[PATCH v3 3/8] flow: add MAC address of LAN local remote hosts to flow

[Jon Maloy <jmaloy@redhat.com>]

When communicating with remote hosts on the local network, some guest
applications want to see the real MAC address of that host instead
of PASST/PASTA's own tap address. The flow_common structure is a
convenient location for storing that address, so we do that in this
commit.

Note that we don´t add actual usage of this address here, that will
be done in later commits.

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

---
v3: - Moved the remote host macaddress from struct flowside to
      struct flow_common. I chose to call it 'omac' as suggested
      by David, although in my understanding the correct name would be
      'emac'. (In general I find the address naming scheme confusing.)
    - Adapted to new signature of function nl_mac_get(), now passing
      it the index of the template interface.
---
 flow.c | 21 ++++++++++++++++++++-
 flow.h |  2 ++
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/flow.c b/flow.c
index da5c813..dcda1a7 100644
--- a/flow.c
+++ b/flow.c
@@ -20,6 +20,7 @@
 #include "flow.h"
 #include "flow_table.h"
 #include "repair.h"
+#include "netlink.h"
 
 const char *flow_state_str[] = {
 	[FLOW_STATE_FREE]	= "FREE",
@@ -438,18 +439,28 @@ struct flowside *flow_target(const struct ctx *c, union flow *flow,
 {
 	char estr[INANY_ADDRSTRLEN], fstr[INANY_ADDRSTRLEN];
 	struct flow_common *f = &flow->f;
-	const struct flowside *ini = &f->side[INISIDE];
+	struct flowside *ini = &f->side[INISIDE];
 	struct flowside *tgt = &f->side[TGTSIDE];
 	uint8_t tgtpif = PIF_NONE;
+	int ifi;
 
 	ASSERT(flow_new_entry == flow && f->state == FLOW_STATE_INI);
 	ASSERT(f->type == FLOW_TYPE_NONE);
 	ASSERT(f->pif[INISIDE] != PIF_NONE && f->pif[TGTSIDE] == PIF_NONE);
 	ASSERT(flow->f.state == FLOW_STATE_INI);
+	memcpy(f->omac, c->our_tap_mac, ETH_ALEN);
 
 	switch (f->pif[INISIDE]) {
 	case PIF_TAP:
 		tgtpif = fwd_nat_from_tap(c, proto, ini, tgt);
+
+		/* If there was no NAT, chances are this is a remote host
+		 * on the template interface's local network segment.
+		 * If so, insert its MAC address
+		 */
+		ifi = inany_v4(&ini->oaddr) ? c->ifi4 : c->ifi6;
+		if (inany_equals(&ini->oaddr, &tgt->eaddr))
+			nl_mac_get(nl_sock, &ini->oaddr, ifi, f->omac);
 		break;
 
 	case PIF_SPLICE:
@@ -458,6 +469,14 @@ struct flowside *flow_target(const struct ctx *c, union flow *flow,
 
 	case PIF_HOST:
 		tgtpif = fwd_nat_from_host(c, proto, ini, tgt);
+
+		/* If there was no NAT, chances are this is a remote host
+		 * on the template interface's local network segment.
+		 * If so, insert its MAC address
+		 */
+		ifi = inany_v4(&ini->eaddr) ? c->ifi4 : c->ifi6;
+		if (inany_equals(&ini->eaddr, &tgt->oaddr))
+			nl_mac_get(nl_sock, &ini->eaddr, ifi, f->omac);
 		break;
 
 	default:
diff --git a/flow.h b/flow.h
index cac618a..3240fb7 100644
--- a/flow.h
+++ b/flow.h
@@ -177,6 +177,7 @@ int flowside_connect(const struct ctx *c, int s,
  * @type:	Type of packet flow
  * @pif[]:	Interface for each side of the flow
  * @side[]:	Information for each side of the flow
+ * @omac:       MAC address of remote endpoint as seen from the guest
  */
 struct flow_common {
 #ifdef __GNUC__
@@ -192,6 +193,7 @@ struct flow_common {
 #endif
 	uint8_t		pif[SIDES];
 	struct flowside	side[SIDES];
+	unsigned char		omac[6];
 };
 
 #define FLOW_INDEX_BITS		17	/* 128k - 1 */
-- 
@@ -177,6 +177,7 @@ int flowside_connect(const struct ctx *c, int s,
  * @type:	Type of packet flow
  * @pif[]:	Interface for each side of the flow
  * @side[]:	Information for each side of the flow
+ * @omac:       MAC address of remote endpoint as seen from the guest
  */
 struct flow_common {
 #ifdef __GNUC__
@@ -192,6 +193,7 @@ struct flow_common {
 #endif
 	uint8_t		pif[SIDES];
 	struct flowside	side[SIDES];
+	unsigned char		omac[6];
 };
 
 #define FLOW_INDEX_BITS		17	/* 128k - 1 */
-- 
2.48.1