Check data directory not used by an active instance before cloning

This involves adding some infrastructure to parse pg_control in a
reasonably version-independent fashion. This will probably be useful
in other contexts where we need to verify the status of a
data directory where the instance isn't running.

Makefile.in

@@ -27,7 +27,7 @@ include Makefile.global
 $(info Building against PostgreSQL $(MAJORVERSION))
 
 REPMGR_CLIENT_OBJS = repmgr-client.o repmgr-action-master.o repmgr-action-standby.o repmgr-action-cluster.o \
-  config.o log.o strutil.o dbutils.o dirutil.o compat.o
+  config.o log.o strutil.o dbutils.o dirutil.o compat.o controldata.o
 REPMGRD_OBJS = repmgrd.o
 
 $(REPMGR_CLIENT_OBJS): repmgr-client.h
@@ -58,6 +58,7 @@ additional-clean:
 	rm -f repmgrd.o
 	rm -f compat.o
 	rm -f config.o
+	rm -f controldata.o
 	rm -f dbutils.o
 	rm -f dirutil.o
 	rm -f log.o

controldata.c

@@ -0,0 +1,110 @@
+/*
+ * controldata.c
+ * Copyright (c) 2ndQuadrant, 2010-2017
+ *
+ * Portions Copyright (c) 1996-2016, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ */
+
+#include <unistd.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+
+#include "postgres_fe.h"
+#include "port/pg_crc32c.h"
+
+#include "repmgr.h"
+#include "controldata.h"
+
+static ControlFileInfo *get_controlfile(char *DataDir);
+
+DBState
+get_db_state(char *data_directory)
+{
+	ControlFileInfo *control_file_info;
+	DBState state;
+
+	control_file_info = get_controlfile(data_directory);
+
+	if (control_file_info->control_file_processed == true)
+		state = control_file_info->control_file->state;
+	else
+		/* if we were unable to parse the control file, assume DB is shut down */
+		state = DB_SHUTDOWNED;
+
+	pfree(control_file_info->control_file);
+	pfree(control_file_info);
+	return state;
+}
+
+const char *
+describe_db_state(DBState state)
+{
+	switch (state)
+	{
+		case DB_STARTUP:
+			return _("starting up");
+		case DB_SHUTDOWNED:
+			return _("shut down");
+		case DB_SHUTDOWNED_IN_RECOVERY:
+			return _("shut down in recovery");
+		case DB_SHUTDOWNING:
+			return _("shutting down");
+		case DB_IN_CRASH_RECOVERY:
+			return _("in crash recovery");
+		case DB_IN_ARCHIVE_RECOVERY:
+			return _("in archive recovery");
+		case DB_IN_PRODUCTION:
+			return _("in production");
+	}
+	return _("unrecognized status code");
+}
+
+
+/*
+ * we maintain our own version of get_controlfile() as we don't care if
+ * the file isn't readable
+ */
+static ControlFileInfo *
+get_controlfile(char *DataDir)
+{
+	ControlFileInfo *control_file_info;
+	int			fd;
+	char		ControlFilePath[MAXPGPATH];
+	pg_crc32c	crc;
+
+	control_file_info = palloc0(sizeof(ControlFileInfo));
+	control_file_info->control_file_processed = false;
+	control_file_info->control_file = palloc0(sizeof(ControlFileData));
+
+	snprintf(ControlFilePath, MAXPGPATH, "%s/global/pg_control", DataDir);
+
+	if ((fd = open(ControlFilePath, O_RDONLY | PG_BINARY, 0)) == -1)
+	{
+		log_debug("could not open file \"%s\" for reading: %s",
+				  ControlFilePath, strerror(errno));
+		return control_file_info;
+	}
+
+	if (read(fd, control_file_info->control_file, sizeof(ControlFileData)) != sizeof(ControlFileData))
+	{
+		log_debug("could not read file \"%s\": %s",
+				  ControlFilePath, strerror(errno));
+		return control_file_info;
+	}
+
+	close(fd);
+
+	control_file_info->control_file_processed = true;
+
+	/*
+	 * We don't check the CRC here as we're potentially checking a pg_control
+	 * file from a different PostgreSQL version to the one repmgr was compiled
+	 * against. However we're only interested in the first few fields, which
+	 * should be constant across supported versions
+	 *
+	 * XXX double-check this
+	 */
+
+	return control_file_info;
+}

controldata.h

@@ -0,0 +1,27 @@
+/*
+ * controldata.h
+ * Copyright (c) 2ndQuadrant, 2010-2017
+ *
+ * Portions Copyright (c) 1996-2016, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ */
+
+#ifndef _CONTROLDATA_H_
+#define _CONTROLDATA_H_
+
+#include "postgres_fe.h"
+#include "catalog/pg_control.h"
+
+typedef struct
+{
+	bool control_file_processed;
+	ControlFileData *control_file;
+} ControlFileInfo;
+
+extern DBState
+get_db_state(char *data_directory);
+
+extern const char *
+describe_db_state(DBState state);
+
+#endif /* _CONTROLDATA_H_ */

repmgr-action-master.c

@@ -138,7 +138,7 @@ do_master_register(void)
 	node_info.priority = config_file_options.priority;
 
 	initPQExpBuffer(&event_description);
-	puts("here");
+
 	if (record_found)
 	{
 		record_created = update_node_record(conn,

repmgr-action-standby.c

@@ -11,6 +11,7 @@
 #include "repmgr.h"
 #include "dirutil.h"
 #include "compat.h"
+#include "controldata.h"
 
 #include "repmgr-client-global.h"
 #include "repmgr-action-standby.h"
@@ -148,15 +149,21 @@ do_standby_clone(void)
 	}
 	else if (mode == barman)
 	{
+		/* XXX in Barman mode it's still possible to connect to the upstream,
+		 * so only fail if that's not available.
+		 */
 		log_error(_("Barman mode requires a data directory"));
 		log_hint(_("use -D/--pgdata to explicitly specify a data directory"));
 		exit(ERR_BAD_CONFIG);
 	}
 
 	/*
-	 * target directory (-D/--pgdata) provided - use that as new data directory
+	 * Target directory (-D/--pgdata) provided - use that as new data directory
 	 * (useful when executing backup on local machine only or creating the backup
 	 * in a different local directory when backup source is a remote host)
+	 *
+	 * Note: if no directory provided, check_source_server() will later set
+	 * local_data_directory from the upstream configuration.
 	 */
 	if (local_data_directory_provided == true)
 	{
@@ -245,6 +252,23 @@ do_standby_clone(void)
 		check_source_server_via_barman();
 	}
 
+	/*
+	 * by this point we should know the target data directory - check
+	 * there's no running Pg instance
+	 */
+	if (is_pg_dir(local_data_directory))
+	{
+		DBState state = get_db_state(local_data_directory);
+
+		if (state != DB_SHUTDOWNED && state != DB_SHUTDOWNED_IN_RECOVERY)
+		{
+			log_error(_("target data directory appears to contain an active PostgreSQL instance"));
+			log_detail(_("instance state is %s"), describe_db_state(state));
+			exit(ERR_BAD_CONFIG);
+		}
+	}
+
+
 	if (upstream_record_found == true)
 	{
 		/*  parse returned upstream conninfo string to recovery primary_conninfo params*/