Documentation/networking/timestamping.rst

11 The interfaces for receiving network packages timestamps are:
37   Generates timestamps on reception, transmission or both. Supports
39   timestamps for stream sockets.
55 SO_TIMESTAMP_OLD returns incorrect timestamps after the year 2038
62 Its struct timespec allows for higher resolution (ns) timestamps than the
68 SO_TIMESTAMPNS_OLD returns incorrect timestamps after the year 2038
91 Some bits are requests to the stack to try to generate timestamps. Any
94 is possible to selectively request timestamps for a subset of packets
97 Timestamps may also be generated for reasons other than being
102   Request rx timestamps generated by the network adapter.
105   Request rx timestamps when data enters the kernel. These timestamps
110   Request tx timestamps generated by the network adapter. This flag
114   Request tx timestamps when data leaves the kernel. These timestamps
121   Request tx timestamps prior to entering the packet scheduler. Kernel
135   Request tx timestamps when all data in the send buffer has been
147 The other three bits control which timestamps will be reported in a
149 effect at the timestamp reporting locations in the stack. Timestamps
154   Report any software timestamps when available.
160   Report hardware timestamps as generated by
173   scheduler. In that case timestamps will be queued onto the error
175   possible to uniquely match timestamps to the original send() calls
190   This option is implemented only for transmit timestamps. There, the
229   timestamps and on IPv6 packets with transmit timestamp. This option
236   Applies to transmit timestamps only. Makes the kernel return the
244   Optional stats that are obtained along with the transmit timestamps.
250   the transmit timestamps, such as how long a certain block of
255   packets with hardware timestamps. The message contains struct
263   Request both hardware and software timestamps for outgoing packets
265   are enabled at the same time. If both timestamps are generated,
270 disambiguate timestamps and SOF_TIMESTAMPING_OPT_TSONLY to operate
280 1.3.4. Enabling timestamps via control messages
285 Using this feature, applications can sample timestamps per sendmsg()
286 without paying the overhead of enabling and disabling timestamps via
304 setsockopt to receive timestamps::
311 1.4 Bytestream Timestamps
329 It is essential that all timestamps implement the same semantics,
335 In practice, timestamps can be correlated with segments of a
374 Timestamps are read using the ancillary data feature of recvmsg().
376 page (`man 7 socket`) describes how timestamps generated with
383 These timestamps are returned in a control message with cmsg_level
400 SO_TIMESTAMPING_OLD returns incorrect timestamps after the year 2038
403 The structure can return up to three timestamps. This is a legacy
404 feature. At least one field is non-zero at any time. Most timestamps
405 are passed in ts[0]. Hardware timestamps are passed in ts[2].
407 ts[1] used to hold hardware timestamps converted to system time.
417 on hardware transmit timestamps.
419 2.1.1 Transmit timestamps with MSG_ERRQUEUE
422 For transmit timestamps the outgoing packet is looped back to the
424 receives the timestamps by calling recvmsg() with flag MSG_ERRQUEUE
431 timestamps, the ee_errno field is ENOMSG. The other ancillary message
483 2.1.2 Receive timestamps
617   adds the timestamps, therefore the original skb has to be freed now.
660 allow the delivery of multiple hardware timestamps for the same packet, so
679   packets in a queue waiting for timestamping and the actual timestamps,
696   timestamps might either be available in-band (through metadata in the
709 performance reasons: timestamps taken as close as possible to the wire have the