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

Commit 977750076d ("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: Eyal Birger <eyal.birger@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eyal Birger 2015-03-01 14:58:31 +02:00 committed by David S. Miller
parent 3bc3b96f3b
commit 744d5a3e9f
3 changed files with 18 additions and 6 deletions
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2
include/linux/skbuff.h
View File

@ -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;
};

18
include/net/sock.h
View File

@ -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,

4
net/socket.c
View File

@ -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,