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

[Breno Leitao]

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 <lei...@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