netdev - [PATCH net-next v3 3/4] net: use skb->priority for overloading skb->dropcount and skb->reserved

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Date:	Mon, 23 Feb 2015 19:52:03 +0200
From:	Eyal Birger <eyal.birger@...il.com>
To:	davem@...emloft.net
Cc:	edumazet@...gle.com, shmulik.ladkani@...il.com,
	netdev@...r.kernel.org, Eyal Birger <eyal.birger@...il.com>
Subject: [PATCH net-next v3 3/4] net: use skb->priority for overloading skb->dropcount and skb->reserved_tailroom instead of skb->mark

Commit 977750076d98 ("af_packet: add interframe drop cmsg (v6)")
unionized skb->mark and skb->dropcount in order to allow recording
of the socket drop count while maintaining struct sk_buff size.

In order to allow for the skb->mark to be fetched by user-space code
it needs to be detached from this union; skb->priority is used
instead.

The purpose of overloading skb->priority is solely for retaining
struct sk_buff size; skb->priority is not used after the skb is
queued to the socket.

Use of aliased fields, skb->dropcount and skb->reserved_tailroom,
is either done after the skb is cloned (e.g. in packet_rcv()) or
before skb->priority is used (e.g. in IGMPv3/MLD/TCP).

Signed-off-by: Eyal Birger <eyal.birger@...il.com>
---
 include/linux/skbuff.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index d898b32..23e77cb 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -625,7 +625,7 @@ struct sk_buff {
 			__u16	csum_offset;
 		};
 	};
-	__u32			priority;
+	__u32			mark;
 	int			skb_iif;
 	__u32			hash;
 	__be16			vlan_proto;
@@ -640,7 +640,7 @@ struct sk_buff {
 	__u32			secmark;
 #endif
 	union {
-		__u32		mark;
+		__u32		priority;
 		__u32		dropcount;
 		__u32		reserved_tailroom;
 	};
-- 
2.1.4

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