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.

1 files changed, 10 insertions, 0 deletions

diff --git a/mysql-test/suite/mariabackup/absolute_ibdata_paths.result b/mysql-test/suite/mariabackup/absolute_ibdata_paths.result
new file mode 100644
index 00000000000..fe211e71f2f
--- /dev/null
+++ b/mysql-test/suite/mariabackup/absolute_ibdata_paths.result
@@ -0,0 +1,10 @@
+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;