From ec38ec127cf6e06e5cb37ede8770be08ba9b8776 Mon Sep 17 00:00:00 2001
From: Ben Walker <benjamin.walker@intel.com>
Date: Thu, 19 Jan 2017 11:02:17 -0700
Subject: [PATCH] nvmf: Handle wrap-around for global cntlids

64k sessions over the lifetime of a single target is something
that really could happen, so handle this case.

Change-Id: Iaed92b9ff6cd078fcd7c1efe88cf0c860c77c4ac
Signed-off-by: Ben Walker <benjamin.walker@intel.com>
---
 lib/nvmf/session.c                 | 49 ++++++++++++++++++++++++++++--
 test/lib/nvmf/session/session_ut.c |  6 ++++
 2 files changed, 52 insertions(+), 3 deletions(-)

diff --git a/lib/nvmf/session.c b/lib/nvmf/session.c
index 040cbef07..397e0a9d8 100644
--- a/lib/nvmf/session.c
+++ b/lib/nvmf/session.c
@@ -32,6 +32,7 @@
  */
 
 #include <arpa/inet.h>
+#include <stdint.h>
 #include <string.h>
 
 #include "session.h"
@@ -47,8 +48,6 @@
 
 #define MIN_KEEP_ALIVE_TIMEOUT 10000
 
-static uint16_t g_next_cntlid = 1;
-
 static void
 nvmf_init_discovery_session_properties(struct spdk_nvmf_session *session)
 {
@@ -191,6 +190,44 @@ invalid_connect_response(struct spdk_nvmf_fabric_connect_rsp *rsp, uint8_t iattr
 	rsp->status_code_specific.invalid.ipo = ipo;
 }
 
+static uint16_t
+spdk_nvmf_session_gen_cntlid(void)
+{
+	static uint16_t cntlid = 0; /* cntlid is static, so its value is preserved */
+	struct spdk_nvmf_subsystem *subsystem;
+	uint16_t count;
+
+	count = UINT16_MAX - 1;
+	do {
+		/* cntlid is an unsigned 16-bit integer, so let it overflow
+		 * back to 0 if necessary.
+		 */
+		cntlid++;
+		if (cntlid == 0) {
+			/* 0 is not a valid cntlid because it is the reserved value in the RDMA
+			 * private data for cntlid. This is the value sent by pre-NVMe-oF 1.1
+			 * initiators.
+			 */
+			cntlid++;
+		}
+
+		/* Check if a subsystem with this cntlid currently exists. This could
+		 * happen for a very long-lived session on a target with many short-lived
+		 * sessions, where cntlid wraps around.
+		 */
+		subsystem = spdk_nvmf_find_subsystem_with_cntlid(cntlid);
+
+		count--;
+
+	} while (subsystem != NULL && count > 0);
+
+	if (count == 0) {
+		return 0;
+	}
+
+	return cntlid;
+}
+
 void
 spdk_nvmf_session_connect(struct spdk_nvmf_conn *conn,
 			  struct spdk_nvmf_fabric_connect_cmd *cmd,
@@ -260,7 +297,13 @@ spdk_nvmf_session_connect(struct spdk_nvmf_conn *conn,
 
 		TAILQ_INIT(&session->connections);
 
-		session->cntlid = g_next_cntlid++;
+		session->cntlid = spdk_nvmf_session_gen_cntlid();
+		if (session->cntlid == 0) {
+			/* Unable to get a cntlid */
+			SPDK_ERRLOG("Reached max simultaneous sessions\n");
+			rsp->status.sc = SPDK_NVME_SC_INTERNAL_DEVICE_ERROR;
+			return;
+		}
 		session->kato = cmd->kato;
 		session->async_event_config.raw = 0;
 		session->num_connections = 0;
diff --git a/test/lib/nvmf/session/session_ut.c b/test/lib/nvmf/session/session_ut.c
index 4224dc2e7..c13b7fa91 100644
--- a/test/lib/nvmf/session/session_ut.c
+++ b/test/lib/nvmf/session/session_ut.c
@@ -44,6 +44,12 @@ SPDK_LOG_REGISTER_TRACE_FLAG("nvmf", SPDK_TRACE_NVMF)
 
 struct spdk_nvmf_globals g_nvmf_tgt;
 
+struct spdk_nvmf_subsystem *
+spdk_nvmf_find_subsystem_with_cntlid(uint16_t cntlid)
+{
+	return NULL;
+}
+
 struct spdk_nvmf_subsystem *
 nvmf_find_subsystem(const char *subnqn)
 {