/*

 *  net/dccp/packet_history.c

 *

 *  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

 *

 *  This code has been developed by the University of Waikato WAND

 *  research group. For further information please see http://www.wand.net.nz/

 *  or e-mail Ian McDonald - ian.mcdonald@jandi.co.nz

 *

 *  This code also uses code from Lulea University, rereleased as GPL by its

 *  authors:

 *  Copyright (c) 2003 Nils-Erik Mattsson, Joacim Haggmark, Magnus Erixzon

 *

 *  Changes to meet Linux coding standards, to make it meet latest ccid3 draft

 *  and to make it work as a loadable module in the DCCP stack written by

 *  Arnaldo Carvalho de Melo <acme@conectiva.com.br>.

 *

 *  Copyright (c) 2005 Arnaldo Carvalho de Melo <acme@conectiva.com.br>

 *

 *  This program is free software; you can redistribute it and/or modify

 *  it under the terms of the GNU General Public License as published by

 *  the Free Software Foundation; either version 2 of the License, or

 *  (at your option) any later version.

 *

 *  This program is distributed in the hope that it will be useful,

 *  but WITHOUT ANY WARRANTY; without even the implied warranty of

 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 *  GNU General Public License for more details.

 *

 *  You should have received a copy of the GNU General Public License

 *  along with this program; if not, write to the Free Software

 *  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

 */

#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

 */

static struct kmem_cache *tfrc_tx_hist_slab;

int __init tfrc_tx_packet_history_init(void)

{

	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;

}

void tfrc_tx_packet_history_exit(void)

{

	if (tfrc_tx_hist_slab != NULL) {

		kmem_cache_destroy(tfrc_tx_hist_slab);

		tfrc_tx_hist_slab = NULL;

	}

}

static struct tfrc_tx_hist_entry *

	tfrc_tx_hist_find_entry(struct tfrc_tx_hist_entry *head, u64 seqno)

{

	while (head != NULL && head->seqno != seqno)

		head = head->next;

	return head;

}

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;

}

void tfrc_tx_hist_purge(struct tfrc_tx_hist_entry **headp)

{

	struct tfrc_tx_hist_entry *head = *headp;

	while (head != NULL) {

		struct tfrc_tx_hist_entry *next = head->next;

		kmem_cache_free(tfrc_tx_hist_slab, head);

		head = next;

	}

	*headp = NULL;

}

u32 tfrc_tx_hist_rtt(struct tfrc_tx_hist_entry *head, const u64 seqno,

		     const ktime_t now)

{

	u32 rtt = 0;

	struct tfrc_tx_hist_entry *packet = tfrc_tx_hist_find_entry(head, seqno);

	if (packet != NULL) {

		rtt = ktime_us_delta(now, packet->stamp);

		/*

		 * Garbage-collect older (irrelevant) entries:

		 */

		tfrc_tx_hist_purge(&packet->next);

	}

	return rtt;

}

/*

 * 	Receiver History Routines

 */

static struct kmem_cache *tfrc_rx_hist_slab;

int __init tfrc_rx_packet_history_init(void)

{

	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;

}

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;

	}

}

static inline void tfrc_rx_hist_entry_from_skb(struct tfrc_rx_hist_entry *entry,

					       const struct sk_buff *skb,

					       const u64 ndp)

{

	const struct dccp_hdr *dh = dccp_hdr(skb);

	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();

}

void tfrc_rx_hist_add_packet(struct tfrc_rx_hist *h,

			     const struct sk_buff *skb,

			     const u64 ndp)

{

	struct tfrc_rx_hist_entry *entry = tfrc_rx_hist_last_rcv(h);

	tfrc_rx_hist_entry_from_skb(entry, skb, ndp);

}

/* has the packet contained in skb been seen before? */

int tfrc_rx_hist_duplicate(struct tfrc_rx_hist *h, struct sk_buff *skb)

{

	const u64 seq = DCCP_SKB_CB(skb)->dccpd_seq;

	int i;

	if (dccp_delta_seqno(tfrc_rx_hist_loss_prev(h)->tfrchrx_seqno, seq) <= 0)

		return 1;

	for (i = 1; i <= h->loss_count; i++)

		if (tfrc_rx_hist_entry(h, i)->tfrchrx_seqno == seq)

			return 1;

	return 0;

}

static void tfrc_rx_hist_swap(struct tfrc_rx_hist *h, const u8 a, const u8 b)

{

	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];

	h->ring[idx_a] = h->ring[idx_b];

	h->ring[idx_b] = tmp;

}

/*

 * 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 __xxx_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 history entry.

