On Tue, Oct 10, 2017 at 4:47 AM, William Tu <u9012...@gmail.com> wrote: > 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; 1. I guess '+4-4' stuff was copied from __gre_tunnel_init(), I'm thinking it may be there for some reason.
2. 'dev->needed_headroom =' and 'dev->mtu =' are really needed ? As I've seen both will be updated in .newlink: ipgre_newlink() -> ip_tunnel_newlink() -> ip_tunnel_bind_dev() > dev->features |= GRE_FEATURES; > dev->hw_features |= GRE_FEATURES; > dev->priv_flags |= IFF_LIVE_ADDR_CHANGE; > -- > 2.7.4 >
