ackvec.c
/*
* net/dccp/ackvec.c
*
* An implementation of Ack Vectors for the DCCP protocol
* Copyright (c) 2007 University of Aberdeen, Scotland, UK
* Copyright (c) 2005 Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
*
* 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; version 2 of the License;
*/
#include "dccp.h"
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/export.h>
static struct kmem_cache *dccp_ackvec_slab;
static struct kmem_cache *dccp_ackvec_record_slab;
struct dccp_ackvec *dccp_ackvec_alloc(const gfp_t priority)
{
struct dccp_ackvec *av = kmem_cache_zalloc(dccp_ackvec_slab, priority);
if (av != NULL) {
av->av_buf_head = av->av_buf_tail = DCCPAV_MAX_ACKVEC_LEN - 1;
INIT_LIST_HEAD(&av->av_records);
}
return av;
}
static void dccp_ackvec_purge_records(struct dccp_ackvec *av)
{
struct dccp_ackvec_record *cur, *next;
list_for_each_entry_safe(cur, next, &av->av_records, avr_node)
kmem_cache_free(dccp_ackvec_record_slab, cur);
INIT_LIST_HEAD(&av->av_records);
}
void dccp_ackvec_free(struct dccp_ackvec *av)
{
if (likely(av != NULL)) {
dccp_ackvec_purge_records(av);
kmem_cache_free(dccp_ackvec_slab, av);
}
}
/**
* dccp_ackvec_update_records - Record information about sent Ack Vectors
* @av: Ack Vector records to update
* @seqno: Sequence number of the packet carrying the Ack Vector just sent
* @nonce_sum: The sum of all buffer nonces contained in the Ack Vector
*/
int dccp_ackvec_update_records(struct dccp_ackvec *av, u64 seqno, u8 nonce_sum)
{
struct dccp_ackvec_record *avr;
avr = kmem_cache_alloc(dccp_ackvec_record_slab, GFP_ATOMIC);
if (avr == NULL)
return -ENOBUFS;
avr->avr_ack_seqno = seqno;
avr->avr_ack_ptr = av->av_buf_head;
avr->avr_ack_ackno = av->av_buf_ackno;
avr->avr_ack_nonce = nonce_sum;
avr->avr_ack_runlen = dccp_ackvec_runlen(av->av_buf + av->av_buf_head);
/*
* When the buffer overflows, we keep no more than one record. This is
* the simplest way of disambiguating sender-Acks dating from before the
* overflow from sender-Acks which refer to after the overflow; a simple
* solution is preferable here since we are handling an exception.
*/
if (av->av_overflow)
dccp_ackvec_purge_records(av);
/*
* Since GSS is incremented for each packet, the list is automatically
* arranged in descending order of @ack_seqno.
*/
list_add(&avr->avr_node, &av->av_records);
dccp_pr_debug("Added Vector, ack_seqno=%llu, ack_ackno=%llu (rl=%u)\n",
(unsigned long long)avr->avr_ack_seqno,
(unsigned long long)avr->avr_ack_ackno,
avr->avr_ack_runlen);
return 0;
}
static struct dccp_ackvec_record *dccp_ackvec_lookup(struct list_head *av_list,
const u64 ackno)
{
struct dccp_ackvec_record *avr;
/*
* Exploit that records are inserted in descending order of sequence
* number, start with the oldest record first. If @ackno is `before'
* the earliest ack_ackno, the packet is too old to be considered.
*/
list_for_each_entry_reverse(avr, av_list, avr_node) {
if (avr->avr_ack_seqno == ackno)
return avr;
if (before48(ackno, avr->avr_ack_seqno))
break;
}
return NULL;
}
/*
* Buffer index and length computation using modulo-buffersize arithmetic.
* Note that, as pointers move from right to left, head is `before' tail.
*/
static inline u16 __ackvec_idx_add(const u16 a, const u16 b)
{
return (a + b) % DCCPAV_MAX_ACKVEC_LEN;
}
static inline u16 __ackvec_idx_sub(const u16 a, const u16 b)
{
return __ackvec_idx_add(a, DCCPAV_MAX_ACKVEC_LEN - b);
}
u16 dccp_ackvec_buflen(const struct dccp_ackvec *av)
{
if (unlikely(av->av_overflow))
return DCCPAV_MAX_ACKVEC_LEN;
return __ackvec_idx_sub(av->av_buf_tail, av->av_buf_head);
}
/**
* dccp_ackvec_update_old - Update previous state as per RFC 4340, 11.4.1
* @av: non-empty buffer to update
* @distance: negative or zero distance of @seqno from buf_ackno downward
* @seqno: the (old) sequence number whose record is to be updated
* @state: state in which packet carrying @seqno was received
*/
static void dccp_ackvec_update_old(struct dccp_ackvec *av, s64 distance,
u64 seqno, enum dccp_ackvec_states state)
{
u16 ptr = av->av_buf_head;
BUG_ON(distance > 0);
if (unlikely(dccp_ackvec_is_empty(av)))
return;
do {
u8 runlen = dccp_ackvec_runlen(av->av_buf + ptr);
if (distance + runlen >= 0) {
/*
* Only update the state if packet has not been received
* yet. This is OK as per the second table in RFC 4340,
* 11.4.1; i.e. here we are using the following table:
* RECEIVED
* 0 1 3
* S +---+---+---+
* T 0 | 0 | 0 | 0 |
* O +---+---+---+
* R 1 | 1 | 1 | 1 |
* E +---+---+---+
* D 3 | 0 | 1 | 3 |
* +---+---+---+
* The "Not Received" state was set by reserve_seats().
