1 files changed, 399 insertions, 200 deletions

diff --git a/net/dccp/ccids/lib/packet_history.c b/net/dccp/ccids/lib/packet_history.c
index 34c4f604772..20af1a69342 100644
--- a/net/dccp/ccids/lib/packet_history.c
+++ b/net/dccp/ccids/lib/packet_history.c
@@ -1,7 +1,8 @@
 /*
  *  net/dccp/packet_history.c
  *
- *  Copyright (c) 2005-6 The University of Waikato, Hamilton, New Zealand.
+ *  Copyright (c) 2007   The University of Aberdeen, Scotland, UK
+ *  Copyright (c) 2005-7 The University of Waikato, Hamilton, New Zealand.
  *
  *  An implementation of the DCCP protocol
  *
@@ -34,267 +35,465 @@
  *  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  */
 
-#include <linux/module.h>
 #include <linux/string.h>
+#include <linux/slab.h>
 #include "packet_history.h"
+#include "../../dccp.h"
+
+/**
+ *  tfrc_tx_hist_entry  -  Simple singly-linked TX history list
+ *  @next:  next oldest entry (LIFO order)
+ *  @seqno: sequence number of this entry
+ *  @stamp: send time of packet with sequence number @seqno
+ */
+struct tfrc_tx_hist_entry {
+	struct tfrc_tx_hist_entry *next;
+	u64			  seqno;
+	ktime_t			  stamp;
+};
 
 /*
- * 	Transmitter History Routines
+ * Transmitter History Routines
  */
-struct dccp_tx_hist *dccp_tx_hist_new(const char *name)
+static struct kmem_cache *tfrc_tx_hist_slab;
+
+int __init tfrc_tx_packet_history_init(void)
 {
-	struct dccp_tx_hist *hist = kmalloc(sizeof(*hist), GFP_ATOMIC);
-	static const char dccp_tx_hist_mask[] = "tx_hist_%s";
-	char *slab_name;
-
-	if (hist == NULL)
-		goto out;
-
-	slab_name = kmalloc(strlen(name) + sizeof(dccp_tx_hist_mask) - 1,
-			    GFP_ATOMIC);
-	if (slab_name == NULL)
-		goto out_free_hist;
-
-	sprintf(slab_name, dccp_tx_hist_mask, name);
-	hist->dccptxh_slab = kmem_cache_create(slab_name,
-					     sizeof(struct dccp_tx_hist_entry),
-					       0, SLAB_HWCACHE_ALIGN,
-					       NULL);
-	if (hist->dccptxh_slab == NULL)
-		goto out_free_slab_name;
-out:
-	return hist;
-out_free_slab_name:
-	kfree(slab_name);
-out_free_hist:
-	kfree(hist);
-	hist = NULL;
-	goto out;
+	tfrc_tx_hist_slab = kmem_cache_create("tfrc_tx_hist",
+					      sizeof(struct tfrc_tx_hist_entry),
+					      0, SLAB_HWCACHE_ALIGN, NULL);
+	return tfrc_tx_hist_slab == NULL ? -ENOBUFS : 0;
 }
 
-EXPORT_SYMBOL_GPL(dccp_tx_hist_new);
-
-void dccp_tx_hist_delete(struct dccp_tx_hist *hist)
+void tfrc_tx_packet_history_exit(void)
 {
-	const char* name = kmem_cache_name(hist->dccptxh_slab);
-
-	kmem_cache_destroy(hist->dccptxh_slab);
-	kfree(name);
-	kfree(hist);
+	if (tfrc_tx_hist_slab != NULL) {
+		kmem_cache_destroy(tfrc_tx_hist_slab);
+		tfrc_tx_hist_slab = NULL;
+	}
 }
 
-EXPORT_SYMBOL_GPL(dccp_tx_hist_delete);
-
-struct dccp_tx_hist_entry *
-	dccp_tx_hist_find_entry(const struct list_head *list, const u64 seq)
+static struct tfrc_tx_hist_entry *
+	tfrc_tx_hist_find_entry(struct tfrc_tx_hist_entry *head, u64 seqno)
 {
-	struct dccp_tx_hist_entry *packet = NULL, *entry;
-
-	list_for_each_entry(entry, list, dccphtx_node)
-		if (entry->dccphtx_seqno == seq) {
-			packet = entry;
-			break;
-		}
+	while (head != NULL && head->seqno != seqno)
+		head = head->next;
 
