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407 lines
12 KiB
407 lines
12 KiB
// SPDX-License-Identifier: GPL-2.0-only |
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/* |
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* net/dccp/ackvec.c |
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* |
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* An implementation of Ack Vectors for the DCCP protocol |
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* Copyright (c) 2007 University of Aberdeen, Scotland, UK |
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* Copyright (c) 2005 Arnaldo Carvalho de Melo <[email protected]> |
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*/ |
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#include "dccp.h" |
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#include <linux/kernel.h> |
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#include <linux/slab.h> |
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#include <linux/export.h> |
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static struct kmem_cache *dccp_ackvec_slab; |
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static struct kmem_cache *dccp_ackvec_record_slab; |
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struct dccp_ackvec *dccp_ackvec_alloc(const gfp_t priority) |
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{ |
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struct dccp_ackvec *av = kmem_cache_zalloc(dccp_ackvec_slab, priority); |
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if (av != NULL) { |
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av->av_buf_head = av->av_buf_tail = DCCPAV_MAX_ACKVEC_LEN - 1; |
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INIT_LIST_HEAD(&av->av_records); |
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} |
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return av; |
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} |
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static void dccp_ackvec_purge_records(struct dccp_ackvec *av) |
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{ |
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struct dccp_ackvec_record *cur, *next; |
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list_for_each_entry_safe(cur, next, &av->av_records, avr_node) |
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kmem_cache_free(dccp_ackvec_record_slab, cur); |
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INIT_LIST_HEAD(&av->av_records); |
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} |
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void dccp_ackvec_free(struct dccp_ackvec *av) |
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{ |
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if (likely(av != NULL)) { |
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dccp_ackvec_purge_records(av); |
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kmem_cache_free(dccp_ackvec_slab, av); |
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} |
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} |
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/** |
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* dccp_ackvec_update_records - Record information about sent Ack Vectors |
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* @av: Ack Vector records to update |
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* @seqno: Sequence number of the packet carrying the Ack Vector just sent |
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* @nonce_sum: The sum of all buffer nonces contained in the Ack Vector |
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*/ |
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int dccp_ackvec_update_records(struct dccp_ackvec *av, u64 seqno, u8 nonce_sum) |
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{ |
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struct dccp_ackvec_record *avr; |
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avr = kmem_cache_alloc(dccp_ackvec_record_slab, GFP_ATOMIC); |
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if (avr == NULL) |
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return -ENOBUFS; |
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avr->avr_ack_seqno = seqno; |
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avr->avr_ack_ptr = av->av_buf_head; |
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avr->avr_ack_ackno = av->av_buf_ackno; |
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avr->avr_ack_nonce = nonce_sum; |
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avr->avr_ack_runlen = dccp_ackvec_runlen(av->av_buf + av->av_buf_head); |
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/* |
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* When the buffer overflows, we keep no more than one record. This is |
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* the simplest way of disambiguating sender-Acks dating from before the |
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* overflow from sender-Acks which refer to after the overflow; a simple |
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* solution is preferable here since we are handling an exception. |
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*/ |
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if (av->av_overflow) |
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dccp_ackvec_purge_records(av); |
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/* |
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* Since GSS is incremented for each packet, the list is automatically |
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* arranged in descending order of @ack_seqno. |
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*/ |
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list_add(&avr->avr_node, &av->av_records); |
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dccp_pr_debug("Added Vector, ack_seqno=%llu, ack_ackno=%llu (rl=%u)\n", |
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(unsigned long long)avr->avr_ack_seqno, |
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(unsigned long long)avr->avr_ack_ackno, |
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avr->avr_ack_runlen); |
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return 0; |
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} |
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static struct dccp_ackvec_record *dccp_ackvec_lookup(struct list_head *av_list, |
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const u64 ackno) |
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{ |
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struct dccp_ackvec_record *avr; |
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/* |
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* Exploit that records are inserted in descending order of sequence |
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* number, start with the oldest record first. If @ackno is `before' |
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* the earliest ack_ackno, the packet is too old to be considered. |
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*/ |
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list_for_each_entry_reverse(avr, av_list, avr_node) { |
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if (avr->avr_ack_seqno == ackno) |
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return avr; |
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if (before48(ackno, avr->avr_ack_seqno)) |
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break; |
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} |
