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socket: Update timestamping Documentation 

With the new y2038 safe timestamping options added, update the
documentation to reflect the changes.

Signed-off-by: Deepa Dinamani <deepa.kernel@gmail.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
hifive-unleashed-5.1
Deepa Dinamani 2019-02-02 07:34:52 -08:00 committed by David S. Miller
parent 9718475e69
commit 9dd49211b8
1 changed files with 38 additions and 5 deletions
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43
Documentation/networking/timestamping.txt
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@ -6,11 +6,21 @@ The interfaces for receiving network packages timestamps are:
* SO_TIMESTAMP * SO_TIMESTAMP
Generates a timestamp for each incoming packet in (not necessarily Generates a timestamp for each incoming packet in (not necessarily
monotonic) system time. Reports the timestamp via recvmsg() in a monotonic) system time. Reports the timestamp via recvmsg() in a
control message as struct timeval (usec resolution). control message in usec resolution.
SO_TIMESTAMP is defined as SO_TIMESTAMP_NEW or SO_TIMESTAMP_OLD
based on the architecture type and time_t representation of libc.
Control message format is in struct __kernel_old_timeval for
SO_TIMESTAMP_OLD and in struct __kernel_sock_timeval for
SO_TIMESTAMP_NEW options respectively.
* SO_TIMESTAMPNS * SO_TIMESTAMPNS
Same timestamping mechanism as SO_TIMESTAMP, but reports the Same timestamping mechanism as SO_TIMESTAMP, but reports the
timestamp as struct timespec (nsec resolution). timestamp as struct timespec in nsec resolution.
SO_TIMESTAMPNS is defined as SO_TIMESTAMPNS_NEW or SO_TIMESTAMPNS_OLD
based on the architecture type and time_t representation of libc.
Control message format is in struct timespec for SO_TIMESTAMPNS_OLD
and in struct __kernel_timespec for SO_TIMESTAMPNS_NEW options
respectively.
* IP_MULTICAST_LOOP + SO_TIMESTAMP[NS] * IP_MULTICAST_LOOP + SO_TIMESTAMP[NS]
Only for multicast:approximate transmit timestamp obtained by Only for multicast:approximate transmit timestamp obtained by
@ -22,7 +32,7 @@ The interfaces for receiving network packages timestamps are:
timestamps for stream sockets. timestamps for stream sockets.
1.1 SO_TIMESTAMP: 1.1 SO_TIMESTAMP (also SO_TIMESTAMP_OLD and SO_TIMESTAMP_NEW):
This socket option enables timestamping of datagrams on the reception This socket option enables timestamping of datagrams on the reception
path. Because the destination socket, if any, is not known early in path. Because the destination socket, if any, is not known early in
@ -31,15 +41,25 @@ same is true for all early receive timestamp options.
For interface details, see `man 7 socket`. For interface details, see `man 7 socket`.
Always use SO_TIMESTAMP_NEW timestamp to always get timestamp in
struct __kernel_sock_timeval format.
1.2 SO_TIMESTAMPNS: SO_TIMESTAMP_OLD returns incorrect timestamps after the year 2038
on 32 bit machines.
1.2 SO_TIMESTAMPNS (also SO_TIMESTAMPNS_OLD and SO_TIMESTAMPNS_NEW):
This option is identical to SO_TIMESTAMP except for the returned data type. This option is identical to SO_TIMESTAMP except for the returned data type.
Its struct timespec allows for higher resolution (ns) timestamps than the Its struct timespec allows for higher resolution (ns) timestamps than the
timeval of SO_TIMESTAMP (ms). timeval of SO_TIMESTAMP (ms).
Always use SO_TIMESTAMPNS_NEW timestamp to always get timestamp in
struct __kernel_timespec format.
1.3 SO_TIMESTAMPING: SO_TIMESTAMPNS_OLD returns incorrect timestamps after the year 2038
on 32 bit machines.
1.3 SO_TIMESTAMPING (also SO_TIMESTAMPING_OLD and SO_TIMESTAMPING_NEW):
Supports multiple types of timestamp requests. As a result, this Supports multiple types of timestamp requests. As a result, this
socket option takes a bitmap of flags, not a boolean. In socket option takes a bitmap of flags, not a boolean. In
@ -323,10 +343,23 @@ SO_TIMESTAMP and SO_TIMESTAMPNS records can be retrieved.
These timestamps are returned in a control message with cmsg_level These timestamps are returned in a control message with cmsg_level
SOL_SOCKET, cmsg_type SCM_TIMESTAMPING, and payload of type SOL_SOCKET, cmsg_type SCM_TIMESTAMPING, and payload of type
For SO_TIMESTAMPING_OLD:
struct scm_timestamping { struct scm_timestamping {
struct timespec ts[3]; struct timespec ts[3];
}; };
For SO_TIMESTAMPING_NEW:
struct scm_timestamping64 {
struct __kernel_timespec ts[3];
Always use SO_TIMESTAMPING_NEW timestamp to always get timestamp in
struct scm_timestamping64 format.
SO_TIMESTAMPING_OLD returns incorrect timestamps after the year 2038
on 32 bit machines.
The structure can return up to three timestamps. This is a legacy The structure can return up to three timestamps. This is a legacy
feature. At least one field is non-zero at any time. Most timestamps feature. At least one field is non-zero at any time. Most timestamps
are passed in ts[0]. Hardware timestamps are passed in ts[2]. are passed in ts[0]. Hardware timestamps are passed in ts[2].