[Issue #203] error out if FIO_FDMAX is exceeded in fio_open

Author: gsmolk

src/backup.c

@@ -352,6 +352,9 @@ do_backup_instance(PGconn *backup_conn, PGNodeInfo *nodeInfo, bool no_sync)
 			dir_list_file(backup_files_list, parray_get(external_dirs, i),
 						  false, true, false, i+1, FIO_DB_HOST);
 
+	/* close ssh session in main thread */
+	fio_disconnect();
+
 	/* Sanity check for backup_files_list, thank you, Windows:
 	 * https://github.com/postgrespro/pg_probackup/issues/48
 	 */
@@ -526,9 +529,6 @@ do_backup_instance(PGconn *backup_conn, PGNodeInfo *nodeInfo, bool no_sync)
 		arg->ret = 1;
 	}
 
-	/* close ssh session in main thread */
-	fio_disconnect();
-
 	/* Run threads */
 	thread_interrupted = false;
 	elog(INFO, "Start transferring data files");

src/utils/file.c

@@ -348,9 +348,9 @@ int fio_open(char const* path, int mode, fio_location location)
 
 		mask = fio_fdset;
 		for (i = 0; (mask & 1) != 0; i++, mask >>= 1);
-		if (i == FIO_FDMAX) {
-			return -1;
-		}
+		if (i == FIO_FDMAX)
+			elog(ERROR, "FIO_FDMAX is exceeded, probably too many remote files has been opened");
+
 		hdr.cop = FIO_OPEN;
 		hdr.handle = i;
 		hdr.size = strlen(path) + 1;