[PATCH v12 5/9] 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>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

---
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.
v4: - Renamed flow_commeon->omac to flow_common->tap_omac to make is
      role in the code clearer
v5: - Modified the criteria for ARP/NDP table lookup like in the
      previous commits.
    - Removed the PIF_TAP lookup case, as David suggested, and did
      instead give the flow->tap_omac field a value marking it as
      non-initialized.
    - Calling the cache table instead of netlink for ARP/NDP lookup.
    - Unconditionally using the potentially translated IP address
      in the lookup, instead of only if NAT really was applied.
v6: - Using MAC_ZERO instead of own definitions
v12:- Using MAC_UNDEF (==ff:ff:ff:ff:ff:ff) instead of MAC_ZERO,
      which is a legal MAC address.
---
 flow.c | 2 ++
 flow.h | 2 ++
 util.h | 2 ++
 3 files changed, 6 insertions(+)

diff --git a/flow.c b/flow.c
index feefda3..df3ce2a 100644
--- a/flow.c
+++ b/flow.c
@@ -449,6 +449,7 @@ struct flowside *flow_target(const struct ctx *c, union flow *flow,
 
 	switch (f->pif[INISIDE]) {
 	case PIF_TAP:
+		memcpy(f->tap_omac, MAC_UNDEF, ETH_ALEN);
 		tgtpif = fwd_nat_from_tap(c, proto, ini, tgt);
 		break;
 
@@ -458,6 +459,7 @@ struct flowside *flow_target(const struct ctx *c, union flow *flow,
 
 	case PIF_HOST:
 		tgtpif = fwd_nat_from_host(c, proto, ini, tgt);
+		fwd_neigh_mac_get(c, &ini->eaddr, f->tap_omac);
 		break;
 
 	default:
diff --git a/flow.h b/flow.h
index cac618a..f342895 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
+ * @tap_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];
+	uint8_t		tap_omac[6];
 };
 
 #define FLOW_INDEX_BITS		17	/* 128k - 1 */
diff --git a/util.h b/util.h
index 22eaac5..6fc8f5d 100644
--- a/util.h
+++ b/util.h
@@ -101,6 +101,8 @@ void abort_with_msg(const char *fmt, ...)
 	((uint8_t [ETH_ALEN]){ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff })
 #define MAC_ZERO		((uint8_t [ETH_ALEN]){ 0 })
 #define MAC_IS_ZERO(addr)	(!memcmp((addr), MAC_ZERO, ETH_ALEN))
+#define MAC_UNDEF		MAC_BROADCAST
+#define MAC_IS_UNDEF(addr)	(!memcmp((addr), MAC_UNDEF, ETH_ALEN))
 
 #ifndef __bswap_constant_16
 #define __bswap_constant_16(x)						\
-- 
2.50.1