BTW the logic in the YaST module already tries to estimate the really available space. It even tries to estimate the journal log size for several file systems like XFS: https://github.com/yast/yast-packager/blob/af6703078dcbe156efc11e808b68410ba98e2f29/src/modules/SpaceCalculation.rb#L250-L277 (Thought I do not know if that code is still up to date, it is 11+ years old...)