On Thu, Dec 29, 2016 at 8:44 AM, Erik Falor <ewfa...@gmail.com> wrote:
> I wish to use sd-bus to query upowerd for my battery's remaining > percentage. I > have begun by adapting the example program from Lennart's blog post > introducing > the sd-bus API: > > http://0pointer.net/blog/the-new-sd-bus-api-of-systemd.html > > However, I cannot succeed in adapting it to my needs. I can read the value > of > the Percentage property with > > $ busctl introspect org.freedesktop.UPower /org/freedesktop/UPower/ > devices/battery_BAT0 > > This shows me that the Percentage is a double value, and that the Get() > method > of the org.freedesktop.DBus.Properties interface returns a variant value. > > I can also retrieve the desired datum with busctl: > > $ busctl call org.freedesktop.UPower \ > /org/freedesktop/UPower/devices/battery_BAT0 \ > org.freedesktop.DBus.Properties Get \ > ss org.freedesktop.UPower.Device Percentage > > I can make the equivalent method call using the sd-bus API from the C > program, > but the program errors out at the call to sd_bus_message_read(). > > When I tell sd_bus_message_read() that my message is of variant type "v", > it > fails with -EINVAL. When I instead give it "d", it fails with -ENXIO. > > What does sd_bus_message_read() expect in the 2nd argument? Or am I doing > something else wrong? > variant is a "container" type – you must first call sd_bus_message_enter_container() before you can access the inner value: sd_bus_message_enter_container(m, 'v', "d"); sd_bus_message_read(m, "d", &out); For convenience you also have sd_bus_get_property() which even does the method call for you. -- Mantas Mikulėnas <graw...@gmail.com>
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