[RFCv2 7/8] Bluetooth: Refactor L2CAP ERTM and streaming transmit segmentation

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Use more common code for ERTM and streaming mode segmentation and
transmission, and begin using skb control block data for delaying
extended or enhanced header generation until just before the packet is
transmitted.  This code is also better suited for resegmentation,
which is needed when L2CAP links are reconfigured after an AMP channel
move.

Signed-off-by: Mat Martineau <mathewm@xxxxxxxxxxxxxx>
---
 include/net/bluetooth/l2cap.h |    1 +
 net/bluetooth/l2cap_core.c    |  154 ++++++++++++++++++++++++-----------------
 2 files changed, 92 insertions(+), 63 deletions(-)

diff --git a/include/net/bluetooth/l2cap.h b/include/net/bluetooth/l2cap.h
index 92c0423..88c128a 100644
--- a/include/net/bluetooth/l2cap.h
+++ b/include/net/bluetooth/l2cap.h
@@ -44,6 +44,7 @@
 #define L2CAP_DEFAULT_MAX_SDU_SIZE	0xFFFF
 #define L2CAP_DEFAULT_SDU_ITIME		0xFFFFFFFF
 #define L2CAP_DEFAULT_ACC_LAT		0xFFFFFFFF
+#define L2CAP_BREDR_MAX_PAYLOAD		1019    /* 3-DH5 packet */
 
 #define L2CAP_DISC_TIMEOUT		msecs_to_jiffies(100)
 #define L2CAP_DISC_REJ_TIMEOUT		msecs_to_jiffies(5000)
diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index 347aaa5..d424b86 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -1636,6 +1636,7 @@ static void l2cap_streaming_send(struct l2cap_chan *chan)
 	while ((skb = skb_dequeue(&chan->tx_q))) {
 		control = __get_control(chan, skb->data + L2CAP_HDR_SIZE);
 		control |= __set_txseq(chan, chan->next_tx_seq);
+		control |= __set_ctrl_sar(chan, bt_cb(skb)->control.sar);
 		__put_control(chan, control, skb->data + L2CAP_HDR_SIZE);
 
 		if (chan->fcs == L2CAP_FCS_CRC16) {
@@ -1708,6 +1709,9 @@ static int l2cap_ertm_send(struct l2cap_chan *chan)
 	if (chan->state != BT_CONNECTED)
 		return -ENOTCONN;
 
+	if (test_bit(CONN_REMOTE_BUSY, &chan->conn_state))
+		return 0;
+
 	while ((skb = chan->tx_send_head) && (!l2cap_tx_window_full(chan))) {
 
 		if (chan->remote_max_tx &&
@@ -1728,6 +1732,7 @@ static int l2cap_ertm_send(struct l2cap_chan *chan)
 
 		control |= __set_reqseq(chan, chan->buffer_seq);
 		control |= __set_txseq(chan, chan->next_tx_seq);
+		control |= __set_ctrl_sar(chan, bt_cb(skb)->control.sar);
 
 		__put_control(chan, control, tx_skb->data + L2CAP_HDR_SIZE);
 
@@ -1923,7 +1928,7 @@ static struct sk_buff *l2cap_create_basic_pdu(struct l2cap_chan *chan,
 
 static struct sk_buff *l2cap_create_iframe_pdu(struct l2cap_chan *chan,
 						struct msghdr *msg, size_t len,
-						u32 control, u16 sdulen)
+						u16 sdulen)
 {
 	struct l2cap_conn *conn = chan->conn;
 	struct sk_buff *skb;
@@ -1958,7 +1963,7 @@ static struct sk_buff *l2cap_create_iframe_pdu(struct l2cap_chan *chan,
 	lh->cid = cpu_to_le16(chan->dcid);
 	lh->len = cpu_to_le16(len + (hlen - L2CAP_HDR_SIZE));
 
-	__put_control(chan, control, skb_put(skb, __ctrl_size(chan)));
+	__put_control(chan, 0, skb_put(skb, __ctrl_size(chan)));
 
 	if (sdulen)
 		put_unaligned_le16(sdulen, skb_put(skb, L2CAP_SDULEN_SIZE));
@@ -1976,57 +1981,78 @@ static struct sk_buff *l2cap_create_iframe_pdu(struct l2cap_chan *chan,
 	return skb;
 }
 
-static int l2cap_sar_segment_sdu(struct l2cap_chan *chan, struct msghdr *msg, size_t len)
+static int l2cap_segment_sdu(struct l2cap_chan *chan,
+			     struct sk_buff_head *seg_queue,
+			     struct msghdr *msg, size_t len)
 {
 	struct sk_buff *skb;
-	struct sk_buff_head sar_queue;
-	u32 control;
-	size_t size = 0;
+	u16 sdu_len;
+	size_t pdu_len;
+	int err = 0;
+	u8 sar;
 
-	skb_queue_head_init(&sar_queue);
-	control = __set_ctrl_sar(chan, L2CAP_SAR_START);
-	skb = l2cap_create_iframe_pdu(chan, msg, chan->remote_mps, control, len);
-	if (IS_ERR(skb))
-		return PTR_ERR(skb);
+	BT_DBG("chan %p, msg %p, len %d", chan, msg, (int)len);
 
