Thank you for your response. It is evident that there is a needfor this features in our system.
Firstly, our customers express their desire to utilize tablespaces
for table management, without necessarily being concerned about
the directory location of these tablespaces.
Secondly, currently PG only supports absolute-path tablespaces, but
in-place tablespaces are very likely to become popular in the future.
Therefore, it is essential to incorporate support for in-place
tablespaces in the pg_upgrade feature. I intend to implement
this functionality in our system to accommodate our customers'
requirements.
It would be highly appreciated if the official PG could also
incorporate support for this feature. 