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return NULL; |
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} |
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/* |
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* Buffer index and length computation using modulo-buffersize arithmetic. |
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* Note that, as pointers move from right to left, head is `before' tail. |
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*/ |
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static inline u16 __ackvec_idx_add(const u16 a, const u16 b) |
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{ |
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return (a + b) % DCCPAV_MAX_ACKVEC_LEN; |
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} |
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static inline u16 __ackvec_idx_sub(const u16 a, const u16 b) |
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{ |
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return __ackvec_idx_add(a, DCCPAV_MAX_ACKVEC_LEN - b); |
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} |
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u16 dccp_ackvec_buflen(const struct dccp_ackvec *av) |
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{ |
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if (unlikely(av->av_overflow)) |
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return DCCPAV_MAX_ACKVEC_LEN; |
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return __ackvec_idx_sub(av->av_buf_tail, av->av_buf_head); |
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} |
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/** |
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* dccp_ackvec_update_old - Update previous state as per RFC 4340, 11.4.1 |
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* @av: non-empty buffer to update |
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* @distance: negative or zero distance of @seqno from buf_ackno downward |
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* @seqno: the (old) sequence number whose record is to be updated |
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* @state: state in which packet carrying @seqno was received |
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*/ |
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static void dccp_ackvec_update_old(struct dccp_ackvec *av, s64 distance, |
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u64 seqno, enum dccp_ackvec_states state) |
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{ |
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u16 ptr = av->av_buf_head; |
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BUG_ON(distance > 0); |
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if (unlikely(dccp_ackvec_is_empty(av))) |
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return; |
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do { |
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u8 runlen = dccp_ackvec_runlen(av->av_buf + ptr); |
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if (distance + runlen >= 0) { |
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/* |
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* Only update the state if packet has not been received |
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* yet. This is OK as per the second table in RFC 4340, |
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* 11.4.1; i.e. here we are using the following table: |
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* RECEIVED |
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* 0 1 3 |
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* S +---+---+---+ |
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* T 0 | 0 | 0 | 0 | |
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* O +---+---+---+ |
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* R 1 | 1 | 1 | 1 | |
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* E +---+---+---+ |
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* D 3 | 0 | 1 | 3 | |
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* +---+---+---+ |
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* The "Not Received" state was set by reserve_seats(). |
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*/ |
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if (av->av_buf[ptr] == DCCPAV_NOT_RECEIVED) |
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av->av_buf[ptr] = state; |
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else |
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dccp_pr_debug("Not changing %llu state to %u\n", |
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(unsigned long long)seqno, state); |
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break; |
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} |
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distance += runlen + 1; |
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ptr = __ackvec_idx_add(ptr, 1); |
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} while (ptr != av->av_buf_tail); |
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} |
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/* Mark @num entries after buf_head as "Not yet received". */ |
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static void dccp_ackvec_reserve_seats(struct dccp_ackvec *av, u16 num) |
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{ |
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u16 start = __ackvec_idx_add(av->av_buf_head, 1), |
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len = DCCPAV_MAX_ACKVEC_LEN - start; |
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/* check for buffer wrap-around */ |
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if (num > len) { |
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memset(av->av_buf + start, DCCPAV_NOT_RECEIVED, len); |
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start = 0; |
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num -= len; |
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} |
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if (num) |
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memset(av->av_buf + start, DCCPAV_NOT_RECEIVED, num); |
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} |
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/** |
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* dccp_ackvec_add_new - Record one or more new entries in Ack Vector buffer |
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* @av: container of buffer to update (can be empty or non-empty) |
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* @num_packets: number of packets to register (must be >= 1) |
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* @seqno: sequence number of the first packet in @num_packets |
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* @state: state in which packet carrying @seqno was received |
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*/ |
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static void dccp_ackvec_add_new(struct dccp_ackvec *av, u32 num_packets, |
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u64 seqno, enum dccp_ackvec_states state) |
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{ |
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u32 num_cells = num_packets; |
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if (num_packets > DCCPAV_BURST_THRESH) { |
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u32 lost_packets = num_packets - 1; |
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DCCP_WARN("Warning: large burst loss (%u)\n", lost_packets); |
