€•       Œsphinx.addnodes”Œdocument”“”)”}”(Œ	rawsource”Œ ”Œchildren”]”(Œtranslations”ŒLanguagesNode”“”)”}”(hhh]”(h Œpending_xref”“”)”}”(hhh]”Œdocutils.nodes”ŒText”“”ŒChinese (Simplified)”…””}”Œparent”hsbaŒ
attributes”}”(Œids”]”Œclasses”]”Œnames”]”Œdupnames”]”Œbackrefs”]”Œ	refdomain”Œstd”Œreftype”Œdoc”Œ	reftarget”Œ+/translations/zh_CN/networking/timestamping”Œmodname”NŒ	classname”NŒrefexplicit”ˆuŒtagname”hhhubh)”}”(hhh]”hŒChinese (Traditional)”…””}”hh2sbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ+/translations/zh_TW/networking/timestamping”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒItalian”…””}”hhFsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ+/translations/it_IT/networking/timestamping”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒJapanese”…””}”hhZsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ+/translations/ja_JP/networking/timestamping”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒKorean”…””}”hhnsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ+/translations/ko_KR/networking/timestamping”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒSpanish”…””}”hh‚sbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ+/translations/sp_SP/networking/timestamping”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubeh}”(h]”h ]”h"]”h$]”h&]”Œcurrent_language”ŒEnglish”uh1h
hhŒ	_document”hŒsource”NŒline”NubhŒcomment”“”)”}”(hŒ SPDX-License-Identifier: GPL-2.0”h]”hŒ SPDX-License-Identifier: GPL-2.0”…””}”hh£sbah}”(h]”h ]”h"]”h$]”h&]”Œ	xml:space”Œpreserve”uh1h¡hhhžhhŸŒE/var/lib/git/docbuild/linux/Documentation/networking/timestamping.rst”h KubhŒsection”“”)”}”(hhh]”(hŒtitle”“”)”}”(hŒTimestamping”h]”hŒTimestamping”…””}”(hh»hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hh¶hžhhŸh³h Kubhµ)”}”(hhh]”(hº)”}”(hŒ1. Control Interfaces”h]”hŒ1. Control Interfaces”…””}”(hhÌhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hhÉhžhhŸh³h K	ubhŒ	paragraph”“”)”}”(hŒ=The interfaces for receiving network packages timestamps are:”h]”hŒ=The interfaces for receiving network packages timestamps are:”…””}”(hhÜhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h KhhÉhžhubhŒdefinition_list”“”)”}”(hhh]”(hŒdefinition_list_item”“”)”}”(hXÔ  SO_TIMESTAMP
Generates a timestamp for each incoming packet in (not necessarily
monotonic) system time. Reports the timestamp via recvmsg() in a
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.
”h]”(hŒterm”“”)”}”(hŒSO_TIMESTAMP”h]”hŒSO_TIMESTAMP”…””}”(hh÷hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hõhŸh³h KhhñubhŒ
definition”“”)”}”(hhh]”hÛ)”}”(hXÆ  Generates a timestamp for each incoming packet in (not necessarily
monotonic) system time. Reports the timestamp via recvmsg() in a
control message in usec resolution.
SO_TIMESTAMP is defined as SO_TIMESTAMP_NEW or SO_TIMESTAMP_OLD
based on the architecture type and time_t representation of libc.
Control message format is in struct __kernel_old_timeval for
SO_TIMESTAMP_OLD and in struct __kernel_sock_timeval for
SO_TIMESTAMP_NEW options respectively.”h]”hXÆ  Generates a timestamp for each incoming packet in (not necessarily
monotonic) system time. Reports the timestamp via recvmsg() in a
control message in usec resolution.
SO_TIMESTAMP is defined as SO_TIMESTAMP_NEW or SO_TIMESTAMP_OLD
based on the architecture type and time_t representation of libc.
Control message format is in struct __kernel_old_timeval for
SO_TIMESTAMP_OLD and in struct __kernel_sock_timeval for
SO_TIMESTAMP_NEW options respectively.”…””}”(hj
  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h Khj  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hhñubeh}”(h]”h ]”h"]”h$]”h&]”uh1hïhŸh³h Khhìubhð)”}”(hX–  SO_TIMESTAMPNS
Same timestamping mechanism as SO_TIMESTAMP, but reports the
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.
”h]”(hö)”}”(hŒSO_TIMESTAMPNS”h]”hŒSO_TIMESTAMPNS”…””}”(hj(  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hõhŸh³h Khj$  ubj  )”}”(hhh]”hÛ)”}”(hX†  Same timestamping mechanism as SO_TIMESTAMP, but reports the
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.”h]”hX†  Same timestamping mechanism as SO_TIMESTAMP, but reports the
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.”…””}”(hj9  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h Khj6  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hj$  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hïhŸh³h Khhìhžhubhð)”}”(hŒIP_MULTICAST_LOOP + SO_TIMESTAMP[NS]
Only for multicast:approximate transmit timestamp obtained by
reading the looped packet receive timestamp.
”h]”(hö)”}”(hŒ$IP_MULTICAST_LOOP + SO_TIMESTAMP[NS]”h]”hŒ$IP_MULTICAST_LOOP + SO_TIMESTAMP[NS]”…””}”(hjW  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hõhŸh³h K"hjS  ubj  )”}”(hhh]”hÛ)”}”(hŒjOnly for multicast:approximate transmit timestamp obtained by
reading the looped packet receive timestamp.”h]”hŒjOnly for multicast:approximate transmit timestamp obtained by
reading the looped packet receive timestamp.”…””}”(hjh  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h K!hje  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hjS  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hïhŸh³h K"hhìhžhubhð)”}”(hŒ¶SO_TIMESTAMPING
Generates timestamps on reception, transmission or both. Supports
multiple timestamp sources, including hardware. Supports generating
timestamps for stream sockets.

