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authorNeil Horman <nhorman@tuxdriver.com>2009-10-02 06:56:41 +0000
committerDavid S. Miller <davem@davemloft.net>2009-10-05 00:21:55 -0700
commit977750076d98c7ff6cbda51858bb5a5894a9d9ab (patch)
tree71b2fca8c6739e7d177996354b99504702a1b946 /net
parentTI DaVinci EMAC: Minor macro related updates (diff)
downloadlinux-dev-977750076d98c7ff6cbda51858bb5a5894a9d9ab.tar.xz
linux-dev-977750076d98c7ff6cbda51858bb5a5894a9d9ab.zip
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 <nhorman@tuxdriver.com> Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com> include/linux/if_packet.h | 2 ++ net/packet/af_packet.c | 33 +++++++++++++++++++++++++++++++++ 2 files changed, 35 insertions(+) Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net')
-rw-r--r--net/packet/af_packet.c33
1 files changed, 33 insertions, 0 deletions
diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index d7ecca0a0c07..d398a9bf6903 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.