Bluetooth: Use event-driven approach for handling ERTM receive buffer

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>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>

1 files changed, 61 insertions, 4 deletions

diff --git a/net/bluetooth/l2cap_sock.c b/net/bluetooth/l2cap_sock.c
index 39082d4e77ce..146b614d10ed 100644
--- a/net/bluetooth/l2cap_sock.c
+++ b/net/bluetooth/l2cap_sock.c
@@ -711,13 +711,15 @@ 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);
 
 	if (sk->sk_state == BT_CONNECT2 && bt_sk(sk)->defer_setup) {
 		sk->sk_state = BT_CONFIG;
 
-		__l2cap_connect_rsp_defer(l2cap_pi(sk)->chan);
+		__l2cap_connect_rsp_defer(pi->chan);
 		release_sock(sk);
 		return 0;
 	}
@@ -725,9 +727,37 @@ 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)
+		return err;
+
+	/* Attempt to put pending rx data in the socket buffer */
+
+	lock_sock(sk);
+
+	if (!test_bit(CONN_LOCAL_BUSY, &pi->chan->conn_state))
+		goto done;
+
+	if (pi->rx_busy_skb) {
+		if (!sock_queue_rcv_skb(sk, pi->rx_busy_skb))
+			pi->rx_busy_skb = NULL;
+		else
+			goto done;
+	}
 
-	return bt_sock_recvmsg(iocb, sock, msg, len, flags);
+	/* Restore data flow when half of the receive buffer is
+	 * available.  This avoids resending large numbers of
+	 * frames.
+	 */
+	if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf >> 1)
+		l2cap_chan_busy(pi->chan, 0);
+
+done:
+	release_sock(sk);
+	return err;
 }
 
 /* Kill socket (only if zapped and orphan)
@@ -811,9 +841,31 @@ 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);
 
-	return sock_queue_rcv_skb(sk, skb);
+	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_skb = skb;
+		l2cap_chan_busy(pi->chan, 1);
+		err = 0;
+	}
+
+	return err;
 }
 
 static void l2cap_sock_close_cb(void *data)
@@ -842,6 +894,11 @@ static void l2cap_sock_destruct(struct sock *sk)
 {
 	BT_DBG("sk %p", sk);
 
+	if (l2cap_pi(sk)->rx_busy_skb) {
+		kfree_skb(l2cap_pi(sk)->rx_busy_skb);
+		l2cap_pi(sk)->rx_busy_skb = NULL;
+	}
+
 	skb_queue_purge(&sk->sk_receive_queue);
 	skb_queue_purge(&sk->sk_write_queue);
 }