”h]”(hö)”}”(hŒSO_TIMESTAMPING”h]”hŒSO_TIMESTAMPING”…””}”(hj†  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hõhŸh³h K(hj‚  ubj  )”}”(hhh]”hÛ)”}”(hŒ¤Generates timestamps on reception, transmission or both. Supports
multiple timestamp sources, including hardware. Supports generating
timestamps for stream sockets.”h]”hŒ¤Generates timestamps on reception, transmission or both. Supports
multiple timestamp sources, including hardware. Supports generating
timestamps for stream sockets.”…””}”(hj—  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h K%hj”  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hj‚  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hïhŸh³h K(hhìhžhubeh}”(h]”h ]”h"]”h$]”h&]”uh1hêhhÉhžhhŸh³h Nubhµ)”}”(hhh]”(hº)”}”(hŒ=1.1 SO_TIMESTAMP (also SO_TIMESTAMP_OLD and SO_TIMESTAMP_NEW)”h]”hŒ=1.1 SO_TIMESTAMP (also SO_TIMESTAMP_OLD and SO_TIMESTAMP_NEW)”…””}”(hjº  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hj·  hžhhŸh³h K+ubhÛ)”}”(hX  This socket option enables timestamping of datagrams on the reception
path. Because the destination socket, if any, is not known early in
the network stack, the feature has to be enabled for all packets. The
same is true for all early receive timestamp options.”h]”hX  This socket option enables timestamping of datagrams on the reception
path. Because the destination socket, if any, is not known early in
the network stack, the feature has to be enabled for all packets. The
same is true for all early receive timestamp options.”…””}”(hjÈ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h K-hj·  hžhubhÛ)”}”(hŒ*For interface details, see `man 7 socket`.”h]”(hŒFor interface details, see ”…””}”(hjÖ  hžhhŸNh NubhŒtitle_reference”“”)”}”(hŒ`man 7 socket`”h]”hŒman 7 socket”…””}”(hjà  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jÞ  hjÖ  ubhŒ.”…””}”(hjÖ  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h K2hj·  hžhubhÛ)”}”(hŒeAlways use SO_TIMESTAMP_NEW timestamp to always get timestamp in
struct __kernel_sock_timeval format.”h]”hŒeAlways use SO_TIMESTAMP_NEW timestamp to always get timestamp in
struct __kernel_sock_timeval format.”…””}”(hjø  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h K4hj·  hžhubhÛ)”}”(hŒUSO_TIMESTAMP_OLD returns incorrect timestamps after the year 2038
on 32 bit machines.”h]”hŒUSO_TIMESTAMP_OLD returns incorrect timestamps after the year 2038
on 32 bit machines.”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h K7hj·  hžhubeh}”(h]”Œ7so-timestamp-also-so-timestamp-old-and-so-timestamp-new”ah ]”h"]”Œ=1.1 so_timestamp (also so_timestamp_old and so_timestamp_new)”ah$]”h&]”uh1h´hhÉhžhhŸh³h K+ubhµ)”}”(hhh]”(hº)”}”(hŒC1.2 SO_TIMESTAMPNS (also SO_TIMESTAMPNS_OLD and SO_TIMESTAMPNS_NEW)”h]”hŒC1.2 SO_TIMESTAMPNS (also SO_TIMESTAMPNS_OLD and SO_TIMESTAMPNS_NEW)”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hj  hžhhŸh³h K;ubhÛ)”}”(hŒ³This option is identical to SO_TIMESTAMP except for the returned data type.
Its struct timespec allows for higher resolution (ns) timestamps than the
timeval of SO_TIMESTAMP (ms).”h]”hŒ³This option is identical to SO_TIMESTAMP except for the returned data type.
Its struct timespec allows for higher resolution (ns) timestamps than the
timeval of SO_TIMESTAMP (ms).”…””}”(hj-  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h K=hj  hžhubhÛ)”}”(hŒcAlways use SO_TIMESTAMPNS_NEW timestamp to always get timestamp in
struct __kernel_timespec format.”h]”hŒcAlways use SO_TIMESTAMPNS_NEW timestamp to always get timestamp in
struct __kernel_timespec format.”…””}”(hj;  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h KAhj  hžhubhÛ)”}”(hŒWSO_TIMESTAMPNS_OLD returns incorrect timestamps after the year 2038
on 32 bit machines.”h]”hŒWSO_TIMESTAMPNS_OLD returns incorrect timestamps after the year 2038
on 32 bit machines.”…””}”(hjI  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h KDhj  hžhubeh}”(h]”Œ=so-timestampns-also-so-timestampns-old-and-so-timestampns-new”ah ]”h"]”ŒC1.2 so_timestampns (also so_timestampns_old and so_timestampns_new)”ah$]”h&]”uh1h´hhÉhžhhŸh³h K;ubhµ)”}”(hhh]”(hº)”}”(hŒF1.3 SO_TIMESTAMPING (also SO_TIMESTAMPING_OLD and SO_TIMESTAMPING_NEW)”h]”hŒF1.3 SO_TIMESTAMPING (also SO_TIMESTAMPING_OLD and SO_TIMESTAMPING_NEW)”…””}”(hjb  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hj_  hžhhŸh³h KHubhÛ)”}”(hŒ{Supports multiple types of timestamp requests. As a result, this
socket option takes a bitmap of flags, not a boolean. In::”h]”hŒzSupports multiple types of timestamp requests. As a result, this
socket option takes a bitmap of flags, not a boolean. In:”…””}”(hjp  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h KJhj_  hžhubhŒliteral_block”“”)”}”(hŒEerr = setsockopt(fd, SOL_SOCKET, SO_TIMESTAMPING, &val, sizeof(val));”h]”hŒEerr = setsockopt(fd, SOL_SOCKET, SO_TIMESTAMPING, &val, sizeof(val));”…””}”hj€  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1j~  hŸh³h KMhj_  hžhubhÛ)”}”(hŒ}val is an integer with any of the following bits set. Setting other
bit returns EINVAL and does not change the current state.”h]”hŒ}val is an integer with any of the following bits set. Setting other
bit returns EINVAL and does not change the current state.”…””}”(hjŽ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h KOhj_  hžhubhÛ)”}”(hŒùThe socket option configures timestamp generation for individual
sk_buffs (1.3.1), timestamp reporting to the socket's error
queue (1.3.2) and options (1.3.3). Timestamp generation can also
be enabled for individual sendmsg calls using cmsg (1.3.4).”h]”hŒûThe socket option configures timestamp generation for individual
sk_buffs (1.3.1), timestamp reporting to the socketâ€™s error
queue (1.3.2) and options (1.3.3). Timestamp generation can also
be enabled for individual sendmsg calls using cmsg (1.3.4).”…””}”(hjœ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h KRhj_  hžhubhµ)”}”(hhh]”(hº)”}”(hŒ1.3.1 Timestamp Generation”h]”hŒ1.3.1 Timestamp Generation”…””}”(hj­  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hjª  hžhhŸh³h KYubhÛ)”}”(hXM  Some bits are requests to the stack to try to generate timestamps. Any
combination of them is valid. Changes to these bits apply to newly
created packets, not to packets already in the stack. As a result, it
is possible to selectively request timestamps for a subset of packets
(e.g., for sampling) by embedding an send() call within two setsockopt
calls, one to enable timestamp generation and one to disable it.
Timestamps may also be generated for reasons other than being
requested by a particular socket, such as when receive timestamping is
enabled system wide, as explained earlier.”h]”hXM  Some bits are requests to the stack to try to generate timestamps. Any
combination of them is valid. Changes to these bits apply to newly
created packets, not to packets already in the stack. As a result, it
is possible to selectively request timestamps for a subset of packets
(e.g., for sampling) by embedding an send() call within two setsockopt
calls, one to enable timestamp generation and one to disable it.
Timestamps may also be generated for reasons other than being
requested by a particular socket, such as when receive timestamping is
enabled system wide, as explained earlier.”…””}”(hj»  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h K[hjª  hžhubhë)”}”(hhh]”(hð)”}”(hŒVSOF_TIMESTAMPING_RX_HARDWARE:
Request rx timestamps generated by the network adapter.
”h]”(hö)”}”(hŒSOF_TIMESTAMPING_RX_HARDWARE:”h]”hŒSOF_TIMESTAMPING_RX_HARDWARE:”…””}”(hjÐ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hõhŸh³h KfhjÌ  ubj  )”}”(hhh]”hÛ)”}”(hŒ7Request rx timestamps generated by the network adapter.”h]”hŒ7Request rx timestamps generated by the network adapter.”…””}”(hjá  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h KfhjÞ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hjÌ  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hïhŸh³h KfhjÉ  ubhð)”}”(hŒ·SOF_TIMESTAMPING_RX_SOFTWARE:
Request rx timestamps when data enters the kernel. These timestamps
are generated just after a device driver hands a packet to the
kernel receive stack.
”h]”(hö)”}”(hŒSOF_TIMESTAMPING_RX_SOFTWARE:”h]”hŒSOF_TIMESTAMPING_RX_SOFTWARE:”…””}”(hjÿ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hõhŸh³h Kkhjû  ubj  )”}”(hhh]”hÛ)”}”(hŒ˜Request rx timestamps when data enters the kernel. These timestamps
are generated just after a device driver hands a packet to the
kernel receive stack.”h]”hŒ˜Request rx timestamps when data enters the kernel. These timestamps
are generated just after a device driver hands a packet to the
kernel receive stack.”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h Kihj  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hjû  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hïhŸh³h KkhjÉ  hžhubhð)”}”(hŒSOF_TIMESTAMPING_TX_HARDWARE:
Request tx timestamps generated by the network adapter. This flag
can be enabled via both socket options and control messages.
”h]”(hö)”}”(hŒSOF_TIMESTAMPING_TX_HARDWARE:”h]”hŒSOF_TIMESTAMPING_TX_HARDWARE:”…””}”(hj.  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hõhŸh³h Kohj*  ubj  )”}”(hhh]”hÛ)”}”(hŒ~Request tx timestamps generated by the network adapter. This flag
can be enabled via both socket options and control messages.”h]”hŒ~Request tx timestamps generated by the network adapter. This flag
can be enabled via both socket options and control messages.”…””}”(hj?  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h Knhj<  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hj*  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hïhŸh³h KohjÉ  hžhubhð)”}”(hXq  SOF_TIMESTAMPING_TX_SOFTWARE:
Request tx timestamps when data leaves the kernel. These timestamps
are generated in the device driver as close as possible, but always
prior to, passing the packet to the network interface. Hence, they
require driver support and may not be available for all devices.
This flag can be enabled via both socket options and control messages.
”h]”(hö)”}”(hŒSOF_TIMESTAMPING_TX_SOFTWARE:”h]”hŒSOF_TIMESTAMPING_TX_SOFTWARE:”…””}”(hj]  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hõhŸh³h KvhjY  ubj  )”}”(hhh]”hÛ)”}”(hXR  Request tx timestamps when data leaves the kernel. These timestamps
are generated in the device driver as close as possible, but always
prior to, passing the packet to the network interface. Hence, they
require driver support and may not be available for all devices.
This flag can be enabled via both socket options and control messages.”h]”hXR  Request tx timestamps when data leaves the kernel. These timestamps
are generated in the device driver as close as possible, but always
prior to, passing the packet to the network interface. Hence, they
require driver support and may not be available for all devices.
This flag can be enabled via both socket options and control messages.”…””}”(hjn  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h Krhjk  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hjY  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hïhŸh³h KvhjÉ  hžhubhð)”}”(hXÿ  SOF_TIMESTAMPING_TX_SCHED:
Request tx timestamps prior to entering the packet scheduler. Kernel
transmit latency is, if long, often dominated by queuing delay. The
difference between this timestamp and one taken at
SOF_TIMESTAMPING_TX_SOFTWARE will expose this latency independent
of protocol processing. The latency incurred in protocol
processing, if any, can be computed by subtracting a userspace
timestamp taken immediately before send() from this timestamp. On
machines with virtual devices where a transmitted packet travels
through multiple devices and, hence, multiple packet schedulers,
a timestamp is generated at each layer. This allows for fine
grained measurement of queuing delay. This flag can be enabled
via both socket options and control messages.
”h]”(hö)”}”(hŒSOF_TIMESTAMPING_TX_SCHED:”h]”hŒSOF_TIMESTAMPING_TX_SCHED:”…””}”(hjŒ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hõhŸh³h K„hjˆ  ubj  )”}”(hhh]”hÛ)”}”(hXã  Request tx timestamps prior to entering the packet scheduler. Kernel
transmit latency is, if long, often dominated by queuing delay. The
difference between this timestamp and one taken at
SOF_TIMESTAMPING_TX_SOFTWARE will expose this latency independent
of protocol processing. The latency incurred in protocol
processing, if any, can be computed by subtracting a userspace
timestamp taken immediately before send() from this timestamp. On
machines with virtual devices where a transmitted packet travels
through multiple devices and, hence, multiple packet schedulers,
a timestamp is generated at each layer. This allows for fine
grained measurement of queuing delay. This flag can be enabled
via both socket options and control messages.”h]”hXã  Request tx timestamps prior to entering the packet scheduler. Kernel
transmit latency is, if long, often dominated by queuing delay. The
difference between this timestamp and one taken at
SOF_TIMESTAMPING_TX_SOFTWARE will expose this latency independent
of protocol processing. The latency incurred in protocol
processing, if any, can be computed by subtracting a userspace
timestamp taken immediately before send() from this timestamp. On
machines with virtual devices where a transmitted packet travels
through multiple devices and, hence, multiple packet schedulers,
a timestamp is generated at each layer. This allows for fine
grained measurement of queuing delay. This flag can be enabled
via both socket options and control messages.”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h Kyhjš  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hjˆ  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hïhŸh³h K„hjÉ  hžhubhð)”}”(hXé  SOF_TIMESTAMPING_TX_ACK:
Request tx timestamps when all data in the send buffer has been
acknowledged. This only makes sense for reliable protocols. It is
currently only implemented for TCP. For that protocol, it may
over-report measurement, because the timestamp is generated when all
data up to and including the buffer at send() was acknowledged: the
cumulative acknowledgment. The mechanism ignores SACK and FACK.
This flag can be enabled via both socket options and control messages.
”h]”(hö)”}”(hŒSOF_TIMESTAMPING_TX_ACK:”h]”hŒSOF_TIMESTAMPING_TX_ACK:”…””}”(hj»  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hõhŸh³h Khj·  ubj  )”}”(hhh]”hÛ)”}”(hXÏ  Request tx timestamps when all data in the send buffer has been
acknowledged. This only makes sense for reliable protocols. It is
currently only implemented for TCP. For that protocol, it may
over-report measurement, because the timestamp is generated when all
data up to and including the buffer at send() was acknowledged: the
cumulative acknowledgment. The mechanism ignores SACK and FACK.
This flag can be enabled via both socket options and control messages.”h]”hXÏ  Request tx timestamps when all data in the send buffer has been
acknowledged. This only makes sense for reliable protocols. It is
currently only implemented for TCP. For that protocol, it may
over-report measurement, because the timestamp is generated when all
data up to and including the buffer at send() was acknowledged: the
cumulative acknowledgment. The mechanism ignores SACK and FACK.
This flag can be enabled via both socket options and control messages.”…””}”(hjÌ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h K‡hjÉ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hj·  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hïhŸh³h KhjÉ  hžhubhð)”}”(hXŒ  SOF_TIMESTAMPING_TX_COMPLETION:
Request tx timestamps on packet tx completion.  The completion
timestamp is generated by the kernel when it receives packet a
completion report from the hardware. Hardware may report multiple
packets at once, and completion timestamps reflect the timing of the
report and not actual tx time. This flag can be enabled via both
socket options and control messages.

”h]”(hö)”}”(hŒSOF_TIMESTAMPING_TX_COMPLETION:”h]”hŒSOF_TIMESTAMPING_TX_COMPLETION:”…””}”(hjê  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hõhŸh³h K–hjæ  ubj  )”}”(hhh]”hÛ)”}”(hXj  Request tx timestamps on packet tx completion.  The completion
timestamp is generated by the kernel when it receives packet a
completion report from the hardware. Hardware may report multiple
packets at once, and completion timestamps reflect the timing of the
report and not actual tx time. This flag can be enabled via both
socket options and control messages.”h]”hXj  Request tx timestamps on packet tx completion.  The completion
timestamp is generated by the kernel when it receives packet a
completion report from the hardware. Hardware may report multiple
packets at once, and completion timestamps reflect the timing of the
report and not actual tx time. This flag can be enabled via both
socket options and control messages.”…””}”(hjû  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h Khjø  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hjæ  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hïhŸh³h K–hjÉ  hžhubeh}”(h]”h ]”h"]”h$]”h&]”uh1hêhjª  hžhhŸh³h Nubeh}”(h]”Œtimestamp-generation”ah ]”h"]”Œ1.3.1 timestamp generation”ah$]”h&]”uh1h´hj_  hžhhŸh³h KYubhµ)”}”(hhh]”(hº)”}”(hŒ1.3.2 Timestamp Reporting”h]”hŒ1.3.2 Timestamp Reporting”…””}”(hj&  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hj#  hžhhŸh³h K™ubhÛ)”}”(hX"  The other three bits control which timestamps will be reported in a
generated control message. Changes to the bits take immediate
effect at the timestamp reporting locations in the stack. Timestamps
are only reported for packets that also have the relevant timestamp
generation request set.”h]”hX"  The other three bits control which timestamps will be reported in a
generated control message. Changes to the bits take immediate
effect at the timestamp reporting locations in the stack. Timestamps
are only reported for packets that also have the relevant timestamp
generation request set.”…””}”(hj4  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h K›hj#  hžhubhë)”}”(hhh]”(hð)”}”(hŒJSOF_TIMESTAMPING_SOFTWARE:
Report any software timestamps when available.
”h]”(hö)”}”(hŒSOF_TIMESTAMPING_SOFTWARE:”h]”hŒSOF_TIMESTAMPING_SOFTWARE:”…””}”(hjI  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hõhŸh³h K¢hjE  ubj  )”}”(hhh]”hÛ)”}”(hŒ.Report any software timestamps when available.”h]”hŒ.Report any software timestamps when available.”…””}”(hjZ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h K¢hjW  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hjE  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hïhŸh³h K¢hjB  ubhð)”}”(hŒFSOF_TIMESTAMPING_SYS_HARDWARE:
This option is deprecated and ignored.
”h]”(hö)”}”(hŒSOF_TIMESTAMPING_SYS_HARDWARE:”h]”hŒSOF_TIMESTAMPING_SYS_HARDWARE:”…””}”(hjx  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hõhŸh³h K¥hjt  ubj  )”}”(hhh]”hÛ)”}”(hŒ&This option is deprecated and ignored.”h]”hŒ&This option is deprecated and ignored.”…””}”(hj‰  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h K¥hj†  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hjt  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hïhŸh³h K¥hjB  hžhubhð)”}”(hŒ˜SOF_TIMESTAMPING_RAW_HARDWARE:
Report hardware timestamps as generated by
SOF_TIMESTAMPING_TX_HARDWARE or SOF_TIMESTAMPING_RX_HARDWARE
when available.