-	return packet;
+	return head;
 }
 
-EXPORT_SYMBOL_GPL(dccp_tx_hist_find_entry);
+int tfrc_tx_hist_add(struct tfrc_tx_hist_entry **headp, u64 seqno)
+{
+	struct tfrc_tx_hist_entry *entry = kmem_cache_alloc(tfrc_tx_hist_slab, gfp_any());
+
+	if (entry == NULL)
+		return -ENOBUFS;
+	entry->seqno = seqno;
+	entry->stamp = ktime_get_real();
+	entry->next  = *headp;
+	*headp	     = entry;
+	return 0;
+}
+EXPORT_SYMBOL_GPL(tfrc_tx_hist_add);
 
-void dccp_tx_hist_purge(struct dccp_tx_hist *hist, struct list_head *list)
+void tfrc_tx_hist_purge(struct tfrc_tx_hist_entry **headp)
 {
-	struct dccp_tx_hist_entry *entry, *next;
+	struct tfrc_tx_hist_entry *head = *headp;
+
+	while (head != NULL) {
+		struct tfrc_tx_hist_entry *next = head->next;
 
-	list_for_each_entry_safe(entry, next, list, dccphtx_node) {
-		list_del_init(&entry->dccphtx_node);
-		dccp_tx_hist_entry_delete(hist, entry);
+		kmem_cache_free(tfrc_tx_hist_slab, head);
+		head = next;
 	}
-}
 
-EXPORT_SYMBOL_GPL(dccp_tx_hist_purge);
+	*headp = NULL;
+}
+EXPORT_SYMBOL_GPL(tfrc_tx_hist_purge);
 
-void dccp_tx_hist_purge_older(struct dccp_tx_hist *hist,
-			      struct list_head *list,
-			      struct dccp_tx_hist_entry *packet)
+u32 tfrc_tx_hist_rtt(struct tfrc_tx_hist_entry *head, const u64 seqno,
+		     const ktime_t now)
 {
-	struct dccp_tx_hist_entry *next;
+	u32 rtt = 0;
+	struct tfrc_tx_hist_entry *packet = tfrc_tx_hist_find_entry(head, seqno);
 
-	list_for_each_entry_safe_continue(packet, next, list, dccphtx_node) {
-		list_del_init(&packet->dccphtx_node);
-		dccp_tx_hist_entry_delete(hist, packet);
+	if (packet != NULL) {
+		rtt = ktime_us_delta(now, packet->stamp);
+		/*
+		 * Garbage-collect older (irrelevant) entries:
+		 */
+		tfrc_tx_hist_purge(&packet->next);
 	}
+
+	return rtt;
 }
+EXPORT_SYMBOL_GPL(tfrc_tx_hist_rtt);
 
-EXPORT_SYMBOL_GPL(dccp_tx_hist_purge_older);
 
 /*
  * 	Receiver History Routines
  */
-struct dccp_rx_hist *dccp_rx_hist_new(const char *name)
+static struct kmem_cache *tfrc_rx_hist_slab;
+
+int __init tfrc_rx_packet_history_init(void)
 {
-	struct dccp_rx_hist *hist = kmalloc(sizeof(*hist), GFP_ATOMIC);
-	static const char dccp_rx_hist_mask[] = "rx_hist_%s";
-	char *slab_name;
-
-	if (hist == NULL)
-		goto out;
-
-	slab_name = kmalloc(strlen(name) + sizeof(dccp_rx_hist_mask) - 1,
-			    GFP_ATOMIC);
-	if (slab_name == NULL)
-		goto out_free_hist;
-
-	sprintf(slab_name, dccp_rx_hist_mask, name);
-	hist->dccprxh_slab = kmem_cache_create(slab_name,
-					     sizeof(struct dccp_rx_hist_entry),
-					       0, SLAB_HWCACHE_ALIGN,
-					       NULL);
-	if (hist->dccprxh_slab == NULL)
-		goto out_free_slab_name;
-out:
-	return hist;
-out_free_slab_name:
-	kfree(slab_name);
-out_free_hist:
-	kfree(hist);
-	hist = NULL;
-	goto out;
+	tfrc_rx_hist_slab = kmem_cache_create("tfrc_rxh_cache",
+					      sizeof(struct tfrc_rx_hist_entry),
+					      0, SLAB_HWCACHE_ALIGN, NULL);
+	return tfrc_rx_hist_slab == NULL ? -ENOBUFS : 0;
 }
 