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/* |
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* We received 1 packet and have a loss of size "num_packets-1" |
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* which we squeeze into num_cells-1 rather than reserving an |
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* entire byte for each lost packet. |
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* The reason is that the vector grows in O(burst_length); when |
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* it grows too large there will no room left for the payload. |
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* This is a trade-off: if a few packets out of the burst show |
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* up later, their state will not be changed; it is simply too |
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* costly to reshuffle/reallocate/copy the buffer each time. |
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* Should such problems persist, we will need to switch to a |
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* different underlying data structure. |
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*/ |
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for (num_packets = num_cells = 1; lost_packets; ++num_cells) { |
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u8 len = min_t(u32, lost_packets, DCCPAV_MAX_RUNLEN); |
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av->av_buf_head = __ackvec_idx_sub(av->av_buf_head, 1); |
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av->av_buf[av->av_buf_head] = DCCPAV_NOT_RECEIVED | len; |
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lost_packets -= len; |
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} |
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} |
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if (num_cells + dccp_ackvec_buflen(av) >= DCCPAV_MAX_ACKVEC_LEN) { |
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DCCP_CRIT("Ack Vector buffer overflow: dropping old entries"); |
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av->av_overflow = true; |
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} |
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av->av_buf_head = __ackvec_idx_sub(av->av_buf_head, num_packets); |
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if (av->av_overflow) |
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av->av_buf_tail = av->av_buf_head; |
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av->av_buf[av->av_buf_head] = state; |
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av->av_buf_ackno = seqno; |
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if (num_packets > 1) |
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dccp_ackvec_reserve_seats(av, num_packets - 1); |
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} |
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/** |
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* dccp_ackvec_input - Register incoming packet in the buffer |
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* @av: Ack Vector to register packet to |
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* @skb: Packet to register |
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*/ |
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void dccp_ackvec_input(struct dccp_ackvec *av, struct sk_buff *skb) |
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{ |
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u64 seqno = DCCP_SKB_CB(skb)->dccpd_seq; |
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enum dccp_ackvec_states state = DCCPAV_RECEIVED; |
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if (dccp_ackvec_is_empty(av)) { |
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dccp_ackvec_add_new(av, 1, seqno, state); |
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av->av_tail_ackno = seqno; |
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} else { |
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s64 num_packets = dccp_delta_seqno(av->av_buf_ackno, seqno); |
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u8 *current_head = av->av_buf + av->av_buf_head; |
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if (num_packets == 1 && |
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dccp_ackvec_state(current_head) == state && |
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dccp_ackvec_runlen(current_head) < DCCPAV_MAX_RUNLEN) { |
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*current_head += 1; |
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av->av_buf_ackno = seqno; |
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} else if (num_packets > 0) { |
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dccp_ackvec_add_new(av, num_packets, seqno, state); |
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} else { |
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dccp_ackvec_update_old(av, num_packets, seqno, state); |
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} |
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} |
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} |
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/** |
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* dccp_ackvec_clear_state - Perform house-keeping / garbage-collection |
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* @av: Ack Vector record to clean |
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* @ackno: last Ack Vector which has been acknowledged |
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* |
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* This routine is called when the peer acknowledges the receipt of Ack Vectors |
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* up to and including @ackno. While based on section A.3 of RFC 4340, here |
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* are additional precautions to prevent corrupted buffer state. In particular, |
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* we use tail_ackno to identify outdated records; it always marks the earliest |
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* packet of group (2) in 11.4.2. |
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*/ |
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void dccp_ackvec_clear_state(struct dccp_ackvec *av, const u64 ackno) |
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{ |
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struct dccp_ackvec_record *avr, *next; |
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u8 runlen_now, eff_runlen; |
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s64 delta; |
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avr = dccp_ackvec_lookup(&av->av_records, ackno); |
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if (avr == NULL) |
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return; |
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/* |
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* Deal with outdated acknowledgments: this arises when e.g. there are |
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* several old records and the acks from the peer come in slowly. In |
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* that case we may still have records that pre-date tail_ackno. |
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*/ |
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delta = dccp_delta_seqno(av->av_tail_ackno, avr->avr_ack_ackno); |
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if (delta < 0) |
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goto free_records; |
