gre: introduce native tunnel support for ERSPAN

The patch adds ERSPAN type II tunnel support.  The implementation
is based on the draft at [1].  One of the purposes is for Linux
box to be able to receive ERSPAN monitoring traffic sent from
the Cisco switch, by creating a ERSPAN tunnel device.
In addition, the patch also adds ERSPAN TX, so Linux virtual
switch can redirect monitored traffic to the ERSPAN tunnel device.
The traffic will be encapsulated into ERSPAN and sent out.

The implementation reuses tunnel key as ERSPAN session ID, and
field 'erspan' as ERSPAN Index fields:
./ip link add dev ers11 type erspan seq key 100 erspan 123 \
			local 172.16.1.200 remote 172.16.1.100

To use the above device as ERSPAN receiver, configure
Nexus 5000 switch as below:

monitor session 100 type erspan-source
  erspan-id 123
  vrf default
  destination ip 172.16.1.200
  source interface Ethernet1/11 both
  source interface Ethernet1/12 both
  no shut
monitor erspan origin ip-address 172.16.1.100 global

[1] https://tools.ietf.org/html/draft-foschiano-erspan-01
[2] iproute2 patch: http://marc.info/?l=linux-netdev&m=150306086924951&w=2
[3] test script: http://marc.info/?l=linux-netdev&m=150231021807304&w=2Signed-off-by: William Tu <u9012063@gmail.com>
Signed-off-by: Meenakshi Vohra <mvohra@vmware.com>
Cc: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
Cc: Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/erspan.h

+#ifndef __LINUX_ERSPAN_H
+#define __LINUX_ERSPAN_H
+
+/*
+ * GRE header for ERSPAN encapsulation (8 octets [34:41]) -- 8 bytes
+ *       0                   1                   2                   3
+ *      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+ *     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ *     |0|0|0|1|0|00000|000000000|00000|    Protocol Type for ERSPAN   |
+ *     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ *     |      Sequence Number (increments per packet per session)      |
+ *     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ *
+ *  Note that in the above GRE header [RFC1701] out of the C, R, K, S,
+ *  s, Recur, Flags, Version fields only S (bit 03) is set to 1. The
+ *  other fields are set to zero, so only a sequence number follows.
+ *
+ *  ERSPAN Type II header (8 octets [42:49])
+ *  0                   1                   2                   3
+ *  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * |  Ver  |          VLAN         | COS | En|T|    Session ID     |
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * |      Reserved         |                  Index                |
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ *
+ * GRE proto ERSPAN type II = 0x88BE, type III = 0x22EB
+ */
+
+#define ERSPAN_VERSION	0x1
+
+#define VER_MASK	0xf000
+#define VLAN_MASK	0x0fff
+#define COS_MASK	0xe000
+#define EN_MASK		0x1800
+#define T_MASK		0x0400
+#define ID_MASK		0x03ff
+#define INDEX_MASK	0xfffff
+
+enum erspan_encap_type {
+	ERSPAN_ENCAP_NOVLAN = 0x0,	/* originally without VLAN tag */
+	ERSPAN_ENCAP_ISL = 0x1,		/* originally ISL encapsulated */
+	ERSPAN_ENCAP_8021Q = 0x2,	/* originally 802.1Q encapsulated */
+	ERSPAN_ENCAP_INFRAME = 0x3,	/* VLAN tag perserved in frame */
+};
+
+struct erspan_metadata {
+	__be32 index;   /* type II */
+};
+
+struct erspanhdr {
+	__be16 ver_vlan;
+#define VER_OFFSET  12
+	__be16 session_id;
+#define COS_OFFSET  13
+#define EN_OFFSET   11
+#define T_OFFSET    10
+	struct erspan_metadata md;
+};
+
+#endif

include/net/ip_tunnels.h

@@ -115,6 +115,9 @@ struct ip_tunnel {
 	u32		o_seqno;	/* The last output seqno */
 	int		tun_hlen;	/* Precalculated header length */
 
+	/* This field used only by ERSPAN */
+	u32		index;		/* ERSPAN type II index */
+
 	struct dst_cache dst_cache;
 
 	struct ip_tunnel_parm parms;

include/uapi/linux/if_ether.h

@@ -66,6 +66,7 @@
 #define ETH_P_ATALK	0x809B		/* Appletalk DDP		*/
 #define ETH_P_AARP	0x80F3		/* Appletalk AARP		*/
 #define ETH_P_8021Q	0x8100          /* 802.1Q VLAN Extended Header  */
+#define ETH_P_ERSPAN	0x88BE		/* ERSPAN type II		*/
 #define ETH_P_IPX	0x8137		/* IPX over DIX			*/
 #define ETH_P_IPV6	0x86DD		/* IPv6 over bluebook		*/
 #define ETH_P_PAUSE	0x8808		/* IEEE Pause frames. See 802.3 31B */

include/uapi/linux/if_tunnel.h

@@ -134,6 +134,7 @@ enum {
 	IFLA_GRE_COLLECT_METADATA,
 	IFLA_GRE_IGNORE_DF,
 	IFLA_GRE_FWMARK,
+	IFLA_GRE_ERSPAN_INDEX,
 	__IFLA_GRE_MAX,
 };