From 977750076d98c7ff6cbda51858bb5a5894a9d9ab Mon Sep 17 00:00:00 2001 From: Neil Horman Date: Fri, 2 Oct 2009 06:56:41 +0000 Subject: af_packet: add interframe drop cmsg (v6) Add Ancilliary data to better represent loss information I've had a few requests recently to provide more detail regarding frame loss during an AF_PACKET packet capture session. Specifically the requestors want to see where in a packet sequence frames were lost, i.e. they want to see that 40 frames were lost between frames 302 and 303 in a packet capture file. In order to do this we need: 1) The kernel to export this data to user space 2) The applications to make use of it This patch addresses item (1). It does this by doing the following: A) Anytime we drop a frame for which we would increment po->stats.tp_drops, we also no increment a stats called po->stats.tp_gap. B) Every time we successfully enqueue a frame to sk_receive_queue, we record the value of po->stats.tp_gap in skb->mark. skb->cb would nominally be the place to record this, but since all the space there is used up, we're overloading skb->mark. Its safe to do since any enqueued packet is guaranteed to be unshared at this point, and skb->mark isn't used for anything else in the rx path to the application. After we record tp_gap in the skb, we zero po->stats.tp_gap. This allows us to keep a counter of the number of frames lost between any two enqueued packets C) When the application goes to dequeue a frame from the packet socket, we look at skb->mark for that frame. If it is non-zero, we add a cmsg chunk to the msghdr of level SOL_PACKET and type PACKET_GAPDATA. Its a 32 bit integer that represents the number of frames lost between this packet and the last previous frame received. Note there is a chance that if there is frame loss after a receive, and then the socket is closed, some gap data might be lost. This is covered by the use of the PACKET_AUXDATA socket option, which gives total loss data. With a bit of math, the final gap can be determined that way. I've tested this patch myself, and it works well. Signed-off-by: Neil Horman Signed-off-by: Eric Dumazet include/linux/if_packet.h | 2 ++ net/packet/af_packet.c | 33 +++++++++++++++++++++++++++++++++ 2 files changed, 35 insertions(+) Signed-off-by: David S. Miller --- net/packet/af_packet.c | 33 +++++++++++++++++++++++++++++++++ 1 file changed, 33 insertions(+) (limited to 'net') diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c index d7ecca0..d398a9b 100644 --- a/net/packet/af_packet.c +++ b/net/packet/af_packet.c @@ -524,6 +524,31 @@ static inline unsigned int run_filter(struct sk_buff *skb, struct sock *sk, } /* + * If we've lost frames since the last time we queued one to the + * sk_receive_queue, we need to record it here. + * This must be called under the protection of the socket lock + * to prevent racing with other softirqs and user space + */ +static inline void record_packet_gap(struct sk_buff *skb, + struct packet_sock *po) +{ + /* + * We overload the mark field here, since we're about + * to enqueue to a receive queue and no body else will + * use this field at this point + */ + skb->mark = po->stats.tp_gap; + po->stats.tp_gap = 0; + return; + +} + +static inline __u32 check_packet_gap(struct sk_buff *skb) +{ + return skb->mark; +} + +/* This function makes lazy skb cloning in hope that most of packets are discarded by BPF. @@ -626,6 +651,7 @@ static int packet_rcv(struct sk_buff *skb, struct net_device *dev, spin_lock(&sk->sk_receive_queue.lock); po->stats.tp_packets++; + record_packet_gap(skb, po); __skb_queue_tail(&sk->sk_receive_queue, skb); spin_unlock(&sk->sk_receive_queue.lock); sk->sk_data_ready(sk, skb->len); @@ -634,6 +660,7 @@ static int packet_rcv(struct sk_buff *skb, struct net_device *dev, drop_n_acct: spin_lock(&sk->sk_receive_queue.lock); po->stats.tp_drops++; + po->stats.tp_gap++; spin_unlock(&sk->sk_receive_queue.lock); drop_n_restore: @@ -811,6 +838,7 @@ drop: ring_is_full: po->stats.tp_drops++; + po->stats.tp_gap++; spin_unlock(&sk->sk_receive_queue.lock); sk->sk_data_ready(sk, 0); @@ -1418,6 +1446,7 @@ static int packet_recvmsg(struct kiocb *iocb, struct socket *sock, struct sk_buff *skb; int copied, err; struct sockaddr_ll *sll; + __u32 gap; err = -EINVAL; if (flags & ~(MSG_PEEK|MSG_DONTWAIT|MSG_TRUNC|MSG_CMSG_COMPAT)) @@ -1496,6 +1525,10 @@ static int packet_recvmsg(struct kiocb *iocb, struct socket *sock, put_cmsg(msg, SOL_PACKET, PACKET_AUXDATA, sizeof(aux), &aux); } + gap = check_packet_gap(skb); + if (gap) + put_cmsg(msg, SOL_PACKET, PACKET_GAPDATA, sizeof(__u32), &gap); + /* * Free or return the buffer as appropriate. Again this * hides all the races and re-entrancy issues from us. -- cgit v1.1