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.

Create ethtool_get_rx_ring_count() to use .get_rx_ring_count if
available, falling back to get_rxnfc() otherwise. It needs to be
non-static, given it will be called by other ethtool functions laters,
as those calling get_rxfh().

Signed-off-by: Breno Leitao <leitao@debian.org>
---
 include/linux/ethtool.h |  2 ++
 net/ethtool/common.h    |  2 ++
 net/ethtool/ioctl.c     | 26 ++++++++++++++++++++++++--
 3 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/include/linux/ethtool.h b/include/linux/ethtool.h
index d7d757e72554e..c869b7f8bce8b 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/common.h b/net/ethtool/common.h
index c4d084dde5bf4..1609cf4e53ebb 100644
--- a/net/ethtool/common.h
+++ b/net/ethtool/common.h
@@ -54,6 +54,8 @@ void ethtool_ringparam_get_cfg(struct net_device *dev,
 			       struct kernel_ethtool_ringparam *kparam,
 			       struct netlink_ext_ack *extack);
 
+int ethtool_get_rx_ring_count(struct net_device *dev);
+
 int __ethtool_get_ts_info(struct net_device *dev, struct kernel_ethtool_ts_info *info);
 int ethtool_get_ts_info_by_phc(struct net_device *dev,
 			       struct kernel_ethtool_ts_info *info,
diff --git a/net/ethtool/ioctl.c b/net/ethtool/ioctl.c
index a0f3de76cea03..5b17e71cb3032 100644
--- a/net/ethtool/ioctl.c
+++ b/net/ethtool/ioctl.c
@@ -1208,6 +1208,26 @@ static noinline_for_stack int ethtool_set_rxnfc(struct net_device *dev,
 	return 0;
 }
 
+int ethtool_get_rx_ring_count(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);
+
+	if (!ops->get_rxnfc)
+		return -EOPNOTSUPP;
+
+	rx_rings.cmd = ETHTOOL_GRXRINGS;
+	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)
@@ -1217,7 +1237,7 @@ static noinline_for_stack int ethtool_get_rxrings(struct net_device *dev,
 	size_t info_size;
 	int ret;
 
-	if (!ops->get_rxnfc)
+	if (!ops->get_rxnfc && !ops->get_rx_ring_count)
 		return -EOPNOTSUPP;
 
 	info_size = sizeof(info);
@@ -1225,10 +1245,12 @@ static noinline_for_stack int ethtool_get_rxrings(struct net_device *dev,
 	if (ret)
 		return ret;
 
-	ret = ops->get_rxnfc(dev, &info, NULL);
+	ret = ethtool_get_rx_ring_count(dev);
 	if (ret < 0)
 		return ret;
 
+	info.data = ret;
+
 	return ethtool_rxnfc_copy_to_user(useraddr, &info, info_size, NULL);
 }
 

-- 
2.47.3