[PATCH 0/2] [RFT] [DCCP]: Bug fix and a new sending-policy interface

[PATCH 0/2] [RFT] [DCCP]: Bug fix and a new sending-policy interface

[Gerrit Renker]

One bug fix and a new packet dequeuing interface for DCCP developed by
Tomasz Grobelny, which has been discussed on dccp@vger.

Patch #1: Bug fix for CCID-3 (ported to CCID-4, too), where a too high t_delta
          (RFC 3448, 4.6) was used. Analysis shows that the t_delta socket 
	  field is not meaningful, it is replaced by an appropriate constant.

Patch #2: Provides a new basis/interface for sending packets, allowing the
          user to set different send policies. This is especially interesting
	  for multimedia applications which have to interact with the congestion
	  control part of DCCP, where packets may be have different priorities
	  (I/P/B video frames, re-synch frames) and may be subject to a
	  playout.


Test tree disclaimer: 
=====================
All patches are eventually meant for mainline but are kept in the DCCP test
tree for testing and possible improvement. Comments and in particular testing
are therefore especially welcome.

The DCCP test tree contains the most recent bug fixes and code updates. The
attribute `test' does not indicate minor quality - all patches have been 
checked, the entire tree is fully bisectable and has been compile-tested on
several different platforms.

It can be checked out from
	git://eden-feed.erg.abdn.ac.uk/dccp_exp
	-> subtree `dccp' for DCCP test tree
	-> subtree `ccid4' for CCID-4 subtree

Further information is on
http://www.linux-foundation.org/en/Net:DCCP_Testing#Experimental_DCCP_source_tree


The University of Aberdeen is a charity registered in Scotland, No SC013683.

[PATCH 1/2] [RFT] [CCID-3]: Bug fix for the inter-packet scheduling algorithm

[Gerrit Renker]

This fixes a subtle bug in the calculation of the inter-packet gap and shows
that t_delta, as it is currently used, is not needed. And hence replaced.

The algorithm from RFC 3448, 4.6 below continually computes a send time t_nom,
which is initialised with the current time t_now; t_gran = 1E6 / HZ specifies
the scheduling granularity, s the packet size, and X the sending rate:

  t_distance = t_nom - t_now;		// in microseconds
  t_delta    = min(t_ipi, t_gran) / 2;	// `delta' parameter in microseconds

  if (t_distance >= t_delta) {
	reschedule after (t_distance / 1000) milliseconds;
  } else {
  	t_ipi  = s / X;			// inter-packet interval in usec
	t_nom += t_ipi;			// compute the next send time
	send packet now;
  }


1) Description of the bug
-------------------------
Rescheduling requires a conversion into milliseconds, due to this call chain:

 * ccid3_hc_tx_send_packet() returns a timeout in milliseconds,
 * this value is converted by msecs_to_jiffies() in dccp_write_xmit(),
 * and finally used as jiffy-expires-value for sk_reset_timer().

The highest jiffy resolution with HZ=1000 is 1 millisecond, so using a higher
granularity does not seem to make much sense here.

As a consequence, values of t_distance < 1000 are truncated to 0. This issue
has so far been resolved by using instead

  if (t_distance >= t_delta + 1000)
	reschedule after (t_distance / 1000) milliseconds;

The bug is in artificially inflating t_delta to t_delta' = t_delta + 1000. This
is unnecessarily large, a more adequate value is t_delta' = max(t_delta, 1000).


2) Consequences of using the corrected t_delta'
-----------------------------------------------
Since t_delta <= t_gran/2 = 10^6/(2*HZ), we have t_delta <= 1000 as long as
HZ >= 500. This means that t_delta' = max(1000, t_delta) is constant at 1000.

On the other hand, when using a coarse HZ value of HZ < 500, we have three
sub-cases that can all be reduced to using another constant of t_gran/2.

 (a) The first case arises when t_ipi > t_gran. Here t_delta' is the constant
     t_delta' = max(1000, t_gran/2) = t_gran/2.

 (b) If t_ipi <= 2000 < t_gran = 10^6/HZ usec, then t_delta = t_ipi/2 <= 1000,
     so that t_delta' = max(1000, t_delta) = 1000 < t_gran/2.

