[PATCH] vlan: allow VLAN ID 0 to be used

[Eric Dumazet <eric.dumazet@gmail.com>]

Eric Dumazet a écrit :
> VLAN id 0 is not usable on current kernel because we use 16 bits in skb to
>  store vlan_tci, and vlan_tci = 0 means there is no VLAN tagging.
> 
> 
> We could use high order bit (0x8000) to tell if vlan tagging is set or not.
> 

Here is the patch I cooked that permitted VLAN 0 to be used with tg3
(and other HW accelerated vlan nics I suppose)

[PATCH] vlan: allow VLAN ID 0 to be used

We currently use a 16 bit field (vlan_tci) to store VLAN ID on a skb.

0 value is used a special value, meaning VLAN ID not set.
This forbids use of VLAN ID 0

As VLAN ID is 12 bits, we can use high order bit as a flag, and
allow VLAN ID 0

Reported-by: Gertjan Hofman <gertjan_hofman@yahoo.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
---
diff --git a/include/linux/if_vlan.h b/include/linux/if_vlan.h
index 7ff9af1..7dfcdb5 100644
--- a/include/linux/if_vlan.h
+++ b/include/linux/if_vlan.h
@@ -105,8 +105,9 @@ static inline void vlan_group_set_device(struct vlan_group *vg,
 	array[vlan_id % VLAN_GROUP_ARRAY_PART_LEN] = dev;
 }
 
-#define vlan_tx_tag_present(__skb)	((__skb)->vlan_tci)
-#define vlan_tx_tag_get(__skb)		((__skb)->vlan_tci)
+#define VLAN_TAG_PRESENT		0x8000
+#define vlan_tx_tag_present(__skb)	((__skb)->vlan_tci & VLAN_TAG_PRESENT)
+#define vlan_tx_tag_get(__skb)		((__skb)->vlan_tci & 0x7fff)
 
 #if defined(CONFIG_VLAN_8021Q) || defined(CONFIG_VLAN_8021Q_MODULE)
 extern struct net_device *vlan_dev_real_dev(const struct net_device *dev);
@@ -231,7 +232,7 @@ static inline struct sk_buff *__vlan_put_tag(struct sk_buff *skb, u16 vlan_tci)
 static inline struct sk_buff *__vlan_hwaccel_put_tag(struct sk_buff *skb,
 						     u16 vlan_tci)
 {
-	skb->vlan_tci = vlan_tci;
+	skb->vlan_tci = VLAN_TAG_PRESENT | vlan_tci;
 	return skb;
 }
 
@@ -284,7 +285,7 @@ static inline int __vlan_hwaccel_get_tag(const struct sk_buff *skb,
 					 u16 *vlan_tci)
 {
 	if (vlan_tx_tag_present(skb)) {
-		*vlan_tci = skb->vlan_tci;
+		*vlan_tci = vlan_tx_tag_get(skb);
 		return 0;
 	} else {
 		*vlan_tci = 0;