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
144   Request tx timestamps on packet tx completion.  The completion
147   packets at once, and completion timestamps reflect the timing of the
155 The other three bits control which timestamps will be reported in a
157 effect at the timestamp reporting locations in the stack. Timestamps
162   Report any software timestamps when available.
168   Report hardware timestamps as generated by
182   scheduler. In that case timestamps will be queued onto the error
184   possible to uniquely match timestamps to the original send() calls
199   This option is implemented only for transmit timestamps. There, the
252   timestamps and on IPv6 packets with transmit timestamp. This option
259   Applies to transmit timestamps only. Makes the kernel return the
267   Optional stats that are obtained along with the transmit timestamps.
273   the transmit timestamps, such as how long a certain block of
278   packets with hardware timestamps. The message contains struct
286   Request both hardware and software timestamps for outgoing packets
288   are enabled at the same time. If both timestamps are generated,
293   Filter out spurious receive timestamps: report a receive timestamp
296   Receive timestamps are generated early in the ingress path, before a
298   timestamps, packets for all socket will receive timestamped packets.
302   requesting transmit timestamps only.
304   Receiving spurious timestamps is generally benign. A process can
310 disambiguate timestamps and SOF_TIMESTAMPING_OPT_TSONLY to operate
320 1.3.4. Enabling timestamps via control messages
325 Using this feature, applications can sample timestamps per sendmsg()
326 without paying the overhead of enabling and disabling timestamps via
344 setsockopt to receive timestamps::
351 1.4 Bytestream Timestamps
369 It is essential that all timestamps implement the same semantics,
375 In practice, timestamps can be correlated with segments of a
415 Timestamps are read using the ancillary data feature of recvmsg().
417 page (`man 7 socket`) describes how timestamps generated with
424 These timestamps are returned in a control message with cmsg_level
441 SO_TIMESTAMPING_OLD returns incorrect timestamps after the year 2038
444 The structure can return up to three timestamps. This is a legacy
445 feature. At least one field is non-zero at any time. Most timestamps
446 are passed in ts[0]. Hardware timestamps are passed in ts[2].
448 ts[1] used to hold hardware timestamps converted to system time.
458 on hardware transmit timestamps.
460 2.1.1 Transmit timestamps with MSG_ERRQUEUE
463 For transmit timestamps the outgoing packet is looped back to the
465 receives the timestamps by calling recvmsg() with flag MSG_ERRQUEUE
472 timestamps, the ee_errno field is ENOMSG. The other ancillary message
524 2.1.2 Receive timestamps
668   adds the timestamps, therefore the original skb has to be freed now.
711 allow the delivery of multiple hardware timestamps for the same packet, so
730   packets in a queue waiting for timestamping and the actual timestamps,
747   timestamps might either be available in-band (through metadata in the
760 performance reasons: timestamps taken as close as possible to the wire have the