Bug#1021644: logind: OnExternalPower is confusedj

[Michael Biebl]

Hi Helmut,

I can reproduce the issue here.
Since we don't ship any Debian specific patches in that regard, it would 
be awesome if you can raise this upstream at

https://github.com/systemd/systemd/issues

I quickly searched through existing PRs and issues but didn't find anything.


Am 12.10.22 um 06:19 schrieb Helmut Grohne:
> Package: systemd
> Version: 251.5-1
> 
> Hi,
> 
> logind seems confused
> 
> # busctl get-property org.freedesktop.login1 /org/freedesktop/login1 org.freedesktop.login1.Manager OnExternalPower
> b true
> # /lib/systemd/systemd-ac-power  --verbose
> no
> #
> 
> The system in question actually is running on battery. Both appear to be
> using the on_ac_power() C function. When running strace on the latter
> one can vaguely guess that on_ac_power() is actually run. When running
> strace on logind however, the sendmsg call happens immediately after the
> recvmsg call, so it seems like on_ac_power() is not actually run, but
> the value is cached or something. During boot, the system in question
> was on ac power.
> 
> Looking closer, I now guess that the issue is here:
> https://sources.debian.org/src/systemd/251.5-2/src/login/logind-dbus.c/?hl=380#L380
> 
> Could it be that the function pointer is converted to boolean rather
> than being called? I.e. could it be that the function should actually be
> called?
> 
> -static BUS_DEFINE_PROPERTY_GET_GLOBAL(property_get_on_external_power, "b", manager_is_on_external_power);
> +static BUS_DEFINE_PROPERTY_GET_GLOBAL(property_get_on_external_power, "b", manager_is_on_external_power());
> 

The macro is defined as src/shared/bus-get-properties.h

#define BUS_DEFINE_PROPERTY_GET_GLOBAL(function, bus_type, val)

so what you say makes sense.

There is a corresponding
#define BUS_DEFINE_PROPERTY_GET(function, bus_type, data_type, get1)
where "get1" is interpreted as a function. This inconsistency between 
those two macros is a bit of a pitfall I assume.

A "grep BUS_DEFINE_PROPERTY_GET_GLOBAL -R" doesn't reveal any other 
occurrences where this might be wrong. So it might just be the one spot 
that you found.

Regards,
Michael


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