logind: fix getting property OnExternalPower via D-Bus

[mbiebl]

The BUS_DEFINE_PROPERTY_GET_GLOBAL macro requires a value as third argument, so we need to call manager_is_on_external_power(). Otherwise the function pointer is interpreted as a boolean and always returns true:

$ busctl get-property org.freedesktop.login1 /org/freedesktop/login1 org.freedesktop.login1.Manager OnExternalPower
b true
$ /lib/systemd/systemd-ac-power  --verbose
no

Thanks: Helmut Grohne
Bug-Debian: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1021644

[mbiebl]

Seems like an obvious backport candidate, so adding the corresponding label

[mbiebl]

From src/shared/bus-get-properties.h

#define BUS_DEFINE_PROPERTY_GET_GLOBAL(function, bus_type, val) 

#define BUS_DEFINE_PROPERTY_GET(function, bus_type, data_type, get1)

and src/login/logind-dbus.c

static BUS_DEFINE_PROPERTY_GET(property_get_docked, "b", Manager, manager_is_docked_or_external_displays);
static BUS_DEFINE_PROPERTY_GET(property_get_lid_closed, "b", Manager, manager_is_lid_closed);
static BUS_DEFINE_PROPERTY_GET_GLOBAL(property_get_on_external_power, "b", manager_is_on_external_power);

This inconsistency in the API is a bit of a pitfall, so a mistake like this one was bound to happen.

[yuwata]

Ouch. LGTM.

[keszybz]

Already in v251.6.