Add a new optional get_rx_ring_count 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_rx_ring_count() if available,
falling back to get_rxnfc() otherwise.

Signed-off-by: Breno Leitao <leitao@debian.org>
---
 include/linux/ethtool.h |  2 ++
 net/ethtool/ioctl.c     | 22 ++++++++++++++++++----
 2 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/include/linux/ethtool.h b/include/linux/ethtool.h
index de5bd76a400ca..2d91fd3102c14 100644
--- a/include/linux/ethtool.h
+++ b/include/linux/ethtool.h
@@ -968,6 +968,7 @@ struct kernel_ethtool_ts_info {
  * @reset: Reset (part of) the device, as specified by a bitmask of
  *	flags from &enum ethtool_reset_flags.  Returns a negative
  *	error code or zero.
+ * @get_rx_ring_count: Return the number of RX rings
  * @get_rxfh_key_size: Get the size of the RX flow hash key.
  *	Returns zero if not supported for this specific device.
  * @get_rxfh_indir_size: Get the size of the RX flow hash indirection table.
@@ -1162,6 +1163,7 @@ struct ethtool_ops {
 	int	(*set_rxnfc)(struct net_device *, struct ethtool_rxnfc *);
 	int	(*flash_device)(struct net_device *, struct ethtool_flash *);
 	int	(*reset)(struct net_device *, u32 *);
+	u32	(*get_rx_ring_count)(struct net_device *dev);
 	u32	(*get_rxfh_key_size)(struct net_device *);
 	u32	(*get_rxfh_indir_size)(struct net_device *);
 	int	(*get_rxfh)(struct net_device *, struct ethtool_rxfh_param *);
diff --git a/net/ethtool/ioctl.c b/net/ethtool/ioctl.c
index 1a9ad47f60313..aba483bc9fd85 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_rx_ring_count)
+		return ops->get_rx_ring_count(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 +1233,14 @@ 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_rx_ring_count)
 		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;
+	info.data = get_num_rxrings(dev);
 
 	return ethtool_rxnfc_copy_to_user(useraddr, &info, info_size, NULL);
 }

-- 
2.47.3