”h]”(hö)”}”(hŒSOF_TIMESTAMPING_RAW_HARDWARE:”h]”hŒSOF_TIMESTAMPING_RAW_HARDWARE:”…””}”(hj§  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hõhŸh³h K«hj£  ubj  )”}”(hhh]”hÛ)”}”(hŒwReport hardware timestamps as generated by
SOF_TIMESTAMPING_TX_HARDWARE or SOF_TIMESTAMPING_RX_HARDWARE
when available.”h]”hŒwReport hardware timestamps as generated by
SOF_TIMESTAMPING_TX_HARDWARE or SOF_TIMESTAMPING_RX_HARDWARE
when available.”…””}”(hj¸  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h K¨hjµ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hj£  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hïhŸh³h K«hjB  hžhubeh}”(h]”h ]”h"]”h$]”h&]”uh1hêhj#  hžhhŸh³h Nubeh}”(h]”Œtimestamp-reporting”ah ]”h"]”Œ1.3.2 timestamp reporting”ah$]”h&]”uh1h´hj_  hžhhŸh³h K™ubhµ)”}”(hhh]”(hº)”}”(hŒ1.3.3 Timestamp Options”h]”hŒ1.3.3 Timestamp Options”…””}”(hjã  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hjà  hžhhŸh³h K®ubhÛ)”}”(hŒ"The interface supports the options”h]”hŒ"The interface supports the options”…””}”(hjñ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h K°hjà  hžhubhë)”}”(hhh]”(hð)”}”(hXK  SOF_TIMESTAMPING_OPT_ID:
Generate a unique identifier along with each packet. A process can
have multiple concurrent timestamping requests outstanding. Packets
can be reordered in the transmit path, for instance in the packet
scheduler. In that case timestamps will be queued onto the error
queue out of order from the original send() calls. It is not always
possible to uniquely match timestamps to the original send() calls
based on timestamp order or payload inspection alone, then.

This option associates each packet at send() with a unique
identifier and returns that along with the timestamp. The identifier
is derived from a per-socket u32 counter (that wraps). For datagram
sockets, the counter increments with each sent packet. For stream
sockets, it increments with every byte. For stream sockets, also set
SOF_TIMESTAMPING_OPT_ID_TCP, see the section below.

The counter starts at zero. It is initialized the first time that
the socket option is enabled. It is reset each time the option is
enabled after having been disabled. Resetting the counter does not
change the identifiers of existing packets in the system.

This option is implemented only for transmit timestamps. There, the
timestamp is always looped along with a struct sock_extended_err.
The option modifies field ee_data to pass an id that is unique
among all possibly concurrently outstanding timestamp requests for
that socket.

The process can optionally override the default generated ID, by
passing a specific ID with control message SCM_TS_OPT_ID (not
supported for TCP sockets)::

  struct msghdr *msg;
  ...
  cmsg                         = CMSG_FIRSTHDR(msg);
  cmsg->cmsg_level             = SOL_SOCKET;
  cmsg->cmsg_type              = SCM_TS_OPT_ID;
  cmsg->cmsg_len               = CMSG_LEN(sizeof(__u32));
  *((__u32 *) CMSG_DATA(cmsg)) = opt_id;
  err = sendmsg(fd, msg, 0);

”h]”(hö)”}”(hŒSOF_TIMESTAMPING_OPT_ID:”h]”hŒSOF_TIMESTAMPING_OPT_ID:”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hõhŸh³h KÙhj  ubj  )”}”(hhh]”(hÛ)”}”(hXÌ  Generate a unique identifier along with each packet. A process can
have multiple concurrent timestamping requests outstanding. Packets
can be reordered in the transmit path, for instance in the packet
scheduler. In that case timestamps will be queued onto the error
queue out of order from the original send() calls. It is not always
possible to uniquely match timestamps to the original send() calls
based on timestamp order or payload inspection alone, then.”h]”hXÌ  Generate a unique identifier along with each packet. A process can
have multiple concurrent timestamping requests outstanding. Packets
can be reordered in the transmit path, for instance in the packet
scheduler. In that case timestamps will be queued onto the error
queue out of order from the original send() calls. It is not always
possible to uniquely match timestamps to the original send() calls
based on timestamp order or payload inspection alone, then.”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h K³hj  ubhÛ)”}”(hX~  This option associates each packet at send() with a unique
identifier and returns that along with the timestamp. The identifier
is derived from a per-socket u32 counter (that wraps). For datagram
sockets, the counter increments with each sent packet. For stream
sockets, it increments with every byte. For stream sockets, also set
SOF_TIMESTAMPING_OPT_ID_TCP, see the section below.”h]”hX~  This option associates each packet at send() with a unique
identifier and returns that along with the timestamp. The identifier
is derived from a per-socket u32 counter (that wraps). For datagram
sockets, the counter increments with each sent packet. For stream
sockets, it increments with every byte. For stream sockets, also set
SOF_TIMESTAMPING_OPT_ID_TCP, see the section below.”…””}”(hj%  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h K»hj  ubhÛ)”}”(hX   The counter starts at zero. It is initialized the first time that
the socket option is enabled. It is reset each time the option is
enabled after having been disabled. Resetting the counter does not
change the identifiers of existing packets in the system.”h]”hX   The counter starts at zero. It is initialized the first time that
the socket option is enabled. It is reset each time the option is
enabled after having been disabled. Resetting the counter does not
change the identifiers of existing packets in the system.”…””}”(hj3  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h KÂhj  ubhÛ)”}”(hX  This option is implemented only for transmit timestamps. There, the
timestamp is always looped along with a struct sock_extended_err.
The option modifies field ee_data to pass an id that is unique
among all possibly concurrently outstanding timestamp requests for
that socket.”h]”hX  This option is implemented only for transmit timestamps. There, the
timestamp is always looped along with a struct sock_extended_err.
The option modifies field ee_data to pass an id that is unique
among all possibly concurrently outstanding timestamp requests for
that socket.”…””}”(hjA  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h KÇhj  ubhÛ)”}”(hŒ›The process can optionally override the default generated ID, by
passing a specific ID with control message SCM_TS_OPT_ID (not
supported for TCP sockets)::”h]”hŒšThe process can optionally override the default generated ID, by
passing a specific ID with control message SCM_TS_OPT_ID (not
supported for TCP sockets):”…””}”(hjO  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h KÍhj  ubj  )”}”(hX  struct msghdr *msg;
...
cmsg                         = CMSG_FIRSTHDR(msg);
cmsg->cmsg_level             = SOL_SOCKET;
cmsg->cmsg_type              = SCM_TS_OPT_ID;
cmsg->cmsg_len               = CMSG_LEN(sizeof(__u32));
*((__u32 *) CMSG_DATA(cmsg)) = opt_id;
err = sendmsg(fd, msg, 0);”h]”hX  struct msghdr *msg;
...
cmsg                         = CMSG_FIRSTHDR(msg);
cmsg->cmsg_level             = SOL_SOCKET;
cmsg->cmsg_type              = SCM_TS_OPT_ID;
cmsg->cmsg_len               = CMSG_LEN(sizeof(__u32));
*((__u32 *) CMSG_DATA(cmsg)) = opt_id;
err = sendmsg(fd, msg, 0);”…””}”hj]  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1j~  hŸh³h KÑhj  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1j  hj  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hïhŸh³h KÙhjÿ  ubhð)”}”(hX  SOF_TIMESTAMPING_OPT_ID_TCP:
Pass this modifier along with SOF_TIMESTAMPING_OPT_ID for new TCP
timestamping applications. SOF_TIMESTAMPING_OPT_ID defines how the
counter increments for stream sockets, but its starting point is
not entirely trivial. This option fixes that.

For stream sockets, if SOF_TIMESTAMPING_OPT_ID is set, this should
always be set too. On datagram sockets the option has no effect.

A reasonable expectation is that the counter is reset to zero with
the system call, so that a subsequent write() of N bytes generates
a timestamp with counter N-1. SOF_TIMESTAMPING_OPT_ID_TCP
implements this behavior under all conditions.

SOF_TIMESTAMPING_OPT_ID without modifier often reports the same,
especially when the socket option is set when no data is in
transmission. If data is being transmitted, it may be off by the
length of the output queue (SIOCOUTQ).

The difference is due to being based on snd_una versus write_seq.
snd_una is the offset in the stream acknowledged by the peer. This
depends on factors outside of process control, such as network RTT.
write_seq is the last byte written by the process. This offset is
not affected by external inputs.

The difference is subtle and unlikely to be noticed when configured
at initial socket creation, when no data is queued or sent. But
SOF_TIMESTAMPING_OPT_ID_TCP behavior is more robust regardless of
when the socket option is set.
”h]”(hö)”}”(hŒSOF_TIMESTAMPING_OPT_ID_TCP:”h]”hŒSOF_TIMESTAMPING_OPT_ID_TCP:”…””}”(hj{  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hõhŸh³h K÷hjw  ubj  )”}”(hhh]”(hÛ)”}”(hŒóPass this modifier along with SOF_TIMESTAMPING_OPT_ID for new TCP
timestamping applications. SOF_TIMESTAMPING_OPT_ID defines how the
counter increments for stream sockets, but its starting point is
not entirely trivial. This option fixes that.”h]”hŒóPass this modifier along with SOF_TIMESTAMPING_OPT_ID for new TCP
timestamping applications. SOF_TIMESTAMPING_OPT_ID defines how the
counter increments for stream sockets, but its starting point is
not entirely trivial. This option fixes that.”…””}”(hjŒ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h KÜhj‰  ubhÛ)”}”(hŒƒFor stream sockets, if SOF_TIMESTAMPING_OPT_ID is set, this should
always be set too. On datagram sockets the option has no effect.”h]”hŒƒFor stream sockets, if SOF_TIMESTAMPING_OPT_ID is set, this should
always be set too. On datagram sockets the option has no effect.”…””}”(hjš  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h Káhj‰  ubhÛ)”}”(hŒîA reasonable expectation is that the counter is reset to zero with
the system call, so that a subsequent write() of N bytes generates
a timestamp with counter N-1. SOF_TIMESTAMPING_OPT_ID_TCP
implements this behavior under all conditions.”h]”hŒîA reasonable expectation is that the counter is reset to zero with
the system call, so that a subsequent write() of N bytes generates
a timestamp with counter N-1. SOF_TIMESTAMPING_OPT_ID_TCP
implements this behavior under all conditions.”…””}”(hj¨  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h Kähj‰  ubhÛ)”}”(hŒäSOF_TIMESTAMPING_OPT_ID without modifier often reports the same,
especially when the socket option is set when no data is in
transmission. If data is being transmitted, it may be off by the
length of the output queue (SIOCOUTQ).”h]”hŒäSOF_TIMESTAMPING_OPT_ID without modifier often reports the same,
especially when the socket option is set when no data is in
transmission. If data is being transmitted, it may be off by the
length of the output queue (SIOCOUTQ).”…””}”(hj¶  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h Kéhj‰  ubhÛ)”}”(hX+  The difference is due to being based on snd_una versus write_seq.
snd_una is the offset in the stream acknowledged by the peer. This
depends on factors outside of process control, such as network RTT.
write_seq is the last byte written by the process. This offset is
not affected by external inputs.”h]”hX+  The difference is due to being based on snd_una versus write_seq.
snd_una is the offset in the stream acknowledged by the peer. This
depends on factors outside of process control, such as network RTT.
write_seq is the last byte written by the process. This offset is
not affected by external inputs.”…””}”(hjÄ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h Kîhj‰  ubhÛ)”}”(hŒäThe difference is subtle and unlikely to be noticed when configured
at initial socket creation, when no data is queued or sent. But
SOF_TIMESTAMPING_OPT_ID_TCP behavior is more robust regardless of
when the socket option is set.”h]”hŒäThe difference is subtle and unlikely to be noticed when configured
at initial socket creation, when no data is queued or sent. But
SOF_TIMESTAMPING_OPT_ID_TCP behavior is more robust regardless of
when the socket option is set.”…””}”(hjÒ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h Kôhj‰  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1j  hjw  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hïhŸh³h K÷hjÿ  hžhubhð)”}”(hXŽ  SOF_TIMESTAMPING_OPT_CMSG:
Support recv() cmsg for all timestamped packets. Control messages
are already supported unconditionally on all packets with receive
timestamps and on IPv6 packets with transmit timestamp. This option
extends them to IPv4 packets with transmit timestamp. One use case
is to correlate packets with their egress device, by enabling socket
option IP_PKTINFO simultaneously.

