int sd_journal_get_field(sd_journal *j, const char *field, const void **data, size_t *l);
int sd_journal_iterate_fields(sd_journal *j, const void **data, size_t *l);
int sd_journal_get_field(sd_journal *j, const char *field, const void **data, size_t *l);
int sd_journal_iterate_fields(sd_journal *j, const void **data, size_t *l);