[PATCH v4 net-next 5/7] net: fix documentation of struct scm_timestamping
From: Miroslav Lichvar <hidden>
Date: 2017-05-18 13:07:15
Subsystem:
documentation, networking [general], the rest · Maintainers:
Jonathan Corbet, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
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 <redacted> --- Documentation/networking/timestamping.txt | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/Documentation/networking/timestamping.txt b/Documentation/networking/timestamping.txt
index 600c6bf..74b7c61 100644
--- a/Documentation/networking/timestamping.txt
+++ b/Documentation/networking/timestamping.txt@@ -321,7 +321,7 @@ 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.
@@ -330,6 +330,12 @@ 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. For this reason it +is not recommended to combine SO_TIMESTAMP(NS) with SO_TIMESTAMPING. + 2.1.1 Transmit timestamps with MSG_ERRQUEUE For transmit timestamps the outgoing packet is looped back to the
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2.9.3