”h]”(hö)”}”(hŒSOF_TIMESTAMPING_OPT_CMSG:”h]”hŒSOF_TIMESTAMPING_OPT_CMSG:”…””}”(hjð  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hõhŸh³h M hjì  ubj  )”}”(hhh]”hÛ)”}”(hXq  Support recv() cmsg for all timestamped packets. Control messages
are already supported unconditionally on all packets with receive
timestamps and on IPv6 packets with transmit timestamp. This option
extends them to IPv4 packets with transmit timestamp. One use case
is to correlate packets with their egress device, by enabling socket
option IP_PKTINFO simultaneously.”h]”hXq  Support recv() cmsg for all timestamped packets. Control messages
are already supported unconditionally on all packets with receive
timestamps and on IPv6 packets with transmit timestamp. This option
extends them to IPv4 packets with transmit timestamp. One use case
is to correlate packets with their egress device, by enabling socket
option IP_PKTINFO simultaneously.”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h Kúhjþ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hjì  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hïhŸh³h M hjÿ  hžhubhð)”}”(hXŠ  SOF_TIMESTAMPING_OPT_TSONLY:
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.
”h]”(hö)”}”(hŒSOF_TIMESTAMPING_OPT_TSONLY:”h]”hŒSOF_TIMESTAMPING_OPT_TSONLY:”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hõhŸh³h Mhj  ubj  )”}”(hhh]”hÛ)”}”(hXl  Applies to transmit timestamps only. Makes the kernel return the
timestamp as a cmsg alongside an empty packet, as opposed to
alongside the original packet. This reduces the amount of memory
charged to the socket's receive budget (SO_RCVBUF) and delivers
the timestamp even if sysctl net.core.tstamp_allow_data is 0.
This option disables SOF_TIMESTAMPING_OPT_CMSG.”h]”hXn  Applies to transmit timestamps only. Makes the kernel return the
timestamp as a cmsg alongside an empty packet, as opposed to
alongside the original packet. This reduces the amount of memory
charged to the socketâ€™s receive budget (SO_RCVBUF) and delivers
the timestamp even if sysctl net.core.tstamp_allow_data is 0.
This option disables SOF_TIMESTAMPING_OPT_CMSG.”…””}”(hj0  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h Mhj-  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hj  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hïhŸh³h Mhjÿ  hžhubhð)”}”(hX  SOF_TIMESTAMPING_OPT_STATS:
Optional stats that are obtained along with the transmit timestamps.
It must be used together with SOF_TIMESTAMPING_OPT_TSONLY. When the
transmit timestamp is available, the stats are available in a
separate control message of type SCM_TIMESTAMPING_OPT_STATS, as a
list of TLVs (struct nlattr) of types. These stats allow the
application to associate various transport layer stats with
the transmit timestamps, such as how long a certain block of
data was limited by peer's receiver window.
”h]”(hö)”}”(hŒSOF_TIMESTAMPING_OPT_STATS:”h]”hŒSOF_TIMESTAMPING_OPT_STATS:”…””}”(hjN  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hõhŸh³h MhjJ  ubj  )”}”(hhh]”hÛ)”}”(hXê  Optional stats that are obtained along with the transmit timestamps.
It must be used together with SOF_TIMESTAMPING_OPT_TSONLY. When the
transmit timestamp is available, the stats are available in a
separate control message of type SCM_TIMESTAMPING_OPT_STATS, as a
list of TLVs (struct nlattr) of types. These stats allow the
application to associate various transport layer stats with
the transmit timestamps, such as how long a certain block of
data was limited by peer's receiver window.”h]”hXì  Optional stats that are obtained along with the transmit timestamps.
It must be used together with SOF_TIMESTAMPING_OPT_TSONLY. When the
transmit timestamp is available, the stats are available in a
separate control message of type SCM_TIMESTAMPING_OPT_STATS, as a
list of TLVs (struct nlattr) of types. These stats allow the
application to associate various transport layer stats with
the transmit timestamps, such as how long a certain block of
data was limited by peerâ€™s receiver window.”…””}”(hj_  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h Mhj\  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hjJ  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hïhŸh³h Mhjÿ  hžhubhð)”}”(hXÞ  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.
”h]”(hö)”}”(hŒSOF_TIMESTAMPING_OPT_PKTINFO:”h]”hŒSOF_TIMESTAMPING_OPT_PKTINFO:”…””}”(hj}  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hõhŸh³h Mhjy  ubj  )”}”(hhh]”hÛ)”}”(hX¿  Enable the SCM_TIMESTAMPING_PKTINFO control message for incoming
packets with hardware timestamps. The message contains struct
scm_ts_pktinfo, which supplies the index of the real interface which
received the packet and its length at layer 2. A valid (non-zero)
interface index will be returned only if CONFIG_NET_RX_BUSY_POLL is
enabled and the driver is using NAPI. The struct contains also two
other fields, but they are reserved and undefined.”h]”hX¿  Enable the SCM_TIMESTAMPING_PKTINFO control message for incoming
packets with hardware timestamps. The message contains struct
scm_ts_pktinfo, which supplies the index of the real interface which
received the packet and its length at layer 2. A valid (non-zero)
interface index will be returned only if CONFIG_NET_RX_BUSY_POLL is
enabled and the driver is using NAPI. The struct contains also two
other fields, but they are reserved and undefined.”…””}”(hjŽ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h Mhj‹  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hjy  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hïhŸh³h Mhjÿ  hžhubhð)”}”(hXJ  SOF_TIMESTAMPING_OPT_TX_SWHW:
Request both hardware and software timestamps for outgoing packets
when SOF_TIMESTAMPING_TX_HARDWARE and SOF_TIMESTAMPING_TX_SOFTWARE
are enabled at the same time. If both timestamps are generated,
two separate messages will be looped to the socket's error queue,
each containing just one timestamp.
”h]”(hö)”}”(hŒSOF_TIMESTAMPING_OPT_TX_SWHW:”h]”hŒSOF_TIMESTAMPING_OPT_TX_SWHW:”…””}”(hj¬  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hõhŸh³h M"hj¨  ubj  )”}”(hhh]”hÛ)”}”(hX+  Request both hardware and software timestamps for outgoing packets
when SOF_TIMESTAMPING_TX_HARDWARE and SOF_TIMESTAMPING_TX_SOFTWARE
are enabled at the same time. If both timestamps are generated,
two separate messages will be looped to the socket's error queue,
each containing just one timestamp.”h]”hX-  Request both hardware and software timestamps for outgoing packets
when SOF_TIMESTAMPING_TX_HARDWARE and SOF_TIMESTAMPING_TX_SOFTWARE
are enabled at the same time. If both timestamps are generated,
two separate messages will be looped to the socketâ€™s error queue,
each containing just one timestamp.”…””}”(hj½  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h Mhjº  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hj¨  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hïhŸh³h M"hjÿ  hžhubhð)”}”(hX.  SOF_TIMESTAMPING_OPT_RX_FILTER:
Filter out spurious receive timestamps: report a receive timestamp
only if the matching timestamp generation flag is enabled.

Receive timestamps are generated early in the ingress path, before a
packet's destination socket is known. If any socket enables receive
timestamps, packets for all socket will receive timestamped packets.
Including those that request timestamp reporting with
SOF_TIMESTAMPING_SOFTWARE and/or SOF_TIMESTAMPING_RAW_HARDWARE, but
do not request receive timestamp generation. This can happen when
requesting transmit timestamps only.