-EXPORT_SYMBOL_GPL(dccp_rx_hist_new);
+void tfrc_rx_packet_history_exit(void)
+{
+	if (tfrc_rx_hist_slab != NULL) {
+		kmem_cache_destroy(tfrc_rx_hist_slab);
+		tfrc_rx_hist_slab = NULL;
+	}
+}
 
-void dccp_rx_hist_delete(struct dccp_rx_hist *hist)
+static inline void tfrc_rx_hist_entry_from_skb(struct tfrc_rx_hist_entry *entry,
+					       const struct sk_buff *skb,
+					       const u32 ndp)
 {
-	const char* name = kmem_cache_name(hist->dccprxh_slab);
+	const struct dccp_hdr *dh = dccp_hdr(skb);
 
-	kmem_cache_destroy(hist->dccprxh_slab);
-	kfree(name);
-	kfree(hist);
+	entry->tfrchrx_seqno = DCCP_SKB_CB(skb)->dccpd_seq;
+	entry->tfrchrx_ccval = dh->dccph_ccval;
+	entry->tfrchrx_type  = dh->dccph_type;
+	entry->tfrchrx_ndp   = ndp;
+	entry->tfrchrx_tstamp = ktime_get_real();
 }
 
-EXPORT_SYMBOL_GPL(dccp_rx_hist_delete);
+void tfrc_rx_hist_add_packet(struct tfrc_rx_hist *h,
+			     const struct sk_buff *skb,
+			     const u32 ndp)
+{
+	struct tfrc_rx_hist_entry *entry = tfrc_rx_hist_last_rcv(h);
+
+	tfrc_rx_hist_entry_from_skb(entry, skb, ndp);
+}
+EXPORT_SYMBOL_GPL(tfrc_rx_hist_add_packet);
 
-int dccp_rx_hist_find_entry(const struct list_head *list, const u64 seq,
-			    u8 *ccval)
+/* has the packet contained in skb been seen before? */
+int tfrc_rx_hist_duplicate(struct tfrc_rx_hist *h, struct sk_buff *skb)
 {
-	struct dccp_rx_hist_entry *packet = NULL, *entry;
+	const u64 seq = DCCP_SKB_CB(skb)->dccpd_seq;
+	int i;
 
-	list_for_each_entry(entry, list, dccphrx_node)
-		if (entry->dccphrx_seqno == seq) {
-			packet = entry;
-			break;
-		}
+	if (dccp_delta_seqno(tfrc_rx_hist_loss_prev(h)->tfrchrx_seqno, seq) <= 0)
+		return 1;
 
-	if (packet)
-		*ccval = packet->dccphrx_ccval;
+	for (i = 1; i <= h->loss_count; i++)
+		if (tfrc_rx_hist_entry(h, i)->tfrchrx_seqno == seq)
+			return 1;
 
-	return packet != NULL;
+	return 0;
 }
+EXPORT_SYMBOL_GPL(tfrc_rx_hist_duplicate);
 
-EXPORT_SYMBOL_GPL(dccp_rx_hist_find_entry);
-struct dccp_rx_hist_entry *
-		dccp_rx_hist_find_data_packet(const struct list_head *list)
+static void tfrc_rx_hist_swap(struct tfrc_rx_hist *h, const u8 a, const u8 b)
 {
-	struct dccp_rx_hist_entry *entry, *packet = NULL;
-
-	list_for_each_entry(entry, list, dccphrx_node)
-		if (entry->dccphrx_type == DCCP_PKT_DATA ||
-		    entry->dccphrx_type == DCCP_PKT_DATAACK) {
-			packet = entry;
-			break;
-		}
+	const u8 idx_a = tfrc_rx_hist_index(h, a),
+		 idx_b = tfrc_rx_hist_index(h, b);
+	struct tfrc_rx_hist_entry *tmp = h->ring[idx_a];
 
