extern int systemd_unit_list(int isuser, int (*callback)(void *closure, const char *name, const char *path, int isuser), void *closure);
extern int systemd_unit_list_all(int (*callback)(void *closure, const char *name, const char *path, int isuser), void *closure);
extern int systemd_unit_list(int isuser, int (*callback)(void *closure, const char *name, const char *path, int isuser), void *closure);
extern int systemd_unit_list_all(int (*callback)(void *closure, const char *name, const char *path, int isuser), void *closure);