netdev: fix repeated netlink messages in queue dump

The context is supposed to record the next queue to dump,
not last dumped. If the dump doesn't fit we will restart
from the already-dumped queue, duplicating the message.

Before this fix and with the selftest improvements later
in this series we see:

  # ./run_kselftest.sh -t drivers/net:queues.py
  timeout set to 45
  selftests: drivers/net: queues.py
  KTAP version 1
  1..2
  # Check| At /root/ksft-net-drv/drivers/net/./queues.py, line 32, in get_queues:
  # Check|     ksft_eq(queues, expected)
  # Check failed 102 != 100
  # Check| At /root/ksft-net-drv/drivers/net/./queues.py, line 32, in get_queues:
  # Check|     ksft_eq(queues, expected)
  # Check failed 101 != 100
  not ok 1 queues.get_queues
  ok 2 queues.addremove_queues
  # Totals: pass:1 fail:1 xfail:0 xpass:0 skip:0 error:0
  not ok 1 selftests: drivers/net: queues.py # exit=1

With the fix:

  # ./ksft-net-drv/run_kselftest.sh -t drivers/net:queues.py
  timeout set to 45
  selftests: drivers/net: queues.py
  KTAP version 1
  1..2
  ok 1 queues.get_queues
  ok 2 queues.addremove_queues
  # Totals: pass:2 fail:0 xfail:0 xpass:0 skip:0 error:0

Fixes: 6b6171d ("netdev-genl: Add netlink framework functions for queue")
Reviewed-by: Joe Damato <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: kuba-moo

net/core/netdev-genl.c

@@ -488,24 +488,21 @@ netdev_nl_queue_dump_one(struct net_device *netdev, struct sk_buff *rsp,
 			 struct netdev_nl_dump_ctx *ctx)
 {
 	int err = 0;
-	int i;
 
 	if (!(netdev->flags & IFF_UP))
 		return err;
 
-	for (i = ctx->rxq_idx; i < netdev->real_num_rx_queues;) {
-		err = netdev_nl_queue_fill_one(rsp, netdev, i,
+	for (; ctx->rxq_idx < netdev->real_num_rx_queues; ctx->rxq_idx++) {
+		err = netdev_nl_queue_fill_one(rsp, netdev, ctx->rxq_idx,
 					       NETDEV_QUEUE_TYPE_RX, info);
 		if (err)
 			return err;
-		ctx->rxq_idx = i++;
 	}
-	for (i = ctx->txq_idx; i < netdev->real_num_tx_queues;) {
-		err = netdev_nl_queue_fill_one(rsp, netdev, i,
+	for (; ctx->txq_idx < netdev->real_num_tx_queues; ctx->txq_idx++) {
+		err = netdev_nl_queue_fill_one(rsp, netdev, ctx->txq_idx,
 					       NETDEV_QUEUE_TYPE_TX, info);
 		if (err)
 			return err;
-		ctx->txq_idx = i++;
 	}
 
 	return err;