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packet_mmap: expose hw packet timestamps to network packet capture utilities

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This patch adds a setting, PACKET_TIMESTAMP, to specify the packet
timestamp source that is exported to capture utilities like tcpdump by
packet_mmap.

PACKET_TIMESTAMP accepts the same integer bit field as
SO_TIMESTAMPING.  However, only the SOF_TIMESTAMPING_SYS_HARDWARE and
SOF_TIMESTAMPING_RAW_HARDWARE values are currently recognized by
PACKET_TIMESTAMP.  SOF_TIMESTAMPING_SYS_HARDWARE takes precedence over
SOF_TIMESTAMPING_RAW_HARDWARE if both bits are set.

If PACKET_TIMESTAMP is not set, a software timestamp generated inside
the networking stack is used (the behavior before this setting was
added).

Signed-off-by: Scott McMillan <scott.a.mcmillan@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Scott McMillan
2010-06-02 05:53:56 -07:00
committed by David S. Miller
parent 7dad171c39
commit 614f60fa9d
3 changed files with 62 additions and 2 deletions
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Documentation/networking/packet_mmap.txt
+26
View File
@@ -493,6 +493,32 @@ The user can also use poll() to check if a buffer is available:
pfd.events = POLLOUT;
retval = poll(&pfd, 1, timeout);
-------------------------------------------------------------------------------
+ PACKET_TIMESTAMP
-------------------------------------------------------------------------------
The PACKET_TIMESTAMP setting determines the source of the timestamp in
the packet meta information. If your NIC is capable of timestamping
packets in hardware, you can request those hardware timestamps to used.
Note: you may need to enable the generation of hardware timestamps with
SIOCSHWTSTAMP.
PACKET_TIMESTAMP accepts the same integer bit field as
SO_TIMESTAMPING. However, only the SOF_TIMESTAMPING_SYS_HARDWARE
and SOF_TIMESTAMPING_RAW_HARDWARE values are recognized by
PACKET_TIMESTAMP. SOF_TIMESTAMPING_SYS_HARDWARE takes precedence over
SOF_TIMESTAMPING_RAW_HARDWARE if both bits are set.
int req = 0;
req |= SOF_TIMESTAMPING_SYS_HARDWARE;
setsockopt(fd, SOL_PACKET, PACKET_TIMESTAMP, (void *) &req, sizeof(req))
If PACKET_TIMESTAMP is not set, a software timestamp generated inside
the networking stack is used (the behavior before this setting was added).
See include/linux/net_tstamp.h and Documentation/networking/timestamping
for more information on hardware timestamps.
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+ THANKS
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