ethtool: Define and apply a default policy for RX flow hash indirection

All drivers that support modification of the RX flow hash indirection
table initialise it in the same way: RX rings are assigned to table
entries in rotation.  Make that default policy explicit by having them
call a ethtool_rxfh_indir_default() function.

In the ethtool core, add support for a zero size value for
ETHTOOL_SRXFHINDIR, which resets the table to this default.

Partly-suggested-by: Matt Carlson <mcarlson@broadcom.com>
Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Acked-by: Shreyas N Bhatewara <sbhatewara@vmware.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 20 insertions, 3 deletions

diff --git a/include/linux/ethtool.h b/include/linux/ethtool.h
index 3b9f09d55b5c..b38bf69310ee 100644
--- a/include/linux/ethtool.h
+++ b/include/linux/ethtool.h
@@ -543,10 +543,15 @@ struct compat_ethtool_rxnfc {
 /**
  * struct ethtool_rxfh_indir - command to get or set RX flow hash indirection
  * @cmd: Specific command number - %ETHTOOL_GRXFHINDIR or %ETHTOOL_SRXFHINDIR
- * @size: On entry, the array size of the user buffer, which may be zero
- *      for %ETHTOOL_GRXFHINDIR.  On return from %ETHTOOL_GRXFHINDIR, the
- *      array size of the hardware indirection table.
+ * @size: On entry, the array size of the user buffer, which may be zero.
+ *      On return from %ETHTOOL_GRXFHINDIR, the array size of the hardware
+ *      indirection table.
  * @ring_index: RX ring/queue index for each hash value
+ *
+ * For %ETHTOOL_GRXFHINDIR, a @size of zero means that only the size
+ * should be returned.  For %ETHTOOL_SRXFHINDIR, a @size of zero means
+ * the table should be reset to default values.  This last feature
+ * is not supported by the original implementations.
  */
 struct ethtool_rxfh_indir {
         __u32   cmd;
@@ -750,6 +755,18 @@ struct net_device;
 u32 ethtool_op_get_link(struct net_device *dev);
 
 /**
+ * ethtool_rxfh_indir_default - get default value for RX flow hash indirection
+ * @index: Index in RX flow hash indirection table
+ * @n_rx_rings: Number of RX rings to use
+ *
+ * This function provides the default policy for RX flow hash indirection.
+ */
+static inline u32 ethtool_rxfh_indir_default(u32 index, u32 n_rx_rings)
+{
+        return index % n_rx_rings;
+}
+
+/**
  * struct ethtool_ops - optional netdev operations
  * @get_settings: Get various device settings including Ethernet link
  *      settings. The @cmd parameter is expected to have been cleared