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Subject[PATCH net-next v5 10/12] socket: Update timestamping Documentation
Date
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>
---
Documentation/networking/timestamping.txt | 43 ++++++++++++++++++++---
1 file changed, 38 insertions(+), 5 deletions(-)

diff --git a/Documentation/networking/timestamping.txt b/Documentation/networking/timestamping.txt
index 9d1432e0aaa8..bbdaf8990031 100644
--- a/Documentation/networking/timestamping.txt
+++ b/Documentation/networking/timestamping.txt
@@ -6,11 +6,21 @@ The interfaces for receiving network packages timestamps are:
* SO_TIMESTAMP
Generates a timestamp for each incoming packet in (not necessarily
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
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]
Only for multicast:approximate transmit timestamp obtained by
@@ -22,7 +32,7 @@ The interfaces for receiving network packages timestamps are:
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
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`.

+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.
Its struct timespec allows for higher resolution (ns) timestamps than the
timeval of SO_TIMESTAMP (ms).

+Always use SO_TIMESTAMPNS_NEW timestamp to always get timestamp in
+struct __kernel_timespec format.
+
+SO_TIMESTAMPNS_OLD returns incorrect timestamps after the year 2038
+on 32 bit machines.

-1.3 SO_TIMESTAMPING:
+1.3 SO_TIMESTAMPING (also SO_TIMESTAMPING_OLD and SO_TIMESTAMPING_NEW):

Supports multiple types of timestamp requests. As a result, this
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
SOL_SOCKET, cmsg_type SCM_TIMESTAMPING, and payload of type

+For SO_TIMESTAMPING_OLD:
+
struct scm_timestamping {
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
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].
--
2.17.1
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