 (c) If 2000 < t_ipi <= t_gran, we have t_delta' = max(t_delta, 1000) = t_ipi/2.

In the second and third cases we have delay values less than t_gran/2, which is
in the order of less than or equal to half a jiffy.

How these are treated depends on how fractions of a jiffy are handled: they
are either always rounded down to 0, or always rounded up to 1 jiffy (assuming
non-zero values). In both cases the error is on average in the order of 50%.

Thus we are not increasing the error when in the second/third case we replace
a value less than t_gran/2 with 0, by setting t_delta' to the constant t_gran/2.


3) Summary
----------
Fixing (1) and considering (2), the patch replaces t_delta with a constant,
whose value depends on CONFIG_HZ, changing the above algorithm to:

  if (t_distance >= t_delta')
	reschedule after (t_distance / 1000) milliseconds;

where t_delta' = 10^6/(2*HZ) if HZ < 500, and t_delta' = 1000 otherwise.

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
---
 net/dccp/ccids/ccid3.h |   19 ++++++++++++++-----
 net/dccp/ccids/ccid3.c |   17 +++++++----------
 2 files changed, 21 insertions(+), 15 deletions(-)

--- a/net/dccp/ccids/ccid3.h
+++ b/net/dccp/ccids/ccid3.h
@@ -47,12 +47,23 @@
 /* Two seconds as per RFC 3448 4.2 */
 #define TFRC_INITIAL_TIMEOUT	   (2 * USEC_PER_SEC)
 
-/* In usecs - half the scheduling granularity as per RFC3448 4.6 */
-#define TFRC_OPSYS_HALF_TIME_GRAN  (USEC_PER_SEC / (2 * HZ))
-
 /* Parameter t_mbi from [RFC 3448, 4.3]: backoff interval in seconds */
 #define TFRC_T_MBI		   64
 
+/*
+ * The t_delta parameter (RFC 3448, 4.6): delays of less than %USEC_PER_MSEC are
+ * rounded down to 0, since sk_reset_timer() here uses millisecond granularity.
+ * Hence we can use a constant t_delta = %USEC_PER_MSEC when HZ >= 500. A coarse
+ * resolution of HZ < 500 means that the error is below one timer tick (t_gran)
+ * when using the constant t_delta  =  t_gran / 2  =  %USEC_PER_SEC / (2 * HZ).
+ */
+#if (HZ >= 500)
+# define TFRC_T_DELTA		   USEC_PER_MSEC
+#else
+# define TFRC_T_DELTA		   USEC_PER_SEC / (2 * HZ)
+# warning Coarse CONFIG_HZ resolution -- higher value recommended for CCID-3.
+#endif
+
 enum ccid3_options {
 	TFRC_OPT_LOSS_EVENT_RATE = 192,
 	TFRC_OPT_LOSS_INTERVALS	 = 193,
@@ -83,7 +94,6 @@ enum ccid3_hc_tx_states {
  * @no_feedback_timer - Handle to no feedback timer
  * @t_ld - Time last doubled during slow start
  * @t_nom - Nominal send time of next packet
- * @delta - Send timer delta (RFC 3448, 4.6) in usecs
  * @hist - Packet history
  */
 struct ccid3_hc_tx_sock {
@@ -101,7 +111,6 @@ struct ccid3_hc_tx_sock {
 	struct timer_list		no_feedback_timer;
 	ktime_t				t_ld;
 	ktime_t				t_nom;
-	u32				delta;
 	struct tfrc_tx_hist_entry	*hist;
 };
 
--- a/net/dccp/ccids/ccid3.c
+++ b/net/dccp/ccids/ccid3.c
@@ -90,19 +90,16 @@ static inline u64 rfc3390_initial_rate(struct sock *sk)
 	return scaled_div(w_init << 6, hctx->rtt);
 }
 
-/*
- * Recalculate t_ipi and delta (should be called whenever X changes)
+/**
+ * ccid3_update_send_interval  -  Calculate new t_ipi = s / X_inst
+ * This respects the granularity of X_inst (64 * bytes/second).
  */
 static void ccid3_update_send_interval(struct ccid3_hc_tx_sock *hctx)
 {
-	/* Calculate new t_ipi = s / X_inst (X_inst is in 64 * bytes/second) */
 	hctx->t_ipi = scaled_div32(((u64)hctx->s) << 6, hctx->x);
 