*/
if (av->av_buf[ptr] == DCCPAV_NOT_RECEIVED)
av->av_buf[ptr] = state;
else
dccp_pr_debug("Not changing %llu state to %u\n",
(unsigned long long)seqno, state);
break;
}
distance += runlen + 1;
ptr = __ackvec_idx_add(ptr, 1);
} while (ptr != av->av_buf_tail);
}
/* Mark @num entries after buf_head as "Not yet received". */
static void dccp_ackvec_reserve_seats(struct dccp_ackvec *av, u16 num)
{
u16 start = __ackvec_idx_add(av->av_buf_head, 1),
len = DCCPAV_MAX_ACKVEC_LEN - start;
/* check for buffer wrap-around */
if (num > len) {
memset(av->av_buf + start, DCCPAV_NOT_RECEIVED, len);
start = 0;
num -= len;
}
if (num)
memset(av->av_buf + start, DCCPAV_NOT_RECEIVED, num);
}
/**
* dccp_ackvec_add_new - Record one or more new entries in Ack Vector buffer
* @av: container of buffer to update (can be empty or non-empty)
* @num_packets: number of packets to register (must be >= 1)
* @seqno: sequence number of the first packet in @num_packets
* @state: state in which packet carrying @seqno was received
*/
static void dccp_ackvec_add_new(struct dccp_ackvec *av, u32 num_packets,
u64 seqno, enum dccp_ackvec_states state)
{
u32 num_cells = num_packets;
if (num_packets > DCCPAV_BURST_THRESH) {
u32 lost_packets = num_packets - 1;
DCCP_WARN("Warning: large burst loss (%u)\n", lost_packets);
/*
* We received 1 packet and have a loss of size "num_packets-1"
* which we squeeze into num_cells-1 rather than reserving an
* entire byte for each lost packet.
* The reason is that the vector grows in O(burst_length); when
* it grows too large there will no room left for the payload.
* This is a trade-off: if a few packets out of the burst show
* up later, their state will not be changed; it is simply too
* costly to reshuffle/reallocate/copy the buffer each time.
* Should such problems persist, we will need to switch to a
* different underlying data structure.
*/
for (num_packets = num_cells = 1; lost_packets; ++num_cells) {
u8 len = min(lost_packets, (u32)DCCPAV_MAX_RUNLEN);
av->av_buf_head = __ackvec_idx_sub(av->av_buf_head, 1);
av->av_buf[av->av_buf_head] = DCCPAV_NOT_RECEIVED | len;
lost_packets -= len;
}
}
if (num_cells + dccp_ackvec_buflen(av) >= DCCPAV_MAX_ACKVEC_LEN) {
DCCP_CRIT("Ack Vector buffer overflow: dropping old entries\n");
av->av_overflow = true;
}
av->av_buf_head = __ackvec_idx_sub(av->av_buf_head, num_packets);
if (av->av_overflow)
av->av_buf_tail = av->av_buf_head;
av->av_buf[av->av_buf_head] = state;
av->av_buf_ackno = seqno;
if (num_packets > 1)
dccp_ackvec_reserve_seats(av, num_packets - 1);
}
/**
* dccp_ackvec_input - Register incoming packet in the buffer
*/
void dccp_ackvec_input(struct dccp_ackvec *av, struct sk_buff *skb)
{
u64 seqno = DCCP_SKB_CB(skb)->dccpd_seq;
enum dccp_ackvec_states state = DCCPAV_RECEIVED;
if (dccp_ackvec_is_empty(av)) {
dccp_ackvec_add_new(av, 1, seqno, state);
av->av_tail_ackno = seqno;
} else {
s64 num_packets = dccp_delta_seqno(av->av_buf_ackno, seqno);
u8 *current_head = av->av_buf + av->av_buf_head;
if (num_packets == 1 &&
dccp_ackvec_state(current_head) == state &&
dccp_ackvec_runlen(current_head) < DCCPAV_MAX_RUNLEN) {
*current_head += 1;
av->av_buf_ackno = seqno;
} else if (num_packets > 0) {
dccp_ackvec_add_new(av, num_packets, seqno, state);
} else {
dccp_ackvec_update_old(av, num_packets, seqno, state);
}
}
}
/**
* dccp_ackvec_clear_state - Perform house-keeping / garbage-collection
* This routine is called when the peer acknowledges the receipt of Ack Vectors
* up to and including @ackno. While based on on section A.3 of RFC 4340, here
* are additional precautions to prevent corrupted buffer state. In particular,
* we use tail_ackno to identify outdated records; it always marks the earliest
* packet of group (2) in 11.4.2.
