/* * 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; } }