[RFC][net-next-2.6 PATCH 3/4] ethtool: set hard_header_len using ETH_FLAG_{TX|RX}VLAN

[John Fastabend <john.r.fastabend@intel.com>]

Toggling the vlan tx|rx hw offloads needs to set the hard_header_len
as well otherwise we end up using LL_RESERVED_SPACE incorrectly.
This results in pskb_expand_head() being used unnecessarily.

This add a check in ethtool_op_set_flags to catch the ETH_FLAG_TXVLAN
flag and set the header length.

Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
---

 net/core/ethtool.c |    9 +++++++++
 1 files changed, 9 insertions(+), 0 deletions(-)

diff --git a/net/core/ethtool.c b/net/core/ethtool.c
index 956a9f4..4f7fe26 100644
--- a/net/core/ethtool.c
+++ b/net/core/ethtool.c
@@ -21,6 +21,7 @@
 #include <linux/uaccess.h>
 #include <linux/vmalloc.h>
 #include <linux/slab.h>
+#include <linux/if_vlan.h>
 
 /*
  * Some useful ethtool_ops methods that're device independent.
@@ -151,6 +152,14 @@ int ethtool_op_set_flags(struct net_device *dev, u32 data, u32 supported)
 	if (data & ~supported)
 		return -EINVAL;
 
+	/* is ETH_FLAGS_TXVLAN being toggled */
+	if ((dev->features & ETH_FLAG_TXVLAN) ^ (data & ETH_FLAG_TXVLAN)) {
+		if (data & ETH_FLAG_TXVLAN)
+			dev->hard_header_len -= VLAN_HLEN;
+		else
+			dev->hard_header_len += VLAN_HLEN;
+	}
+
 	dev->features = ((dev->features & ~flags_dup_features) |
 			 (data & flags_dup_features));
 	return 0;