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| author | Stefan Puiu <stefan.puiu@gmail.com> | 2014-04-24 11:25:19 +0200 |
|---|---|---|
| committer | Michael Kerrisk <mtk.manpages@gmail.com> | 2014-04-24 11:52:39 +0200 |
| commit | a29edaeef6e79fc70236ea334564b97a1d1d8c7c (patch) | |
| tree | 5c1d5e69055af89b973b6792d06e6733bb6c85de /man7/packet.7 | |
| parent | 84f573db6009fa8c69f2d4122a7a47c4ec90020c (diff) | |
| download | man-pages-a29edaeef6e79fc70236ea334564b97a1d1d8c7c.tar.gz | |
packet.7: Status in PACKET_RX_RING is actually a bit mask
Stefan:
I'm playing with the PACKET_RX_RING option to packet sockets and I
noticed that the status field from the tpacket_hdr structures
inside the mmaped buffer is actually a bit mask. I'm testing with
4Gbps traffic rates and sometimes I get status=5. I'm using Ubuntu
12.04 with a 3.8.0-29 kernel, and at least from the code (I got it
using "sudo apt-get source linux-image-$(uname -r)") it seems the
5 means TP_STATUS_USER | TP_STATUS_LOSING. The 3.8.0 kernel code
has this line in tpacket_rcv():
/*
* LOSING will be reported till you read the stats,
* because it's COR - Clear On Read.
* Anyways, moving it for V1/V2 only as V3 doesn't need this
* at packet level.
*/
if (po->stats.tp_drops)
status |= TP_STATUS_LOSING;
Daniel:
Now to your question. It can easily be seen from the if_packet.h header
file http://lingrok.org/xref/linux-net-next/include/uapi/linux/if_packet.h#93
that TP_STATUS_* are individual bits that are set in tp_status field.
TP_STATUS_USER simply means a frame was received in the ring and is
ready for user space to be processed. If the field also indicates
TP_STATUS_LOSING then this means that there were packet drops in the
rx ring itself so a user knows it didn't get all traffic. This bit
is being reset on getsockopt() when querying PACKET_STATISTICS,
otherwise it stays. Drops occur when the ring buffer was not emptied
fast enough by user space (so no free slot with TP_STATUS_KERNEL), e.g.
due to high incoming traffic load. However, the current frame you're
reading that has TP_STATUS_USER|TP_STATUS_LOSING is fine by itself.
Acked-by: Daniel Borkmann <dborkman@redhat.com>
Acked-by: Carsten Andrich <carsten.andrich@tu-ilmenau.de>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Diffstat (limited to 'man7/packet.7')
| -rw-r--r-- | man7/packet.7 | 8 |
1 files changed, 4 insertions, 4 deletions
diff --git a/man7/packet.7 b/man7/packet.7 index bd915c9b52..11bca48fd5 100644 --- a/man7/packet.7 +++ b/man7/packet.7 @@ -9,7 +9,7 @@ .\" .\" $Id: packet.7,v 1.13 2000/08/14 08:03:45 ak Exp $ .\" -.TH PACKET 7 2014-04-23 "Linux" "Linux Programmer's Manual" +.TH PACKET 7 2014-04-24 "Linux" "Linux Programmer's Manual" .SH NAME packet \- packet interface on device level .SH SYNOPSIS @@ -364,9 +364,9 @@ The packet socket owns all slots with status .BR TP_STATUS_KERNEL . After filling a slot, it changes the status of the slot to transfer ownership to the application. -During normal operation, the new status is -.BR TP_STATUS_USER , -to signal that a correctly received packet has been stored. +During normal operation, the new status has the +.BR TP_STATUS_USER +bit set to signal that a received packet has been stored. When the application has finished processing a packet, it transfers ownership of the slot back to the socket by setting the status to .BR TP_STATUS_KERNEL . |