 */

static void __do_track_loss(struct tfrc_rx_hist *h, struct sk_buff *skb, u64 n1)

{

	u64 s0 = tfrc_rx_hist_loss_prev(h)->tfrchrx_seqno,

	    s1 = DCCP_SKB_CB(skb)->dccpd_seq;

	if (!dccp_loss_free(s0, s1, n1)) {	/* gap between S0 and S1 */

		h->loss_count = 1;

		tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_entry(h, 1), skb, n1);

	}

}

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;

	if (likely(dccp_delta_seqno(s1, s2) > 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 */

	if (dccp_loss_free(s0, s2, n2)) {

		u64 n1 = tfrc_rx_hist_entry(h, 1)->tfrchrx_ndp;

		if (dccp_loss_free(s2, s1, n1)) {

			/* 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 {	/* gap 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)

{

	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;

	if (likely(dccp_delta_seqno(s2, s3) > 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 */

	if (dccp_delta_seqno(s1, s3) > 0) {		/* S1  <  S3  <  S2 */

		/*

		 * Reorder history to insert S3 between S1 and S2

		 */

		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 */

	if (dccp_loss_free(s0, s3, n3)) {

		u64 n1 = tfrc_rx_hist_entry(h, 1)->tfrchrx_ndp;

		if (dccp_loss_free(s3, s1, n1)) {

			/* hole between S0 and S1 filled by S3 */

			u64 n2 = tfrc_rx_hist_entry(h, 2)->tfrchrx_ndp;

			if (dccp_loss_free(s1, s2, n2)) {

				/* 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:  S0  <  S3  <  S1  <  S2;  gap between S0 and S3

	 * Reorder history to insert S3 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;

}

/* recycle RX history records to continue loss detection if necessary */

static void __three_after_loss(struct tfrc_rx_hist *h)

{

	/*

	 * At this stage we know already that there is a gap between S0 and S1

	 * (since S0 was the highest sequence number received before detecting

	 * the loss). To recycle the loss record, it is	thus only necessary to

	 * check for other possible gaps between S1/S2 and between S2/S3.

	 */

	u64 s1 = tfrc_rx_hist_entry(h, 1)->tfrchrx_seqno,

	    s2 = tfrc_rx_hist_entry(h, 2)->tfrchrx_seqno,

	    s3 = tfrc_rx_hist_entry(h, 3)->tfrchrx_seqno;

	u64 n2 = tfrc_rx_hist_entry(h, 2)->tfrchrx_ndp,

	    n3 = tfrc_rx_hist_entry(h, 3)->tfrchrx_ndp;

	if (dccp_loss_free(s1, s2, n2)) {

		if (dccp_loss_free(s2, s3, n3)) {

			/* no gap between S2 and S3: 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;

	}

}

/**

 *  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.

 *  Since it also takes care of reordering during loss detection and updates the

 *  records accordingly, the caller should not perform any more RX history

 *  operations when loss_count is greater than 0 after calling this function.

 */

int tfrc_rx_handle_loss(struct tfrc_rx_hist *h,

			struct tfrc_loss_hist *lh,

			struct sk_buff *skb, const u64 ndp,

			u32 (*calc_first_li)(struct sock *), struct sock *sk)

{

	int is_new_loss = 0;

	if (h->loss_count == 0) {

		__do_track_loss(h, skb, ndp);

	} else 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;

}

int tfrc_rx_hist_alloc(struct tfrc_rx_hist *h)

{

	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;

out_free:

	while (i-- != 0) {

		kmem_cache_free(tfrc_rx_hist_slab, h->ring[i]);

		h->ring[i] = NULL;

	}

	return -ENOBUFS;

}

void tfrc_rx_hist_purge(struct tfrc_rx_hist *h)

{

	int i;

	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;

		}

}

/**

 * 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];

}

/**

 * 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;

}