Filter: Add MPLS label route attribute

Add support to set or read outgoing MPLS labels using filters. Currently
this supports the addition of one label per route for the first next hop.

Minor changes by committer.

doc/bird.sgml

@@ -1716,6 +1716,15 @@ Common route attributes are:
 	are merged to one ECMP route during export to the Kernel protocol
 	(with active <ref id="krt-merge-paths" name="marge paths"> option).
 
+	<tag><label id="rta-gw-mpls"><m/int/ gw_mpls</tag>
+	Outgoing MPLS label attached to route (i.e., incoming MPLS label on the
+	next hop router for this label-switched path). Reading returns the label
+	value and setting it sets it to the start of the label stack. Setting
+	implicit-NULL label (3) disables the MPLS label stack. Only the first
+	next hop and only one label in the label stack supported right now. This
+	is experimental option, will be likely changed in the future to handle
+	full MPLS label stack.
+
 	<tag><label id="rta-igp-metric"><m/int/ igp_metric</tag>
 	The optional attribute that can be used to specify a distance to the
 	network for routes that do not have a native protocol metric attribute

filter/config.Y

@@ -278,7 +278,7 @@ CF_KEYWORDS(FUNCTION, PRINT, PRINTN, UNSET, RETURN,
 	SET, STRING, BGPMASK, BGPPATH, CLIST, ECLIST, LCLIST,
 	IF, THEN, ELSE, CASE,
 	TRUE, FALSE, RT, RO, UNKNOWN, GENERIC,
-	FROM, GW, NET, MASK, PROTO, SOURCE, SCOPE, DEST, IFNAME, IFINDEX, WEIGHT,
+	FROM, GW, NET, MASK, PROTO, SOURCE, SCOPE, DEST, IFNAME, IFINDEX, WEIGHT, GW_MPLS,
 	PREFERENCE,
 	ROA_CHECK, ASN, SRC, DST,
 	IS_V4, IS_V6,
@@ -751,6 +751,7 @@ static_attr:
  | IFNAME  { $$ = f_new_static_attr(T_STRING,     SA_IFNAME,	0); }
  | IFINDEX { $$ = f_new_static_attr(T_INT,        SA_IFINDEX,	1); }
  | WEIGHT  { $$ = f_new_static_attr(T_INT,        SA_WEIGHT,	0); }
+ | GW_MPLS { $$ = f_new_static_attr(T_INT,        SA_GW_MPLS,	0); }
  ;
 
 term:

filter/data.h

@@ -100,6 +100,7 @@ enum f_sa_code {
   SA_IFNAME,
   SA_IFINDEX,
   SA_WEIGHT,
+  SA_GW_MPLS,
 } PACKED;
 
 /* Static attribute definition (members of struct rta) */

filter/f-inst.c

@@ -533,6 +533,7 @@
       case SA_IFNAME:	RESULT(sa.f_type, s, rta->nh.iface ? rta->nh.iface->name : ""); break;
       case SA_IFINDEX:	RESULT(sa.f_type, i, rta->nh.iface ? rta->nh.iface->index : 0); break;
       case SA_WEIGHT:	RESULT(sa.f_type, i, rta->nh.weight + 1); break;
+      case SA_GW_MPLS:	RESULT(sa.f_type, i, rta->nh.labels ? rta->nh.label[0] : MPLS_NULL); break;
 
       default:
 	bug("Invalid static attribute access (%u/%u)", sa.f_type, sa.sa_code);
@@ -569,6 +570,7 @@
 	  rta->nh.iface = n->iface;
 	  rta->nh.next = NULL;
 	  rta->hostentry = NULL;
+	  rta->nh.labels = 0;
 	}
 	break;
 
@@ -587,6 +589,7 @@
 	  rta->nh.iface = NULL;
 	  rta->nh.next = NULL;
 	  rta->hostentry = NULL;
+	  rta->nh.labels = 0;
 	}
 	break;
 
@@ -601,6 +604,22 @@
 	  rta->nh.iface = ifa;
 	  rta->nh.next = NULL;
 	  rta->hostentry = NULL;
+	  rta->nh.labels = 0;
+	}
+	break;
+
+      case SA_GW_MPLS:
+	{
+	  if (v1.val.i >= 0x100000)
+	    runtime( "Invalid MPLS label" );
+
+	  if (v1.val.i != MPLS_NULL)
+	  {
+	    rta->nh.label[0] = v1.val.i;
+	    rta->nh.labels = 1;
+	  }
+	  else
+	    rta->nh.labels = 0;
 	}
 	break;
 

lib/ip.h

@@ -47,6 +47,8 @@
 #define IP6_HEADER_LENGTH	40
 #define UDP_HEADER_LENGTH	8
 
+#define MPLS_NULL		3
+
 
 /* IANA Address Family Numbers */
 /* https://www.iana.org/assignments/address-family-numbers/address-family-numbers.xhtml */