[PATCH] af-packet: Add flag to distinguish VID 0 from no-vlan.

[PATCH] af-packet: Add flag to distinguish VID 0 from no-vlan.

[greearb]

From: Ben Greear <greearb@candelatech.com>

Currently, user-space cannot determine if a 0 tcp_vlan_tci
means there is no VLAN tag or the VLAN ID was zero.

Add flag to make this explicit.  User-space can check for
TP_STATUS_VLAN_VALID || tp_vlan_tci > 0, which will be backwards
compatible. Older could would have just checked for tp_vlan_tci,
so it will work no worse than before.

Signed-off-by: Ben Greear <greearb@candelatech.com>
---
:100644 100644 72bfa5a... 6d66ce1... M	include/linux/if_packet.h
:100644 100644 658edd1... 885d76d... M	net/packet/af_packet.c
 include/linux/if_packet.h |    1 +
 net/packet/af_packet.c    |    7 ++++++-
 2 files changed, 7 insertions(+), 1 deletions(-)

diff --git a/include/linux/if_packet.h b/include/linux/if_packet.h
index 72bfa5a..6d66ce1 100644
--- a/include/linux/if_packet.h
+++ b/include/linux/if_packet.h
@@ -70,6 +70,7 @@ struct tpacket_auxdata {
 #define TP_STATUS_COPY		0x2
 #define TP_STATUS_LOSING	0x4
 #define TP_STATUS_CSUMNOTREADY	0x8
+#define TP_STATUS_VLAN_VALID   0x10 /* auxdata has valid tp_vlan_tci */
 
 /* Tx ring - header status */
 #define TP_STATUS_AVAILABLE	0x0
diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 658edd1..885d76d 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -1772,7 +1772,12 @@ static int packet_recvmsg(struct kiocb *iocb, struct socket *sock,
 		aux.tp_snaplen = skb->len;
 		aux.tp_mac = 0;
 		aux.tp_net = skb_network_offset(skb);
-		aux.tp_vlan_tci = vlan_tx_tag_get(skb);
+		if (vlan_tx_tag_present(skb)) {
+			aux.tp_vlan_tci = vlan_tx_tag_get(skb);
+			aux.tp_status |= TP_STATUS_VLAN_VALID;
+		}
+		else
+			aux.tp_vlan_tci = 0;
 
 		put_cmsg(msg, SOL_PACKET, PACKET_AUXDATA, sizeof(aux), &aux);
 	}
-- 
1.7.3.4

Re: [PATCH] af-packet: Add flag to distinguish VID 0 from no-vlan.

[David Miller]

From: greearb@candelatech.com
Date: Wed, 25 May 2011 16:36:35 -0700

> From: Ben Greear <greearb@candelatech.com>
> 
> Currently, user-space cannot determine if a 0 tcp_vlan_tci
> means there is no VLAN tag or the VLAN ID was zero.
> 
> Add flag to make this explicit.  User-space can check for
> TP_STATUS_VLAN_VALID || tp_vlan_tci > 0, which will be backwards
> compatible. Older could would have just checked for tp_vlan_tci,
> so it will work no worse than before.
> 
> Signed-off-by: Ben Greear <greearb@candelatech.com>

Please do this in tpacket_rcv() too, otherwise the feature
bit won't be available to mmap() users of AF_PACKET.

Thanks.