[PATCH net 3/4] amt: make pre-query report drops visible

[Omar Ramadan <omar@blockcast.net>]

A gateway cannot forward an IGMP or MLD report until it has received the
relay's Membership Query for that family. The query supplies the nonce and
interval echoed by the Membership Update, so dropping an early report is
required, but doing so silently leaves operators with a dark multicast path
and no indication why the join never happened.

Emit a family-specific debug message before taking the existing drop path.
That path already increments tx_dropped, so each discarded report is
accounted exactly once.

Signed-off-by: Omar Ramadan <omar@blockcast.net>
---
 drivers/net/amt.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/net/amt.c b/drivers/net/amt.c
index 17dceeaa1..79f2f59bf 100644
--- a/drivers/net/amt.c
+++ b/drivers/net/amt.c
@@ -1251,9 +1251,17 @@ static netdev_tx_t amt_dev_xmit(struct sk_buff *skb, struct net_device *dev)
 		/* Gateway only passes IGMP/MLD packets */
 		if (!report)
 			goto free;
+		/* A validated report can only be forwarded after the relay's
+		 * family-specific Membership Query supplies the state echoed
+		 * by the Membership Update. Log this readiness failure before
+		 * the shared drop path accounts it.
+		 */
 		if ((!v6 && !READ_ONCE(amt->ready4)) ||
-		    (v6 && !READ_ONCE(amt->ready6)))
+		    (v6 && !READ_ONCE(amt->ready6))) {
+			netdev_dbg(dev, "drop %s report: no Membership Query for this family yet\n",
+				   v6 ? "MLD" : "IGMP");
 			goto free;
+		}
 		if (amt_send_membership_update(amt, skb,  v6))
 			goto free;
 		goto unlock;
-- 
2.43.0