Bluetooth: compute LE flow credits based on recvbuf space

Previously LE flow credits were returned to the
sender even if the socket's receive buffer was
full. This meant that no back-pressure
was applied to the sender, thus it continued to
send data, resulting in data loss without any
error being reported. Furthermore, the amount
of credits was essentially fixed to a small
amount, leading to reduced performance.

This is fixed by computing the number of returned
LE flow credits based on the estimated available
space in the receive buffer of an L2CAP socket.
Consequently, if the receive buffer is full, no
credits are returned until the buffer is read and
thus cleared by user-space.

Since the computation of available receive buffer
space can only be performed approximately (due to
sk_buff overhead) and the receive buffer size may
be changed by user-space after flow credits have
been sent, superfluous received data is temporary
stored within l2cap_pinfo. This is necessary
because Bluetooth LE provides no retransmission
mechanism once the data has been acked by the
physical layer.

If receive buffer space estimation is not possible
at the moment, we fall back to providing credits
for one full packet as before. This is currently
the case during connection setup, when MPS is not
yet available.

Fixes: b1c325c23d75 ("Bluetooth: Implement returning of LE L2CAP credits")
Signed-off-by: Sebastian Urban <surban@surban.net>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>

1 files changed, 10 insertions, 1 deletions

diff --git a/include/net/bluetooth/l2cap.h b/include/net/bluetooth/l2cap.h
index 7d4a3e766e7b..5cfdc813491a 100644
--- a/include/net/bluetooth/l2cap.h
+++ b/include/net/bluetooth/l2cap.h
@@ -554,6 +554,9 @@ struct l2cap_chan {
 	__u16		tx_credits;
 	__u16		rx_credits;
 
+	/* estimated available receive buffer space or -1 if unknown */
+	ssize_t		rx_avail;
+
 	__u8		tx_state;
 	__u8		rx_state;
 
@@ -688,10 +691,15 @@ struct l2cap_user {
 /* ----- L2CAP socket info ----- */
 #define l2cap_pi(sk) ((struct l2cap_pinfo *) sk)
 
+struct l2cap_rx_busy {
+	struct list_head	list;
+	struct sk_buff		*skb;
+};
+
 struct l2cap_pinfo {
 	struct bt_sock		bt;
 	struct l2cap_chan	*chan;
-	struct sk_buff		*rx_busy_skb;
+	struct list_head	rx_busy;
 };
 
 enum {
@@ -949,6 +957,7 @@ int l2cap_chan_connect(struct l2cap_chan *chan, __le16 psm, u16 cid,
 int l2cap_chan_reconfigure(struct l2cap_chan *chan, __u16 mtu);
 int l2cap_chan_send(struct l2cap_chan *chan, struct msghdr *msg, size_t len);
 void l2cap_chan_busy(struct l2cap_chan *chan, int busy);
+void l2cap_chan_rx_avail(struct l2cap_chan *chan, ssize_t rx_avail);
 int l2cap_chan_check_security(struct l2cap_chan *chan, bool initiator);
 void l2cap_chan_set_defaults(struct l2cap_chan *chan);
 int l2cap_ertm_init(struct l2cap_chan *chan);