[PATCH RFC net-next 4/7] net: ethtool: add get_rxrings callback to optimize RX ring queries

[Breno Leitao <leitao@xxxxxxxxxx>]

Add a new optional get_rxrings callback in ethtool_ops to allow drivers
to provide the number of RX rings directly without going through the
full get_rxnfc flow classification interface.

Modify ethtool_get_rxrings() to use get_rxrings() if available,
falling back to get_rxnfc() otherwise.

Signed-off-by: Breno Leitao <leitao@xxxxxxxxxx>
---
 include/linux/ethtool.h |  1 +
 net/ethtool/ioctl.c     | 25 +++++++++++++++++++++----
 2 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/include/linux/ethtool.h b/include/linux/ethtool.h
index de5bd76a400ca..4f6da35a77eb1 100644
--- a/include/linux/ethtool.h
+++ b/include/linux/ethtool.h
@@ -1141,6 +1141,7 @@ struct ethtool_ops {
 				 struct ethtool_ringparam *,
 				 struct kernel_ethtool_ringparam *,
 				 struct netlink_ext_ack *);
+	int	(*get_rxrings)(struct net_device *dev);
 	void	(*get_pause_stats)(struct net_device *dev,
 				   struct ethtool_pause_stats *pause_stats);
 	void	(*get_pauseparam)(struct net_device *,
diff --git a/net/ethtool/ioctl.c b/net/ethtool/ioctl.c
index 1a9ad47f60313..2f3dbef9eb712 100644
--- a/net/ethtool/ioctl.c
+++ b/net/ethtool/ioctl.c
@@ -1208,6 +1208,22 @@ static noinline_for_stack int ethtool_set_rxnfc(struct net_device *dev,
 	return 0;
 }
 
+static int get_num_rxrings(struct net_device *dev)
+{
+	const struct ethtool_ops *ops = dev->ethtool_ops;
+	struct ethtool_rxnfc rx_rings;
+	int ret;
+
+	if (ops->get_rxrings)
+		return ops->get_rxrings(dev);
+
+	ret = ops->get_rxnfc(dev, &rx_rings, NULL);
+	if (ret < 0)
+		return ret;
+
+	return rx_rings.data;
+}
+
 static noinline_for_stack int ethtool_get_rxrings(struct net_device *dev,
 						  u32 cmd,
 						  void __user *useraddr)
@@ -1217,16 +1233,17 @@ static noinline_for_stack int ethtool_get_rxrings(struct net_device *dev,
 	const struct ethtool_ops *ops = dev->ethtool_ops;
 	int ret;
 
-	if (!ops->get_rxnfc)
+	if (!ops->get_rxnfc && !ops->get_rxrings)
 		return -EOPNOTSUPP;
 
 	ret = ethtool_rxnfc_copy_struct(cmd, &info, &info_size, useraddr);
 	if (ret)
 		return ret;
 
-	ret = ops->get_rxnfc(dev, &info, NULL);
-	if (ret < 0)
-		return ret;
+	if (WARN_ON_ONCE(info.cmd != ETHTOOL_GRXRINGS))
+		return -EOPNOTSUPP;
+
+	info.data = get_num_rxrings(dev);
 
 	return ethtool_rxnfc_copy_to_user(useraddr, &info, info_size, NULL);
 }

-- 
2.47.3