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@debian.org>
---
 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

On Fri, Sep 05, 2025 at 10:07:23AM -0700, Breno Leitao wrote:
> 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@debian.org>
> ---
>  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);

Hi Breno,

Please also add get_rxrings to the Kernel doc for struct ethtool_ops.

>  	void	(*get_pause_stats)(struct net_device *dev,
>  				   struct ethtool_pause_stats *pause_stats);
>  	void	(*get_pauseparam)(struct net_device *,

On Fri, 05 Sep 2025 10:07:23 -0700 Breno Leitao wrote:
> +	int	(*get_rxrings)(struct net_device *dev);

I think this can return u32..
The drivers can't possibly fail to know how many queues they have.
We already do that for get_rxfh_*_size callbacks

>  	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)

This one has to indeed keep returning int, until we get rid of
get_rxnfc fallback completely.

> +{
> +	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;

I think malicious user space can trigger this warning with a TOCTOU
race. Let's skip the check, it's not really needed?

> +	info.data = get_num_rxrings(dev);

On Fri, 5 Sep 2025 16:42:53 -0700 Jakub Kicinski wrote:
> On Fri, 05 Sep 2025 10:07:23 -0700 Breno Leitao wrote:
> > +	int	(*get_rxrings)(struct net_device *dev);  
> 
> I think this can return u32..

Two more things, actually - get_rx_ring_count would sound a little bit
more in line with the get_rxfh_*_size helpers. And let's put it
somewhere closer to the rxfh callbacks. It's actually mostly used by
RXFH AKA RSS code.