net: export a helper for adding up queue stats

Older drivers and drivers with lower queue counts often have a static
array of queues, rather than allocating structs for each queue on demand.
Add a helper for adding up qstats from a queue range. Expectation is
that driver will pass a queue range [netdev->real_num_*x_queues, MAX).
It was tempting to always use num_*x_queues as the end, but virtio
seems to clamp its queue count after allocating the netdev. And this
way we can trivaly reuse the helper for [0, real_..).

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Link: https://patch.msgid.link/20250507003221.823267-2-kuba@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

include/net/netdev_queues.h

@@ -103,6 +103,12 @@ struct netdev_stat_ops {
 			       struct netdev_queue_stats_tx *tx);
 };
 
+void netdev_stat_queue_sum(struct net_device *netdev,
+			   int rx_start, int rx_end,
+			   struct netdev_queue_stats_rx *rx_sum,
+			   int tx_start, int tx_end,
+			   struct netdev_queue_stats_tx *tx_sum);
+
 /**
  * struct netdev_queue_mgmt_ops - netdev ops for queue management
  *

net/core/netdev-genl.c

@@ -708,25 +708,66 @@ netdev_nl_stats_by_queue(struct net_device *netdev, struct sk_buff *rsp,
 	return 0;
 }
 
+/**
+ * netdev_stat_queue_sum() - add up queue stats from range of queues
+ * @netdev:	net_device
+ * @rx_start:	index of the first Rx queue to query
+ * @rx_end:	index after the last Rx queue (first *not* to query)
+ * @rx_sum:	output Rx stats, should be already initialized
+ * @tx_start:	index of the first Tx queue to query
+ * @tx_end:	index after the last Tx queue (first *not* to query)
+ * @tx_sum:	output Tx stats, should be already initialized
+ *
+ * Add stats from [start, end) range of queue IDs to *x_sum structs.
+ * The sum structs must be already initialized. Usually this
+ * helper is invoked from the .get_base_stats callbacks of drivers
+ * to account for stats of disabled queues. In that case the ranges
+ * are usually [netdev->real_num_*x_queues, netdev->num_*x_queues).
+ */
+void netdev_stat_queue_sum(struct net_device *netdev,
+			   int rx_start, int rx_end,
+			   struct netdev_queue_stats_rx *rx_sum,
+			   int tx_start, int tx_end,
+			   struct netdev_queue_stats_tx *tx_sum)
+{
+	const struct netdev_stat_ops *ops;
+	struct netdev_queue_stats_rx rx;
+	struct netdev_queue_stats_tx tx;
+	int i;
+
+	ops = netdev->stat_ops;
+
+	for (i = rx_start; i < rx_end; i++) {
+		memset(&rx, 0xff, sizeof(rx));
+		if (ops->get_queue_stats_rx)
+			ops->get_queue_stats_rx(netdev, i, &rx);
+		netdev_nl_stats_add(rx_sum, &rx, sizeof(rx));
+	}
+	for (i = tx_start; i < tx_end; i++) {
+		memset(&tx, 0xff, sizeof(tx));
+		if (ops->get_queue_stats_tx)
+			ops->get_queue_stats_tx(netdev, i, &tx);
+		netdev_nl_stats_add(tx_sum, &tx, sizeof(tx));
+	}
+}
+EXPORT_SYMBOL(netdev_stat_queue_sum);
+
 static int
 netdev_nl_stats_by_netdev(struct net_device *netdev, struct sk_buff *rsp,
 			  const struct genl_info *info)
 {
-	struct netdev_queue_stats_rx rx_sum, rx;
-	struct netdev_queue_stats_tx tx_sum, tx;
-	const struct netdev_stat_ops *ops;
+	struct netdev_queue_stats_rx rx_sum;
+	struct netdev_queue_stats_tx tx_sum;
 	void *hdr;
-	int i;
 
-	ops = netdev->stat_ops;
 	/* Netdev can't guarantee any complete counters */
-	if (!ops->get_base_stats)
+	if (!netdev->stat_ops->get_base_stats)
 		return 0;
 
 	memset(&rx_sum, 0xff, sizeof(rx_sum));
 	memset(&tx_sum, 0xff, sizeof(tx_sum));
 
-	ops->get_base_stats(netdev, &rx_sum, &tx_sum);
+	netdev->stat_ops->get_base_stats(netdev, &rx_sum, &tx_sum);
 
 	/* The op was there, but nothing reported, don't bother */
 	if (!memchr_inv(&rx_sum, 0xff, sizeof(rx_sum)) &&
@@ -739,18 +780,8 @@ netdev_nl_stats_by_netdev(struct net_device *netdev, struct sk_buff *rsp,
 	if (nla_put_u32(rsp, NETDEV_A_QSTATS_IFINDEX, netdev->ifindex))
 		goto nla_put_failure;
 
-	for (i = 0; i < netdev->real_num_rx_queues; i++) {
-		memset(&rx, 0xff, sizeof(rx));
-		if (ops->get_queue_stats_rx)
-			ops->get_queue_stats_rx(netdev, i, &rx);
-		netdev_nl_stats_add(&rx_sum, &rx, sizeof(rx));
-	}
-	for (i = 0; i < netdev->real_num_tx_queues; i++) {
-		memset(&tx, 0xff, sizeof(tx));
-		if (ops->get_queue_stats_tx)
-			ops->get_queue_stats_tx(netdev, i, &tx);
-		netdev_nl_stats_add(&tx_sum, &tx, sizeof(tx));
-	}
+	netdev_stat_queue_sum(netdev, 0, netdev->real_num_rx_queues, &rx_sum,
+			      0, netdev->real_num_tx_queues, &tx_sum);
 
 	if (netdev_nl_stats_write_rx(rsp, &rx_sum) ||
 	    netdev_nl_stats_write_tx(rsp, &tx_sum))