Add selection to layer mask

[MichaJo]

Hi everyone,
i'm a long time user of GIMP.
But this i don't know:
How can i add a selection to an existing layer mask?
How can i subtract a selection from an existing layer mask?
Currently i make "Mask to Selection"
then i add or subtract a selection
then i delete the existing mask
and "Add Layer Mask..." with "Selection"

Second method:
Make an selection while editing the layer mask and bucket fill this selection with white or respectively black.

is there a shorter way such as "Add selection to existing mask" ?


Regards

Michael