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| author | Miroslav Lichvar <mlichvar@redhat.com> | 2017-05-19 18:52:39 +0300 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2017-05-21 20:37:32 +0300 |
| commit | 67953d47bb24e63d209705f745a0de411a4c6578 (patch) | |
| tree | 4c8eea80b7c24c08766f395e0b3ce7b5045f048b /Documentation | |
| parent | aad9c8c470f2a8321a99eb053630ce0e199558d6 (diff) | |
| download | linux-67953d47bb24e63d209705f745a0de411a4c6578.tar.xz | |
net: fix documentation of struct scm_timestamping
The scm_timestamping struct may return multiple non-zero fields, e.g.
when both software and hardware RX timestamping is enabled, or when the
SO_TIMESTAMP(NS) option is combined with SCM_TIMESTAMPING and a false
software timestamp is generated in the recvmsg() call in order to always
return a SCM_TIMESTAMP(NS) message.
CC: Richard Cochran <richardcochran@gmail.com>
CC: Willem de Bruijn <willemb@google.com>
Signed-off-by: Miroslav Lichvar <mlichvar@redhat.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/networking/timestamping.txt | 8 |
1 files changed, 7 insertions, 1 deletions
diff --git a/Documentation/networking/timestamping.txt b/Documentation/networking/timestamping.txt index ce11e3a08c0d..50eb0e554778 100644 --- a/Documentation/networking/timestamping.txt +++ b/Documentation/networking/timestamping.txt @@ -322,7 +322,7 @@ struct scm_timestamping { }; The structure can return up to three timestamps. This is a legacy -feature. Only one field is non-zero at any time. Most timestamps +feature. At least one field is non-zero at any time. Most timestamps are passed in ts[0]. Hardware timestamps are passed in ts[2]. ts[1] used to hold hardware timestamps converted to system time. @@ -331,6 +331,12 @@ a HW PTP clock source, to allow time conversion in userspace and optionally synchronize system time with a userspace PTP stack such as linuxptp. For the PTP clock API, see Documentation/ptp/ptp.txt. +Note that if the SO_TIMESTAMP or SO_TIMESTAMPNS option is enabled +together with SO_TIMESTAMPING using SOF_TIMESTAMPING_SOFTWARE, a false +software timestamp will be generated in the recvmsg() call and passed +in ts[0] when a real software timestamp is missing. This happens also +on hardware transmit timestamps. + 2.1.1 Transmit timestamps with MSG_ERRQUEUE For transmit timestamps the outgoing packet is looped back to the |