Receiving spurious timestamps is generally benign. A process can
ignore the unexpected non-zero value. But it makes behavior subtly
dependent on other sockets. This flag isolates the socket for more
deterministic behavior.
”h]”(hö)”}”(hŒSOF_TIMESTAMPING_OPT_RX_FILTER:”h]”hŒSOF_TIMESTAMPING_OPT_RX_FILTER:”…””}”(hjÛ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hõhŸh³h M3hj×  ubj  )”}”(hhh]”(hÛ)”}”(hŒ}Filter out spurious receive timestamps: report a receive timestamp
only if the matching timestamp generation flag is enabled.”h]”hŒ}Filter out spurious receive timestamps: report a receive timestamp
only if the matching timestamp generation flag is enabled.”…””}”(hjì  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h M%hjé  ubhÛ)”}”(hX®  Receive timestamps are generated early in the ingress path, before a
packet's destination socket is known. If any socket enables receive
timestamps, packets for all socket will receive timestamped packets.
Including those that request timestamp reporting with
SOF_TIMESTAMPING_SOFTWARE and/or SOF_TIMESTAMPING_RAW_HARDWARE, but
do not request receive timestamp generation. This can happen when
requesting transmit timestamps only.”h]”hX°  Receive timestamps are generated early in the ingress path, before a
packetâ€™s destination socket is known. If any socket enables receive
timestamps, packets for all socket will receive timestamped packets.
Including those that request timestamp reporting with
SOF_TIMESTAMPING_SOFTWARE and/or SOF_TIMESTAMPING_RAW_HARDWARE, but
do not request receive timestamp generation. This can happen when
requesting transmit timestamps only.”…””}”(hjú  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h M(hjé  ubhÛ)”}”(hŒÞReceiving spurious timestamps is generally benign. A process can
ignore the unexpected non-zero value. But it makes behavior subtly
dependent on other sockets. This flag isolates the socket for more
deterministic behavior.”h]”hŒÞReceiving spurious timestamps is generally benign. A process can
ignore the unexpected non-zero value. But it makes behavior subtly
dependent on other sockets. This flag isolates the socket for more
deterministic behavior.”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h M0hjé  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1j  hj×  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hïhŸh³h M3hjÿ  hžhubeh}”(h]”h ]”h"]”h$]”h&]”uh1hêhjà  hžhhŸh³h NubhÛ)”}”(hŒÅNew applications are encouraged to pass SOF_TIMESTAMPING_OPT_ID to
disambiguate timestamps and SOF_TIMESTAMPING_OPT_TSONLY to operate
regardless of the setting of sysctl net.core.tstamp_allow_data.”h]”hŒÅNew applications are encouraged to pass SOF_TIMESTAMPING_OPT_ID to
disambiguate timestamps and SOF_TIMESTAMPING_OPT_TSONLY to operate
regardless of the setting of sysctl net.core.tstamp_allow_data.”…””}”(hj(  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h M5hjà  hžhubhÛ)”}”(hX2  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
combined with SOF_TIMESTAMPING_OPT_TSONLY.”h]”hX2  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
combined with SOF_TIMESTAMPING_OPT_TSONLY.”…””}”(hj6  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h M9hjà  hžhubeh}”(h]”Œtimestamp-options”ah ]”h"]”Œ1.3.3 timestamp options”ah$]”h&]”uh1h´hj_  hžhhŸh³h K®ubhµ)”}”(hhh]”(hº)”}”(hŒ/1.3.4. Enabling timestamps via control messages”h]”hŒ/1.3.4. Enabling timestamps via control messages”…””}”(hjO  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hjL  hžhhŸh³h MAubhÛ)”}”(hX#  In addition to socket options, timestamp generation can be requested
per write via cmsg, only for SOF_TIMESTAMPING_TX_* (see Section 1.3.1).
Using this feature, applications can sample timestamps per sendmsg()
without paying the overhead of enabling and disabling timestamps via
setsockopt::”h]”hX"  In addition to socket options, timestamp generation can be requested
per write via cmsg, only for SOF_TIMESTAMPING_TX_* (see Section 1.3.1).
Using this feature, applications can sample timestamps per sendmsg()
without paying the overhead of enabling and disabling timestamps via
setsockopt:”…””}”(hj]  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h MChjL  hžhubj  )”}”(hX©  struct msghdr *msg;
...
cmsg                         = CMSG_FIRSTHDR(msg);
cmsg->cmsg_level             = SOL_SOCKET;
cmsg->cmsg_type              = SO_TIMESTAMPING;
cmsg->cmsg_len               = CMSG_LEN(sizeof(__u32));
*((__u32 *) CMSG_DATA(cmsg)) = SOF_TIMESTAMPING_TX_SCHED |
                               SOF_TIMESTAMPING_TX_SOFTWARE |
                               SOF_TIMESTAMPING_TX_ACK;
err = sendmsg(fd, msg, 0);”h]”hX©  struct msghdr *msg;
...
cmsg                         = CMSG_FIRSTHDR(msg);
cmsg->cmsg_level             = SOL_SOCKET;
cmsg->cmsg_type              = SO_TIMESTAMPING;
cmsg->cmsg_len               = CMSG_LEN(sizeof(__u32));
*((__u32 *) CMSG_DATA(cmsg)) = SOF_TIMESTAMPING_TX_SCHED |
                               SOF_TIMESTAMPING_TX_SOFTWARE |
                               SOF_TIMESTAMPING_TX_ACK;
err = sendmsg(fd, msg, 0);”…””}”hjk  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1j~  hŸh³h MIhjL  hžhubhÛ)”}”(hŒnThe SOF_TIMESTAMPING_TX_* flags set via cmsg will override
the SOF_TIMESTAMPING_TX_* flags set via setsockopt.”h]”hŒnThe SOF_TIMESTAMPING_TX_* flags set via cmsg will override
the SOF_TIMESTAMPING_TX_* flags set via setsockopt.”…””}”(hjy  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h MThjL  hžhubhÛ)”}”(hŒcMoreover, applications must still enable timestamp reporting via
setsockopt to receive timestamps::”h]”hŒbMoreover, applications must still enable timestamp reporting via
setsockopt to receive timestamps:”…””}”(hj‡  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h MWhjL  hžhubj  )”}”(hŒª__u32 val = SOF_TIMESTAMPING_SOFTWARE |
            SOF_TIMESTAMPING_OPT_ID /* or any other flag */;
err = setsockopt(fd, SOL_SOCKET, SO_TIMESTAMPING, &val, sizeof(val));”h]”hŒª__u32 val = SOF_TIMESTAMPING_SOFTWARE |
            SOF_TIMESTAMPING_OPT_ID /* or any other flag */;
err = setsockopt(fd, SOL_SOCKET, SO_TIMESTAMPING, &val, sizeof(val));”…””}”hj•  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1j~  hŸh³h MZhjL  hžhubeh}”(h]”Œ(enabling-timestamps-via-control-messages”ah ]”h"]”Œ/1.3.4. enabling timestamps via control messages”ah$]”h&]”uh1h´hj_  hžhhŸh³h MAubeh}”(h]”Œ@so-timestamping-also-so-timestamping-old-and-so-timestamping-new”ah ]”h"]”ŒF1.3 so_timestamping (also so_timestamping_old and so_timestamping_new)”ah$]”h&]”uh1h´hhÉhžhhŸh³h KHubhµ)”}”(hhh]”(hº)”}”(hŒ1.4 Bytestream Timestamps”h]”hŒ1.4 Bytestream Timestamps”…””}”(hj¶  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hj³  hžhhŸh³h M`ubhÛ)”}”(hXw  The SO_TIMESTAMPING interface supports timestamping of bytes in a
bytestream. Each request is interpreted as a request for when the
entire contents of the buffer has passed a timestamping point. That
is, for streams option SOF_TIMESTAMPING_TX_SOFTWARE will record
when all bytes have reached the device driver, regardless of how
many packets the data has been converted into.”h]”hXw  The SO_TIMESTAMPING interface supports timestamping of bytes in a
bytestream. Each request is interpreted as a request for when the
entire contents of the buffer has passed a timestamping point. That
is, for streams option SOF_TIMESTAMPING_TX_SOFTWARE will record
when all bytes have reached the device driver, regardless of how
many packets the data has been converted into.”…””}”(hjÄ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h Mbhj³  hžhubhÛ)”}”(hX¦  In general, bytestreams have no natural delimiters and therefore
correlating a timestamp with data is non-trivial. A range of bytes
may be split across segments, any segments may be merged (possibly
coalescing sections of previously segmented buffers associated with
independent send() calls). Segments can be reordered and the same
byte range can coexist in multiple segments for protocols that
implement retransmissions.”h]”hX¦  In general, bytestreams have no natural delimiters and therefore
correlating a timestamp with data is non-trivial. A range of bytes
may be split across segments, any segments may be merged (possibly
coalescing sections of previously segmented buffers associated with
independent send() calls). Segments can be reordered and the same
byte range can coexist in multiple segments for protocols that
implement retransmissions.”…””}”(hjÒ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h Mihj³  hžhubhÛ)”}”(hXI  It is essential that all timestamps implement the same semantics,
regardless of these possible transformations, as otherwise they are
incomparable. Handling "rare" corner cases differently from the
simple case (a 1:1 mapping from buffer to skb) is insufficient
because performance debugging often needs to focus on such outliers.”h]”hXM  It is essential that all timestamps implement the same semantics,
regardless of these possible transformations, as otherwise they are
incomparable. Handling â€œrareâ€ corner cases differently from the
simple case (a 1:1 mapping from buffer to skb) is insufficient
because performance debugging often needs to focus on such outliers.”…””}”(hjà  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h Mqhj³  hžhubhÛ)”}”(hXv  In practice, timestamps can be correlated with segments of a
bytestream consistently, if both semantics of the timestamp and the
timing of measurement are chosen correctly. This challenge is no
different from deciding on a strategy for IP fragmentation. There, the
definition is that only the first fragment is timestamped. For
bytestreams, we chose that a timestamp is generated only when all
bytes have passed a point. SOF_TIMESTAMPING_TX_ACK as defined is easy to
implement and reason about. An implementation that has to take into
account SACK would be more complex due to possible transmission holes
and out of order arrival.”h]”hXv  In practice, timestamps can be correlated with segments of a
bytestream consistently, if both semantics of the timestamp and the
timing of measurement are chosen correctly. This challenge is no
different from deciding on a strategy for IP fragmentation. There, the
definition is that only the first fragment is timestamped. For
bytestreams, we chose that a timestamp is generated only when all
bytes have passed a point. SOF_TIMESTAMPING_TX_ACK as defined is easy to
implement and reason about. An implementation that has to take into
account SACK would be more complex due to possible transmission holes
and out of order arrival.”…””}”(hjî  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h Mwhj³  hžhubhÛ)”}”(hXÖ  On the host, TCP can also break the simple 1:1 mapping from buffer to
skbuff as a result of Nagle, cork, autocork, segmentation and GSO. The
implementation ensures correctness in all cases by tracking the
individual last byte passed to send(), even if it is no longer the
last byte after an skbuff extend or merge operation. It stores the
relevant sequence number in skb_shinfo(skb)->tskey. Because an skbuff
has only one such field, only one timestamp can be generated.”h]”hXÖ  On the host, TCP can also break the simple 1:1 mapping from buffer to
skbuff as a result of Nagle, cork, autocork, segmentation and GSO. The
implementation ensures correctness in all cases by tracking the
individual last byte passed to send(), even if it is no longer the
last byte after an skbuff extend or merge operation. It stores the
relevant sequence number in skb_shinfo(skb)->tskey. Because an skbuff
has only one such field, only one timestamp can be generated.”…””}”(hjü  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h M‚hj³  hžhubhÛ)”}”(hXû  In rare cases, a timestamp request can be missed if two requests are
collapsed onto the same skb. A process can detect this situation by
enabling SOF_TIMESTAMPING_OPT_ID and comparing the byte offset at
send time with the value returned for each timestamp. It can prevent
the situation by always flushing the TCP stack in between requests,
for instance by enabling TCP_NODELAY and disabling TCP_CORK and
autocork. After linux-4.7, a better way to prevent coalescing is
to use MSG_EOR flag at sendmsg() time.”h]”hXû  In rare cases, a timestamp request can be missed if two requests are
collapsed onto the same skb. A process can detect this situation by
enabling SOF_TIMESTAMPING_OPT_ID and comparing the byte offset at
send time with the value returned for each timestamp. It can prevent
the situation by always flushing the TCP stack in between requests,
for instance by enabling TCP_NODELAY and disabling TCP_CORK and
autocork. After linux-4.7, a better way to prevent coalescing is
to use MSG_EOR flag at sendmsg() time.”…””}”(hj
  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h MŠhj³  hžhubhÛ)”}”(hX¢  These precautions ensure that the timestamp is generated only when all
bytes have passed a timestamp point, assuming that the network stack
itself does not reorder the segments. The stack indeed tries to avoid
reordering. The one exception is under administrator control: it is
possible to construct a packet scheduler configuration that delays
segments from the same stream differently. Such a setup would be
unusual.”h]”hX¢  These precautions ensure that the timestamp is generated only when all
bytes have passed a timestamp point, assuming that the network stack
itself does not reorder the segments. The stack indeed tries to avoid
reordering. The one exception is under administrator control: it is
possible to construct a packet scheduler configuration that delays
segments from the same stream differently. Such a setup would be
unusual.”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h M“hj³  hžhubeh}”(h]”Œbytestream-timestamps”ah ]”h"]”Œ1.4 bytestream timestamps”ah$]”h&]”uh1h´hhÉhžhhŸh³h M`ubeh}”(h]”Œcontrol-interfaces”ah ]”h"]”Œ1. control interfaces”ah$]”h&]”uh1h´hh¶hžhhŸh³h K	ubhµ)”}”(hhh]”(hº)”}”(hŒ2 Data Interfaces”h]”hŒ2 Data Interfaces”…””}”(hj9  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hj6  hžhhŸh³h MubhÛ)”}”(hŒüTimestamps are read using the ancillary data feature of recvmsg().
See `man 3 cmsg` for details of this interface. The socket manual
page (`man 7 socket`) describes how timestamps generated with
SO_TIMESTAMP and SO_TIMESTAMPNS records can be retrieved.”h]”(hŒGTimestamps are read using the ancillary data feature of recvmsg().
See ”…””}”(hjG  hžhhŸNh Nubjß  )”}”(hŒ`man 3 cmsg`”h]”hŒ
man 3 cmsg”…””}”(hjO  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jÞ  hjG  ubhŒ8 for details of this interface. The socket manual
page (”…””}”(hjG  hžhhŸNh Nubjß  )”}”(hŒ`man 7 socket`”h]”hŒman 7 socket”…””}”(hja  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jÞ  hjG  ubhŒc) describes how timestamps generated with
SO_TIMESTAMP and SO_TIMESTAMPNS records can be retrieved.”…””}”(hjG  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h MŸhj6  hžhubhµ)”}”(hhh]”(hº)”}”(hŒ2.1 SCM_TIMESTAMPING records”h]”hŒ2.1 SCM_TIMESTAMPING records”…””}”(hj|  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hjy  hžhhŸh³h M¦ubhÛ)”}”(hŒ~These timestamps are returned in a control message with cmsg_level
SOL_SOCKET, cmsg_type SCM_TIMESTAMPING, and payload of type”h]”hŒ~These timestamps are returned in a control message with cmsg_level
SOL_SOCKET, cmsg_type SCM_TIMESTAMPING, and payload of type”…””}”(hjŠ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h M¨hjy  hžhubhÛ)”}”(hŒFor SO_TIMESTAMPING_OLD::”h]”hŒFor SO_TIMESTAMPING_OLD:”…””}”(hj˜  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h M«hjy  hžhubj  )”}”(hŒ;struct scm_timestamping {
        struct timespec ts[3];
};”h]”hŒ;struct scm_timestamping {
        struct timespec ts[3];
};”…””}”hj¦  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1j~  hŸh³h M­hjy  hžhubhÛ)”}”(hŒFor SO_TIMESTAMPING_NEW::”h]”hŒFor SO_TIMESTAMPING_NEW:”…””}”(hj´  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h M±hjy  hžhubj  )”}”(hŒCstruct scm_timestamping64 {
        struct __kernel_timespec ts[3];”h]”hŒCstruct scm_timestamping64 {
        struct __kernel_timespec ts[3];”…””}”hjÂ  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1j~  hŸh³h M³hjy  hžhubhÛ)”}”(hŒeAlways use SO_TIMESTAMPING_NEW timestamp to always get timestamp in
struct scm_timestamping64 format.”h]”hŒeAlways use SO_TIMESTAMPING_NEW timestamp to always get timestamp in
struct scm_timestamping64 format.”…””}”(hjÐ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h M¶hjy  hžhubhÛ)”}”(hŒXSO_TIMESTAMPING_OLD returns incorrect timestamps after the year 2038
on 32 bit machines.”h]”hŒXSO_TIMESTAMPING_OLD returns incorrect timestamps after the year 2038
on 32 bit machines.”…””}”(hjÞ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h M¹hjy  hžhubhÛ)”}”(hŒÄThe 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].”h]”hŒÄThe 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].”…””}”(hjì  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h M¼hjy  hžhubhÛ)”}”(hXO  ts[1] used to hold hardware timestamps converted to system time.
Instead, expose the hardware clock device on the NIC directly as
a HW PTP clock source, to allow time conversion in userspace and
optionally synchronize system time with a userspace PTP stack such
as linuxptp. For the PTP clock API, see Documentation/driver-api/ptp.rst.”h]”hXO  ts[1] used to hold hardware timestamps converted to system time.
Instead, expose the hardware clock device on the NIC directly as
a HW PTP clock source, to allow time conversion in userspace and
optionally synchronize system time with a userspace PTP stack such
as linuxptp. For the PTP clock API, see Documentation/driver-api/ptp.rst.”…””}”(hjú  hžhhŸNh Nuba•šö      h}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h MÀhjy  hžhubhÛ)”}”(hX5  Note that if the SO_TIMESTAMP or SO_TIMESTAMPNS option is enabled
together with SO_TIMESTAMPING using SOF_TIMESTAMPING_SOFTWARE, a false
software timestamp will be generated in the recvmsg() call and passed
in ts[0] when a real software timestamp is missing. This happens also
on hardware transmit timestamps.”h]”hX5  Note that if the SO_TIMESTAMP or SO_TIMESTAMPNS option is enabled
together with SO_TIMESTAMPING using SOF_TIMESTAMPING_SOFTWARE, a false
software timestamp will be generated in the recvmsg() call and passed
in ts[0] when a real software timestamp is missing. This happens also
on hardware transmit timestamps.”…””}”(hj	  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h MÆhjy  hžhubhµ)”}”(hhh]”(hº)”}”(hŒ+2.1.1 Transmit timestamps with MSG_ERRQUEUE”h]”hŒ+2.1.1 Transmit timestamps with MSG_ERRQUEUE”…””}”(hj	  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hj	  hžhhŸh³h MÍubhÛ)”}”(hXŒ  For transmit timestamps the outgoing packet is looped back to the
socket's error queue with the send timestamp(s) attached. A process
receives the timestamps by calling recvmsg() with flag MSG_ERRQUEUE
set and with a msg_control buffer sufficiently large to receive the
relevant metadata structures. The recvmsg call returns the original
outgoing data packet with two ancillary messages attached.”h]”hXŽ  For transmit timestamps the outgoing packet is looped back to the
socketâ€™s error queue with the send timestamp(s) attached. A process
receives the timestamps by calling recvmsg() with flag MSG_ERRQUEUE
set and with a msg_control buffer sufficiently large to receive the
relevant metadata structures. The recvmsg call returns the original
outgoing data packet with two ancillary messages attached.”…””}”(hj'	  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h MÏhj	  hžhubhÛ)”}”(hX*  A message of cm_level SOL_IP(V6) and cm_type IP(V6)_RECVERR
embeds a struct sock_extended_err. This defines the error type. For
timestamps, the ee_errno field is ENOMSG. The other ancillary message
will have cm_level SOL_SOCKET and cm_type SCM_TIMESTAMPING. This
embeds the struct scm_timestamping.”h]”hX*  A message of cm_level SOL_IP(V6) and cm_type IP(V6)_RECVERR
embeds a struct sock_extended_err. This defines the error type. For
timestamps, the ee_errno field is ENOMSG. The other ancillary message
will have cm_level SOL_SOCKET and cm_type SCM_TIMESTAMPING. This
embeds the struct scm_timestamping.”…””}”(hj5	  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h MÖhj	  hžhubhµ)”}”(hhh]”(hº)”}”(hŒ2.1.1.2 Timestamp types”h]”hŒ2.1.1.2 Timestamp types”…””}”(hjF	  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hjC	  hžhhŸh³h MÞubhÛ)”}”(hŒÌThe semantics of the three struct timespec are defined by field
ee_info in the extended error structure. It contains a value of
type SCM_TSTAMP_* to define the actual timestamp passed in
scm_timestamping.”h]”hŒÌThe semantics of the three struct timespec are defined by field
ee_info in the extended error structure. It contains a value of
type SCM_TSTAMP_* to define the actual timestamp passed in
scm_timestamping.”…””}”(hjT	  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h MàhjC	  hžhubhÛ)”}”(hXp  The SCM_TSTAMP_* types are 1:1 matches to the SOF_TIMESTAMPING_*
control fields discussed previously, with one exception. For legacy
reasons, SCM_TSTAMP_SND is equal to zero and can be set for both
SOF_TIMESTAMPING_TX_HARDWARE and SOF_TIMESTAMPING_TX_SOFTWARE. It
is the first if ts[2] is non-zero, the second otherwise, in which
case the timestamp is stored in ts[0].”h]”hXp  The SCM_TSTAMP_* types are 1:1 matches to the SOF_TIMESTAMPING_*
control fields discussed previously, with one exception. For legacy
reasons, SCM_TSTAMP_SND is equal to zero and can be set for both
SOF_TIMESTAMPING_TX_HARDWARE and SOF_TIMESTAMPING_TX_SOFTWARE. It
is the first if ts[2] is non-zero, the second otherwise, in which
case the timestamp is stored in ts[0].”…””}”(hjb	  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h MåhjC	  hžhubeh}”(h]”Œtimestamp-types”ah ]”h"]”Œ2.1.1.2 timestamp types”ah$]”h&]”uh1h´hj	  hžhhŸh³h MÞubhµ)”}”(hhh]”(hº)”}”(hŒ2.1.1.3 Fragmentation”h]”hŒ2.1.1.3 Fragmentation”…””}”(hj{	  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hjx	  hžhhŸh³h MîubhÛ)”}”(hŒàFragmentation of outgoing datagrams is rare, but is possible, e.g., by
explicitly disabling PMTU discovery. If an outgoing packet is fragmented,
then only the first fragment is timestamped and returned to the sending
socket.”h]”hŒàFragmentation of outgoing datagrams is rare, but is possible, e.g., by
explicitly disabling PMTU discovery. If an outgoing packet is fragmented,
then only the first fragment is timestamped and returned to the sending
socket.”…””}”(hj‰	  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h Mðhjx	  hžhubeh}”(h]”Œfragmentation”ah ]”h"]”Œ2.1.1.3 fragmentation”ah$]”h&]”uh1h´hj	  hžhhŸh³h Mîubhµ)”}”(hhh]”(hº)”}”(hŒ2.1.1.4 Packet Payload”h]”hŒ2.1.1.4 Packet Payload”…””}”(hj¢	  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hjŸ	  hžhhŸh³h M÷ubhÛ)”}”(hXÜ  The calling application is often not interested in receiving the whole
packet payload that it passed to the stack originally: the socket
error queue mechanism is just a method to piggyback the timestamp on.
In this case, the application can choose to read datagrams with a
smaller buffer, possibly even of length 0. The payload is truncated
accordingly. Until the process calls recvmsg() on the error queue,
however, the full packet is queued, taking up budget from SO_RCVBUF.”h]”hXÜ  The calling application is often not interested in receiving the whole
packet payload that it passed to the stack originally: the socket
error queue mechanism is just a method to piggyback the timestamp on.
In this case, the application can choose to read datagrams with a
smaller buffer, possibly even of length 0. The payload is truncated
accordingly. Until the process calls recvmsg() on the error queue,
however, the full packet is queued, taking up budget from SO_RCVBUF.”…””}”(hj°	  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h MùhjŸ	  hžhubeh}”(h]”Œpacket-payload”ah ]”h"]”Œ2.1.1.4 packet payload”ah$]”h&]”uh1h´hj	  hžhhŸh³h M÷ubhµ)”}”(hhh]”(hº)”}”(hŒ2.1.1.5 Blocking Read”h]”hŒ2.1.1.5 Blocking Read”…””}”(hjÉ	  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hjÆ	  hžhhŸh³h MubhÛ)”}”(hX8  Reading from the error queue is always a non-blocking operation. To
block waiting on a timestamp, use poll or select. poll() will return
POLLERR in pollfd.revents if any data is ready on the error queue.
There is no need to pass this flag in pollfd.events. This flag is
ignored on request. See also `man 2 poll`.”h]”(hX+  Reading from the error queue is always a non-blocking operation. To
block waiting on a timestamp, use poll or select. poll() will return
POLLERR in pollfd.revents if any data is ready on the error queue.
There is no need to pass this flag in pollfd.events. This flag is
ignored on request. See also ”…””}”(hj×	  hžhhŸNh Nubjß  )”}”(hŒ`man 2 poll`”h]”hŒ
man 2 poll”…””}”(hjß	  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jÞ  hj×	  ubhŒ.”…””}”(hj×	  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h MhjÆ	  hžhubeh}”(h]”Œblocking-read”ah ]”h"]”Œ2.1.1.5 blocking read”ah$]”h&]”uh1h´hj	  hžhhŸh³h Mubeh}”(h]”Œ%transmit-timestamps-with-msg-errqueue”ah ]”h"]”Œ+2.1.1 transmit timestamps with msg_errqueue”ah$]”h&]”uh1h´hjy  hžhhŸh³h MÍubhµ)”}”(hhh]”(hº)”}”(hŒ2.1.2 Receive timestamps”h]”hŒ2.1.2 Receive timestamps”…””}”(hj