-	return packet;
+	h->ring[idx_a] = h->ring[idx_b];
+	h->ring[idx_b] = tmp;
 }
 
-EXPORT_SYMBOL_GPL(dccp_rx_hist_find_data_packet);
+/*
+ * Private helper functions for loss detection.
+ *
+ * In the descriptions, `Si' refers to the sequence number of entry number i,
+ * whose NDP count is `Ni' (lower case is used for variables).
+ * Note: All __after_loss functions expect that a test against duplicates has
+ *       been performed already: the seqno of the skb must not be less than the
+ *       seqno of loss_prev; and it must not equal that of any valid hist_entry.
+ */
+static void __one_after_loss(struct tfrc_rx_hist *h, struct sk_buff *skb, u32 n2)
+{
+	u64 s0 = tfrc_rx_hist_loss_prev(h)->tfrchrx_seqno,
+	    s1 = tfrc_rx_hist_entry(h, 1)->tfrchrx_seqno,
+	    s2 = DCCP_SKB_CB(skb)->dccpd_seq;
+	int n1 = tfrc_rx_hist_entry(h, 1)->tfrchrx_ndp,
+	   d12 = dccp_delta_seqno(s1, s2), d2;
+
+	if (d12 > 0) {			/* S1  <  S2 */
+		h->loss_count = 2;
+		tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_entry(h, 2), skb, n2);
+		return;
+	}
+
+	/* S0  <  S2  <  S1 */
+	d2 = dccp_delta_seqno(s0, s2);
 