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/* |
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* Deal with overlapping Ack Vectors: don't subtract more than the |
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* number of packets between tail_ackno and ack_ackno. |
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*/ |
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eff_runlen = delta < avr->avr_ack_runlen ? delta : avr->avr_ack_runlen; |
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runlen_now = dccp_ackvec_runlen(av->av_buf + avr->avr_ack_ptr); |
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/* |
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* The run length of Ack Vector cells does not decrease over time. If |
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* the run length is the same as at the time the Ack Vector was sent, we |
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* free the ack_ptr cell. That cell can however not be freed if the run |
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* length has increased: in this case we need to move the tail pointer |
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* backwards (towards higher indices), to its next-oldest neighbour. |
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*/ |
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if (runlen_now > eff_runlen) { |
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av->av_buf[avr->avr_ack_ptr] -= eff_runlen + 1; |
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av->av_buf_tail = __ackvec_idx_add(avr->avr_ack_ptr, 1); |
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/* This move may not have cleared the overflow flag. */ |
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if (av->av_overflow) |
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av->av_overflow = (av->av_buf_head == av->av_buf_tail); |
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} else { |
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av->av_buf_tail = avr->avr_ack_ptr; |
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/* |
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* We have made sure that avr points to a valid cell within the |
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* buffer. This cell is either older than head, or equals head |
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* (empty buffer): in both cases we no longer have any overflow. |
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*/ |
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av->av_overflow = 0; |
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} |
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/* |
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* The peer has acknowledged up to and including ack_ackno. Hence the |
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* first packet in group (2) of 11.4.2 is the successor of ack_ackno. |
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*/ |
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av->av_tail_ackno = ADD48(avr->avr_ack_ackno, 1); |
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free_records: |
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list_for_each_entry_safe_from(avr, next, &av->av_records, avr_node) { |
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list_del(&avr->avr_node); |
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kmem_cache_free(dccp_ackvec_record_slab, avr); |
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} |
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} |
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/* |
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* Routines to keep track of Ack Vectors received in an skb |
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*/ |
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int dccp_ackvec_parsed_add(struct list_head *head, u8 *vec, u8 len, u8 nonce) |
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{ |
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struct dccp_ackvec_parsed *new = kmalloc(sizeof(*new), GFP_ATOMIC); |
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if (new == NULL) |
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return -ENOBUFS; |
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new->vec = vec; |
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new->len = len; |
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new->nonce = nonce; |
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list_add_tail(&new->node, head); |
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return 0; |
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} |
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EXPORT_SYMBOL_GPL(dccp_ackvec_parsed_add); |
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void dccp_ackvec_parsed_cleanup(struct list_head *parsed_chunks) |
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{ |
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struct dccp_ackvec_parsed *cur, *next; |
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list_for_each_entry_safe(cur, next, parsed_chunks, node) |
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kfree(cur); |
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INIT_LIST_HEAD(parsed_chunks); |
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} |
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EXPORT_SYMBOL_GPL(dccp_ackvec_parsed_cleanup); |
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int __init dccp_ackvec_init(void) |
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{ |
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dccp_ackvec_slab = kmem_cache_create("dccp_ackvec", |
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sizeof(struct dccp_ackvec), 0, |
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SLAB_HWCACHE_ALIGN, NULL); |
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if (dccp_ackvec_slab == NULL) |
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goto out_err; |
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dccp_ackvec_record_slab = kmem_cache_create("dccp_ackvec_record", |
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sizeof(struct dccp_ackvec_record), |
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0, SLAB_HWCACHE_ALIGN, NULL); |
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if (dccp_ackvec_record_slab == NULL) |
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goto out_destroy_slab; |
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return 0; |
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out_destroy_slab: |
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kmem_cache_destroy(dccp_ackvec_slab); |
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dccp_ackvec_slab = NULL; |
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out_err: |
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DCCP_CRIT("Unable to create Ack Vector slab cache"); |
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return -ENOBUFS; |
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} |
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void dccp_ackvec_exit(void) |
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{ |
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kmem_cache_destroy(dccp_ackvec_slab); |
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dccp_ackvec_slab = NULL; |
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kmem_cache_destroy(dccp_ackvec_record_slab); |
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dccp_ackvec_record_slab = NULL; |
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}
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