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 the maximum inter-packet gap is t_mbi = 64 sec.

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>

diff --git a/net/dccp/ccid.h b/net/dccp/ccid.h
index 430a3c24f9707c60a1e03768b032e38e12328e1f..d27054ba215973fc928fc462148e7c3cdfbbe3ea 100644 (file)
--- a/net/dccp/ccid.h
+++ b/net/dccp/ccid.h
@@ -129,13 +129,41 @@ 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,

diff --git a/net/dccp/ccids/ccid3.c b/net/dccp/ccids/ccid3.c
index 0751a8fa936aa81d8b78145dd5f37f40796722e6..0d406f82e4330244d925ed117a1eadc1c67517dd 100644 (file)
--- a/net/dccp/ccids/ccid3.c
+++ b/net/dccp/ccids/ccid3.c
@@ -269,11 +269,11 @@ out:
        sock_put(sk);
 }
 
-/*
- * returns
- *   > 0: delay (in msecs) that should pass before actually sending
- *   = 0: can send immediately
- *   < 0: error condition; do not send packet
+/**
+ * ccid3_hc_tx_send_packet  -  Delay-based dequeueing of TX packets
+ * @skb: next packet candidate to send on @sk
+ * This function uses the convention of ccid_packet_dequeue_eval() and
+ * returns a millisecond-delay value between 0 and t_mbi = 64000 msec.
  */
 static int ccid3_hc_tx_send_packet(struct sock *sk, struct sk_buff *skb)
 {
@@ -349,7 +349,7 @@ static int ccid3_hc_tx_send_packet(struct sock *sk, struct sk_buff *skb)
 
        /* set the nominal send time for the next following packet */
        hctx->t_nom = ktime_add_us(hctx->t_nom, hctx->t_ipi);
-       return 0;
+       return CCID_PACKET_SEND_AT_ONCE;
 }
 
 static void ccid3_hc_tx_packet_sent(struct sock *sk, unsigned int len)