-void dccp_rx_hist_add_packet(struct dccp_rx_hist *hist,
-			    struct list_head *rx_list,
-			    struct list_head *li_list,
-			    struct dccp_rx_hist_entry *packet,
-			    u64 nonloss_seqno)
+	if (d2 == 1 || n2 >= d2) {	/* S2 is direct successor of S0 */
+		int d21 = -d12;
+
+		if (d21 == 1 || n1 >= d21) {
+			/* hole is filled: S0, S2, and S1 are consecutive */
+			h->loss_count = 0;
+			h->loss_start = tfrc_rx_hist_index(h, 1);
+		} else
+			/* gap between S2 and S1: just update loss_prev */
+			tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_loss_prev(h), skb, n2);
+
+	} else {			/* hole between S0 and S2 */
+		/*
+		 * Reorder history to insert S2 between S0 and s1
+		 */
+		tfrc_rx_hist_swap(h, 0, 3);
+		h->loss_start = tfrc_rx_hist_index(h, 3);
+		tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_entry(h, 1), skb, n2);
+		h->loss_count = 2;
+	}
+}
+
+/* return 1 if a new loss event has been identified */
+static int __two_after_loss(struct tfrc_rx_hist *h, struct sk_buff *skb, u32 n3)
 {
-	struct dccp_rx_hist_entry *entry, *next;
-	u8 num_later = 0;
-
-	list_add(&packet->dccphrx_node, rx_list);
-
-	num_later = TFRC_RECV_NUM_LATE_LOSS + 1;
-
-	if (!list_empty(li_list)) {
-		list_for_each_entry_safe(entry, next, rx_list, dccphrx_node) {
-			if (num_later == 0) {
-				if (after48(nonloss_seqno,
-				   entry->dccphrx_seqno)) {
-					list_del_init(&entry->dccphrx_node);
-					dccp_rx_hist_entry_delete(hist, entry);
-				}
-			} else if (dccp_rx_hist_entry_data_packet(entry))
-				--num_later;
-		}
-	} else {
-		int step = 0;
-		u8 win_count = 0; /* Not needed, but lets shut up gcc */
-		int tmp;
+	u64 s0 = tfrc_rx_hist_loss_prev(h)->tfrchrx_seqno,
+	    s1 = tfrc_rx_hist_entry(h, 1)->tfrchrx_seqno,
+	    s2 = tfrc_rx_hist_entry(h, 2)->tfrchrx_seqno,
+	    s3 = DCCP_SKB_CB(skb)->dccpd_seq;
+	int n1 = tfrc_rx_hist_entry(h, 1)->tfrchrx_ndp,
+	   d23 = dccp_delta_seqno(s2, s3), d13, d3, d31;
+
+	if (d23 > 0) {			/* S2  <  S3 */
+		h->loss_count = 3;
+		tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_entry(h, 3), skb, n3);
+		return 1;
+	}
+
+	/* S3  <  S2 */
+	d13 = dccp_delta_seqno(s1, s3);
+
+	if (d13 > 0) {
 		/*
-		 * We have no loss interval history so we need at least one
-		 * rtt:s of data packets to approximate rtt.
+		 * The sequence number order is S1, S3, S2
+		 * Reorder history to insert entry between S1 and S2
 		 */
-		list_for_each_entry_safe(entry, next, rx_list, dccphrx_node) {
-			if (num_later == 0) {
-				switch (step) {
-				case 0:
-					step = 1;
-					/* OK, find next data packet */
-					num_later = 1;
-					break;
-				case 1:
-					step = 2;
-					/* OK, find next data packet */
-					num_later = 1;
-					win_count = entry->dccphrx_ccval;
-					break;
-				case 2:
-					tmp = win_count - entry->dccphrx_ccval;
-					if (tmp < 0)
-						tmp += TFRC_WIN_COUNT_LIMIT;
-					if (tmp > TFRC_WIN_COUNT_PER_RTT + 1) {
-						/*
-						 * We have found a packet older
-						 * than one rtt remove the rest
-						 */
-						step = 3;
-					} else /* OK, find next data packet */
-						num_later = 1;
-					break;
-				case 3:
-					list_del_init(&entry->dccphrx_node);
-					dccp_rx_hist_entry_delete(hist, entry);
-					break;
-				}
-			} else if (dccp_rx_hist_entry_data_packet(entry))
-				--num_later;
+		tfrc_rx_hist_swap(h, 2, 3);
+		tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_entry(h, 2), skb, n3);
+		h->loss_count = 3;
+		return 1;
+	}
+
+	/* S0  <  S3  <  S1 */
+	d31 = -d13;
+	d3  = dccp_delta_seqno(s0, s3);
+
+	if (d3 == 1 || n3 >= d3) {	/* S3 is a successor of S0 */
+
+		if (d31 == 1 || n1 >= d31) {
+			/* hole between S0 and S1 filled by S3 */
+			int  d2 = dccp_delta_seqno(s1, s2),
+			     n2 = tfrc_rx_hist_entry(h, 2)->tfrchrx_ndp;
+
+			if (d2 == 1 || n2 >= d2) {
+				/* entire hole filled by S0, S3, S1, S2 */
+				h->loss_start = tfrc_rx_hist_index(h, 2);
+				h->loss_count = 0;
+			} else {
+				/* gap remains between S1 and S2 */
+				h->loss_start = tfrc_rx_hist_index(h, 1);
+				h->loss_count = 1;
+			}
+
+		} else /* gap exists between S3 and S1, loss_count stays at 2 */
+			tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_loss_prev(h), skb, n3);
+
+		return 0;
+	}
+
+	/*
+	 * The remaining case: S3 is not a successor of S0.
+	 * Sequence order is S0, S3, S1, S2; reorder to insert between S0 and S1
+	 */
+	tfrc_rx_hist_swap(h, 0, 3);
+	h->loss_start = tfrc_rx_hist_index(h, 3);
+	tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_entry(h, 1), skb, n3);
+	h->loss_count = 3;
+
+	return 1;
+}
+
+/* return the signed modulo-2^48 sequence number distance from entry e1 to e2 */
+static s64 tfrc_rx_hist_delta_seqno(struct tfrc_rx_hist *h, u8 e1, u8 e2)
+{
+	DCCP_BUG_ON(e1 > h->loss_count || e2 > h->loss_count);
+
+	return dccp_delta_seqno(tfrc_rx_hist_entry(h, e1)->tfrchrx_seqno,
+				tfrc_rx_hist_entry(h, e2)->tfrchrx_seqno);
+}
+
+/* recycle RX history records to continue loss detection if necessary */
+static void __three_after_loss(struct tfrc_rx_hist *h)
+{
+	/*
+	 * The distance between S0 and S1 is always greater than 1 and the NDP
+	 * count of S1 is smaller than this distance. Otherwise there would
+	 * have been no loss. Hence it is only necessary to see whether there
+	 * are further missing data packets between S1/S2 and S2/S3.
+	 */
+	int d2 = tfrc_rx_hist_delta_seqno(h, 1, 2),
+	    d3 = tfrc_rx_hist_delta_seqno(h, 2, 3),
+	    n2 = tfrc_rx_hist_entry(h, 2)->tfrchrx_ndp,
+	    n3 = tfrc_rx_hist_entry(h, 3)->tfrchrx_ndp;
+
+	if (d2 == 1 || n2 >= d2) {	/* S2 is successor to S1 */
+
+		if (d3 == 1 || n3 >= d3) {
+			/* S3 is successor of S2: entire hole is filled */
+			h->loss_start = tfrc_rx_hist_index(h, 3);
+			h->loss_count = 0;
+		} else {
+			/* gap between S2 and S3 */
+			h->loss_start = tfrc_rx_hist_index(h, 2);
+			h->loss_count = 1;
 		}
+
+	} else {			/* gap between S1 and S2 */
+		h->loss_start = tfrc_rx_hist_index(h, 1);
+		h->loss_count = 2;
 	}
 }
 
