dccp: Return-value convention of hc_tx_send_packet()

This patch reorganises the return value convention of the CCID TX sending
function, to permit more flexible schemes, as required by subsequent patches.

Currently the convention is
 * values < 0     mean error,
 * a value == 0   means "send now", and
 * a value x > 0  means "send in x milliseconds".

The patch provides symbolic constants and a function to interpret return values.

In addition, it caps the maximum positive return value to 0xFFFF milliseconds,
corresponding to 65.535 seconds.  This is possible since in CCID-3/4 the
maximum possible inter-packet gap is fixed at t_mbi = 64 sec.

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 31 insertions, 3 deletions

diff --git a/net/dccp/ccid.h b/net/dccp/ccid.h
index 117fb093dcaf..75c3582a7678 100644
--- a/net/dccp/ccid.h
+++ b/net/dccp/ccid.h
@@ -134,13 +134,41 @@ static inline int ccid_get_current_tx_ccid(struct dccp_sock *dp)
 extern void ccid_hc_rx_delete(struct ccid *ccid, struct sock *sk);
 extern void ccid_hc_tx_delete(struct ccid *ccid, struct sock *sk);
 
+/*
+ * Congestion control of queued data packets via CCID decision.
+ *
+ * The TX CCID performs its congestion-control by indicating whether and when a
+ * queued packet may be sent, using the return code of ccid_hc_tx_send_packet().
+ * The following modes are supported via the symbolic constants below:
+ * - timer-based pacing    (CCID returns a delay value in milliseconds);
+ * - autonomous dequeueing (CCID internally schedules dccps_xmitlet).
+ */
+
+enum ccid_dequeueing_decision {
+        CCID_PACKET_SEND_AT_ONCE =       0x00000,  /* "green light": no delay */
+        CCID_PACKET_DELAY_MAX =          0x0FFFF,  /* maximum delay in msecs  */
+        CCID_PACKET_DELAY =              0x10000,  /* CCID msec-delay mode */
+        CCID_PACKET_WILL_DEQUEUE_LATER = 0x20000,  /* CCID autonomous mode */
+        CCID_PACKET_ERR =                0xF0000,  /* error condition */
+};
+
+static inline int ccid_packet_dequeue_eval(const int return_code)
+{
+        if (return_code < 0)
+                return CCID_PACKET_ERR;
+        if (return_code == 0)
+                return CCID_PACKET_SEND_AT_ONCE;
+        if (return_code <= CCID_PACKET_DELAY_MAX)
+                return CCID_PACKET_DELAY;
+        return return_code;
+}
+
 static inline int ccid_hc_tx_send_packet(struct ccid *ccid, struct sock *sk,
                                          struct sk_buff *skb)
 {
-        int rc = 0;
         if (ccid->ccid_ops->ccid_hc_tx_send_packet != NULL)
-                rc = ccid->ccid_ops->ccid_hc_tx_send_packet(sk, skb);
-        return rc;
+                return ccid->ccid_ops->ccid_hc_tx_send_packet(sk, skb);
+        return CCID_PACKET_SEND_AT_ONCE;
 }
 
 static inline void ccid_hc_tx_packet_sent(struct ccid *ccid, struct sock *sk,