-	/* Calculate new delta by delta = min(t_ipi / 2, t_gran / 2) */
-	hctx->delta = min_t(u32, hctx->t_ipi / 2, TFRC_OPSYS_HALF_TIME_GRAN);
-
-	ccid3_pr_debug("t_ipi=%u, delta=%u, s=%u, X=%u\n", hctx->t_ipi,
-		       hctx->delta, hctx->s, (unsigned)(hctx->x >> 6));
+	ccid3_pr_debug("t_ipi=%u, s=%u, X=%u\n", hctx->t_ipi,
+		       hctx->s, (unsigned)(hctx->x >> 6));
 }
 
 static u32 ccid3_hc_tx_idle_rtt(struct ccid3_hc_tx_sock *hctx, ktime_t now)
@@ -336,8 +333,8 @@ static int ccid3_hc_tx_send_packet(struct sock *sk, struct sk_buff *skb)
 		 * else
 		 *       // send the packet in (t_nom - t_now) milliseconds.
 		 */
-		if (delay - (s64)hctx->delta >= 1000)
-			return (u32)delay / 1000L;
+		if (delay >= TFRC_T_DELTA)
+			return (u32)delay / USEC_PER_MSEC;
 
 		ccid3_hc_tx_update_win_count(hctx, now);
 	}


The University of Aberdeen is a charity registered in Scotland, No SC013683.

[PATCH 2/2] [RFT] [DCCP]: Policy-based packet dequeueing

[Gerrit Renker]

From: Tomasz Grobelny <tomasz@grobelny.oswiecenia.net>

This patch adds a generic infrastructure for policy-based dequeueing of 
TX packets and provides two policies:
 * a simple FIFO policy (which is the default) and
 * a priority based policy (set via socket options).
Both policies honour the tx_qlen sysctl for the maximum size of the write
queue (can be overridden via socket options). 

The priority policy uses skb->priority internally to assign an u32 priority
identifier, using the same ranking as SO_PRIORITY. The skb->priority field
is set to 0 when the packet leaves DCCP. The priority is supplied as ancillary
data using cmsg(3), the patch also provides the requisite parsing routines.

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
---
 Documentation/networking/dccp.txt |   19 +++++
 include/linux/dccp.h              |   19 +++++
 net/dccp/Makefile                 |    2 
 net/dccp/dccp.h                   |   12 +++
 net/dccp/output.c                 |    7 --
 net/dccp/proto.c                  |   67 +++++++++++++++++++-
 net/dccp/qpolicy.c                |  126 ++++++++++++++++++++++++++++++++++++++
 7 files changed, 244 insertions(+), 8 deletions(-)

--- a/Documentation/networking/dccp.txt
+++ b/Documentation/networking/dccp.txt
@@ -45,6 +45,25 @@ http://linux-net.osdl.org/index.php/DCCP
 
 Socket options
 ==============
+DCCP_SOCKOPT_QPOLICY_ID sets the dequeuing policy for outgoing packets. It takes
+a policy ID as argument and can only be set before the connection (i.e. changes
+during an established connection are not supported). Currently, two policies are
+defined: the "simple" policy (DCCPQ_POLICY_SIMPLE), which does nothing special,
+and a priority-based variant (DCCPQ_POLICY_PRIO). The latter allows to pass an
+u32 priority value as ancillary data to sendmsg(), where higher numbers indicate
+a higher packet priority (similar to SO_PRIORITY). This ancillary data needs to
+be formatted using a cmsg(3) message header filled in as follows:
+	cmsg->cmsg_level = SOL_DCCP;
+	cmsg->cmsg_type	 = DCCP_SCM_PRIORITY;
+	cmsg->cmsg_len	 = CMSG_LEN(sizeof(uint32_t));	/* or CMSG_LEN(4) */
+
+DCCP_SOCKOPT_QPOLICY_TXQLEN sets the maximum length of the output queue. A zero
+value is always interpreted as unbounded queue length. If different from zero,
+the interpretation of this parameter depends on the current dequeuing policy
+(see above): the "simple" policy will enforce a fixed queue size by returning
+EAGAIN, whereas the "prio" policy enforces a fixed queue length by dropping the
+lowest-priority packet first. The default value for this parameter is
+initialised from /proc/sys/net/dccp/default/tx_qlen.
 
