Features:
+* sd-device: add an API for opening a child device, given a device object
+
+* sd-device: add an API for acquiring list of child devices, given a device
+ objects (i.e. all child dirents that dirs or symlinks to dirs)
+
+* sd-device: maybe pin the sysfs dir with an fd, during the entire runtime of
+ an sd_device, then always work based on that.
+
* add small wrapper around qemu that implements sd_notify/AF_VSOCK + machined and
maybe some other stuff and boots it