src: add datatype->describe()

As an alternative to print the datatype values when no symbol table is
available. Use it to print protocols available via getprotobynumber()
which actually refers to /etc/protocols.

Not very efficient, getprotobynumber() causes a series of open()/close()
calls on /etc/protocols, but this is called from a non-critical path.

Closes: https://bugzilla.netfilter.org/show_bug.cgi?id=1503
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/src/expression.c b/src/expression.c
index 0c5276d1..9fdf23d9 100644
--- a/src/expression.c
+++ b/src/expression.c
@@ -172,6 +172,8 @@ void expr_describe(const struct expr *expr, struct output_ctx *octx)
 			nft_print(octx, "(in hexadecimal):\n");
 		symbol_table_print(edtype->sym_tbl, edtype,
 				   expr->byteorder, octx);
+	} else if (edtype->describe) {
+		edtype->describe(octx);
 	}
 }