 DCCP_SOCKOPT_SERVICE sets the service. The specification mandates use of
 service codes (RFC 4340, sec. 8.1.2); if this socket option is not set,
--- a/net/dccp/dccp.h
+++ b/net/dccp/dccp.h
@@ -215,6 +215,18 @@ extern void dccp_reqsk_send_ack(struct s
 extern void dccp_send_sync(struct sock *sk, const u64 seq,
 			   const enum dccp_pkt_type pkt_type);
 
+/*
+ * TX Packet Dequeueing Interface
+ */
+extern void		dccp_qpolicy_push(struct sock *sk, struct sk_buff *skb);
+extern bool		dccp_qpolicy_full(struct sock *sk);
+extern void		dccp_qpolicy_drop(struct sock *sk, struct sk_buff *skb);
+extern struct sk_buff	*dccp_qpolicy_top(struct sock *sk);
+extern struct sk_buff	*dccp_qpolicy_pop(struct sock *sk);
+
+/*
+ * TX Packet Output and TX Timers
+ */
 extern void dccp_write_xmit(struct sock *sk);
 extern void dccp_write_space(struct sock *sk);
 extern void dccp_flush_write_queue(struct sock *sk, long *time_budget);
--- a/net/dccp/Makefile
+++ b/net/dccp/Makefile
@@ -1,7 +1,7 @@
 obj-$(CONFIG_IP_DCCP) += dccp.o dccp_ipv4.o
 
 dccp-y := ccid.o feat.o input.o minisocks.o options.o \
-	  output.o proto.o timer.o ackvec.o
+	  qpolicy.o output.o proto.o timer.o ackvec.o
 