*/
void dccp_ackvec_clear_state(struct dccp_ackvec *av, const u64 ackno)
{
struct dccp_ackvec_record *avr, *next;
u8 runlen_now, eff_runlen;
s64 delta;
avr = dccp_ackvec_lookup(&av->av_records, ackno);
if (avr == NULL)
return;
/*
* Deal with outdated acknowledgments: this arises when e.g. there are
* several old records and the acks from the peer come in slowly. In
* that case we may still have records that pre-date tail_ackno.
*/
delta = dccp_delta_seqno(av->av_tail_ackno, avr->avr_ack_ackno);
if (delta < 0)
goto free_records;
/*
* Deal with overlapping Ack Vectors: don't subtract more than the
* number of packets between tail_ackno and ack_ackno.
*/
eff_runlen = delta < avr->avr_ack_runlen ? delta : avr->avr_ack_runlen;
runlen_now = dccp_ackvec_runlen(av->av_buf + avr->avr_ack_ptr);
/*
* The run length of Ack Vector cells does not decrease over time. If
* the run length is the same as at the time the Ack Vector was sent, we
* free the ack_ptr cell. That cell can however not be freed if the run
* length has increased: in this case we need to move the tail pointer
* backwards (towards higher indices), to its next-oldest neighbour.
*/
if (runlen_now > eff_runlen) {
av->av_buf[avr->avr_ack_ptr] -= eff_runlen + 1;
av->av_buf_tail = __ackvec_idx_add(avr->avr_ack_ptr, 1);
/* This move may not have cleared the overflow flag. */
if (av->av_overflow)
av->av_overflow = (av->av_buf_head == av->av_buf_tail);
} else {
av->av_buf_tail = avr->avr_ack_ptr;
/*
* We have made sure that avr points to a valid cell within the
* buffer. This cell is either older than head, or equals head
* (empty buffer): in both cases we no longer have any overflow.
*/
av->av_overflow = 0;
}
/*
* The peer has acknowledged up to and including ack_ackno. Hence the
* first packet in group (2) of 11.4.2 is the successor of ack_ackno.
*/
av->av_tail_ackno = ADD48(avr->avr_ack_ackno, 1);
free_records:
list_for_each_entry_safe_from(avr, next, &av->av_records, avr_node) {
list_del(&avr->avr_node);
kmem_cache_free(dccp_ackvec_record_slab, avr);
}
}
/*
* Routines to keep track of Ack Vectors received in an skb
*/
int dccp_ackvec_parsed_add(struct list_head *head, u8 *vec, u8 len, u8 nonce)
{
struct dccp_ackvec_parsed *new = kmalloc(sizeof(*new), GFP_ATOMIC);
if (new == NULL)
return -ENOBUFS;
new->vec = vec;
new->len = len;
new->nonce = nonce;
list_add_tail(&new->node, head);
return 0;
}
EXPORT_SYMBOL_GPL(dccp_ackvec_parsed_add);
void dccp_ackvec_parsed_cleanup(struct list_head *parsed_chunks)
{
struct dccp_ackvec_parsed *cur, *next;
list_for_each_entry_safe(cur, next, parsed_chunks, node)
kfree(cur);
INIT_LIST_HEAD(parsed_chunks);
}
EXPORT_SYMBOL_GPL(dccp_ackvec_parsed_cleanup);
int __init dccp_ackvec_init(void)
{
dccp_ackvec_slab = kmem_cache_create("dccp_ackvec",
sizeof(struct dccp_ackvec), 0,
SLAB_HWCACHE_ALIGN, NULL);
if (dccp_ackvec_slab == NULL)
goto out_err;
dccp_ackvec_record_slab = kmem_cache_create("dccp_ackvec_record",
sizeof(struct dccp_ackvec_record),
0, SLAB_HWCACHE_ALIGN, NULL);
if (dccp_ackvec_record_slab == NULL)
goto out_destroy_slab;
return 0;
out_destroy_slab:
kmem_cache_destroy(dccp_ackvec_slab);
dccp_ackvec_slab = NULL;
out_err:
DCCP_CRIT("Unable to create Ack Vector slab cache");
return -ENOBUFS;
}
void dccp_ackvec_exit(void)
{
if (dccp_ackvec_slab != NULL) {
kmem_cache_destroy(dccp_ackvec_slab);
dccp_ackvec_slab = NULL;
}
if (dccp_ackvec_record_slab != NULL) {
kmem_cache_destroy(dccp_ackvec_record_slab);
dccp_ackvec_record_slab = NULL;
}
}
