sd_event_source_set_description, sd_event_source_get_description — Set or retrieve descriptive names of event sources
#include <systemd/sd-event.h>
int sd_event_source_set_description( | sd_event_source *source, | 
const char *description); | 
int sd_event_source_get_description( | sd_event_source *source, | 
const char **description); | 
sd_event_source_set_description() may
    be used to set an arbitrary descriptive name for the event source
    object specified as source. This name will
    be used in debugging messages generated by
    sd-event(3)
    for this event source, and may be queried using
    sd_event_source_get_description() for
    debugging purposes. The description parameter shall
    point to a NUL-terminated string or be
    NULL. In the latter case, the descriptive
    name will be unset. The string is copied internally, hence the
    description argument is not referenced
    after the function returns.
sd_event_source_get_description() may
    be used to query the current descriptive name assigned to the
    event source object source. It returns a
    pointer to the current name in description,
    stored in memory internal to the event source. The memory is
    invalidated when the event source is destroyed or the descriptive
    name is changed.
Event source objects generally have no description set when
    they are created, except for UNIX signal event sources created
    with
    sd_event_add_signal(3),
    whose descriptive name is initialized to the signal's C constant
    name (e.g. "SIGINT" or
    "SIGTERM").
On success, sd_event_source_set_description() and
    sd_event_source_get_description() return a non-negative 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.