[PATCH net] ip6_tunnel: update mtu properly for ARPHRD_ETHER tunnel device in tx path

[Xin Long]

Now when updating mtu in tx path, it doesn't consider ARPHRD_ETHER tunnel
device, like ip6gre_tap tunnel, for which it should also subtract ether
header to get the correct mtu.

Signed-off-by: Xin Long <lucien....@gmail.com>
---
 net/ipv6/ip6_tunnel.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/net/ipv6/ip6_tunnel.c b/net/ipv6/ip6_tunnel.c
index f2f21c2..a1c2444 100644
--- a/net/ipv6/ip6_tunnel.c
+++ b/net/ipv6/ip6_tunnel.c
@@ -1043,6 +1043,7 @@ int ip6_tnl_xmit(struct sk_buff *skb, struct net_device 
*dev, __u8 dsfield,
        struct dst_entry *dst = NULL, *ndst = NULL;
        struct net_device *tdev;
        int mtu;
+       unsigned int eth_hlen = t->dev->type == ARPHRD_ETHER ? ETH_HLEN : 0;
        unsigned int psh_hlen = sizeof(struct ipv6hdr) + t->encap_hlen;
        unsigned int max_headroom = psh_hlen;
        bool use_cache = false;
@@ -1124,7 +1125,7 @@ int ip6_tnl_xmit(struct sk_buff *skb, struct net_device 
*dev, __u8 dsfield,
                                     t->parms.name);
                goto tx_err_dst_release;
        }
-       mtu = dst_mtu(dst) - psh_hlen - t->tun_hlen;
+       mtu = dst_mtu(dst) - eth_hlen - psh_hlen - t->tun_hlen;
        if (encap_limit >= 0) {
                max_headroom += 8;
                mtu -= 8;
@@ -1133,7 +1134,7 @@ int ip6_tnl_xmit(struct sk_buff *skb, struct net_device 
*dev, __u8 dsfield,
                mtu = IPV6_MIN_MTU;
        if (skb_dst(skb) && !t->parms.collect_md)
                skb_dst(skb)->ops->update_pmtu(skb_dst(skb), NULL, skb, mtu);
-       if (skb->len - t->tun_hlen > mtu && !skb_is_gso(skb)) {
+       if (skb->len - t->tun_hlen - eth_hlen > mtu && !skb_is_gso(skb)) {
                *pmtu = mtu;
                err = -EMSGSIZE;
                goto tx_err_dst_release;
-- 
2.1.0