[PATCHv3 net-next 03/16] udp: support sctp over udp in skb_udp_tunnel_segment

[Xin Long]

For the gso of sctp over udp packets, sctp_gso_segment() will be called in
skb_udp_tunnel_segment(), we need to set transport_header to sctp header.

As all the current HWs can't handle both crc checksum and udp checksum at
the same time, the crc checksum has to be done in sctp_gso_segment() by
removing the NETIF_F_SCTP_CRC flag from the features.

Meanwhile, if the HW can't do udp checksum, csum and csum_start has to be
set correctly, and udp checksum will be done in __skb_udp_tunnel_segment()
by calling gso_make_checksum().

Thanks to Paolo, Marcelo and Guillaume for helping with this one.

v1->v2:
  - no change.
v2->v3:
  - remove the he NETIF_F_SCTP_CRC flag from the features.
  - set csum and csum_start in sctp_gso_make_checksum().

Signed-off-by: Xin Long <lucien....@gmail.com>
---
 net/ipv4/udp_offload.c | 3 +++
 net/sctp/offload.c     | 6 +++++-
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c
index e67a66f..4d31255 100644
--- a/net/ipv4/udp_offload.c
+++ b/net/ipv4/udp_offload.c
@@ -49,6 +49,7 @@ static struct sk_buff *__skb_udp_tunnel_segment(struct 
sk_buff *skb,
        __skb_pull(skb, tnl_hlen);
        skb_reset_mac_header(skb);
        skb_set_network_header(skb, skb_inner_network_offset(skb));
+       skb_set_transport_header(skb, skb_inner_transport_offset(skb));
        skb->mac_len = skb_inner_network_offset(skb);
        skb->protocol = new_protocol;
 
@@ -67,6 +68,8 @@ static struct sk_buff *__skb_udp_tunnel_segment(struct 
sk_buff *skb,
                                      (NETIF_F_HW_CSUM | NETIF_F_IP_CSUM))));
 
        features &= skb->dev->hw_enc_features;
+       /* CRC checksum can't be handled by HW when it's a udp tunneling 
packet. */
+       features &= ~NETIF_F_SCTP_CRC;
 
        /* The only checksum offload we care about from here on out is the
         * outer one so strip the existing checksum feature flags and
diff --git a/net/sctp/offload.c b/net/sctp/offload.c
index 74847d6..9f6f818 100644
--- a/net/sctp/offload.c
+++ b/net/sctp/offload.c
@@ -27,7 +27,11 @@ static __le32 sctp_gso_make_checksum(struct sk_buff *skb)
 {
        skb->ip_summed = CHECKSUM_NONE;
        skb->csum_not_inet = 0;
-       gso_reset_checksum(skb, ~0);
+       /* csum and csum_start in gso cb may be needed to do the udp
+        * checksum when it's a udp tunneling packet.
+        */
+       SKB_GSO_CB(skb)->csum = (__force __wsum)~0;
+       SKB_GSO_CB(skb)->csum_start = skb_headroom(skb) + skb->len;
        return sctp_compute_cksum(skb, skb_transport_offset(skb));
 }
 
-- 
2.1.0