 dccp_ipv4-y := ipv4.o
 
--- /dev/null
+++ b/net/dccp/qpolicy.c
@@ -0,0 +1,126 @@
+/*
+ *  net/dccp/qpolicy.c
+ *
+ *  Policy-based packet dequeueing interface for DCCP.
+ *
+ *  Copyright (c) 2008 Tomasz Grobelny <tomasz@grobelny.oswiecenia.net>
+ *
+ *  This program is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU General Public License v2
+ *  as published by the Free Software Foundation.
+ */
+#include "dccp.h"
+
+/*
+ *	Simple Dequeueing Policy:
+ *	If tx_qlen is different from 0, enqueue up to tx_qlen elements.
+ */
+static void qpolicy_simple_push(struct sock *sk, struct sk_buff *skb)
+{
+	skb_queue_tail(&sk->sk_write_queue, skb);
+}
+
+static bool qpolicy_simple_full(struct sock *sk)
+{
+	return dccp_sk(sk)->dccps_tx_qlen &&
+	       sk->sk_write_queue.qlen >= dccp_sk(sk)->dccps_tx_qlen;
+}
+
+static struct sk_buff *qpolicy_simple_top(struct sock *sk)
+{
+	return skb_peek(&sk->sk_write_queue);
+}
+
+/*
+ *	Priority-based Dequeueing Policy:
+ *	If tx_qlen is different from 0 and the queue has reached its upper bound
+ *	of tx_qlen elements, replace older packets lowest-priority-first.
+ */
+static struct sk_buff *qpolicy_prio_best_skb(struct sock *sk)
+{
+	struct sk_buff *skb, *best = NULL;
+
+	skb_queue_walk(&sk->sk_write_queue, skb)
+		if (best == NULL || skb->priority > best->priority)
+			best = skb;
+	return best;
+}
+
+static struct sk_buff *qpolicy_prio_worst_skb(struct sock *sk)
+{
+	struct sk_buff *skb, *worst = NULL;
+
+	skb_queue_walk(&sk->sk_write_queue, skb)
+		if (worst == NULL || skb->priority < worst->priority)
+			worst = skb;
+	return worst;
+}
+
+static bool qpolicy_prio_full(struct sock *sk)
+{
+	if (qpolicy_simple_full(sk))
+		dccp_qpolicy_drop(sk, qpolicy_prio_worst_skb(sk));
+	return false;
+}
+
+/**
+ * struct dccp_qpolicy_operations  -  TX Packet Dequeueing Interface
+ * @push: add a new @skb to the write queue
+ * @full: indicates that no more packets will be admitted
+ * @top:  peeks at whatever the queueing policy defines as its `top'
+ */
+static struct dccp_qpolicy_operations {
+	void		(*push)	(struct sock *sk, struct sk_buff *skb);
+	bool		(*full) (struct sock *sk);
+	struct sk_buff*	(*top)  (struct sock *sk);
+
+} qpol_table[DCCPQ_POLICY_MAX] = {
+	[DCCPQ_POLICY_SIMPLE] = {
+		.push = qpolicy_simple_push,
+		.full = qpolicy_simple_full,
+		.top  = qpolicy_simple_top,
+	},
+	[DCCPQ_POLICY_PRIO] = {
+		.push = qpolicy_simple_push,
+		.full = qpolicy_prio_full,
+		.top  = qpolicy_prio_best_skb,
+	},
+};
+
+/*
+ *	Externally visible interface
+ */
+void dccp_qpolicy_push(struct sock *sk, struct sk_buff *skb)
+{
+	qpol_table[dccp_sk(sk)->dccps_qpolicy].push(sk, skb);
+}
+
+bool dccp_qpolicy_full(struct sock *sk)
+{
+	return qpol_table[dccp_sk(sk)->dccps_qpolicy].full(sk);
+}
+
+void dccp_qpolicy_drop(struct sock *sk, struct sk_buff *skb)
+{
+	if (skb != NULL) {
+		skb_unlink(skb, &sk->sk_write_queue);
+		kfree_skb(skb);
+	}
+}
+
+struct sk_buff *dccp_qpolicy_top(struct sock *sk)
+{
+	return qpol_table[dccp_sk(sk)->dccps_qpolicy].top(sk);
+}
+
+struct sk_buff *dccp_qpolicy_pop(struct sock *sk)
+{
+	struct sk_buff *skb = dccp_qpolicy_top(sk);
+
+	/* Clear any skb fields that we used internally */
+	skb->priority = 0;
+
+	if (skb)
+		skb_unlink(skb, &sk->sk_write_queue);
+	return skb;
+}
--- a/net/dccp/output.c
+++ b/net/dccp/output.c
@@ -238,7 +238,7 @@ static void dccp_xmit_packet(struct sock
 {
 	int err, len;
 	struct dccp_sock *dp = dccp_sk(sk);
-	struct sk_buff *skb = skb_dequeue(&sk->sk_write_queue);
+	struct sk_buff *skb = dccp_qpolicy_pop(sk);
 
 	if (unlikely(skb == NULL))
 		return;
@@ -328,7 +328,7 @@ void dccp_write_xmit(struct sock *sk)
 	struct dccp_sock *dp = dccp_sk(sk);
 	struct sk_buff *skb;
 
-	while ((skb = skb_peek(&sk->sk_write_queue))) {
+	while ((skb = dccp_qpolicy_top(sk))) {
 		int rc = ccid_hc_tx_send_packet(dp->dccps_hc_tx_ccid, sk, skb);
 
 		switch (ccid_packet_dequeue_eval(rc)) {
@@ -342,8 +342,7 @@ void dccp_write_xmit(struct sock *sk)
 			dccp_xmit_packet(sk);
 			break;
 		case CCID_PACKET_ERR:
-			skb_dequeue(&sk->sk_write_queue);
-			kfree_skb(skb);
+			dccp_qpolicy_drop(sk, skb);
 			dccp_pr_debug("packet discarded due to err=%d\n", rc);
 		}
 	}
--- a/include/linux/dccp.h
+++ b/include/linux/dccp.h
@@ -195,6 +195,19 @@ enum dccp_feature_numbers {
 	DCCPF_MAX_CCID_SPECIFIC = 255,
 };
 
