netdev: support dumping a single netdev in qstats

Having to filter the right ifindex in the tests is a bit tedious.
Add support for dumping qstats for a single ifindex.

Reviewed-by: David Ahern <dsahern@kernel.org>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20240420023543.3300306-2-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Documentation/netlink/specs/netdev.yaml

@@ -486,6 +486,7 @@ operations:
       dump:
         request:
           attributes:
+            - ifindex
             - scope
         reply:
           attributes:

net/core/netdev-genl-gen.c

@@ -70,6 +70,7 @@ static const struct nla_policy netdev_napi_get_dump_nl_policy[NETDEV_A_NAPI_IFIN
 
 /* NETDEV_CMD_QSTATS_GET - dump */
 static const struct nla_policy netdev_qstats_get_nl_policy[NETDEV_A_QSTATS_SCOPE + 1] = {
+	[NETDEV_A_QSTATS_IFINDEX] = NLA_POLICY_MIN(NLA_U32, 1),
 	[NETDEV_A_QSTATS_SCOPE] = NLA_POLICY_MASK(NLA_UINT, 0x1),
 };
 

net/core/netdev-genl.c

@@ -639,35 +639,61 @@ netdev_nl_stats_by_netdev(struct net_device *netdev, struct sk_buff *rsp,
 	return -EMSGSIZE;
 }
 
+static int
+netdev_nl_qstats_get_dump_one(struct net_device *netdev, unsigned int scope,
+			      struct sk_buff *skb, const struct genl_info *info,
+			      struct netdev_nl_dump_ctx *ctx)
+{
+	if (!netdev->stat_ops)
+		return 0;
+
+	switch (scope) {
+	case 0:
+		return netdev_nl_stats_by_netdev(netdev, skb, info);
+	case NETDEV_QSTATS_SCOPE_QUEUE:
+		return netdev_nl_stats_by_queue(netdev, skb, info, ctx);
+	}
+
+	return -EINVAL;	/* Should not happen, per netlink policy */
+}
+
 int netdev_nl_qstats_get_dumpit(struct sk_buff *skb,
 				struct netlink_callback *cb)
 {
 	struct netdev_nl_dump_ctx *ctx = netdev_dump_ctx(cb);
 	const struct genl_info *info = genl_info_dump(cb);
 	struct net *net = sock_net(skb->sk);
 	struct net_device *netdev;
+	unsigned int ifindex;
 	unsigned int scope;
 	int err = 0;
 
 	scope = 0;
 	if (info->attrs[NETDEV_A_QSTATS_SCOPE])
 		scope = nla_get_uint(info->attrs[NETDEV_A_QSTATS_SCOPE]);
 
-	rtnl_lock();
-	for_each_netdev_dump(net, netdev, ctx->ifindex) {
-		if (!netdev->stat_ops)
-			continue;
+	ifindex = 0;
+	if (info->attrs[NETDEV_A_QSTATS_IFINDEX])
+		ifindex = nla_get_u32(info->attrs[NETDEV_A_QSTATS_IFINDEX]);
 
-		switch (scope) {
-		case 0:
-			err = netdev_nl_stats_by_netdev(netdev, skb, info);
-			break;
-		case NETDEV_QSTATS_SCOPE_QUEUE:
-			err = netdev_nl_stats_by_queue(netdev, skb, info, ctx);
-			break;
+	rtnl_lock();
+	if (ifindex) {
+		netdev = __dev_get_by_index(net, ifindex);
+		if (netdev && netdev->stat_ops) {
+			err = netdev_nl_qstats_get_dump_one(netdev, scope, skb,
+							    info, ctx);
+		} else {
+			NL_SET_BAD_ATTR(info->extack,
+					info->attrs[NETDEV_A_QSTATS_IFINDEX]);
+			err = netdev ? -EOPNOTSUPP : -ENODEV;
+		}
+	} else {
+		for_each_netdev_dump(net, netdev, ctx->ifindex) {
+			err = netdev_nl_qstats_get_dump_one(netdev, scope, skb,
+							    info, ctx);
+			if (err < 0)
+				break;
 		}
-		if (err < 0)
-			break;
 	}
 	rtnl_unlock();