We currently use a 16 bit field (vlan_tci) to store VLAN ID/PRIO on a skb.
Null value is used as a special value, meaning vlan tagging not enabled.
This forbids use of null vlan ID.
As pointed by David, some drivers use the 3 high order bits (PRIO)
As VLAN ID is 12 bits, we can use the remaining bit (CFI) as a flag, and
allow null VLAN ID.
In case future code really wants to use VLAN_CFI_MASK, we'll have to use
a bit outside of vlan_tci.
#define VLAN_PRIO_MASK 0xe000 /* Priority Code Point */
#define VLAN_PRIO_SHIFT 13
#define VLAN_CFI_MASK 0x1000 /* Canonical Format Indicator */
#define VLAN_TAG_PRESENT VLAN_CFI_MASK
#define VLAN_VID_MASK 0x0fff /* VLAN Identifier */
Reported-by: Gertjan Hofman <gertjan_hofman@yahoo.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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