diff options
author | Neil Horman <nhorman@tuxdriver.com> | 2009-10-02 06:56:41 +0000 |
---|---|---|
committer | David S. Miller <davem@davemloft.net> | 2009-10-05 00:21:55 -0700 |
commit | 977750076d98c7ff6cbda51858bb5a5894a9d9ab (patch) | |
tree | 71b2fca8c6739e7d177996354b99504702a1b946 /include | |
parent | 69ef9694099802f7feeb23182dfb869e7c5f76f0 (diff) |
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 'include')
-rw-r--r-- | include/linux/if_packet.h | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/include/linux/if_packet.h b/include/linux/if_packet.h index dea7d6b7cf98..e5d200f53fc3 100644 --- a/include/linux/if_packet.h +++ b/include/linux/if_packet.h @@ -48,11 +48,13 @@ struct sockaddr_ll #define PACKET_RESERVE 12 #define PACKET_TX_RING 13 #define PACKET_LOSS 14 +#define PACKET_GAPDATA 15 struct tpacket_stats { unsigned int tp_packets; unsigned int tp_drops; + unsigned int tp_gap; }; struct tpacket_auxdata |