`systemctl show UNIT -p ActiveState -p UnitFileState` currently calls:
`org.freedesktop.DBus.Properties.GetAll("")`
PID 1 therefore generates and serializes properties from every interface, while
systemctl discards everything except the requested properties.
The standard D-Bus Properties interface supports either one property with
`Get()` or all properties of an interface with `GetAll()`. It has no operation
for retrieving several selected properties in one call.
I want to add a new D-Bus method to request only specific properties, like:
`GetUnitProperties(unit, ["ActiveState", "UnitFileState"]) -> {"ActiveState":
..., "UnitFileState": ...}`
Another possible location would be a method on the unit object itself:
`GetProperties(["ActiveState", "UnitFileState"]) → a{sv}`
This would allow `systemctl show -p ...` to avoid generating unrelated
properties while preserving a single D-Bus round trip.
Would such an API be appropriate? I understand that the longer-term direction
may be Varlink, but this question concerns optimizing the existing D-Bus
interface and clients that continue to use it.
Thank you,
Roman Perehonchuk
