From 49ca0d8bfaf3bc46d5eef60ce67b00eb195bd392 Mon Sep 17 00:00:00 2001 From: Willem de Bruijn Date: Fri, 30 Jan 2015 13:29:31 -0500 Subject: net-timestamp: no-payload option Add timestamping option SOF_TIMESTAMPING_OPT_TSONLY. For transmit timestamps, this loops timestamps on top of empty packets. Doing so reduces the pressure on SO_RCVBUF. Payload inspection and cmsg reception (aside from timestamps) are no longer possible. This works together with a follow on patch that allows administrators to only allow tx timestamping if it does not loop payload or metadata. Signed-off-by: Willem de Bruijn ---- Changes (rfc -> v1) - add documentation - remove unnecessary skb->len test (thanks to Richard Cochran) Signed-off-by: David S. Miller --- Documentation/networking/timestamping.txt | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) (limited to 'Documentation/networking') diff --git a/Documentation/networking/timestamping.txt b/Documentation/networking/timestamping.txt index a5c784c..5f09226 100644 --- a/Documentation/networking/timestamping.txt +++ b/Documentation/networking/timestamping.txt @@ -162,6 +162,27 @@ SOF_TIMESTAMPING_OPT_CMSG: option IP_PKTINFO simultaneously. +SOF_TIMESTAMPING_OPT_TSONLY: + + Applies to transmit timestamps only. Makes the kernel return the + timestamp as a cmsg alongside an empty packet, as opposed to + alongside the original packet. This reduces the amount of memory + charged to the socket's receive budget (SO_RCVBUF) and delivers + the timestamp even if sysctl net.core.tstamp_allow_data is 0. + This option disables SOF_TIMESTAMPING_OPT_CMSG. + + +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. + +An exception is when a process needs additional cmsg data, for +instance SOL_IP/IP_PKTINFO to detect the egress network interface. +Then pass option SOF_TIMESTAMPING_OPT_CMSG. This option depends on +having access to the contents of the original packet, so cannot be +combined with SOF_TIMESTAMPING_OPT_TSONLY. + + 1.4 Bytestream Timestamps The SO_TIMESTAMPING interface supports timestamping of bytes in a -- cgit v1.1