Remove the unnecessary -4 and +4 bytes at mtu and headroom calculation.
In addition, erspan uses fixed 8-byte gre header, so add ERSPAN_GREHDR_LEN
macro for better readability.
Now tunnel->hlen = grehdr(8) + erspanhdr(8) = 16 byte.
The mtu should be ETH_DATA_LEN - 16 - iph(20) = 1464.
After the ip_tunnel_bind_dev(), the mtu is adjusted to
1464 - 14 (dev->hard_header_len) = 1450.
The maximum skb->len the erspan tunnel can carry without
being truncated is 1450 + 14 = 1464 byte.
Signed-off-by: William Tu <u9012...@gmail.com>
Cc: Xin Long <lucien....@gmail.com>
---
include/net/erspan.h | 1 +
net/ipv4/ip_gre.c | 11 +++++------
2 files changed, 6 insertions(+), 6 deletions(-)
diff --git a/include/net/erspan.h b/include/net/erspan.h
index ca94fc86865e..e28294e248d0 100644
--- a/include/net/erspan.h
+++ b/include/net/erspan.h
@@ -28,6 +28,7 @@
*/
#define ERSPAN_VERSION 0x1
+#define ERSPAN_GREHDR_LEN 8 /* ERSPAN has fixed 8-byte GRE header */
#define VER_MASK 0xf000
#define VLAN_MASK 0x0fff
diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index 286065c35959..6e6e4c4811cc 100644
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -569,8 +569,7 @@ static void erspan_fb_xmit(struct sk_buff *skb, struct
net_device *dev,
key = &tun_info->key;
- /* ERSPAN has fixed 8 byte GRE header */
- tunnel_hlen = 8 + sizeof(struct erspanhdr);
+ tunnel_hlen = ERSPAN_GREHDR_LEN + sizeof(struct erspanhdr);
rt = prepare_fb_xmit(skb, dev, &fl, tunnel_hlen);
if (!rt)
@@ -591,7 +590,7 @@ static void erspan_fb_xmit(struct sk_buff *skb, struct
net_device *dev,
erspan_build_header(skb, tunnel_id_to_key32(key->tun_id),
ntohl(md->index), truncate);
- gre_build_header(skb, 8, TUNNEL_SEQ,
+ gre_build_header(skb, ERSPAN_GREHDR_LEN, TUNNEL_SEQ,
htons(ETH_P_ERSPAN), 0, htonl(tunnel->o_seqno++));
df = key->tun_flags & TUNNEL_DONT_FRAGMENT ? htons(IP_DF) : 0;
@@ -1242,14 +1241,14 @@ static int erspan_tunnel_init(struct net_device *dev)
struct ip_tunnel *tunnel = netdev_priv(dev);
int t_hlen;
- tunnel->tun_hlen = 8;
+ tunnel->tun_hlen = ERSPAN_GREHDR_LEN;
tunnel->parms.iph.protocol = IPPROTO_GRE;
tunnel->hlen = tunnel->tun_hlen + tunnel->encap_hlen +
sizeof(struct erspanhdr);
t_hlen = tunnel->hlen + sizeof(struct iphdr);
- dev->needed_headroom = LL_MAX_HEADER + t_hlen + 4;
- dev->mtu = ETH_DATA_LEN - t_hlen - 4;
+ dev->needed_headroom = LL_MAX_HEADER + t_hlen;
+ dev->mtu = ETH_DATA_LEN - t_hlen;
dev->features |= GRE_FEATURES;
dev->hw_features |= GRE_FEATURES;
dev->priv_flags |= IFF_LIVE_ADDR_CHANGE;
--
2.7.4