  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hj
  hžhhŸh³h MubhÛ)”}”(hXÕ  On reception, there is no reason to read from the socket error queue.
The SCM_TIMESTAMPING ancillary data is sent along with the packet data
on a normal recvmsg(). Since this is not a socket error, it is not
accompanied by a message SOL_IP(V6)/IP(V6)_RECVERROR. In this case,
the meaning of the three fields in struct scm_timestamping is
implicitly defined. ts[0] holds a software timestamp if set, ts[1]
is again deprecated and ts[2] holds a hardware timestamp if set.”h]”hXÕ  On reception, there is no reason to read from the socket error queue.
The SCM_TIMESTAMPING ancillary data is sent along with the packet data
on a normal recvmsg(). Since this is not a socket error, it is not
accompanied by a message SOL_IP(V6)/IP(V6)_RECVERROR. In this case,
the meaning of the three fields in struct scm_timestamping is
implicitly defined. ts[0] holds a software timestamp if set, ts[1]
is again deprecated and ts[2] holds a hardware timestamp if set.”…””}”(hj
  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h Mhj
  hžhubeh}”(h]”Œreceive-timestamps”ah ]”h"]”Œ2.1.2 receive timestamps”ah$]”h&]”uh1h´hjy  hžhhŸh³h Mubeh}”(h]”Œscm-timestamping-records”ah ]”h"]”Œ2.1 scm_timestamping records”ah$]”h&]”uh1h´hj6  hžhhŸh³h M¦ubeh}”(h]”Œdata-interfaces”ah ]”h"]”Œ2 data interfaces”ah$]”h&]”uh1h´hh¶hžhhŸh³h Mubhµ)”}”(hhh]”(hº)”}”(hŒD3. Hardware Timestamping configuration: ETHTOOL_MSG_TSCONFIG_SET/GET”h]”hŒD3. Hardware Timestamping configuration: ETHTOOL_MSG_TSCONFIG_SET/GET”…””}”(hjA
  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hj>
  hžhhŸh³h MubhÛ)”}”(hŒ¶Hardware time stamping must also be initialized for each device driver
that is expected to do hardware time stamping. The parameter is defined in
include/uapi/linux/net_tstamp.h as::”h]”hŒµHardware time stamping must also be initialized for each device driver
that is expected to do hardware time stamping. The parameter is defined in
include/uapi/linux/net_tstamp.h as:”…””}”(hjO
  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h Mhj>
  hžhubj  )”}”(hŒ¾struct hwtstamp_config {
        int flags;      /* no flags defined right now, must be zero */
        int tx_type;    /* HWTSTAMP_TX_* */
        int rx_filter;  /* HWTSTAMP_FILTER_* */
};”h]”hŒ¾struct hwtstamp_config {
        int flags;      /* no flags defined right now, must be zero */
        int tx_type;    /* HWTSTAMP_TX_* */
        int rx_filter;  /* HWTSTAMP_FILTER_* */
};”…””}”hj]
  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1j~  hŸh³h Mhj>
  hžhubhÛ)”}”(hXI  Desired behavior is passed into the kernel and to a specific device by
calling the tsconfig netlink socket ``ETHTOOL_MSG_TSCONFIG_SET``.
The ``ETHTOOL_A_TSCONFIG_TX_TYPES``, ``ETHTOOL_A_TSCONFIG_RX_FILTERS`` and
``ETHTOOL_A_TSCONFIG_HWTSTAMP_FLAGS`` netlink attributes are then used to set
the struct hwtstamp_config accordingly.”h]”(hŒkDesired behavior is passed into the kernel and to a specific device by
calling the tsconfig netlink socket ”…””}”(hjk
  hžhhŸNh NubhŒliteral”“”)”}”(hŒ``ETHTOOL_MSG_TSCONFIG_SET``”h]”hŒETHTOOL_MSG_TSCONFIG_SET”…””}”(hju
  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1js
  hjk
  ubhŒ.
The ”…””}”(hjk
  hžhhŸNh Nubjt
  )”}”(hŒ``ETHTOOL_A_TSCONFIG_TX_TYPES``”h]”hŒETHTOOL_A_TSCONFIG_TX_TYPES”…””}”(hj‡
  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1js
  hjk
  ubhŒ, ”…””}”(hjk
  hžhhŸNh Nubjt
  )”}”(hŒ!``ETHTOOL_A_TSCONFIG_RX_FILTERS``”h]”hŒETHTOOL_A_TSCONFIG_RX_FILTERS”…””}”(hj™
  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1js
  hjk
  ubhŒ and
”…””}”(hjk
  hžhhŸNh Nubjt
  )”}”(hŒ%``ETHTOOL_A_TSCONFIG_HWTSTAMP_FLAGS``”h]”hŒ!ETHTOOL_A_TSCONFIG_HWTSTAMP_FLAGS”…””}”(hj«
  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1js
  hjk
  ubhŒP netlink attributes are then used to set
the struct hwtstamp_config accordingly.”…””}”(hjk
  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h M%hj>
  hžhubhÛ)”}”(hŒáThe ``ETHTOOL_A_TSCONFIG_HWTSTAMP_PROVIDER`` netlink nested attribute is used
to select the source of the hardware time stamping. It is composed of an index
for the device source and a qualifier for the type of time stamping.”h]”(hŒThe ”…””}”(hjÃ
  hžhhŸNh Nubjt
  )”}”(hŒ(``ETHTOOL_A_TSCONFIG_HWTSTAMP_PROVIDER``”h]”hŒ$ETHTOOL_A_TSCONFIG_HWTSTAMP_PROVIDER”…””}”(hjË
  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1js
  hjÃ
  ubhŒµ netlink nested attribute is used
to select the source of the hardware time stamping. It is composed of an index
for the device source and a qualifier for the type of time stamping.”…””}”(hjÃ
  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h M+hj>
  hžhubhÛ)”}”(hX°  Drivers are free to use a more permissive configuration than the requested
configuration. It is expected that drivers should only implement directly the
most generic mode that can be supported. For example if the hardware can
support HWTSTAMP_FILTER_PTP_V2_EVENT, then it should generally always upscale
HWTSTAMP_FILTER_PTP_V2_L2_SYNC, and so forth, as HWTSTAMP_FILTER_PTP_V2_EVENT
is more generic (and more useful to applications).”h]”hX°  Drivers are free to use a more permissive configuration than the requested
configuration. It is expected that drivers should only implement directly the
most generic mode that can be supported. For example if the hardware can
support HWTSTAMP_FILTER_PTP_V2_EVENT, then it should generally always upscale
HWTSTAMP_FILTER_PTP_V2_L2_SYNC, and so forth, as HWTSTAMP_FILTER_PTP_V2_EVENT
is more generic (and more useful to applications).”…””}”(hjã
  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h M/hj>
  hžhubhÛ)”}”(hXA  A driver which supports hardware time stamping shall update the struct
with the actual, possibly more permissive configuration. If the
requested packets cannot be time stamped, then nothing should be
changed and ERANGE shall be returned (in contrast to EINVAL, which
indicates that SIOCSHWTSTAMP is not supported at all).”h]”hXA  A driver which supports hardware time stamping shall update the struct
with the actual, possibly more permissive configuration. If the
requested packets cannot be time stamped, then nothing should be
changed and ERANGE shall be returned (in contrast to EINVAL, which
indicates that SIOCSHWTSTAMP is not supported at all).”…””}”(hjñ
  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h M6hj>
  hžhubhÛ)”}”(hŒ½Only a processes with admin rights may change the configuration. User
space is responsible to ensure that multiple processes don't interfere
with each other and that the settings are reset.”h]”hŒ¿Only a processes with admin rights may change the configuration. User
space is responsible to ensure that multiple processes donâ€™t interfere
with each other and that the settings are reset.”…””}”(hjÿ
  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h M<hj>
  hžhubhÛ)”}”(hŒqAny process can read the actual configuration by requesting tsconfig netlink
socket ``ETHTOOL_MSG_TSCONFIG_GET``.”h]”(hŒTAny process can read the actual configuration by requesting tsconfig netlink
socket ”…””}”(hj  hžhhŸNh Nubjt
  )”}”(hŒ``ETHTOOL_MSG_TSCONFIG_GET``”h]”hŒETHTOOL_MSG_TSCONFIG_GET”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1js
  hj  ubhŒ.”…””}”(hj  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h M@hj>
  hžhubhÛ)”}”(hXù  The legacy configuration is the use of the ioctl(SIOCSHWTSTAMP) with a pointer
to a struct ifreq whose ifr_data points to a struct hwtstamp_config.
The tx_type and rx_filter are hints to the driver what it is expected to do.
If the requested fine-grained filtering for incoming packets is not
supported, the driver may time stamp more than just the requested types
of packets. ioctl(SIOCGHWTSTAMP) is used in the same way as the
ioctl(SIOCSHWTSTAMP). However, this has not been implemented in all drivers.”h]”hXù  The legacy configuration is the use of the ioctl(SIOCSHWTSTAMP) with a pointer
to a struct ifreq whose ifr_data points to a struct hwtstamp_config.
The tx_type and rx_filter are hints to the driver what it is expected to do.
If the requested fine-grained filtering for incoming packets is not
supported, the driver may time stamp more than just the requested types
of packets. ioctl(SIOCGHWTSTAMP) is used in the same way as the
ioctl(SIOCSHWTSTAMP). However, this has not been implemented in all drivers.”…””}”(hj-  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h MChj>
  hžhubj  )”}”(hXB  /* possible values for hwtstamp_config->tx_type */
enum {
        /*
        * no outgoing packet will need hardware time stamping;
        * should a packet arrive which asks for it, no hardware
        * time stamping will be done
        */
        HWTSTAMP_TX_OFF,

