Return-Path: From: Eyal Birger To: davem@davemloft.net Cc: willemb@google.com, edumazet@google.com, shmulik.ladkani@gmail.com, linux-bluetooth@vger.kernel.org, marcel@holtmann.org, netdev@vger.kernel.org, Eyal Birger Subject: [PATCH net-next v3 7/7] net: move skb->dropcount to skb->cb[] Date: Sun, 1 Mar 2015 14:58:31 +0200 Message-Id: <1425214711-9562-8-git-send-email-eyal.birger@gmail.com> In-Reply-To: <1425214711-9562-1-git-send-email-eyal.birger@gmail.com> References: <1425214711-9562-1-git-send-email-eyal.birger@gmail.com> List-ID: 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. 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 --- include/linux/skbuff.h | 2 -- include/net/sock.h | 18 ++++++++++++++++-- net/socket.c | 4 ++-- 3 files changed, 18 insertions(+), 6 deletions(-) diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index d898b32..bba1330 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -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; }; diff --git a/include/net/sock.h b/include/net/sock.h index 0996fe4..38369d3 100644 --- a/include/net/sock.h +++ b/include/net/sock.h @@ -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, diff --git a/net/socket.c b/net/socket.c index bbedbfc..b78cf60 100644 --- a/net/socket.c +++ b/net/socket.c @@ -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, -- 2.1.4