bpf: Drop mpls from bpf_fib_lookup

MPLS support will not be submitted this dev cycle, but in working on it
I do see a few changes are needed to the API. For now, drop mpls from the
API. Since the fields in question are unions, the mpls fields can be added
back later without affecting the uapi.

Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

include/uapi/linux/bpf.h

@@ -1852,10 +1852,10 @@ union bpf_attr {
  *		If lookup is successful and result shows packet is to be
  *		forwarded, the neighbor tables are searched for the nexthop.
  *		If successful (ie., FIB lookup shows forwarding and nexthop
- *		is resolved), the nexthop address is returned in ipv4_dst,
- *		ipv6_dst or mpls_out based on family, smac is set to mac
- *		address of egress device, dmac is set to nexthop mac address,
- *		rt_metric is set to metric from route.
+ *		is resolved), the nexthop address is returned in ipv4_dst
+ *		or ipv6_dst based on family, smac is set to mac address of
+ *		egress device, dmac is set to nexthop mac address, rt_metric
+ *		is set to metric from route (IPv4/IPv6 only).
  *
  *             *plen* argument is the size of the passed in struct.
  *             *flags* argument can be a combination of one or more of the
@@ -2537,8 +2537,10 @@ struct bpf_raw_tracepoint_args {
 #define BPF_FIB_LOOKUP_OUTPUT  BIT(1)
 
 struct bpf_fib_lookup {
-	/* input */
-	__u8	family;   /* network family, AF_INET, AF_INET6, AF_MPLS */
+	/* input:  network family for lookup (AF_INET, AF_INET6)
+	 * output: network family of egress nexthop
+	 */
+	__u8	family;
 
 	/* set if lookup is to consider L4 data - e.g., FIB rules */
 	__u8	l4_protocol;
@@ -2554,22 +2556,20 @@ struct bpf_fib_lookup {
 		__u8	tos;		/* AF_INET  */
 		__be32	flowlabel;	/* AF_INET6 */
 
-		/* output: metric of fib result */
-		__u32 rt_metric;
+		/* output: metric of fib result (IPv4/IPv6 only) */
+		__u32	rt_metric;
 	};
 
 	union {
-		__be32		mpls_in;
 		__be32		ipv4_src;
 		__u32		ipv6_src[4];  /* in6_addr; network order */
 	};
 
-	/* input to bpf_fib_lookup, *dst is destination address.
-	 * output: bpf_fib_lookup sets to gateway address
+	/* input to bpf_fib_lookup, ipv{4,6}_dst is destination address in
+	 * network header. output: bpf_fib_lookup sets to gateway address
+	 * if FIB lookup returns gateway route
 	 */
 	union {
-		/* return for MPLS lookups */
-		__be32		mpls_out[4];  /* support up to 4 labels */
 		__be32		ipv4_dst;
 		__u32		ipv6_dst[4];  /* in6_addr; network order */
 	};