        /*
        * enables hardware time stamping for outgoing packets;
        * the sender of the packet decides which are to be
        * time stamped by setting SOF_TIMESTAMPING_TX_SOFTWARE
        * before sending the packet
        */
        HWTSTAMP_TX_ON,
};

/* possible values for hwtstamp_config->rx_filter */
enum {
        /* time stamp no incoming packet at all */
        HWTSTAMP_FILTER_NONE,

        /* time stamp any incoming packet */
        HWTSTAMP_FILTER_ALL,

        /* return value: time stamp all packets requested plus some others */
        HWTSTAMP_FILTER_SOME,

        /* PTP v1, UDP, any kind of event packet */
        HWTSTAMP_FILTER_PTP_V1_L4_EVENT,

        /* for the complete list of values, please check
        * the include file include/uapi/linux/net_tstamp.h
        */
};”h]”hXB  /* possible values for hwtstamp_config->tx_type */
enum {
        /*
        * no outgoing packet will need hardware time stamping;
        * should a packet arrive which asks for it, no hardware
        * time stamping will be done
        */
        HWTSTAMP_TX_OFF,

        /*
        * enables hardware time stamping for outgoing packets;
        * the sender of the packet decides which are to be
        * time stamped by setting SOF_TIMESTAMPING_TX_SOFTWARE
        * before sending the packet
        */
        HWTSTAMP_TX_ON,
};

/* possible values for hwtstamp_config->rx_filter */
enum {
        /* time stamp no incoming packet at all */
        HWTSTAMP_FILTER_NONE,

        /* time stamp any incoming packet */
        HWTSTAMP_FILTER_ALL,

        /* return value: time stamp all packets requested plus some others */
        HWTSTAMP_FILTER_SOME,

        /* PTP v1, UDP, any kind of event packet */
        HWTSTAMP_FILTER_PTP_V1_L4_EVENT,

        /* for the complete list of values, please check
        * the include file include/uapi/linux/net_tstamp.h
        */
};”…””}”hj;  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1j~  hŸh³h MMhj>
  hžhubhµ)”}”(hhh]”(hº)”}”(hŒ83.1 Hardware Timestamping Implementation: Device Drivers”h]”hŒ83.1 Hardware Timestamping Implementation: Device Drivers”…””}”(hjL  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hjI  hžhhŸh³h MsubhÛ)”}”(hX/  A driver which supports hardware time stamping must support the
ndo_hwtstamp_set NDO or the legacy SIOCSHWTSTAMP ioctl and update the
supplied struct hwtstamp_config with the actual values as described in
the section on SIOCSHWTSTAMP. It should also support ndo_hwtstamp_get or
the legacy SIOCGHWTSTAMP.”h]”hX/  A driver which supports hardware time stamping must support the
ndo_hwtstamp_set NDO or the legacy SIOCSHWTSTAMP ioctl and update the
supplied struct hwtstamp_config with the actual values as described in
the section on SIOCSHWTSTAMP. It should also support ndo_hwtstamp_get or
the legacy SIOCGHWTSTAMP.”…””}”(hjZ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h MuhjI  hžhubhÛ)”}”(hŒ¼Time stamps for received packets must be stored in the skb. To get a pointer
to the shared time stamp structure of the skb call skb_hwtstamps(). Then
set the time stamps in the structure::”h]”hŒ»Time stamps for received packets must be stored in the skb. To get a pointer
to the shared time stamp structure of the skb call skb_hwtstamps(). Then
set the time stamps in the structure:”…””}”(hjh  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h M{hjI  hžhubj  )”}”(hŒªstruct skb_shared_hwtstamps {
        /* hardware time stamp transformed into duration
        * since arbitrary point in time
        */
        ktime_t     hwtstamp;
};”h]”hŒªstruct skb_shared_hwtstamps {
        /* hardware time stamp transformed into duration
        * since arbitrary point in time
        */
        ktime_t     hwtstamp;
};”…””}”hjv  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1j~  hŸh³h MhjI  hžhubhÛ)”}”(hŒ@Time stamps for outgoing packets are to be generated as follows:”h]”hŒ@Time stamps for outgoing packets are to be generated as follows:”…””}”(hj„  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h M†hjI  hžhubhŒbullet_list”“”)”}”(hhh]”(hŒ	list_item”“”)”}”(hŒžIn hard_start_xmit(), check if (skb_shinfo(skb)->tx_flags & SKBTX_HW_TSTAMP)
is set no-zero. If yes, then the driver is expected to do hardware time
stamping.”h]”hÛ)”}”(hŒžIn hard_start_xmit(), check if (skb_shinfo(skb)->tx_flags & SKBTX_HW_TSTAMP)
is set no-zero. If yes, then the driver is expected to do hardware time
stamping.”h]”hŒžIn hard_start_xmit(), check if (skb_shinfo(skb)->tx_flags & SKBTX_HW_TSTAMP)
is set no-zero. If yes, then the driver is expected to do hardware time
stamping.”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h Mˆhj™  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j—  hj”  hžhhŸh³h Nubj˜  )”}”(hX  If this is possible for the skb and requested, then declare
that the driver is doing the time stamping by setting the flag
SKBTX_IN_PROGRESS in skb_shinfo(skb)->tx_flags , e.g. with::

    skb_shinfo(skb)->tx_flags |= SKBTX_IN_PROGRESS;

