path: root/Documentation/networking
diff options
authorWillem de Bruijn <>2015-01-30 13:29:31 -0500
committerDavid S. Miller <>2015-02-02 18:46:51 -0800
commit49ca0d8bfaf3bc46d5eef60ce67b00eb195bd392 (patch)
treed2f55a32923f6d91fcb2e0d0e0b6d2d4eb6f9abd /Documentation/networking
parent9766e97af1b901ffbb36fcc648e50626d926bb24 (diff)
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 <>
Diffstat (limited to 'Documentation/networking')
1 files changed, 21 insertions, 0 deletions
diff --git a/Documentation/networking/timestamping.txt b/Documentation/networking/timestamping.txt
index a5c784c89312..5f0922613f1a 100644
--- a/Documentation/networking/timestamping.txt
+++ b/Documentation/networking/timestamping.txt
@@ -162,6 +162,27 @@ SOF_TIMESTAMPING_OPT_CMSG:
option IP_PKTINFO simultaneously.
+ 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
1.4 Bytestream Timestamps
The SO_TIMESTAMPING interface supports timestamping of bytes in a