-EXPORT_SYMBOL_GPL(dccp_rx_hist_add_packet);
+/**
+ *  tfrc_rx_handle_loss  -  Loss detection and further processing
+ *  @h:		    The non-empty RX history object
+ *  @lh:	    Loss Intervals database to update
+ *  @skb:	    Currently received packet
+ *  @ndp:	    The NDP count belonging to @skb
+ *  @calc_first_li: Caller-dependent computation of first loss interval in @lh
+ *  @sk:	    Used by @calc_first_li (see tfrc_lh_interval_add)
+ *  Chooses action according to pending loss, updates LI database when a new
+ *  loss was detected, and does required post-processing. Returns 1 when caller
+ *  should send feedback, 0 otherwise.
+ */
+int tfrc_rx_handle_loss(struct tfrc_rx_hist *h,
+			struct tfrc_loss_hist *lh,
+			struct sk_buff *skb, u32 ndp,
+			u32 (*calc_first_li)(struct sock *), struct sock *sk)
+{
+	int is_new_loss = 0;
 
-void dccp_rx_hist_purge(struct dccp_rx_hist *hist, struct list_head *list)
+	if (h->loss_count == 1) {
+		__one_after_loss(h, skb, ndp);
+	} else if (h->loss_count != 2) {
+		DCCP_BUG("invalid loss_count %d", h->loss_count);
+	} else if (__two_after_loss(h, skb, ndp)) {
+		/*
+		 * Update Loss Interval database and recycle RX records
+		 */
+		is_new_loss = tfrc_lh_interval_add(lh, h, calc_first_li, sk);
+		__three_after_loss(h);
+	}
+	return is_new_loss;
+}
+EXPORT_SYMBOL_GPL(tfrc_rx_handle_loss);
+
+int tfrc_rx_hist_alloc(struct tfrc_rx_hist *h)
 {
-	struct dccp_rx_hist_entry *entry, *next;
+	int i;
+
+	for (i = 0; i <= TFRC_NDUPACK; i++) {
+		h->ring[i] = kmem_cache_alloc(tfrc_rx_hist_slab, GFP_ATOMIC);
+		if (h->ring[i] == NULL)
+			goto out_free;
+	}
+
+	h->loss_count = h->loss_start = 0;
+	return 0;
 
-	list_for_each_entry_safe(entry, next, list, dccphrx_node) {
-		list_del_init(&entry->dccphrx_node);
-		kmem_cache_free(hist->dccprxh_slab, entry);
+out_free:
+	while (i-- != 0) {
+		kmem_cache_free(tfrc_rx_hist_slab, h->ring[i]);
+		h->ring[i] = NULL;
 	}
+	return -ENOBUFS;
 }
+EXPORT_SYMBOL_GPL(tfrc_rx_hist_alloc);
+
+void tfrc_rx_hist_purge(struct tfrc_rx_hist *h)
+{
+	int i;
 
