netfilter: nft_tunnel: track register operations

Check if the destination register already contains the data that this
tunnel expression performs. This allows to skip this redundant operation.
If the destination contains a different selector, update the register
tracking information. This patch does not perform bitwise tracking.
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nft_tunnel.c

@@ -17,6 +17,7 @@ struct nft_tunnel {
 	enum nft_tunnel_keys	key:8;
 	u8			dreg;
 	enum nft_tunnel_mode	mode:8;
+	u8			len;
 };
 
 static void nft_tunnel_get_eval(const struct nft_expr *expr,
@@ -101,6 +102,7 @@ static int nft_tunnel_get_init(const struct nft_ctx *ctx,
 		priv->mode = NFT_TUNNEL_MODE_NONE;
 	}
 
+	priv->len = len;
 	return nft_parse_register_store(ctx, tb[NFTA_TUNNEL_DREG], &priv->dreg,
 					NULL, NFT_DATA_VALUE, len);
 }
@@ -122,6 +124,31 @@ static int nft_tunnel_get_dump(struct sk_buff *skb,
 	return -1;
 }
 
+static bool nft_tunnel_get_reduce(struct nft_regs_track *track,
+				  const struct nft_expr *expr)
+{
+	const struct nft_tunnel *priv = nft_expr_priv(expr);
+	const struct nft_tunnel *tunnel;
+
+	if (!nft_reg_track_cmp(track, expr, priv->dreg)) {
+		nft_reg_track_update(track, expr, priv->dreg, priv->len);
+		return false;
+	}
+
+	tunnel = nft_expr_priv(track->regs[priv->dreg].selector);
+	if (priv->key != tunnel->key ||
+	    priv->dreg != tunnel->dreg ||
+	    priv->mode != tunnel->mode) {
+		nft_reg_track_update(track, expr, priv->dreg, priv->len);
+		return false;
+	}
+
+	if (!track->regs[priv->dreg].bitwise)
+		return true;
+
+	return false;
+}
+
 static struct nft_expr_type nft_tunnel_type;
 static const struct nft_expr_ops nft_tunnel_get_ops = {
 	.type		= &nft_tunnel_type,
@@ -129,6 +156,7 @@ static const struct nft_expr_ops nft_tunnel_get_ops = {
 	.eval		= nft_tunnel_get_eval,
 	.init		= nft_tunnel_get_init,
 	.dump		= nft_tunnel_get_dump,
+	.reduce		= nft_tunnel_get_reduce,
 };
 
 static struct nft_expr_type nft_tunnel_type __read_mostly = {