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Diffstat (limited to 'Documentation/networking/packet_mmap.txt')
| -rw-r--r-- | Documentation/networking/packet_mmap.txt | 26 |
1 files changed, 26 insertions, 0 deletions
diff --git a/Documentation/networking/packet_mmap.txt b/Documentation/networking/packet_mmap.txt index 98f71a5cef0..2546aa4dc23 100644 --- a/Documentation/networking/packet_mmap.txt +++ b/Documentation/networking/packet_mmap.txt @@ -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. + -------------------------------------------------------------------------------- + THANKS -------------------------------------------------------------------------------- |