-EXPORT_SYMBOL_GPL(dccp_rx_hist_purge);
+	for (i = 0; i <= TFRC_NDUPACK; ++i)
+		if (h->ring[i] != NULL) {
+			kmem_cache_free(tfrc_rx_hist_slab, h->ring[i]);
+			h->ring[i] = NULL;
+		}
+}
+EXPORT_SYMBOL_GPL(tfrc_rx_hist_purge);
 
+/**
+ * tfrc_rx_hist_rtt_last_s - reference entry to compute RTT samples against
+ */
+static inline struct tfrc_rx_hist_entry *
+			tfrc_rx_hist_rtt_last_s(const struct tfrc_rx_hist *h)
+{
+	return h->ring[0];
+}
 
-MODULE_AUTHOR("Ian McDonald <ian.mcdonald@jandi.co.nz>, "
-	      "Arnaldo Carvalho de Melo <acme@ghostprotocols.net>");
-MODULE_DESCRIPTION("DCCP TFRC library");
-MODULE_LICENSE("GPL");
+/**
+ * tfrc_rx_hist_rtt_prev_s: previously suitable (wrt rtt_last_s) RTT-sampling entry
+ */
+static inline struct tfrc_rx_hist_entry *
+			tfrc_rx_hist_rtt_prev_s(const struct tfrc_rx_hist *h)
+{
+	return h->ring[h->rtt_sample_prev];
+}
+
+/**
+ * tfrc_rx_hist_sample_rtt  -  Sample RTT from timestamp / CCVal
+ * Based on ideas presented in RFC 4342, 8.1. Returns 0 if it was not able
+ * to compute a sample with given data - calling function should check this.
+ */
+u32 tfrc_rx_hist_sample_rtt(struct tfrc_rx_hist *h, const struct sk_buff *skb)
+{
+	u32 sample = 0,
+	    delta_v = SUB16(dccp_hdr(skb)->dccph_ccval,
+			    tfrc_rx_hist_rtt_last_s(h)->tfrchrx_ccval);
+
+	if (delta_v < 1 || delta_v > 4) {	/* unsuitable CCVal delta */
+		if (h->rtt_sample_prev == 2) {	/* previous candidate stored */
+			sample = SUB16(tfrc_rx_hist_rtt_prev_s(h)->tfrchrx_ccval,
+				       tfrc_rx_hist_rtt_last_s(h)->tfrchrx_ccval);
+			if (sample)
+				sample = 4 / sample *
+				         ktime_us_delta(tfrc_rx_hist_rtt_prev_s(h)->tfrchrx_tstamp,
+							tfrc_rx_hist_rtt_last_s(h)->tfrchrx_tstamp);
+			else    /*
+				 * FIXME: This condition is in principle not
+				 * possible but occurs when CCID is used for
+				 * two-way data traffic. I have tried to trace
+				 * it, but the cause does not seem to be here.
+				 */
+				DCCP_BUG("please report to dccp@vger.kernel.org"
+					 " => prev = %u, last = %u",
+					 tfrc_rx_hist_rtt_prev_s(h)->tfrchrx_ccval,
+					 tfrc_rx_hist_rtt_last_s(h)->tfrchrx_ccval);
+		} else if (delta_v < 1) {
+			h->rtt_sample_prev = 1;
+			goto keep_ref_for_next_time;
+		}
+
+	} else if (delta_v == 4) /* optimal match */
+		sample = ktime_to_us(net_timedelta(tfrc_rx_hist_rtt_last_s(h)->tfrchrx_tstamp));
+	else {			 /* suboptimal match */
+		h->rtt_sample_prev = 2;
+		goto keep_ref_for_next_time;
+	}
+
+	if (unlikely(sample > DCCP_SANE_RTT_MAX)) {
+		DCCP_WARN("RTT sample %u too large, using max\n", sample);
+		sample = DCCP_SANE_RTT_MAX;
+	}
+
+	h->rtt_sample_prev = 0;	       /* use current entry as next reference */
+keep_ref_for_next_time:
+
+	return sample;
+}
+EXPORT_SYMBOL_GPL(tfrc_rx_hist_sample_rtt);