Prevent relative configuration file path being stored in the repmgr metadata

The configuration file path is stored to make remote execution of repmgr
(e.g. during "repmgr standby switchover") simpler, so relative paths
make no sense.

Addresses GitHub #332

configfile.c

@@ -73,6 +73,59 @@ load_config(const char *config_file, bool verbose, bool terse, t_configuration_o
 		strncpy(config_file_path, config_file, MAXPGPATH);
 		canonicalize_path(config_file_path);
 
+		/* relative path supplied - convert to absolute path */
+		if (config_file_path[0] != '/')
+		{
+			PQExpBufferData fullpath;
+			char *pwd = NULL;
+
+			initPQExpBuffer(&fullpath);
+
+			/*
+			 * we'll attempt to use $PWD to derive the effective path; getcwd()
+			 * will likely resolve symlinks, which may result in a path which
+			 * isn't permanent (e.g. if filesystem mountpoints change).
+			 */
+			pwd = getenv("PWD");
+
+			if (pwd != NULL)
+			{
+				appendPQExpBuffer(&fullpath,
+								  "%s", pwd);
+			}
+			else
+			{
+				/* $PWD not available - fall back to getcwd() */
+				char cwd[MAXPGPATH] = "";
+
+				if (getcwd(cwd, MAXPGPATH) == NULL)
+				{
+					log_error(_("unable to execute getcwd()"));
+					log_detail("%s", strerror(errno));
+
+					termPQExpBuffer(&fullpath);
+					exit(ERR_BAD_CONFIG);
+				}
+
+				appendPQExpBuffer(&fullpath,
+								  "%s",
+								  cwd);
+			}
+
+			appendPQExpBuffer(&fullpath,
+							  "/%s", config_file_path);
+
+			log_debug("relative configuration file converted to:\n  \"%s\"",
+					  fullpath.data);
+
+			strncpy(config_file_path, fullpath.data, MAXPGPATH);
+
+			termPQExpBuffer(&fullpath);
+
+			canonicalize_path(config_file_path);
+		}
+
+
 		if (stat(config_file_path, &stat_config) != 0)
 		{
 			log_error(_("provided configuration file \"%s\" not found: %s"),
@@ -81,6 +134,7 @@ load_config(const char *config_file, bool verbose, bool terse, t_configuration_o
 			exit(ERR_BAD_CONFIG);
 		}
 
+
 		if (verbose == true)
 		{
 			log_notice(_("using provided configuration file \"%s\""), config_file);