Split tap_ip_send() into IPv4 and IPv6 specific functions

The IPv4 and IPv6 paths in tap_ip_send() have very little in common, and
it turns out that every caller (statically) knows if it is using IPv4 or
IPv6.  So split into separate tap_ip4_send() and tap_ip6_send() functions.
Use a new tap_l2_hdr() function for the very small common part.

While we're there, make some minor cleanups:
  - We were double writing some fields in the IPv6 header, so that it
    temporary matched the pseudo-header for checksum calculation.  With
    recent checksum reworks, this isn't neccessary any more.
  - We don't use any IPv4 header options, so use some sizeof() constructs
    instead of some open coded values for header length.
  - The comment used to say that the flow label was for TCP over IPv6, but
    in fact the only thing we used it for was DHCPv6 over UDP traffic

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/tap.h b/tap.h
index a8da8bb..011ba8e 100644
--- a/tap.h
+++ b/tap.h
@@ -9,8 +9,10 @@
 in_addr_t tap_ip4_daddr(const struct ctx *c);
 const struct in6_addr *tap_ip6_daddr(const struct ctx *c,
 				     const struct in6_addr *src);
-void tap_ip_send(const struct ctx *c, const struct in6_addr *src, uint8_t proto,
-		 const char *in, size_t len, uint32_t flow);
+void tap_ip4_send(const struct ctx *c, in_addr_t src, uint8_t proto,
+		  const char *in, size_t len);
+void tap_ip6_send(const struct ctx *c, const struct in6_addr *src,
+		  uint8_t proto, const char *in, size_t len, uint32_t flow);
 int tap_send(const struct ctx *c, const void *data, size_t len);
 void tap_handler(struct ctx *c, int fd, uint32_t events,
 		 const struct timespec *now);