datapath: Fix VLAN insertion behavior on Linux 2.6.27 and 2.6.28.

The behavior of __vlan_put_tag() has changed over time:

     - In 2.6.26 and earlier, it adjusted both MAC and network header
       pointers.  (The latter didn't make any sense.)

     - In 2.6.27 and 2.6.28, it did not adjust any header pointers at all.

     - In 2.6.29 and later, it adjusts the MAC header pointer only.

The behavior in 2.6.26 and earlier, and in 2.2.29 and later, works OK for
Open vSwitch.  The 2.6.27 and 2.6.28 behavior *almost* works OK, with a few
subtle problems.  If an action that sets a VLAN tag is followed by an
action that strips a VLAN tag, the "strip" action silently fails.  This is
because vlan_pull_tag() in datapath/actions.c sees the encapsulated
protocol, not the 802.1Q protocol, because the MAC header was not adjusted
and does not point to the 802.1Q header.  If multiple set-VLAN actions
occur in a single flow, the second and later actions will fail for the same
reason.

This commit fixes the problem by ensuring that __vlan_put_tag() always
behaves as in 2.6.29 and later.

Reported-by: Reid Price <reid@nicira.com>
Bug #2867.

2 files changed, 47 insertions, 0 deletions

diff --git a/datapath/linux-2.6/Modules.mk b/datapath/linux-2.6/Modules.mk
index f5f13e2c8..baa6f53cd 100644
--- a/datapath/linux-2.6/Modules.mk
+++ b/datapath/linux-2.6/Modules.mk
@@ -16,6 +16,7 @@ openvswitch_headers += \
 	linux-2.6/compat-2.6/include/linux/if.h \
 	linux-2.6/compat-2.6/include/linux/if_arp.h \
 	linux-2.6/compat-2.6/include/linux/if_ether.h \
+	linux-2.6/compat-2.6/include/linux/if_vlan.h \
 	linux-2.6/compat-2.6/include/linux/in.h \
 	linux-2.6/compat-2.6/include/linux/inetdevice.h \
 	linux-2.6/compat-2.6/include/linux/ip.h \
diff --git a/datapath/linux-2.6/compat-2.6/include/linux/if_vlan.h b/datapath/linux-2.6/compat-2.6/include/linux/if_vlan.h
new file mode 100644
index 000000000..3bede9302
--- /dev/null
+++ b/datapath/linux-2.6/compat-2.6/include/linux/if_vlan.h
@@ -0,0 +1,46 @@
+#ifndef __LINUX_IF_VLAN_WRAPPER_H
+#define __LINUX_IF_VLAN_WRAPPER_H 1
+
+#include_next <linux/if_vlan.h>
+
+/*
+ * The behavior of __vlan_put_tag() has changed over time:
+ *
+ *      - In 2.6.26 and earlier, it adjusted both MAC and network header
+ *        pointers.  (The latter didn't make any sense.)
+ *
+ *      - In 2.6.27 and 2.6.28, it did not adjust any header pointers at all.
+ *
+ *      - In 2.6.29 and later, it adjusts the MAC header pointer only.
+ *
+ * This is the version from 2.6.33.  We unconditionally substitute this version
+ * to avoid the need to guess whether the version in the kernel tree is
+ * acceptable.
+ */
+#define __vlan_put_tag rpl_vlan_put_tag
+static inline struct sk_buff *__vlan_put_tag(struct sk_buff *skb, u16 vlan_tci)
+{
+	struct vlan_ethhdr *veth;
+
+	if (skb_cow_head(skb, VLAN_HLEN) < 0) {
+		kfree_skb(skb);
+		return NULL;
+	}
+	veth = (struct vlan_ethhdr *)skb_push(skb, VLAN_HLEN);
+
+	/* Move the mac addresses to the beginning of the new header. */
+	memmove(skb->data, skb->data + VLAN_HLEN, 2 * VLAN_ETH_ALEN);
+	skb->mac_header -= VLAN_HLEN;
+
+	/* first, the ethernet type */
+	veth->h_vlan_proto = htons(ETH_P_8021Q);
+
+	/* now, the TCI */
+	veth->h_vlan_TCI = htons(vlan_tci);
+
+	skb->protocol = htons(ETH_P_8021Q);
+
+	return skb;
+}
+
+#endif	/* linux/if_vlan.h wrapper */