-	__skb_queue_tail(&sar_queue, skb);
-	len -= chan->remote_mps;
-	size += chan->remote_mps;
+	/* It is critical that ERTM PDUs fit in a single HCI fragment,
+	 * so fragmented skbs are not used.  The HCI layer's handling
+	 * of fragmented skbs is not compatible with ERTM's queueing.
+	 */
+
+	/* PDU size is derived from the HCI MTU */
+	pdu_len = chan->conn->mtu;
+
+	pdu_len = min_t(size_t, pdu_len, L2CAP_BREDR_MAX_PAYLOAD);
+
+	/* Adjust for largest possible L2CAP overhead. */
+	pdu_len -= L2CAP_EXT_HDR_SIZE + L2CAP_FCS_SIZE;
+
+	/* Remote device may have requested smaller PDUs */
+	pdu_len = min_t(size_t, pdu_len, chan->remote_mps);
+
+	if (len <= pdu_len) {
+		sar = L2CAP_SAR_UNSEGMENTED;
+		sdu_len = 0;
+		pdu_len = len;
+	} else {
+		sar = L2CAP_SAR_START;
+		sdu_len = len;
+		pdu_len -= L2CAP_SDULEN_SIZE;
+	}
 
 	while (len > 0) {
-		size_t buflen;
+		skb = l2cap_create_iframe_pdu(chan, msg, pdu_len, sdu_len);
 
-		if (len > chan->remote_mps) {
-			control = __set_ctrl_sar(chan, L2CAP_SAR_CONTINUE);
-			buflen = chan->remote_mps;
-		} else {
-			control = __set_ctrl_sar(chan, L2CAP_SAR_END);
-			buflen = len;
-		}
-
-		skb = l2cap_create_iframe_pdu(chan, msg, buflen, control, 0);
 		if (IS_ERR(skb)) {
-			skb_queue_purge(&sar_queue);
+			__skb_queue_purge(seg_queue);
 			return PTR_ERR(skb);
 		}
 
-		__skb_queue_tail(&sar_queue, skb);
-		len -= buflen;
-		size += buflen;
-	}
-	skb_queue_splice_tail(&sar_queue, &chan->tx_q);
-	if (chan->tx_send_head == NULL)
-		chan->tx_send_head = sar_queue.next;
+		bt_cb(skb)->control.sar = sar;
+		__skb_queue_tail(seg_queue, skb);
 
-	return size;
+		len -= pdu_len;
+		if (sdu_len) {
+			sdu_len = 0;
+			pdu_len += L2CAP_SDULEN_SIZE;
+		}
+
+		if (len <= pdu_len) {
+			sar = L2CAP_SAR_END;
+			pdu_len = len;
+		} else {
+			sar = L2CAP_SAR_CONTINUE;
+		}
+	}
+
+	return err;
 }
 
 int l2cap_chan_send(struct l2cap_chan *chan, struct msghdr *msg, size_t len,
 								u32 priority)
 {
 	struct sk_buff *skb;
-	u32 control;
 	int err;
+	struct sk_buff_head seg_queue;
 
 	/* Connectionless channel */
 	if (chan->chan_type == L2CAP_CHAN_CONN_LESS) {
@@ -2055,42 +2081,44 @@ int l2cap_chan_send(struct l2cap_chan *chan, struct msghdr *msg, size_t len,
 
 	case L2CAP_MODE_ERTM:
 	case L2CAP_MODE_STREAMING:
-		/* Entire SDU fits into one PDU */
-		if (len <= chan->remote_mps) {
-			control = __set_ctrl_sar(chan, L2CAP_SAR_UNSEGMENTED);
-			skb = l2cap_create_iframe_pdu(chan, msg, len, control,
-									0);
-			if (IS_ERR(skb))
-				return PTR_ERR(skb);
-
-			__skb_queue_tail(&chan->tx_q, skb);
-
-			if (chan->tx_send_head == NULL)
-				chan->tx_send_head = skb;
-
-		} else {
-			/* Segment SDU into multiples PDUs */
-			err = l2cap_sar_segment_sdu(chan, msg, len);
-			if (err < 0)
-				return err;
+		/* Check outgoing MTU */
+		if (len > chan->omtu) {
+			err = -EMSGSIZE;
+			break;
 		}
 
-		if (chan->mode == L2CAP_MODE_STREAMING) {
+		__skb_queue_head_init(&seg_queue);
+
+		/* Do segmentation before calling in to the state machine,
+		 * since it's possible to block while waiting for memory
+		 * allocation.
+		 */
+		err = l2cap_segment_sdu(chan, &seg_queue, msg, len);
+
+		/* The channel could have been closed while segmenting,
+		 * check that it is still connected.
+		 */
+		if (chan->state != BT_CONNECTED) {
+			__skb_queue_purge(&seg_queue);
+			err = -ENOTCONN;
+		}
+
+		if (err)
+			break;
+
+		skb_queue_splice_tail_init(&seg_queue, &chan->tx_q);
+		if (chan->mode == L2CAP_MODE_ERTM)
+			err = l2cap_ertm_send(chan);
+		else
 			l2cap_streaming_send(chan);
-			err = len;
-			break;
-		}
 
-		if (test_bit(CONN_REMOTE_BUSY, &chan->conn_state) &&
-				test_bit(CONN_WAIT_F, &chan->conn_state)) {
-			err = len;
-			break;
-		}
-
-		err = l2cap_ertm_send(chan);
 		if (err >= 0)
 			err = len;
 
+		/* If the skbs were not queued for sending, they'll still be in
+		 * seg_queue and need to be purged.
+		 */
+		__skb_queue_purge(&seg_queue);
 		break;
 
 	default:
-- 
1.7.10

--
Mat Martineau
Employee of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum
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