This introduces a new framework to handle device features setting.
It consists of:
  - new fields in struct net_device:
	+ hw_features - features that hw/driver supports toggling
	+ wanted_features - features that user wants enabled, when possible
  - new netdev_ops:
	+ feat = ndo_fix_features(dev, feat) - API checking constraints for
		enabling features or their combinations
	+ ndo_set_features(dev) - API updating hardware state to match
		changed dev->features
  - new ethtool commands:
	+ ETHTOOL_GFEATURES/ETHTOOL_SFEATURES: get/set dev->wanted_features
		and trigger device reconfiguration if resulting dev->features
		changed
	+ ETHTOOL_GSTRINGS(ETH_SS_FEATURES): get feature bits names (meaning)

Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
---
 include/linux/ethtool.h   |   86 +++++++++++++++++++++++++
 include/linux/netdevice.h |   44 ++++++++++++-
 net/core/dev.c            |   47 ++++++++++++--
 net/core/ethtool.c        |  154 +++++++++++++++++++++++++++++++++++++++++----
 4 files changed, 312 insertions(+), 19 deletions(-)

diff --git a/include/linux/ethtool.h b/include/linux/ethtool.h
index 1908929..b832083 100644
--- a/include/linux/ethtool.h
+++ b/include/linux/ethtool.h

@@ -251,6 +251,7 @@ enum ethtool_stringset {
 	ETH_SS_STATS,
 	ETH_SS_PRIV_FLAGS,
 	ETH_SS_NTUPLE_FILTERS,
+	ETH_SS_FEATURES,
 };
 
 /* for passing string sets for data tagging */

@@ -523,6 +524,88 @@ struct ethtool_flash {
 	char	data[ETHTOOL_FLASH_MAX_FILENAME];
 };
 
+/* for returning and changing feature sets */
+
+/**
+ * struct ethtool_get_features_block - block with state of 32 features
+ * @avaliable: mask of changeable features

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index c7d7074..6490860 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h

@@ -783,6 +783,16 @@ struct netdev_tc_txq {
  *	Set hardware filter for RFS.  rxq_index is the target queue index;
  *	flow_id is a flow ID to be passed to rps_may_expire_flow() later.
  *	Return the filter ID on success, or a negative error code.
+ *
+ * u32 (*ndo_fix_features)(struct net_device *dev, u32 features);
+ *	Modifies features supported by device depending on device-specific
+ *	constraints. Should not modify hardware state.

@@ -954,6 +974,12 @@ struct net_device {
 #define NETIF_F_TSO6		(SKB_GSO_TCPV6 << NETIF_F_GSO_SHIFT)
 #define NETIF_F_FSO		(SKB_GSO_FCOE << NETIF_F_GSO_SHIFT)
 
+	/* Features valid for ethtool to change */
+	/* = all defined minus driver/device-class-related */
+#define NETIF_F_NEVER_CHANGE	(NETIF_F_VLAN_CHALLENGED | \
+				  NETIF_F_LLTX | NETIF_F_NETNS_LOCAL)

+#define NETIF_F_ETHTOOL_BITS	(0x1f3fffff & ~NETIF_F_NEVER_CHANGE)
+
 	/* List of features with software fallbacks. */
 #define NETIF_F_GSO_SOFTWARE	(NETIF_F_TSO | NETIF_F_TSO_ECN | \
 				 NETIF_F_TSO6 | NETIF_F_UFO)

@@ -964,6 +990,12 @@ struct net_device {
 #define NETIF_F_V6_CSUM		(NETIF_F_GEN_CSUM | NETIF_F_IPV6_CSUM)
 #define NETIF_F_ALL_CSUM	(NETIF_F_V4_CSUM | NETIF_F_V6_CSUM)
 
+#define NETIF_F_ALL_TSO 	(NETIF_F_TSO | NETIF_F_TSO6 | NETIF_F_TSO_ECN)
+
+#define NETIF_F_ALL_TX_OFFLOADS	(NETIF_F_ALL_CSUM | NETIF_F_SG | \
+				 NETIF_F_FRAGLIST | NETIF_F_ALL_TSO | \
+				 NETIF_F_SCTP_CSUM | NETIF_F_FCOE_CRC)
+
 	/*
 	 * If one device supports one of these features, then enable them
 	 * for all in netdev_increment_features.

diff --git a/net/core/dev.c b/net/core/dev.c
index ddd5df2..0ccbee6 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c

@@ -5267,6 +5273,35 @@ u32 netdev_fix_features(struct net_device *dev, u32 features)
 }
 EXPORT_SYMBOL(netdev_fix_features);
 
+void netdev_update_features(struct net_device *dev)
+{
+	u32 features;
+	int err = 0;
+
+	features = netdev_get_wanted_features(dev);
+
+	if (dev->netdev_ops->ndo_fix_features)
+		features = dev->netdev_ops->ndo_fix_features(dev, features);
+
+	/* driver might be less strict about feature dependencies */
+	features = netdev_fix_features(dev, features);
+
+	if (dev->features == features)
+		return;
+
+	netdev_info(dev, "Features changed: 0x%08x -> 0x%08x\n",
+		dev->features, features);
+
+	if (dev->netdev_ops->ndo_set_features)
+		err = dev->netdev_ops->ndo_set_features(dev, features);
+
+	if (!err)
+		dev->features = features;
+	else if (err < 0)
+		netdev_err(dev, "set_features() failed (%d)\n", err);

diff --git a/net/core/ethtool.c b/net/core/ethtool.c
index 5984ee0..1420edd 100644
--- a/net/core/ethtool.c
+++ b/net/core/ethtool.c

@@ -55,6 +55,7 @@ int ethtool_op_set_tx_csum(struct net_device *dev, u32 data)
 
 	return 0;
 }
+EXPORT_SYMBOL(ethtool_op_set_tx_csum);
 
 int ethtool_op_set_tx_hw_csum(struct net_device *dev, u32 data)
 {

@@ -171,6 +172,136 @@ EXPORT_SYMBOL(ethtool_ntuple_flush);
 
 /* Handlers for each ethtool command */
 
+#define ETHTOOL_DEV_FEATURE_WORDS	1
+
+static int ethtool_get_features(struct net_device *dev, void __user *useraddr)
+{
+	struct ethtool_gfeatures cmd = {
+		.cmd = ETHTOOL_GFEATURES,
+		.size = ETHTOOL_DEV_FEATURE_WORDS,
+	};
+	struct ethtool_get_features_block features[ETHTOOL_DEV_FEATURE_WORDS] = {
+		{
+			.available = dev->hw_features,
+			.requested = dev->wanted_features,
+			.active = dev->features,
+			.never_changed = NETIF_F_NEVER_CHANGE,
+		},
+	};
+	u32 __user *sizeaddr;
+	u32 in_size;
+
+	sizeaddr = useraddr + offsetof(struct ethtool_gfeatures, size);
+	if (get_user(in_size, sizeaddr))
+		return -EFAULT;
+
+	if (in_size < ETHTOOL_DEV_FEATURE_WORDS)
+		return -EINVAL;