net: add new control message for incoming HW-timestamped packets
authorMiroslav Lichvar <mlichvar@redhat.com>
Fri, 19 May 2017 15:52:38 +0000 (17:52 +0200)
committerDavid S. Miller <davem@davemloft.net>
Sun, 21 May 2017 17:37:32 +0000 (13:37 -0400)
commitaad9c8c470f2a8321a99eb053630ce0e199558d6
tree8b98ee6312da615961395f30ed0d650528d54fc7
parent90b602f80397657429373ca009f98aec4dd3c553
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>
Documentation/networking/timestamping.txt
include/uapi/asm-generic/socket.h
include/uapi/linux/net_tstamp.h
net/socket.c