net: add new control message for incoming HW-timestamped packets

Add SOF_TIMESTAMPING_OPT_PKTINFO option to request a new control message
for incoming packets with hardware timestamps. It contains the index of
the real interface which received the packet and the length of the
packet at layer 2.

The index is useful with bonding, bridges and other interfaces, where
IP_PKTINFO doesn't allow applications to determine which PHC made the
timestamp. With the L2 length (and link speed) it is possible to
transpose preamble timestamps to trailer timestamps, which are used in
the NTP protocol.

While this information could be provided by two new socket options
independently from timestamping, it doesn't look like they would be very
useful. With this option any performance impact is limited to hardware
timestamping.

Use dev_get_by_napi_id() to get the device and its index. On kernels
with disabled CONFIG_NET_RX_BUSY_POLL or drivers not using NAPI, a zero
index will be returned in the control message.

CC: Richard Cochran <richardcochran@gmail.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Miroslav Lichvar <mlichvar@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 10 insertions, 0 deletions

diff --git a/Documentation/networking/timestamping.txt b/Documentation/networking/timestamping.txt
index 96f50694a748..ce11e3a08c0d 100644
--- a/Documentation/networking/timestamping.txt
+++ b/Documentation/networking/timestamping.txt
@@ -193,6 +193,16 @@ SOF_TIMESTAMPING_OPT_STATS:
   the transmit timestamps, such as how long a certain block of
   data was limited by peer's receiver window.
 
+SOF_TIMESTAMPING_OPT_PKTINFO:
+
+  Enable the SCM_TIMESTAMPING_PKTINFO control message for incoming
+  packets with hardware timestamps. The message contains struct
+  scm_ts_pktinfo, which supplies the index of the real interface which
+  received the packet and its length at layer 2. A valid (non-zero)
+  interface index will be returned only if CONFIG_NET_RX_BUSY_POLL is
+  enabled and the driver is using NAPI. The struct contains also two
+  other fields, but they are reserved and undefined.
+
 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.