add partition should not reset data directory back to default

create table partest(

id int(10) unsigned not null auto_increment,

val int(10) unsigned not null default 0,

primary key (id, val)

) engine=InnoDB

default charset=utf8mb4

data directory='/tmp/maria-partest/';

insert into partest(val) values(1);

insert into partest(val) values(1001);

~# ls -alh /tmp/maria-partest/test/

total 128K

drwxrwx--- 2 mysql mysql   25 Nov 16 23:01 .

drwxrwx--- 3 mysql mysql   18 Nov 16 22:55 ..

-rw-rw---- 1 mysql mysql 128K Nov 16 23:01 partest.ibd

~# ls -alh /var/lib/mysql/test/

total 12K

drwx------ 2 mysql mysql  58 Nov 16 23:22 .

drwxr-xr-x 5 mysql mysql 289 Nov 16 22:49 ..

-rw-rw---- 1 mysql mysql  65 Nov 16 21:39 db.opt

-rw-rw---- 1 mysql mysql 947 Nov 16 23:22 partest.frm

-rw-rw---- 1 mysql mysql  35 Nov 16 23:22 partest.isl

alter table partest partition by range(val)(

partition p0 values less than (1000),

partition p1 values less than (2000),

partition pFFFF values less than maxvalue

);

~# ls -alh /tmp/maria-partest/test/

total 0

drwxrwx--- 2 mysql mysql  6 Nov 16 23:09 .

drwxrwx--- 3 mysql mysql 18 Nov 16 22:55 ..

~# ls -alh /var/lib/mysql/test/

total 300K

drwx------ 2 mysql mysql  133 Nov 16 23:11 .

drwxr-xr-x 5 mysql mysql  289 Nov 16 22:49 ..

-rw-rw---- 1 mysql mysql   65 Nov 16 21:39 db.opt

-rw-rw---- 1 mysql mysql 1.2K Nov 16 23:11 partest.frm

-rw-rw---- 1 mysql mysql   44 Nov 16 23:11 partest.par

-rw-rw---- 1 mysql mysql  96K Nov 16 23:09 partest#P#p0.ibd

-rw-rw---- 1 mysql mysql  96K Nov 16 23:09 partest#P#p1.ibd

-rw-rw---- 1 mysql mysql  96K Nov 16 23:09 partest#P#pFFFF.ibd