tc: m_vlan: Add vlan modify action

The 'vlan modify' action allows to replace an existing 802.1q tag
according to user provided settings.
It accepts same arguments as the 'vlan push' action.

For example, this replaces vid 6 with vid 5:

 # tc filter add dev veth0 parent ffff: pref 1 protocol 802.1q \
      basic match 'meta(vlan mask 0xfff eq 6)' \
      action vlan modify id 5 continue

Signed-off-by: Shmulik Ladkani <shmulik.ladkani@gmail.com>

man/man8/tc-vlan.8

@@ -6,7 +6,7 @@ vlan - vlan manipulation module
 .in +8
 .ti -8
 .BR tc " ... " "action vlan" " { " pop " |"
-.IR PUSH " } [ " CONTROL " ]"
+.IR PUSH " | " MODIFY " } [ " CONTROL " ]"
 
 .ti -8
 .IR PUSH " := "
@@ -16,6 +16,14 @@ vlan - vlan manipulation module
 .IR VLANPRIO " ] "
 .BI id " VLANID"
 
+.ti -8
+.IR MODIFY " := "
+.BR modify " [ " protocol
+.IR VLANPROTO " ]"
+.BR " [ " priority
+.IR VLANPRIO " ] "
+.BI id " VLANID"
+
 .ti -8
 .IR CONTROL " := { "
 .BR reclassify " | " pipe " | " drop " | " continue " | " pass " }"
@@ -23,16 +31,16 @@ vlan - vlan manipulation module
 The
 .B vlan
 action allows to perform 802.1Q en- or decapsulation on a packet, reflected by
-the two operation modes
+the operation modes
-.IR POP " and " PUSH .
+.IR POP ", " PUSH " and " MODIFY .
 The
 .I POP
 mode is simple, as no further information is required to just drop the
 outer-most VLAN encapsulation. The
-.I PUSH
+.IR PUSH " and " MODIFY
-mode on the other hand requires at least a
+modes require at least a
 .I VLANID
-and allows to optionally choose the
+and allow to optionally choose the
 .I VLANPROTO
 to use.
 .SH OPTIONS
@@ -45,6 +53,11 @@ Encapsulation mode. Requires at least
 .B id
 option.
 .TP
+.B modify
+Replace mode. Existing 802.1Q tag is replaced. Requires at least
+.B id
+option.
+.TP
 .BI id " VLANID"
 Specify the VLAN ID to encapsulate into.
 .I VLANID

tc/m_vlan.c

@@ -19,10 +19,17 @@
 #include "tc_util.h"
 #include <linux/tc_act/tc_vlan.h>
 
+static const char * const action_names[] = {
+	[TCA_VLAN_ACT_POP] = "pop",
+	[TCA_VLAN_ACT_PUSH] = "push",
+	[TCA_VLAN_ACT_MODIFY] = "modify",
+};
+
 static void explain(void)
 {
 	fprintf(stderr, "Usage: vlan pop\n");
 	fprintf(stderr, "       vlan push [ protocol VLANPROTO ] id VLANID [ priority VLANPRIO ] [CONTROL]\n");
+	fprintf(stderr, "       vlan modify [ protocol VLANPROTO ] id VLANID [ priority VLANPRIO ] [CONTROL]\n");
 	fprintf(stderr, "       VLANPROTO is one of 802.1Q or 802.1AD\n");
 	fprintf(stderr, "            with default: 802.1Q\n");
 	fprintf(stderr, "       CONTROL := reclassify | pipe | drop | continue | pass\n");
@@ -34,6 +41,11 @@ static void usage(void)
 	exit(-1);
 }
 
+static bool has_push_attribs(int action)
+{
+	return action == TCA_VLAN_ACT_PUSH || action == TCA_VLAN_ACT_MODIFY;
+}
+
 static int parse_vlan(struct action_util *a, int *argc_p, char ***argv_p,
 		      int tca_id, struct nlmsghdr *n)
 {
@@ -71,9 +83,17 @@ static int parse_vlan(struct action_util *a, int *argc_p, char ***argv_p,
 				return -1;
 			}
 			action = TCA_VLAN_ACT_PUSH;
+		} else if (matches(*argv, "modify") == 0) {
+			if (action) {
+				fprintf(stderr, "unexpected \"%s\" - action already specified\n",
+					*argv);
+				explain();
+				return -1;
+			}
+			action = TCA_VLAN_ACT_MODIFY;
 		} else if (matches(*argv, "id") == 0) {
-			if (action != TCA_VLAN_ACT_PUSH) {
+			if (!has_push_attribs(action)) {
-				fprintf(stderr, "\"%s\" is only valid for push\n",
+				fprintf(stderr, "\"%s\" is only valid for push/modify\n",
 					*argv);
 				explain();
 				return -1;
@@ -83,8 +103,8 @@ static int parse_vlan(struct action_util *a, int *argc_p, char ***argv_p,
 				invarg("id is invalid", *argv);
 			id_set = 1;
 		} else if (matches(*argv, "protocol") == 0) {
-			if (action != TCA_VLAN_ACT_PUSH) {
+			if (!has_push_attribs(action)) {
-				fprintf(stderr, "\"%s\" is only valid for push\n",
+				fprintf(stderr, "\"%s\" is only valid for push/modify\n",
 					*argv);
 				explain();
 				return -1;
@@ -94,8 +114,8 @@ static int parse_vlan(struct action_util *a, int *argc_p, char ***argv_p,
 				invarg("protocol is invalid", *argv);
 			proto_set = 1;
 		} else if (matches(*argv, "priority") == 0) {
-			if (action != TCA_VLAN_ACT_PUSH) {
+			if (!has_push_attribs(action)) {
-				fprintf(stderr, "\"%s\" is only valid for push\n",
+				fprintf(stderr, "\"%s\" is only valid for push/modify\n",
 					*argv);
 				explain();
 				return -1;
@@ -129,8 +149,9 @@ static int parse_vlan(struct action_util *a, int *argc_p, char ***argv_p,
 		}
 	}
 
-	if (action == TCA_VLAN_ACT_PUSH && !id_set) {
+	if (has_push_attribs(action) && !id_set) {
-		fprintf(stderr, "id needs to be set for push\n");
+		fprintf(stderr, "id needs to be set for %s\n",
+			action_names[action]);
 		explain();
 		return -1;
 	}
@@ -186,7 +207,8 @@ static int print_vlan(struct action_util *au, FILE *f, struct rtattr *arg)
 		fprintf(f, " pop");
 		break;
 	case TCA_VLAN_ACT_PUSH:
-		fprintf(f, " push");
+	case TCA_VLAN_ACT_MODIFY:
+		fprintf(f, " %s", action_names[parm->v_action]);
 		if (tb[TCA_VLAN_PUSH_VLAN_ID]) {
 			val = rta_getattr_u16(tb[TCA_VLAN_PUSH_VLAN_ID]);
 			fprintf(f, " id %u", val);