+/* DCCP socket control message types for cmsg */
+enum dccp_cmsg_type {
+	DCCP_SCM_PRIORITY = 1,
+	DCCP_SCM_MAX
+};
+
+/* DCCP priorities for outgoing/queued packets */
+enum dccp_packet_dequeueing_policy {
+	DCCPQ_POLICY_SIMPLE,
+	DCCPQ_POLICY_PRIO,
+	DCCPQ_POLICY_MAX
+};
+
 /* DCCP socket options */
 #define DCCP_SOCKOPT_PACKET_SIZE	1 /* XXX deprecated, without effect */
 #define DCCP_SOCKOPT_SERVICE		2
@@ -208,6 +221,8 @@ enum dccp_feature_numbers {
 #define DCCP_SOCKOPT_CCID		13
 #define DCCP_SOCKOPT_TX_CCID		14
 #define DCCP_SOCKOPT_RX_CCID		15
+#define DCCP_SOCKOPT_QPOLICY_ID		16
+#define DCCP_SOCKOPT_QPOLICY_TXQLEN	17
 #define DCCP_SOCKOPT_CCID_RX_INFO	128
 #define DCCP_SOCKOPT_CCID_TX_INFO	192
 
@@ -459,6 +474,8 @@ struct dccp_ackvec;
  * @dccps_hc_rx_ccid - CCID used for the receiver (or receiving half-connection)
  * @dccps_hc_tx_ccid - CCID used for the sender (or sending half-connection)
  * @dccps_options_received - parsed set of retrieved options
+ * @dccps_qpolicy - TX dequeueing policy, one of %dccp_packet_dequeueing_policy
+ * @dccps_tx_qlen - maximum length of the TX queue
  * @dccps_role - role of this sock, one of %dccp_role
  * @dccps_hc_rx_insert_options - receiver wants to add options when acking
  * @dccps_hc_tx_insert_options - sender wants to add options when sending
@@ -501,6 +518,8 @@ struct dccp_sock {
 	struct ccid			*dccps_hc_rx_ccid;
 	struct ccid			*dccps_hc_tx_ccid;
 	struct dccp_options_received	dccps_options_received;
+	__u8				dccps_qpolicy;
+	__u32				dccps_tx_qlen;
 	enum dccp_role			dccps_role:2;
 	__u8				dccps_hc_rx_insert_options:1;
 	__u8				dccps_hc_tx_insert_options:1;
--- a/net/dccp/proto.c
+++ b/net/dccp/proto.c
@@ -186,6 +186,7 @@ int dccp_init_sock(struct sock *sk, cons
 	dp->dccps_rate_last	= jiffies;
 	dp->dccps_role		= DCCP_ROLE_UNDEFINED;
 	dp->dccps_service	= DCCP_SERVICE_CODE_IS_ABSENT;
+	dp->dccps_tx_qlen	= sysctl_dccp_tx_qlen;
 
 	INIT_LIST_HEAD(&dp->dccps_featneg);
 	/* control socket doesn't need feat nego */
@@ -539,6 +540,20 @@ static int do_dccp_setsockopt(struct soc
 	case DCCP_SOCKOPT_RECV_CSCOV:
 		err = dccp_setsockopt_cscov(sk, val, true);
 		break;
+	case DCCP_SOCKOPT_QPOLICY_ID:
+		if (sk->sk_state != DCCP_CLOSED)
+			err = -EISCONN;
+		else if (val < 0 || val >= DCCPQ_POLICY_MAX)
+			err = -EINVAL;
+		else
+			dp->dccps_qpolicy = val;
+		break;
+	case DCCP_SOCKOPT_QPOLICY_TXQLEN:
+		if (val < 0)
+			err = -EINVAL;
+		else
+			dp->dccps_tx_qlen = val;
+		break;
 	default:
 		err = -ENOPROTOOPT;
 		break;
@@ -642,6 +657,12 @@ static int do_dccp_getsockopt(struct soc
 	case DCCP_SOCKOPT_RECV_CSCOV:
 		val = dp->dccps_pcrlen;
 		break;
+	case DCCP_SOCKOPT_QPOLICY_ID:
+		val = dp->dccps_qpolicy;
+		break;
+	case DCCP_SOCKOPT_QPOLICY_TXQLEN:
+		val = dp->dccps_tx_qlen;
+		break;
 	case 128 ... 191:
 		return ccid_hc_rx_getsockopt(dp->dccps_hc_rx_ccid, sk, optname,
 					     len, (u32 __user *)optval, optlen);
@@ -684,6 +705,43 @@ int compat_dccp_getsockopt(struct sock *
 EXPORT_SYMBOL_GPL(compat_dccp_getsockopt);
 #endif
 
