MDEV-15780 : Mariabackup with absolute paths in innodb_data_file_path

System tablespace can be specified with absolute path, if innodb_data_home_dir
is empty.

This was not handled well  by mariabackup

1. In backup phase, empty innodb_data_home_dir variable from server was
not recognized. full paths were stored in backup-my.ini, even if
it stored all files locally. thus prepare phase would not find the system
tablespace files.

2. In copy-back phase, copy would not be done to the absolute destination
path, as path would be stripped with trim_dotslash

This patch fixes the above defects.

extra/mariabackup/backup_copy.cc

@@ -975,6 +975,9 @@ copy_file(ds_ctxt_t *datasink,
 	datafile_cur_t		 cursor;
 	xb_fil_cur_result_t	 res;
 	const char		*action;
+	const char	*dst_path =
+		(xtrabackup_copy_back || xtrabackup_move_back)?
+		dst_file_path : trim_dotslash(dst_file_path);
 
 	if (!datafile_open(src_file_path, &cursor, thread_n)) {
 		goto error_close;
@@ -982,8 +985,7 @@ copy_file(ds_ctxt_t *datasink,
 
 	strncpy(dst_name, cursor.rel_path, sizeof(dst_name));
 
-	dstfile = ds_open(datasink, trim_dotslash(dst_file_path),
-			  &cursor.statinfo);
+	dstfile = ds_open(datasink, dst_path, &cursor.statinfo);
 	if (dstfile == NULL) {
 		msg("[%02u] error: "
 			"cannot open the destination stream for %s\n",

extra/mariabackup/backup_mysql.cc

@@ -477,7 +477,7 @@ get_mysql_vars(MYSQL *connection)
 			innodb_data_file_path_var, MYF(MY_FAE));
 	}
 
-	if (innodb_data_home_dir_var && *innodb_data_home_dir_var) {
+	if (innodb_data_home_dir_var) {
 		innobase_data_home_dir = my_strdup(
 			innodb_data_home_dir_var, MYF(MY_FAE));
 	}
@@ -1521,6 +1521,44 @@ write_xtrabackup_info(MYSQL *connection)
 
 extern const char *innodb_checksum_algorithm_names[];
 
+#ifdef _WIN32
+#include <algorithm>
+#endif
+
+static std::string make_local_paths(const char *data_file_path)
+{
+	if (strchr(data_file_path, '/') == 0
+#ifdef _WIN32
+		&& strchr(data_file_path, '\\') == 0
+#endif
+		){
+		return std::string(data_file_path);
+	}
+
+	std::ostringstream buf;
+
+	char *dup = strdup(innobase_data_file_path);
+	ut_a(dup);
+	char *p;
+	char * token = strtok_r(dup, ";", &p);
+	while (token) {
+		if (buf.tellp())
+			buf << ";";
+
+		char *fname = strrchr(token, '/');
+#ifdef _WIN32
+		fname = std::max(fname,strrchr(token, '\\'));
+#endif
+		if (fname)
+			buf << fname + 1;
+		else
+			buf << token;
+		token = strtok_r(NULL, ";", &p);
+	}
+	free(dup);
+	return buf.str();
+}
+
 bool write_backup_config_file()
 {
 	int rc= backup_file_printf("backup-my.cnf",
@@ -1541,7 +1579,7 @@ bool write_backup_config_file()
 		"%s\n",
 		innodb_checksum_algorithm_names[srv_checksum_algorithm],
 		innodb_checksum_algorithm_names[srv_log_checksum_algorithm],
-		innobase_data_file_path,
+		make_local_paths(innobase_data_file_path).c_str(),
 		srv_n_log_files,
 		innobase_log_file_size,
 		srv_page_size,

mysql-test/suite/mariabackup/absolute_ibdata_paths.opt

+--innodb --innodb-data-home-dir= --innodb-data-file-path=$MYSQLTEST_VARDIR/tmp/absolute_path_ibdata1:3M;ibdata_second:1M:autoextend
\ No newline at end of file

mysql-test/suite/mariabackup/absolute_ibdata_paths.result

+CREATE TABLE t(i INT) ENGINE INNODB;
+INSERT INTO t VALUES(1);
+# xtrabackup backup
+# remove datadir
+# xtrabackup copy back
+# restart server
+SELECT * from t;
+i
+1
+DROP TABLE t;

mysql-test/suite/mariabackup/absolute_ibdata_paths.test

+# This test just backs up and restores empty database
+# Innodb system tablespace is specified with absolute path in  the .opt file
+CREATE TABLE t(i INT) ENGINE INNODB;
+INSERT INTO t VALUES(1);
+echo # xtrabackup backup;
+
+let $targetdir=$MYSQLTEST_VARDIR/tmp/backup;
+let $_innodb_data_file_path=`select @@innodb_data_file_path`;
+let $_innodb_data_home_dir=`select @@innodb_data_home_dir`;
+let $_datadir= `SELECT @@datadir`;
+
+--disable_result_log
+exec $XTRABACKUP --defaults-file=$MYSQLTEST_VARDIR/my.cnf --backup --target-dir=$targetdir;
+--enable_result_log
+exec $XTRABACKUP  --prepare --target-dir=$targetdir;
+
+--source include/shutdown_mysqld.inc
+echo # remove datadir;
+rmdir $_datadir;
+#remove out-of-datadir ibdata1
+remove_file $MYSQLTEST_VARDIR/tmp/absolute_path_ibdata1;
+echo # xtrabackup copy back;
+exec $XTRABACKUP --defaults-file=$MYSQLTEST_VARDIR/my.cnf --copy-back --datadir=$_datadir --target-dir=$targetdir "--innodb_data_file_path=$_innodb_data_file_path" --innodb_data_home_dir=$_innodb_data_home_dir;
+echo # restart server;
+--source include/start_mysqld.inc
+--enable_result_log
+
+SELECT * from t;
+DROP TABLE t;
+rmdir $targetdir;
+