From 82001cfd79f9263338490c4e221e698203979072 Mon Sep 17 00:00:00 2001
From: Martine Lenders <m.lenders@fu-berlin.de>
Date: Tue, 29 Jan 2019 13:25:59 +0100
Subject: [PATCH] gnrc_ipv6_nib: expose non-randomized part of NS-backoff
calculation
This was primarily done so the backoff can be tested
---
.../gnrc/network_layer/ipv6/nib/_nib-arsm.c | 16 ++------
.../gnrc/network_layer/ipv6/nib/_nib-arsm.h | 37 +++++++++++++++++++
2 files changed, 41 insertions(+), 12 deletions(-)
diff --git a/sys/net/gnrc/network_layer/ipv6/nib/_nib-arsm.c b/sys/net/gnrc/network_layer/ipv6/nib/_nib-arsm.c
index e14a6fd030..cf96fac888 100644
--- a/sys/net/gnrc/network_layer/ipv6/nib/_nib-arsm.c
+++ b/sys/net/gnrc/network_layer/ipv6/nib/_nib-arsm.c
@@ -514,18 +514,10 @@ bool _is_reachable(_nib_onl_entry_t *entry)
static inline uint32_t _exp_backoff_retrans_timer(uint8_t ns_sent,
uint32_t retrans_timer)
{
- uint32_t tmp = random_uint32_range(NDP_MIN_RANDOM_FACTOR,
- NDP_MAX_RANDOM_FACTOR);
-
- /* backoff according to https://tools.ietf.org/html/rfc7048 with
- * BACKOFF_MULTIPLE == 2 */
- tmp = (uint32_t)(((uint64_t)(((uint32_t) 1) << ns_sent) * retrans_timer *
- tmp) / US_PER_MS);
- /* random factors were statically multiplied with 1000 ^ */
- if (tmp > NDP_MAX_RETRANS_TIMER_MS) {
- tmp = NDP_MAX_RETRANS_TIMER_MS;
- }
- return tmp;
+ uint32_t factor = random_uint32_range(NDP_MIN_RANDOM_FACTOR,
+ NDP_MAX_RANDOM_FACTOR);
+
+ return _exp_backoff_retrans_timer_factor(ns_sent, retrans_timer, factor);
}
#if GNRC_IPV6_NIB_CONF_REDIRECT
diff --git a/sys/net/gnrc/network_layer/ipv6/nib/_nib-arsm.h b/sys/net/gnrc/network_layer/ipv6/nib/_nib-arsm.h
index abfdb8f263..aa7210992b 100644
--- a/sys/net/gnrc/network_layer/ipv6/nib/_nib-arsm.h
+++ b/sys/net/gnrc/network_layer/ipv6/nib/_nib-arsm.h
@@ -81,6 +81,43 @@ void _snd_uc_ns(_nib_onl_entry_t *nbr, bool reset);
void _handle_sl2ao(gnrc_netif_t *netif, const ipv6_hdr_t *ipv6,
const icmpv6_hdr_t *icmpv6, const ndp_opt_t *sl2ao);
+/**
+ * @brief Calculates truncated exponential back-off for retransmission timer
+ * for neighbor solicitations based on a randomized factor
+ *
+ * The truncation is at @ref NDP_MAX_RETRANS_TIMER_MS. as suggested in
+ * [RFC 7048, section 3](https://tools.ietf.org/html/rfc7048#section-3).
+ *
+ * @param[in] ns_sent Neighbor solicitations sent up until now. Must be
+ * lesser than or equal to @ref NDP_MAX_NS_NUMOF.
+ * @param[in] retrans_timer Currently configured retransmission timer in ms.
+ * @param[in] factor An equally distributed factor between
+ * @ref NDP_MIN_RANDOM_FACTOR and (exclusive)
+ * @ref NDP_MAX_RANDOM_FACTOR.
+ *
+ * @pre (NDP_MIN_RANDOM_FACTOR <= factor < NDP_MAX_RANDOM_FACTOR)
+ * @pre (ns_sent <= NDP_MAX_NS_NUMOF)
+ *
+ * @return exponential back-off of the retransmission timer
+ */
+static inline uint32_t _exp_backoff_retrans_timer_factor(uint8_t ns_sent,
+ uint32_t retrans_timer,
+ uint32_t factor)
+{
+ assert(NDP_MIN_RANDOM_FACTOR <= factor);
+ assert(factor < NDP_MAX_RANDOM_FACTOR);
+ assert(ns_sent <= NDP_MAX_NS_NUMOF);
+ /* backoff according to https://tools.ietf.org/html/rfc7048 with
+ * BACKOFF_MULTIPLE == 2 */
+ uint32_t res = (uint32_t)(((uint64_t)(((uint32_t) 1) << ns_sent) *
+ retrans_timer * factor) / US_PER_MS);
+ /* random factors were statically multiplied with 1000 */
+ if (res > NDP_MAX_RETRANS_TIMER_MS) {
+ res = NDP_MAX_RETRANS_TIMER_MS;
+ }
+ return res;
+}
+
#if GNRC_IPV6_NIB_CONF_ARSM || defined(DOXYGEN)
/**
* @brief Handler for @ref GNRC_IPV6_NIB_SND_UC_NS and
--
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