+static int dccp_msghdr_parse(struct msghdr *msg, struct sk_buff *skb)
+{
+	struct cmsghdr *cmsg = CMSG_FIRSTHDR(msg);
+
+	/*
+	 * Assign an (opaque) qpolicy priority value to skb->priority.
+	 *
+	 * We are overloading this skb field for use with the qpolicy subystem.
+	 * The skb->priority is normally used for the SO_PRIORITY option, which
+	 * is initialised from sk_priority. Since the assignment of sk_priority
+	 * to skb->priority happens later (on layer 3), we overload this field
+	 * for use with queueing priorities as long as the skb is on layer 4.
+	 * The default priority value (if nothing is set) is 0.
+	 */
+	skb->priority = 0;
+
+	for (; cmsg != NULL; cmsg = CMSG_NXTHDR(msg, cmsg)) {
+
+		if (!CMSG_OK(msg, cmsg))
+			return -EINVAL;
+
+		if (cmsg->cmsg_level != SOL_DCCP)
+			continue;
+
+		switch (cmsg->cmsg_type) {
+		case DCCP_SCM_PRIORITY:
+			if (cmsg->cmsg_len != CMSG_LEN(sizeof(__u32)))
+				return -EINVAL;
+			skb->priority = *(__u32 *)CMSG_DATA(cmsg);
+			break;
+		default:
+			return -EINVAL;
+		}
+	}
+	return 0;
+}
+
 int dccp_sendmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
 		 size_t len)
 {
@@ -699,8 +757,7 @@ int dccp_sendmsg(struct kiocb *iocb, str
 
 	lock_sock(sk);
 
-	if (sysctl_dccp_tx_qlen &&
-	    (sk->sk_write_queue.qlen >= sysctl_dccp_tx_qlen)) {
+	if (dccp_qpolicy_full(sk)) {
 		rc = -EAGAIN;
 		goto out_release;
 	}
@@ -728,7 +785,11 @@ int dccp_sendmsg(struct kiocb *iocb, str
 	if (rc != 0)
 		goto out_discard;
 
-	skb_queue_tail(&sk->sk_write_queue, skb);
+	rc = dccp_msghdr_parse(msg, skb);
+	if (rc != 0)
+		goto out_discard;
+
+	dccp_qpolicy_push(sk, skb);
 	dccp_write_xmit(sk);
 out_release:
 	release_sock(sk);


The University of Aberdeen is a charity registered in Scotland, No SC013683.

Re: [PATCH 2/2] [RFT] [DCCP]: Policy-based packet dequeueing

[Tomasz Grobelny]

Dnia Monday 12 of May 2008, napisałeś:
> From: Tomasz Grobelny <tomasz@grobelny.oswiecenia.net>
>
> This patch adds a generic infrastructure for policy-based dequeueing of
> TX packets and provides two policies:
>  * a simple FIFO policy (which is the default) and
>  * a priority based policy (set via socket options).
> Both policies honour the tx_qlen sysctl for the maximum size of the write
> queue (can be overridden via socket options).
>
> The priority policy uses skb->priority internally to assign an u32 priority
> identifier, using the same ranking as SO_PRIORITY. The skb->priority field
> is set to 0 when the packet leaves DCCP. The priority is supplied as
> ancillary data using cmsg(3), the patch also provides the requisite parsing
> routines.
>
> Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: Tomasz Grobelny <tomasz@grobelny.oswiecenia.net>

I hope that's how you sign off patches (I'm doing it for the first time).
-- 
Regards,
Tomasz Grobelny