From aa089820ab661dbd29194934b63946d140dacd8d Mon Sep 17 00:00:00 2001
From: Ian Barwick <ian@2ndquadrant.com>
Date: Fri, 10 Nov 2017 14:35:17 +0900
Subject: [PATCH] repmgrd: check shared library is loaded

If this isn't the case, "repmgrd" will appear to run but not handle
failover correctly.

Address GitHub #337.
---
 dbutils.c | 22 +++++++++++++++++++++-
 dbutils.h |  1 +
 repmgr.c  |  1 -
 repmgrd.c | 18 ++++++++++++++++++
 4 files changed, 40 insertions(+), 2 deletions(-)

diff --git a/dbutils.c b/dbutils.c
index 9525f882..ac839076 100644
--- a/dbutils.c
+++ b/dbutils.c
@@ -1554,7 +1554,7 @@ repmgrd_set_local_node_id(PGconn *conn, int local_node_id)
 	initPQExpBuffer(&query);
 
 	appendPQExpBuffer(&query,
-					  " SELECT repmgr.set_local_node_id(%i)",
+					  "SELECT repmgr.set_local_node_id(%i)",
 					  local_node_id);
 
 	res = PQexec(conn, query.data);
@@ -1572,6 +1572,26 @@ repmgrd_set_local_node_id(PGconn *conn, int local_node_id)
 
 
 
+int
+repmgrd_get_local_node_id(PGconn *conn)
+{
+	PGresult   *res = NULL;
+	int			local_node_id = UNKNOWN_NODE_ID;
+
+	res = PQexec(conn, "SELECT repmgr.get_local_node_id()");
+
+	if (!PQgetisnull(res, 0, 0))
+	{
+		local_node_id = atoi(PQgetvalue(res, 0, 0));
+	}
+
+	PQclear(res);
+
+	return local_node_id;
+}
+
+
+
 /* ================ */
 /* result functions */
 /* ================ */
diff --git a/dbutils.h b/dbutils.h
index 8c78c05a..5fbfb16c 100644
--- a/dbutils.h
+++ b/dbutils.h
@@ -382,6 +382,7 @@ bool		can_use_pg_rewind(PGconn *conn, const char *data_directory, PQExpBufferDat
 int			get_ready_archive_files(PGconn *conn, const char *data_directory);
 bool		identify_system(PGconn *repl_conn, t_system_identification *identification);
 bool		repmgrd_set_local_node_id(PGconn *conn, int local_node_id);
+int			repmgrd_get_local_node_id(PGconn *conn);
 
 /* extension functions */
 ExtensionStatus get_repmgr_extension_status(PGconn *conn);
diff --git a/repmgr.c b/repmgr.c
index 29bb183b..a12fc4d9 100644
--- a/repmgr.c
+++ b/repmgr.c
@@ -124,7 +124,6 @@ _PG_init(void)
 {
 	elog(DEBUG1, "repmgr init");
 
-	/* error here? */
 	if (!process_shared_preload_libraries_in_progress)
 		return;
 
diff --git a/repmgrd.c b/repmgrd.c
index e850bb5c..8f88aeaa 100644
--- a/repmgrd.c
+++ b/repmgrd.c
@@ -332,6 +332,24 @@ main(int argc, char **argv)
 
 	repmgrd_set_local_node_id(local_conn, config_file_options.node_id);
 
+	{
+		/*
+		 * sanity-check that the shared library is loaded and shared memory
+		 * can be written by attempting to retrieve the previously stored node_id
+		 */
+		int stored_local_node_id = UNKNOWN_NODE_ID;
+
+		stored_local_node_id = repmgrd_get_local_node_id(local_conn);
+
+		if (stored_local_node_id == UNKNOWN_NODE_ID)
+		{
+			log_error(_("unable to write to shared memory"));
+			log_hint(_("ensure \"shared_preload_libraries\" includes \"repmgr\""));
+			PQfinish(local_conn);
+			terminate(ERR_BAD_CONFIG);
+		}
+	}
+
 	if (config_file_options.replication_type == REPLICATION_TYPE_BDR)
 	{
 		log_debug("node id is %i", local_node_info.node_id);