expected_tx_seq) {
+                if (pi->conn_state & L2CAP_CONN_UNDER_REJ)
+                        pi->conn_state &= ~L2CAP_CONN_UNDER_REJ;
 
-        err = l2cap_sar_reassembly_sdu(sk, skb, rx_control);
-        if (err < 0)
-                return err;
+                err = l2cap_sar_reassembly_sdu(sk, skb, rx_control);
+                if (err < 0)
+                        return err;
+
+                pi->expected_tx_seq = (pi->expected_tx_seq + 1) % 64;
+                pi->num_to_ack = (pi->num_to_ack + 1) % L2CAP_DEFAULT_NUM_TO_ACK;
+                if (pi->num_to_ack == L2CAP_DEFAULT_NUM_TO_ACK - 1) {
+                        tx_control |= L2CAP_SUPER_RCV_READY;
+                        tx_control |= pi->expected_tx_seq << L2CAP_CTRL_REQSEQ_SHIFT;
+                        goto send;
+                }
+        } else {
+                /* Unexpected txSeq. Send a REJ S-frame */
+                kfree_skb(skb);
+                if (!(pi->conn_state & L2CAP_CONN_UNDER_REJ)) {
+                        tx_control |= L2CAP_SUPER_REJECT;
+                        tx_control |= pi->expected_tx_seq << L2CAP_CTRL_REQSEQ_SHIFT;
+                        pi->conn_state |= L2CAP_CONN_UNDER_REJ;
 
-        pi->expected_tx_seq = (pi->expected_tx_seq + 1) % 64;
-        pi->num_to_ack = (pi->num_to_ack + 1) % L2CAP_DEFAULT_NUM_TO_ACK;
-        if (pi->num_to_ack == L2CAP_DEFAULT_NUM_TO_ACK - 1) {
-                tx_control |= L2CAP_CTRL_FRAME_TYPE;
-                tx_control |= L2CAP_SUPER_RCV_READY;
-                tx_control |= pi->expected_tx_seq << L2CAP_CTRL_REQSEQ_SHIFT;
-                err = l2cap_send_sframe(pi, tx_control);
+                        goto send;
+                }
         }
-        return err;
+        return 0;
+
+send:
+        return l2cap_send_sframe(pi, tx_control);
 }
 
 static inline int l2cap_data_channel_sframe(struct sock *sk, u16 rx_control, struct sk_buff *skb)
@@ -2982,8 +2996,18 @@ static inline int l2cap_data_channel_sframe(struct sock *sk, u16 rx_control, str
                 l2cap_ertm_send(sk);
                 break;
 
-        case L2CAP_SUPER_RCV_NOT_READY:
         case L2CAP_SUPER_REJECT:
+                pi->expected_ack_seq = __get_reqseq(rx_control);
+                l2cap_drop_acked_frames(sk);
+
+                sk->sk_send_head = TX_QUEUE(sk)->next;
+                pi->next_tx_seq = pi->expected_ack_seq;
+
+                l2cap_ertm_send(sk);
+
+                break;
+
+        case L2CAP_SUPER_RCV_NOT_READY:
         case L2CAP_SUPER_SELECT_REJECT:
                 break;
         }
@@ -3030,6 +3054,11 @@ static inline int l2cap_data_channel(struct l2cap_conn *conn, u16 cid, struct sk
                 if (__is_sar_start(control))
                         len -= 2;
 
+                /*
+                 * We can just drop the corrupted I-frame here.
+                 * Receiver will miss it and start proper recovery
+                 * procedures and ask retransmission.
+                 */
                 if (len > L2CAP_DEFAULT_MAX_PDU_SIZE)
                         goto drop;