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Commit 744d5a3e authored by Eyal Birger's avatar Eyal Birger Committed by David S. Miller
Browse files

net: move skb->dropcount to skb->cb[] 



Commit 97775007 ("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.

skb->dropcount was introduced since there was no available room
in skb->cb[] in packet sockets. However, its introduction led to
the inability to export skb->mark, or any other aliased field to
userspace if so desired.

Moving the dropcount metric to skb->cb[] eliminates this problem
at the expense of 4 bytes less in skb->cb[] for protocol families
using it.

Signed-off-by: default avatarEyal Birger <eyal.birger@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 3bc3b96f

include/linux/skbuff.h

+0 −2
Original line number Diff line number Diff line
@@ -492,7 +492,6 @@ static inline u32 skb_mstamp_us_delta(const struct skb_mstamp *t1, 
  *	@napi_id: id of the NAPI struct this skb came from

 *	@secmark: security marking

 *	@mark: Generic packet mark

 *	@dropcount: total number of sk_receive_queue overflows

 *	@vlan_proto: vlan encapsulation protocol

 *	@vlan_tci: vlan tag control information

 *	@inner_protocol: Protocol (encapsulation)
@@ -641,7 +640,6 @@ struct sk_buff { 
#endif

	union {

		__u32		mark;

		__u32		dropcount;

		__u32		reserved_tailroom;

	};

include/net/sock.h

+16 −2
Original line number Diff line number Diff line
@@ -2078,13 +2078,27 @@ static inline int sock_intr_errno(long timeo) 
	return timeo == MAX_SCHEDULE_TIMEOUT ? -ERESTARTSYS : -EINTR;

}



struct sock_skb_cb {

	u32 dropcount;

};



/* Store sock_skb_cb at the end of skb->cb[] so protocol families

 * using skb->cb[] would keep using it directly and utilize its

 * alignement guarantee.

 */

#define SOCK_SKB_CB_OFFSET ((FIELD_SIZEOF(struct sk_buff, cb) - \

			    sizeof(struct sock_skb_cb)))



#define SOCK_SKB_CB(__skb) ((struct sock_skb_cb *)((__skb)->cb + \

			    SOCK_SKB_CB_OFFSET))



#define sock_skb_cb_check_size(size) \

	BUILD_BUG_ON((size) > FIELD_SIZEOF(struct sk_buff, cb))

	BUILD_BUG_ON((size) > SOCK_SKB_CB_OFFSET)



static inline void

sock_skb_set_dropcount(const struct sock *sk, struct sk_buff *skb)

{

	skb->dropcount = atomic_read(&sk->sk_drops);

	SOCK_SKB_CB(skb)->dropcount = atomic_read(&sk->sk_drops);

}



void __sock_recv_timestamp(struct msghdr *msg, struct sock *sk,

net/socket.c

+2 −2
Original line number Diff line number Diff line
@@ -731,9 +731,9 @@ EXPORT_SYMBOL_GPL(__sock_recv_wifi_status); 
static inline void sock_recv_drops(struct msghdr *msg, struct sock *sk,

				   struct sk_buff *skb)

{

	if (sock_flag(sk, SOCK_RXQ_OVFL) && skb && skb->dropcount)

	if (sock_flag(sk, SOCK_RXQ_OVFL) && skb && SOCK_SKB_CB(skb)->dropcount)

		put_cmsg(msg, SOL_SOCKET, SO_RXQ_OVFL,

			sizeof(__u32), &skb->dropcount);

			sizeof(__u32), &SOCK_SKB_CB(skb)->dropcount);

}



void __sock_recv_ts_and_drops(struct msghdr *msg, struct sock *sk,