netdev - [PATCH net-next v2 2/3] net: use skb->priority for overloading skb->dropcount and skb->reserved

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Message-Id: <1423715535-884-3-git-send-email-eyal.birger@gmail.com>
Date:	Thu, 12 Feb 2015 06:32:14 +0200
From:	Eyal Birger <eyal.birger@...il.com>
To:	davem@...emloft.net
Cc:	netdev@...r.kernel.org, edumazet@...gle.com,
	shmulik.ladkani@...il.com, Eyal Birger <eyal.birger@...il.com>
Subject: [PATCH net-next v2 2/3] 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.

Signed-off-by: Eyal Birger <eyal.birger@...il.com>
----
The purpose of overloading skb->priority is solely for retaining
struct sk_buff size; skb->priority is not used after the skb queued
to the socket and has the same guarentee of not being shared as
skb->mark.
---
 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 1bb36ed..23f1a94 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -621,7 +621,7 @@ struct sk_buff {
 			__u16	csum_offset;
 		};
 	};
-	__u32			priority;
+	__u32			mark;
 	int			skb_iif;
 	__u32			hash;
 	__be16			vlan_proto;
@@ -636,7 +636,7 @@ struct sk_buff {
 	__u32			secmark;
 #endif
 	union {
-		__u32		mark;
+		__u32		priority;
 		__u32		dropcount;
 		__u32		reserved_tailroom;
 	};
-- 
2.1.4

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