[nft PATCH] expr: make map lookup expression as an argument in vmap statement

[Son Dinh <dinhtrason@xxxxxxxxx>]

Support nested map lookups combined with vmap lookup as shown
in the example below. This syntax enables flexibility to use the
values of a map as keys for looking up vmap when users have two
distinct maps for different purposes and do not want to alter any
packet-related objects (e.g., packet mark, ct mark, ip fields)
to store the value returned from the first map lookup for the
final vmap lookup.

Command:
   add rule ip table-a ip saddr map @map1 vmap @map2

Output:

   chain table-a {
           ip saddr map @map1 vmap @map2
   }

It also supports multiple map lookups prior to vmap if users need
to use multiple maps for the same query, such as

   chain table-a {
           ip saddr map @map1 map @map2 vmap @map3
   }

Closes: https://bugzilla.netfilter.org/show_bug.cgi?id=1736

Signed-off-by: Son Dinh <dinhtrason@xxxxxxxxx>
---
 src/evaluate.c            |  2 +-
 src/netlink_delinearize.c | 12 +++++++-----
 src/parser_bison.y        |  8 ++++++++
 3 files changed, 16 insertions(+), 6 deletions(-)

diff --git src/evaluate.c src/evaluate.c
index 1682ba58..07c26d16 100644
--- src/evaluate.c
+++ src/evaluate.c
@@ -2052,7 +2052,7 @@ static int expr_evaluate_map(struct eval_ctx *ctx, struct expr **expr)
 	expr_set_context(&ctx->ectx, NULL, 0);
 	if (expr_evaluate(ctx, &map->map) < 0)
 		return -1;
-	if (expr_is_constant(map->map))
+	if (map->map->etype != EXPR_MAP && expr_is_constant(map->map))
 		return expr_error(ctx->msgs, map->map,
 				  "Map expression can not be constant");
 
diff --git src/netlink_delinearize.c src/netlink_delinearize.c
index da9f7a91..f8968a25 100644
--- src/netlink_delinearize.c
+++ src/netlink_delinearize.c
@@ -428,11 +428,13 @@ static void netlink_parse_lookup(struct netlink_parse_ctx *ctx,
 		return netlink_error(ctx, loc,
 				     "Lookup expression has no left hand side");
 
-	if (left->len < set->key->len) {
-		expr_free(left);
-		left = netlink_parse_concat_expr(ctx, loc, sreg, set->key->len);
-		if (left == NULL)
-			return;
+	if (left->etype != EXPR_MAP) {
+		if (left->len < set->key->len) {
+			expr_free(left);
+			left = netlink_parse_concat_expr(ctx, loc, sreg, set->key->len);
+			if (left == NULL)
+				return;
+		}
 	}
 
 	right = set_ref_expr_alloc(loc, set);
diff --git src/parser_bison.y src/parser_bison.y
index 61bed761..26b5a50a 100644
--- src/parser_bison.y
+++ src/parser_bison.y
@@ -3254,6 +3254,10 @@ verdict_stmt		:	verdict_expr
 			;
 
 verdict_map_stmt	:	concat_expr	VMAP	verdict_map_expr
+			{
+				$$ = map_expr_alloc(&@$, $1, $3);
+			}
+			|	map_expr	VMAP	verdict_map_expr
 			{
 				$$ = map_expr_alloc(&@$, $1, $3);
 			}
@@ -4579,6 +4583,10 @@ multiton_rhs_expr	:	prefix_rhs_expr
 			;
 
 map_expr		:	concat_expr	MAP	rhs_expr
+			{
+				$$ = map_expr_alloc(&@$, $1, $3);
+			}
+			| map_expr MAP rhs_expr
 			{
 				$$ = map_expr_alloc(&@$, $1, $3);
 			}
-- 
2.44.0.windows.1