sd_bus_slot_set_description, sd_bus_slot_get_description — Set or query the description of bus slot objects
#include <systemd/sd-bus.h>
int sd_bus_slot_set_description( | sd_bus_slot* slot, | 
const char *description); | 
int sd_bus_slot_get_description( | sd_bus_slot* bus, | 
const char **description); | 
sd_bus_slot_set_description() sets the description string
    that is used in logging to the specified string. The string is copied internally
    and freed when the bus slot object is deallocated. The
    description argument may be NULL, in
    which case the description is unset.
sd_bus_slot_get_description() returns a description string in
    description. If the string is not set, e.g. with
    sd_bus_slot_set_description(), and the slot is a bus match callback slot,
    the match string will be returned. Otherwise, -ENXIO is returned.
    
On success, these functions return 0 or a positive integer. On failure, they return a negative errno-style error code.
These APIs are implemented as a shared
  library, which can be compiled and linked to with the
  libsystemd pkg-config(1)
  file.