ethtool: Name the 'no change' value for setting RSS hash key but not indir table

We usually allocate special values of u32 fields starting from the top
down, so also change the value to 0xffffffff.  As these operations
haven't been included in a stable release yet, it's not too late to
change.
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

include/uapi/linux/ethtool.h

@@ -850,7 +850,8 @@ struct ethtool_rxfh_indir {
  * struct ethtool_rxfh - command to get/set RX flow hash indir or/and hash key.
  * @cmd: Specific command number - %ETHTOOL_GRSSH or %ETHTOOL_SRSSH
  * @rss_context: RSS context identifier.
- * @indir_size: On entry, the array size of the user buffer, which may be zero.
+ * @indir_size: On entry, the array size of the user buffer, which may be zero,
+ *		or (for %ETHTOOL_SRSSH), %ETH_RXFH_INDIR_NO_CHANGE.
  *		On return from %ETHTOOL_GRSSH, the array size of the hardware
  *		indirection table.
  * @key_size:	On entry, the array size of the user buffer in bytes,
@@ -861,10 +862,10 @@ struct ethtool_rxfh_indir {
  *		of size @indir_size followed by hash key of size @key_size.
  *
  * For %ETHTOOL_GRSSH, a @indir_size and key_size of zero means that only the
- * size should be returned.  For %ETHTOOL_SRSSH, a @indir_size of 0xDEADBEEF
- * means that indir table setting is not requested and a @indir_size of zero
- * means the indir table should be reset to default values.  This last feature
- * is not supported by the original implementations.
+ * size should be returned.  For %ETHTOOL_SRSSH, an @indir_size of
+ * %ETH_RXFH_INDIR_NO_CHANGE means that indir table setting is not requested
+ * and a @indir_size of zero means the indir table should be reset to default
+ * values.
  */
 struct ethtool_rxfh {
 	__u32   cmd;
@@ -874,6 +875,7 @@ struct ethtool_rxfh {
 	__u32	rsvd[2];
 	__u32   rss_config[0];
 };
+#define ETH_RXFH_INDIR_NO_CHANGE	0xffffffff
 
 /**
  * struct ethtool_rx_ntuple_flow_spec - specification for RX flow filter

net/core/ethtool.c

@@ -803,12 +803,13 @@ static noinline_for_stack int ethtool_set_rxfh(struct net_device *dev,
 
 	/* If either indir or hash key is valid, proceed further.
 	 */
-	if ((user_indir_size && ((user_indir_size != 0xDEADBEEF) &&
-				 user_indir_size != dev_indir_size)) ||
+	if ((user_indir_size &&
+	     user_indir_size != ETH_RXFH_INDIR_NO_CHANGE &&
+	     user_indir_size != dev_indir_size) ||
 	    (user_key_size && (user_key_size != dev_key_size)))
 		return -EINVAL;
 
-	if (user_indir_size != 0xDEADBEEF)
+	if (user_indir_size != ETH_RXFH_INDIR_NO_CHANGE)
 		indir_bytes = dev_indir_size * sizeof(indir[0]);
 
 	rss_config = kzalloc(indir_bytes + user_key_size, GFP_USER);
@@ -821,9 +822,10 @@ static noinline_for_stack int ethtool_set_rxfh(struct net_device *dev,
 		goto out;
 
 	/* user_indir_size == 0 means reset the indir table to default.
-	 * user_indir_size == 0xDEADBEEF means indir setting is not requested.
+	 * user_indir_size == ETH_RXFH_INDIR_NO_CHANGE means leave it unchanged.
 	 */
-	if (user_indir_size && user_indir_size != 0xDEADBEEF) {
+	if (user_indir_size &&
+	    user_indir_size != ETH_RXFH_INDIR_NO_CHANGE) {
 		indir = (u32 *)rss_config;
 		ret = ethtool_copy_validate_indir(indir,
 						  useraddr + rss_cfg_offset,