void mf_format_subfield(const struct mf_subfield *, struct ds *);
-char *mf_parse_subfield__(struct mf_subfield *sf, const char **s);
-const char *mf_parse_subfield(struct mf_subfield *, const char *);
+char *mf_parse_subfield__(struct mf_subfield *sf, const char **s)
+ WARN_UNUSED_RESULT;
+char *mf_parse_subfield(struct mf_subfield *, const char *s)
+ WARN_UNUSED_RESULT;
enum ofperr mf_check_src(const struct mf_subfield *, const struct flow *);
enum ofperr mf_check_dst(const struct mf_subfield *, const struct flow *);