From d99012561ac5f80b17a53cff4f6d58c3ceb801ea Mon Sep 17 00:00:00 2001
From: "Martine S. Lenders" <m.lenders@fu-berlin.de>
Date: Thu, 30 Jan 2020 17:03:28 +0100
Subject: [PATCH] gnrc_ipv6_ext_frag: add configuration option to keep oldest
 entry

---
 sys/include/net/gnrc/ipv6/ext.h                     | 13 +++++++++++++
 sys/net/gnrc/network_layer/ipv6/ext/frag/Kconfig    |  7 +++++++
 .../ipv6/ext/frag/gnrc_ipv6_ext_frag.c              |  3 ++-
 3 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/sys/include/net/gnrc/ipv6/ext.h b/sys/include/net/gnrc/ipv6/ext.h
index e06b650e41..f7118cbcca 100644
--- a/sys/include/net/gnrc/ipv6/ext.h
+++ b/sys/include/net/gnrc/ipv6/ext.h
@@ -88,6 +88,19 @@ extern "C" {
 #define CONFIG_GNRC_IPV6_EXT_FRAG_RBUF_TIMEOUT_US  (10U * US_PER_SEC)
 #endif
 
+/**
+ * @brief   Do not override oldest datagram when reassembly buffer is full
+ *
+ * @note    Only applicable with [gnrc_ipv6_ext_frag](@ref net_gnrc_ipv6_ext_frag) module
+ *
+ * When not set, it will cause the reassembly buffer to override the oldest
+ * entry when a fragment for a new datagram is received. When set to 1, no entry
+ * will be overwritten (they will still timeout normally)
+ */
+#ifdef DOXYGEN
+#define CONFIG_GNRC_IPV6_EXT_FRAG_RBUF_DO_NOT_OVERRIDE
+#endif
+
 /** @} **/
 
 /**
diff --git a/sys/net/gnrc/network_layer/ipv6/ext/frag/Kconfig b/sys/net/gnrc/network_layer/ipv6/ext/frag/Kconfig
index 192ea13f12..b4820917f6 100644
--- a/sys/net/gnrc/network_layer/ipv6/ext/frag/Kconfig
+++ b/sys/net/gnrc/network_layer/ipv6/ext/frag/Kconfig
@@ -40,4 +40,11 @@ config GNRC_IPV6_EXT_FRAG_RBUF_TIMEOUT_US
     help
         This value is expressed in microseconds.
 
+config GNRC_IPV6_EXT_FRAG_RBUF_DO_NOT_OVERRIDE
+    bool "Do not override oldest datagram when reassembly buffer is full"
+    help
+        When not set, it will cause the reassembly buffer to override the oldest
+        entry when a fragment for a new datagram is received. When set to 1, no
+        entry will be overwritten (they will still timeout normally)
+
 endif # KCONFIG_MODULE_GNRC_IPV6_EXT_FRAG
diff --git a/sys/net/gnrc/network_layer/ipv6/ext/frag/gnrc_ipv6_ext_frag.c b/sys/net/gnrc/network_layer/ipv6/ext/frag/gnrc_ipv6_ext_frag.c
index 95b756a0a2..a807831d59 100644
--- a/sys/net/gnrc/network_layer/ipv6/ext/frag/gnrc_ipv6_ext_frag.c
+++ b/sys/net/gnrc/network_layer/ipv6/ext/frag/gnrc_ipv6_ext_frag.c
@@ -557,7 +557,8 @@ gnrc_ipv6_ext_frag_rbuf_t *gnrc_ipv6_ext_frag_rbuf_get(ipv6_hdr_t *ipv6,
             oldest = tmp;
         }
     }
-    if (res == NULL) {
+    if ((res == NULL) &&
+        !IS_ACTIVE(CONFIG_GNRC_IPV6_EXT_FRAG_RBUF_DO_NOT_OVERRIDE)) {
         assert(oldest != NULL); /* reassembly buffer is full, so there needs
                                  * to be an oldest entry */
         DEBUG("ipv6_ext_frag: dropping oldest entry\n");