erspan: Add type I version 0 support.

The Type I ERSPAN frame format is based on the barebones
IP + GRE(4-byte) encapsulation on top of the raw mirrored frame.
Both type I and II use 0x88BE as protocol type. Unlike type II
and III, no sequence number or key is required.
To creat a type I erspan tunnel device:
  $ ip link add dev erspan11 type erspan \
            local 172.16.1.100 remote 172.16.1.200 \
            erspan_ver 0

Signed-off-by: William Tu <u9012063@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/erspan.h

@@ -2,7 +2,19 @@
 #define __LINUX_ERSPAN_H
 
 /*
- * GRE header for ERSPAN encapsulation (8 octets [34:41]) -- 8 bytes
+ * GRE header for ERSPAN type I encapsulation (4 octets [34:37])
+ *      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|0|0|00000|000000000|00000|    Protocol Type for ERSPAN   |
+ *     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ *
+ *  The Type I ERSPAN frame format is based on the barebones IP + GRE
+ *  encapsulation (as described above) on top of the raw mirrored frame.
+ *  There is no extra ERSPAN header.
+ *
+ *
+ * GRE header for ERSPAN type II and II encapsulation (8 octets [34:41])
  *       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
  *     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
@@ -43,7 +55,7 @@
  * |                  Platform Specific Info                       |
  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  *
- * GRE proto ERSPAN type II = 0x88BE, type III = 0x22EB
+ * GRE proto ERSPAN type I/II = 0x88BE, type III = 0x22EB
  */
 
 #include <uapi/linux/erspan.h>
@@ -139,6 +151,9 @@ static inline u8 get_hwid(const struct erspan_md2 *md2)
 
 static inline int erspan_hdr_len(int version)
 {
+	if (version == 0)
+		return 0;
+
 	return sizeof(struct erspan_base_hdr) +
 	       (version == 1 ? ERSPAN_V1_MDSIZE : ERSPAN_V2_MDSIZE);
 }

net/ipv4/ip_gre.c

@@ -248,6 +248,15 @@ static void gre_err(struct sk_buff *skb, u32 info)
 	ipgre_err(skb, info, &tpi);
 }
 
+static bool is_erspan_type1(int gre_hdr_len)
+{
+	/* Both ERSPAN type I (version 0) and type II (version 1) use
+	 * protocol 0x88BE, but the type I has only 4-byte GRE header,
+	 * while type II has 8-byte.
+	 */
+	return gre_hdr_len == 4;
+}
+
 static int erspan_rcv(struct sk_buff *skb, struct tnl_ptk_info *tpi,
 		      int gre_hdr_len)
 {
@@ -262,17 +271,26 @@ static int erspan_rcv(struct sk_buff *skb, struct tnl_ptk_info *tpi,
 	int len;
 
 	itn = net_generic(net, erspan_net_id);
-
 	iph = ip_hdr(skb);
+	if (is_erspan_type1(gre_hdr_len)) {
+		ver = 0;
+		tunnel = ip_tunnel_lookup(itn, skb->dev->ifindex,
+					  tpi->flags | TUNNEL_NO_KEY,
+					  iph->saddr, iph->daddr, 0);
+	} else {
 		ershdr = (struct erspan_base_hdr *)(skb->data + gre_hdr_len);
 		ver = ershdr->ver;
-
 		tunnel = ip_tunnel_lookup(itn, skb->dev->ifindex,
 					  tpi->flags | TUNNEL_KEY,
 					  iph->saddr, iph->daddr, tpi->key);
+	}
 
 	if (tunnel) {
+		if (is_erspan_type1(gre_hdr_len))
+			len = gre_hdr_len;
+		else
 			len = gre_hdr_len + erspan_hdr_len(ver);
+
 		if (unlikely(!pskb_may_pull(skb, len)))
 			return PACKET_REJECT;
 
@@ -665,7 +683,10 @@ static netdev_tx_t erspan_xmit(struct sk_buff *skb,
 	}
 
 	/* Push ERSPAN header */
-	if (tunnel->erspan_ver == 1) {
+	if (tunnel->erspan_ver == 0) {
+		proto = htons(ETH_P_ERSPAN);
+		tunnel->parms.o_flags &= ~TUNNEL_SEQ;
+	} else if (tunnel->erspan_ver == 1) {
 		erspan_build_header(skb, ntohl(tunnel->parms.o_key),
 				    tunnel->index,
 				    truncate, true);
@@ -1066,7 +1087,10 @@ static int erspan_validate(struct nlattr *tb[], struct nlattr *data[],
 	if (ret)
 		return ret;
 
-	/* ERSPAN should only have GRE sequence and key flag */
+	if (nla_get_u8(data[IFLA_GRE_ERSPAN_VER]) == 0)
+		return 0;
+
+	/* ERSPAN type II/III should only have GRE sequence and key flag */
 	if (data[IFLA_GRE_OFLAGS])
 		flags |= nla_get_be16(data[IFLA_GRE_OFLAGS]);
 	if (data[IFLA_GRE_IFLAGS])
@@ -1174,7 +1198,7 @@ static int erspan_netlink_parms(struct net_device *dev,
 	if (data[IFLA_GRE_ERSPAN_VER]) {
 		t->erspan_ver = nla_get_u8(data[IFLA_GRE_ERSPAN_VER]);
 
-		if (t->erspan_ver != 1 && t->erspan_ver != 2)
+		if (t->erspan_ver > 2)
 			return -EINVAL;
 	}
 
@@ -1259,7 +1283,11 @@ static int erspan_tunnel_init(struct net_device *dev)
 {
 	struct ip_tunnel *tunnel = netdev_priv(dev);
 
-	tunnel->tun_hlen = 8;
+	if (tunnel->erspan_ver == 0)
+		tunnel->tun_hlen = 4; /* 4-byte GRE hdr. */
+	else
+		tunnel->tun_hlen = 8; /* 8-byte GRE hdr. */
+
 	tunnel->parms.iph.protocol = IPPROTO_GRE;
 	tunnel->hlen = tunnel->tun_hlen + tunnel->encap_hlen +
 		       erspan_hdr_len(tunnel->erspan_ver);
@@ -1456,8 +1484,8 @@ static int ipgre_fill_info(struct sk_buff *skb, const struct net_device *dev)
 	struct ip_tunnel_parm *p = &t->parms;
 	__be16 o_flags = p->o_flags;
 
-	if (t->erspan_ver == 1 || t->erspan_ver == 2) {
+	if (t->erspan_ver <= 2) {
-		if (!t->collect_md)
+		if (t->erspan_ver != 0 && !t->collect_md)
 			o_flags |= TUNNEL_KEY;
 
 		if (nla_put_u8(skb, IFLA_GRE_ERSPAN_VER, t->erspan_ver))
@@ -1466,7 +1494,7 @@ static int ipgre_fill_info(struct sk_buff *skb, const struct net_device *dev)
 		if (t->erspan_ver == 1) {
 			if (nla_put_u32(skb, IFLA_GRE_ERSPAN_INDEX, t->index))
 				goto nla_put_failure;
-		} else {
+		} else if (t->erspan_ver == 2) {
 			if (nla_put_u8(skb, IFLA_GRE_ERSPAN_DIR, t->dir))
 				goto nla_put_failure;
 			if (nla_put_u16(skb, IFLA_GRE_ERSPAN_HWID, t->hwid))