[PATCH v6 7/8] tap: change signature of function tap_push_l2h()

[Jon Maloy <jmaloy@redhat.com>]

In the following commits it must be possible for the callers of
function tap_push_l2h() to specify which source MAC address should
be added to the ethernet header sent over the tap interface. As
a preparation, we now add a new argument to that function, still
without actually using it.

Signed-off-by: Jon Maloy <jmaloy@redhat.com>

---
v3: -Improved comment for src_mac argument, as suggested by Stefano.
v4: -Re-added comment in tap.c and remove redundant argument check
     in tap_push_l2()
v5: -Ensured that MAC argument to tap_push_l2h() never is NULL.
v6: -Clarification of comment about ARP lookup
---
 tap.c | 16 +++++++++-------
 tap.h |  3 ++-
 tcp.c |  5 +++--
 3 files changed, 14 insertions(+), 10 deletions(-)

diff --git a/tap.c b/tap.c
index 74557e1..a390be8 100644
--- a/tap.c
+++ b/tap.c
@@ -171,17 +171,19 @@ const struct in6_addr *tap_ip6_daddr(const struct ctx *c,
  * tap_push_l2h() - Build an L2 header for an inbound packet
  * @c:		Execution context
  * @buf:	Buffer address at which to generate header
+ * @src_mac:	MAC address to be used as source for message.
  * @proto:	Ethernet protocol number for L3
  *
  * Return: pointer at which to write the packet's payload
  */
-void *tap_push_l2h(const struct ctx *c, void *buf, uint16_t proto)
+void *tap_push_l2h(const struct ctx *c, void *buf,
+		   const void *src_mac, uint16_t proto)
 {
 	struct ethhdr *eh = (struct ethhdr *)buf;
 
-	/* TODO: ARP table lookup */
+	/* TODO: ARP lookup on tap side */
 	memcpy(eh->h_dest, c->guest_mac, ETH_ALEN);
-	memcpy(eh->h_source, c->our_tap_mac, ETH_ALEN);
+	memcpy(eh->h_source, src_mac, ETH_ALEN);
 	eh->h_proto = ntohs(proto);
 	return eh + 1;
 }
@@ -261,7 +263,7 @@ void tap_udp4_send(const struct ctx *c, struct in_addr src, in_port_t sport,
 {
 	size_t l4len = dlen + sizeof(struct udphdr);
 	char buf[USHRT_MAX];
-	struct iphdr *ip4h = tap_push_l2h(c, buf, ETH_P_IP);
+	struct iphdr *ip4h = tap_push_l2h(c, buf, c->our_tap_mac, ETH_P_IP);
 	struct udphdr *uh = tap_push_ip4h(ip4h, src, dst, l4len, IPPROTO_UDP);
 	char *data = tap_push_uh4(uh, src, sport, dst, dport, in, dlen);
 
@@ -281,7 +283,7 @@ void tap_icmp4_send(const struct ctx *c, struct in_addr src, struct in_addr dst,
 		    const void *in, size_t l4len)
 {
 	char buf[USHRT_MAX];
-	struct iphdr *ip4h = tap_push_l2h(c, buf, ETH_P_IP);
+	struct iphdr *ip4h = tap_push_l2h(c, buf, c->our_tap_mac, ETH_P_IP);
 	struct icmphdr *icmp4h = tap_push_ip4h(ip4h, src, dst,
 					       l4len, IPPROTO_ICMP);
 
@@ -367,7 +369,7 @@ void tap_udp6_send(const struct ctx *c,
 {
 	size_t l4len = dlen + sizeof(struct udphdr);
 	char buf[USHRT_MAX];
-	struct ipv6hdr *ip6h = tap_push_l2h(c, buf, ETH_P_IPV6);
+	struct ipv6hdr *ip6h = tap_push_l2h(c, buf, c->our_tap_mac, ETH_P_IPV6);
 	struct udphdr *uh = tap_push_ip6h(ip6h, src, dst,
 					  l4len, IPPROTO_UDP, flow);
 	char *data = tap_push_uh6(uh, src, sport, dst, dport, in, dlen);
@@ -389,7 +391,7 @@ void tap_icmp6_send(const struct ctx *c,
 		    const void *in, size_t l4len)
 {
 	char buf[USHRT_MAX];
-	struct ipv6hdr *ip6h = tap_push_l2h(c, buf, ETH_P_IPV6);
+	struct ipv6hdr *ip6h = tap_push_l2h(c, buf, c->our_tap_mac, ETH_P_IPV6);
 	struct icmp6hdr *icmp6h = tap_push_ip6h(ip6h, src, dst, l4len,
 						IPPROTO_ICMPV6, 0);
 
diff --git a/tap.h b/tap.h
index 21db4d2..02f7761 100644
--- a/tap.h
+++ b/tap.h
@@ -70,7 +70,8 @@ static inline void tap_hdr_update(struct tap_hdr *thdr, size_t l2len)
 }
 
 unsigned long tap_l2_max_len(const struct ctx *c);
-void *tap_push_l2h(const struct ctx *c, void *buf, uint16_t proto);
+void *tap_push_l2h(const struct ctx *c, void *buf,
+		   const void *src_mac, uint16_t proto);
 void *tap_push_ip4h(struct iphdr *ip4h, struct in_addr src,
 		     struct in_addr dst, size_t l4len, uint8_t proto);
 void *tap_push_uh4(struct udphdr *uh, struct in_addr src, in_port_t sport,
diff --git a/tcp.c b/tcp.c
index 76fc0e4..b44fa62 100644
--- a/tcp.c
+++ b/tcp.c
@@ -1922,7 +1922,8 @@ static void tcp_rst_no_conn(const struct ctx *c, int af,
 		return;
 
 	if (af == AF_INET) {
-		struct iphdr *ip4h = tap_push_l2h(c, buf, ETH_P_IP);
+		struct iphdr *ip4h = tap_push_l2h(c, buf, c->our_tap_mac,
+						  ETH_P_IP);
 		const struct in_addr *rst_src = daddr;
 		const struct in_addr *rst_dst = saddr;
 
@@ -1932,7 +1933,7 @@ static void tcp_rst_no_conn(const struct ctx *c, int af,
 					      *rst_src, *rst_dst);
 
 	} else {
-		struct ipv6hdr *ip6h = tap_push_l2h(c, buf, ETH_P_IPV6);
+		struct ipv6hdr *ip6h = tap_push_l2h(c, buf, c->our_tap_mac, ETH_P_IPV6);
 		const struct in6_addr *rst_src = daddr;
 		const struct in6_addr *rst_dst = saddr;
 
-- 
@@ -1922,7 +1922,8 @@ static void tcp_rst_no_conn(const struct ctx *c, int af,
 		return;
 
 	if (af == AF_INET) {
-		struct iphdr *ip4h = tap_push_l2h(c, buf, ETH_P_IP);
+		struct iphdr *ip4h = tap_push_l2h(c, buf, c->our_tap_mac,
+						  ETH_P_IP);
 		const struct in_addr *rst_src = daddr;
 		const struct in_addr *rst_dst = saddr;
 
@@ -1932,7 +1933,7 @@ static void tcp_rst_no_conn(const struct ctx *c, int af,
 					      *rst_src, *rst_dst);
 
 	} else {
-		struct ipv6hdr *ip6h = tap_push_l2h(c, buf, ETH_P_IPV6);
+		struct ipv6hdr *ip6h = tap_push_l2h(c, buf, c->our_tap_mac, ETH_P_IPV6);
 		const struct in6_addr *rst_src = daddr;
 		const struct in6_addr *rst_dst = saddr;
 
-- 
2.50.1