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| -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 |