gre: Use struct for parsing GRE header.

GRE is a somewhat annoying protocol because the header is variable
length.  However, it does have a few fields that are always present
so we can make the parsing seem less magical by using a struct for
those fields instead of building it up field by field.

diff --git a/datapath/vport-gre.c b/datapath/vport-gre.c
index 33966db..2bddc87 100644 (file)
--- a/datapath/vport-gre.c
+++ b/datapath/vport-gre.c
@@ -44,6 +44,11 @@
  * number of options. */
 #define GRE_HEADER_SECTION 4
 
+struct gre_base_hdr {
+       __be16 flags;
+       __be16 protocol;
+};
+
 struct mutable_config {
        struct rcu_head rcu;
 
@@ -567,18 +572,17 @@ static void create_gre_header(struct sk_buff *skb,
                              const struct mutable_config *mutable)
 {
        struct iphdr *iph = ip_hdr(skb);
-       __be16 *flags = (__be16 *)(iph + 1);
-       __be16 *protocol = flags + 1;
+       struct gre_base_hdr *greh = (struct gre_base_hdr *)(iph + 1);
        __be32 *options = (__be32 *)((u8 *)iph + mutable->tunnel_hlen
                                               - GRE_HEADER_SECTION);
 
-       *protocol = htons(ETH_P_TEB);
-       *flags = 0;
+       greh->protocol = htons(ETH_P_TEB);
+       greh->flags = 0;
 
        /* Work backwards over the options so the checksum is last. */
        if (mutable->port_config.out_key ||
            mutable->port_config.flags & GRE_F_OUT_KEY_ACTION) {
-               *flags |= GRE_KEY;
+               greh->flags |= GRE_KEY;
 
                if (mutable->port_config.flags & GRE_F_OUT_KEY_ACTION)
                        *options = OVS_CB(skb)->tun_id;
@@ -589,7 +593,7 @@ static void create_gre_header(struct sk_buff *skb,
        }
 
        if (mutable->port_config.flags & GRE_F_OUT_CSUM) {
-               *flags |= GRE_CSUM;
+               greh->flags |= GRE_CSUM;
 
                *options = 0;
                *(__sum16 *)options = csum_fold(skb_checksum(skb,
@@ -628,27 +632,26 @@ static int check_checksum(struct sk_buff *skb)
 static int parse_gre_header(struct iphdr *iph, __be16 *flags, __be32 *key)
 {
        /* IP and ICMP protocol handlers check that the IHL is valid. */
-       __be16 *flagsp = (__be16 *)((u8 *)iph + (iph->ihl << 2));
-       __be16 *protocol = flagsp + 1;
-       __be32 *options = (__be32 *)(protocol + 1);
+       struct gre_base_hdr *greh = (struct gre_base_hdr *)((u8 *)iph + (iph->ihl << 2));
+       __be32 *options = (__be32 *)(greh + 1);
        int hdr_len;
 
-       *flags = *flagsp;
+       *flags = greh->flags;
 
-       if (*flags & (GRE_VERSION | GRE_ROUTING))
+       if (greh->flags & (GRE_VERSION | GRE_ROUTING))
                return -EINVAL;
 
-       if (*protocol != htons(ETH_P_TEB))
+       if (greh->protocol != htons(ETH_P_TEB))
                return -EINVAL;
 
        hdr_len = GRE_HEADER_SECTION;
 
-       if (*flags & GRE_CSUM) {
+       if (greh->flags & GRE_CSUM) {
                hdr_len += GRE_HEADER_SECTION;
                options++;
        }
 
-       if (*flags & GRE_KEY) {
+       if (greh->flags & GRE_KEY) {
                hdr_len += GRE_HEADER_SECTION;
 
                *key = *options;
@@ -656,7 +659,7 @@ static int parse_gre_header(struct iphdr *iph, __be16 *flags, __be32 *key)
        } else
                *key = 0;
 
-       if (*flags & GRE_SEQ)
+       if (greh->flags & GRE_SEQ)
                hdr_len += GRE_HEADER_SECTION;
 
        return hdr_len;