datapath: Add compatibility with sk_buff's vlan_tci before 2.6.33.

[sliver-openvswitch.git] / datapath / vlan.h

diff --git a/datapath/vlan.h b/datapath/vlan.h
index 02a6290..7e1084e 100644 (file)
--- a/datapath/vlan.h
+++ b/datapath/vlan.h
@@ -13,6 +13,29 @@
 #include <linux/skbuff.h>
 #include <linux/version.h>
 
+/**
+ * DOC: VLAN tag manipulation.
+ *
+ * &struct sk_buff handling of VLAN tags has evolved over time:
+ *
+ * In 2.6.26 and earlier, VLAN tags did not have any generic representation in
+ * an skb, other than as a raw 802.1Q header inside the packet data.
+ *
+ * In 2.6.27 &struct sk_buff added a @vlan_tci member.  Between 2.6.27 and
+ * 2.6.32, its value was the raw contents of the 802.1Q TCI field, or zero if
+ * no 802.1Q header was present.  This worked OK except for the corner case of
+ * an 802.1Q header with an all-0-bits TCI, which could not be represented.
+ *
+ * In 2.6.33, @vlan_tci semantics changed.  Now, if an 802.1Q header is
+ * present, then the VLAN_TAG_PRESENT bit is always set.  This fixes the
+ * all-0-bits TCI corner case.
+ *
+ * For compatibility we emulate the 2.6.33+ behavior on earlier kernel
+ * versions.  The client must not access @vlan_tci directly.  Instead, use
+ * vlan_get_tci() to read it or vlan_set_tci() to write it, with semantics
+ * equivalent to those on 2.6.33+.
+ */
+
 #if LINUX_VERSION_CODE < KERNEL_VERSION(2,6,27)
 #define NEED_VLAN_FIELD
 #endif
@@ -22,11 +45,18 @@ static inline void vlan_copy_skb_tci(struct sk_buff *skb) { }
 
 static inline u16 vlan_get_tci(struct sk_buff *skb)
 {
+#if LINUX_VERSION_CODE < KERNEL_VERSION(2,6,33)
+       if (skb->vlan_tci)
+               return skb->vlan_tci | VLAN_TAG_PRESENT;
+#endif
        return skb->vlan_tci;
 }
 
 static inline void vlan_set_tci(struct sk_buff *skb, u16 vlan_tci)
 {
+#if LINUX_VERSION_CODE < KERNEL_VERSION(2,6,33)
+       vlan_tci &= ~VLAN_TAG_PRESENT;
+#endif
        skb->vlan_tci = vlan_tci;
 }
 #else