From be8e9eb3750639aa5cffb3f764ca080caed41bd0 Mon Sep 17 00:00:00 2001 From: Jason Xing Date: Mon, 9 Sep 2024 09:56:11 +0800 Subject: net-timestamp: introduce SOF_TIMESTAMPING_OPT_RX_FILTER flag introduce a new flag SOF_TIMESTAMPING_OPT_RX_FILTER in the receive path. User can set it with SOF_TIMESTAMPING_SOFTWARE to filter out rx software timestamp report, especially after a process turns on netstamp_needed_key which can time stamp every incoming skb. Previously, we found out if an application starts first which turns on netstamp_needed_key, then another one only passing SOF_TIMESTAMPING_SOFTWARE could also get rx timestamp. Now we handle this case by introducing this new flag without breaking users. Quoting Willem to explain why we need the flag: "why a process would want to request software timestamp reporting, but not receive software timestamp generation. The only use I see is when the application does request SOF_TIMESTAMPING_SOFTWARE | SOF_TIMESTAMPING_TX_SOFTWARE." Similarly, this new flag could also be used for hardware case where we can set it with SOF_TIMESTAMPING_RAW_HARDWARE, then we won't receive hardware receive timestamp. Another thing about errqueue in this patch I have a few words to say: In this case, we need to handle the egress path carefully, or else reporting the tx timestamp will fail. Egress path and ingress path will finally call sock_recv_timestamp(). We have to distinguish them. Errqueue is a good indicator to reflect the flow direction. Suggested-by: Willem de Bruijn Signed-off-by: Jason Xing Reviewed-by: Willem de Bruijn Link: https://patch.msgid.link/20240909015612.3856-2-kerneljasonxing@gmail.com Signed-off-by: Jakub Kicinski --- Documentation/networking/timestamping.rst | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) (limited to 'Documentation') diff --git a/Documentation/networking/timestamping.rst b/Documentation/networking/timestamping.rst index 9c7773271393..8199e6917671 100644 --- a/Documentation/networking/timestamping.rst +++ b/Documentation/networking/timestamping.rst @@ -267,6 +267,23 @@ SOF_TIMESTAMPING_OPT_TX_SWHW: two separate messages will be looped to the socket's error queue, each containing just one timestamp. +SOF_TIMESTAMPING_OPT_RX_FILTER: + Filter out spurious receive timestamps: report a receive timestamp + only if the matching timestamp generation flag is enabled. + + Receive timestamps are generated early in the ingress path, before a + packet's destination socket is known. If any socket enables receive + timestamps, packets for all socket will receive timestamped packets. + Including those that request timestamp reporting with + SOF_TIMESTAMPING_SOFTWARE and/or SOF_TIMESTAMPING_RAW_HARDWARE, but + do not request receive timestamp generation. This can happen when + requesting transmit timestamps only. + + Receiving spurious timestamps is generally benign. A process can + ignore the unexpected non-zero value. But it makes behavior subtly + dependent on other sockets. This flag isolates the socket for more + deterministic behavior. + New applications are encouraged to pass SOF_TIMESTAMPING_OPT_ID to disambiguate timestamps and SOF_TIMESTAMPING_OPT_TSONLY to operate regardless of the setting of sysctl net.core.tstamp_allow_data. -- cgit v1.2.3