You might want to keep a pointer to the associated skb for the next step
and not free the skb. A driver not supporting hardware time stamping doesn't
do that. A driver must never touch sk_buff::tstamp! It is used to store
software generated time stamps by the network subsystem.”h]”(hÛ)”}”(hŒ·If this is possible for the skb and requested, then declare
that the driver is doing the time stamping by setting the flag
SKBTX_IN_PROGRESS in skb_shinfo(skb)->tx_flags , e.g. with::”h]”hŒ¶If this is possible for the skb and requested, then declare
that the driver is doing the time stamping by setting the flag
SKBTX_IN_PROGRESS in skb_shinfo(skb)->tx_flags , e.g. with:”…””}”(hjµ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h M‹hj±  ubj  )”}”(hŒ/skb_shinfo(skb)->tx_flags |= SKBTX_IN_PROGRESS;”h]”hŒ/skb_shinfo(skb)->tx_flags |= SKBTX_IN_PROGRESS;”…””}”hjÃ  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1j~  hŸh³h Mhj±  ubhÛ)”}”(hX  You might want to keep a pointer to the associated skb for the next step
and not free the skb. A driver not supporting hardware time stamping doesn't
do that. A driver must never touch sk_buff::tstamp! It is used to store
software generated time stamps by the network subsystem.”h]”hX  You might want to keep a pointer to the associated skb for the next step
and not free the skb. A driver not supporting hardware time stamping doesnâ€™t
do that. A driver must never touch sk_buff::tstamp! It is used to store
software generated time stamps by the network subsystem.”…””}”(hjÑ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h M‘hj±  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1j—  hj”  hžhhŸh³h Nubj˜  )”}”(hŒàDriver should call skb_tx_timestamp() as close to passing sk_buff to hardware
as possible. skb_tx_timestamp() provides a software time stamp if requested
and hardware timestamping is not possible (SKBTX_IN_PROGRESS not set).”h]”hÛ)”}”(hŒàDriver should call skb_tx_timestamp() as close to passing sk_buff to hardware
as possible. skb_tx_timestamp() provides a software time stamp if requested
and hardware timestamping is not possible (SKBTX_IN_PROGRESS not set).”h]”hŒàDriver should call skb_tx_timestamp() as close to passing sk_buff to hardware
as possible. skb_tx_timestamp() provides a software time stamp if requested
and hardware timestamping is not possible (SKBTX_IN_PROGRESS not set).”…””}”(hjé  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h M•hjå  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j—  hj”  hžhhŸh³h Nubj˜  )”}”(hXa  As soon as the driver has sent the packet and/or obtained a
hardware time stamp for it, it passes the time stamp back by
calling skb_tstamp_tx() with the original skb, the raw
hardware time stamp. skb_tstamp_tx() clones the original skb and
adds the timestamps, therefore the original skb has to be freed now.
If obtaining the hardware time stamp somehow fails, then the driver
should not fall back to software time stamping. The rationale is that
this would occur at a later time in the processing pipeline than other
software time stamping and therefore could lead to unexpected deltas
between time stamps.
”h]”hÛ)”}”(hX`  As soon as the driver has sent the packet and/or obtained a
hardware time stamp for it, it passes the time stamp back by
calling skb_tstamp_tx() with the original skb, the raw
hardware time stamp. skb_tstamp_tx() clones the original skb and
adds the timestamps, therefore the original skb has to be freed now.
If obtaining the hardware time stamp somehow fails, then the driver
should not fall back to software time stamping. The rationale is that
this would occur at a later time in the processing pipeline than other
software time stamping and therefore could lead to unexpected deltas
between time stamps.”h]”hX`  As soon as the driver has sent the packet and/or obtained a
hardware time stamp for it, it passes the time stamp back by
calling skb_tstamp_tx() with the original skb, the raw
hardware time stamp. skb_tstamp_tx() clones the original skb and
adds the timestamps, therefore the original skb has to be freed now.
If obtaining the hardware time stamp somehow fails, then the driver
should not fall back to software time stamping. The rationale is that
this would occur at a later time in the processing pipeline than other
software time stamping and therefore could lead to unexpected deltas
between time stamps.”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h M˜hjý  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j—  hj”  hžhhŸh³h Nubeh}”(h]”h ]”h"]”h$]”h&]”Œbullet”Œ-”uh1j’  hŸh³h MˆhjI  hžhubeh}”(h]”Œ3hardware-timestamping-implementation-device-drivers”ah ]”h"]”Œ83.1 hardware timestamping implementation: device drivers”ah$]”h&]”uh1h´hj>
  hžhhŸh³h Msubhµ)”}”(hhh]”(hº)”}”(hŒ:3.2 Special considerations for stacked PTP Hardware Clocks”h]”hŒ:3.2 Special considerations for stacked PTP Hardware Clocks”…””}”(hj(  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hj%  hžhhŸh³h M¤ubhÛ)”}”(hX®  There are situations when there may be more than one PHC (PTP Hardware Clock)
in the data path of a packet. The kernel has no explicit mechanism to allow the
user to select which PHC to use for timestamping Ethernet frames. Instead, the
assumption is that the outermost PHC is always the most preferable, and that
kernel drivers collaborate towards achieving that goal. Currently there are 3
cases of stacked PHCs, detailed below:”h]”hX®  There are situations when there may be more than one PHC (PTP Hardware Clock)
in the data path of a packet. The kernel has no explicit mechanism to allow the
user to select which PHC to use for timestamping Ethernet frames. Instead, the
assumption is that the outermost PHC is always the most preferable, and that
kernel drivers collaborate towards achieving that goal. Currently there are 3
cases of stacked PHCs, detailed below:”…””}”(hj6  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h M¦hj%  hžhubhµ)”}”(hhh]”(hº)”}”(hŒ43.2.1 DSA (Distributed Switch Architecture) switches”h]”hŒ43.2.1 DSA (Distributed Switch Architecture) switches”…””}”(hjG  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hjD  hžhhŸh³h M®ubhÛ)”}”(hXÒ  These are Ethernet switches which have one of their ports connected to an
(otherwise completely unaware) host Ethernet interface, and perform the role of
a port multiplier with optional forwarding acceleration features.  Each DSA
switch port is visible to the user as a standalone (virtual) network interface,
and its network I/O is performed, under the hood, indirectly through the host
interface (redirecting to the host port on TX, and intercepting frames on RX).”h]”hXÒ  These are Ethernet switches which have one of their ports connected to an
(otherwise completely unaware) host Ethernet interface, and perform the role of
a port multiplier with optional forwarding acceleration features.  Each DSA
switch port is visible to the user as a standalone (virtual) network interface,
and its network I/O is performed, under the hood, indirectly through the host
interface (redirecting to the host port on TX, and intercepting frames on RX).”…””}”(hjU  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h M°hjD  hžhubhÛ)”}”(hXÚ  When a DSA switch is attached to a host port, PTP synchronization has to
suffer, since the switch's variable queuing delay introduces a path delay
jitter between the host port and its PTP partner. For this reason, some DSA
switches include a timestamping clock of their own, and have the ability to
perform network timestamping on their own MAC, such that path delays only
measure wire and PHY propagation latencies. Timestamping DSA switches are
supported in Linux and expose the same ABI as any other network interface (save
for the fact that the DSA interfaces are in fact virtual in terms of network
I/O, they do have their own PHC).  It is typical, but not mandatory, for all
interfaces of a DSA switch to share the same PHC.”h]”hXÜ  When a DSA switch is attached to a host port, PTP synchronization has to
suffer, since the switchâ€™s variable queuing delay introduces a path delay
jitter between the host port and its PTP partner. For this reason, some DSA
switches include a timestamping clock of their own, and have the ability to
perform network timestamping on their own MAC, such that path delays only
measure wire and PHY propagation latencies. Timestamping DSA switches are
supported in Linux and expose the same ABI as any other network interface (save
for the fact that the DSA interfaces are in fact virtual in terms of network
I/O, they do have their own PHC).  It is typical, but not mandatory, for all
interfaces of a DSA switch to share the same PHC.”…””}”(hjc  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h M·hjD  hžhubhÛ)”}”(hX  By design, PTP timestamping with a DSA switch does not need any special
handling in the driver for the host port it is attached to.  However, when the
host port also supports PTP timestamping, DSA will take care of intercepting
the ``.ndo_eth_ioctl`` calls towards the host port, and block attempts to enable
hardware timestamping on it. This is because the SO_TIMESTAMPING API does not
allow the delivery of multiple hardware timestamps for the same packet, so
anybody else except for the DSA switch port must be prevented from doing so.”h]”(hŒèBy design, PTP timestamping with a DSA switch does not need any special
handling in the driver for the host port it is attached to.  However, when the
host port also supports PTP timestamping, DSA will take care of intercepting
the ”…””}”(hjq  hžhhŸNh Nubjt
  )”}”(hŒ``.ndo_eth_ioctl``”h]”hŒ.ndo_eth_ioctl”…””}”(hjy  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1js
  hjq  ubhX    calls towards the host port, and block attempts to enable
hardware timestamping on it. This is because the SO_TIMESTAMPING API does not
allow the delivery of multiple hardware timestamps for the same packet, so
anybody else except for the DSA switch port must be prevented from doing so.”…””}”(hjq  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h MÂhjD  hžhubhÛ)”}”(hŒUIn the generic layer, DSA provides the following infrastructure for PTP
timestamping:”h]”hŒUIn the generic layer, DSA provides the following infrastructure for PTP
timestamping:”…””}”(hj‘  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h MÊhjD  hžhubj“  )”}”(hhh]”(j˜  )”}”(hX3  ``.port_txtstamp()``: a hook called prior to the transmission of
packets with a hardware TX timestamping request from user space.
This is required for two-step timestamping, since the hardware
timestamp becomes available after the actual MAC transmission, so the
driver must be prepared to correlate the timestamp with the original
packet so that it can re-enqueue the packet back into the socket's
error queue. To save the packet for when the timestamp becomes
available, the driver can call ``skb_clone_sk`` , save the clone pointer
in skb->cb and enqueue a tx skb queue. Typically, a switch will have a
PTP TX timestamp register (or sometimes a FIFO) where the timestamp
becomes available. In case of a FIFO, the hardware might store
key-value pairs of PTP sequence ID/message type/domain number and the
actual timestamp. To perform the correlation correctly between the
packets in a queue waiting for timestamping and the actual timestamps,
drivers can use a BPF classifier (``ptp_classify_raw``) to identify
the PTP transport type, and ``ptp_parse_header`` to interpret the PTP
header fields. There may be an IRQ that is raised upon this
timestamp's availability, or the driver might have to poll after
invoking ``dev_queue_xmit()`` towards the host interface.
One-step TX timestamping do not require packet cloning, since there is
no follow-up message required by the PTP protocol (because the
TX timestamp is embedded into the packet by the MAC), and therefore
user space does not expect the packet annotated with the TX timestamp
to be re-enqueued into its socket's error queue.
”h]”hÛ)”}”(hX2  ``.port_txtstamp()``: a hook called prior to the transmission of
packets with a hardware TX timestamping request from user space.
This is required for two-step timestamping, since the hardware
timestamp becomes available after the actual MAC transmission, so the
driver must be prepared to correlate the timestamp with the original
packet so that it can re-enqueue the packet back into the socket's
error queue. To save the packet for when the timestamp becomes
available, the driver can call ``skb_clone_sk`` , save the clone pointer
in skb->cb and enqueue a tx skb queue. Typically, a switch will have a
PTP TX timestamp register (or sometimes a FIFO) where the timestamp
becomes available. In case of a FIFO, the hardware might store
key-value pairs of PTP sequence ID/message type/domain number and the
actual timestamp. To perform the correlation correctly between the
packets in a queue waiting for timestamping and the actual timestamps,
drivers can use a BPF classifier (``ptp_classify_raw``) to identify
the PTP transport type, and ``ptp_parse_header`` to interpret the PTP
header fields. There may be an IRQ that is raised upon this
timestamp's availability, or the driver might have to poll after
invoking ``dev_queue_xmit()`` towards the host interface.
One-step TX timestamping do not require packet cloning, since there is
no follow-up message required by the PTP protocol (because the
TX timestamp is embedded into the packet by the MAC), and therefore
user space does not expect the packet annotated with the TX timestamp
to be re-enqueued into its socket's error queue.”h]”(jt
  )”}”(hŒ``.port_txtstamp()``”h]”hŒ.port_txtstamp()”…””}”(hjª  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1js
  hj¦  ubhXÛ  : a hook called prior to the transmission of
packets with a hardware TX timestamping request from user space.
This is required for two-step timestamping, since the hardware
timestamp becomes available after the actual MAC transmission, so the
driver must be prepared to correlate the timestamp with the original
packet so that it can re-enqueue the packet back into the socketâ€™s
error queue. To save the packet for when the timestamp becomes
available, the driver can call ”…””}”(hj¦  hžhhŸNh Nubjt
  )”}”(hŒ``skb_clone_sk``”h]”hŒskb_clone_sk”…””}”(hj¼  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1js
  hj¦  ubhXÖ   , save the clone pointer
in skb->cb and enqueue a tx skb queue. Typically, a switch will have a
PTP TX timestamp register (or sometimes a FIFO) where the timestamp
becomes available. In case of a FIFO, the hardware might store
key-value pairs of PTP sequence ID/message type/domain number and the
actual timestamp. To perform the correlation correctly between the
packets in a queue waiting for timestamping and the actual timestamps,
drivers can use a BPF classifier (”…””}”(hj¦  hžhhŸNh Nubjt
  )”}”(hŒ``ptp_classify_raw``”h]”hŒptp_classify_raw”…””}”(hjÎ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1js
  hj¦  ubhŒ*) to identify
the PTP transport type, and ”…””}”(hj¦  hžhhŸNh Nubjt
  )”}”(hŒ``ptp_parse_header``”h]”hŒptp_parse_header”…””}”(hjà  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1js
  hj¦  ubhŒž to interpret the PTP
header fields. There may be an IRQ that is raised upon this
timestampâ€™s availability, or the driver might have to poll after
invoking ”…””}”(hj¦  hžhhŸNh Nubjt
  )”}”(hŒ``dev_queue_xmit()``”h]”hŒdev_queue_xmit()”…””}”(hjò  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1js
  hj¦  ubhX_   towards the host interface.
One-step TX timestamping do not require packet cloning, since there is
no follow-up message required by the PTP protocol (because the
TX timestamp is embedded into the packet by the MAC), and therefore
user space does not expect the packet annotated with the TX timestamp
to be re-enqueued into its socketâ€™s error queue.”…””}”(hj¦  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h MÍhj¢  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j—  hjŸ  hžhhŸh³h Nubj˜  )”}”(hXÙ  ``.port_rxtstamp()``: On RX, the BPF classifier is run by DSA to
identify PTP event messages (any other packets, including PTP general
messages, are not timestamped). The original (and only) timestampable
skb is provided to the driver, for it to annotate it with a timestamp,
if that is immediately available, or defer to later. On reception,
timestamps might either be available in-band (through metadata in the
DSA header, or attached in other ways to the packet), or out-of-band
(through another RX timestamping FIFO). Deferral on RX is typically
necessary when retrieving the timestamp needs a sleepable context. In
that case, it is the responsibility of the DSA driver to call
``netif_rx()`` on the freshly timestamped skb.
”h]”hÛ)”}”(hXØ  ``.port_rxtstamp()``: On RX, the BPF classifier is run by DSA to
identify PTP event messages (any other packets, including PTP general
messages, are not timestamped). The original (and only) timestampable
skb is provided to the driver, for it to annotate it with a timestamp,
if that is immediately available, or defer to later. On reception,
timestamps might either be available in-band (through metadata in the
DSA header, or attached in other ways to the packet), or out-of-band
(through another RX timestamping FIFO). Deferral on RX is typically
necessary when retrieving the timestamp needs a sleepable context. In
that case, it is the responsibility of the DSA driver to call
``netif_rx()`` on the freshly timestamped skb.”h]”(jt
  )”}”(hŒ``.port_rxtstamp()``”h]”hŒ.port_rxtstamp()”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1js
  hj  ubhX–  : On RX, the BPF classifier is run by DSA to
identify PTP event messages (any other packets, including PTP general
messages, are not timestamped). The original (and only) timestampable
skb is provided to the driver, for it to annotate it with a timestamp,
if that is immediately available, or defer to later. On reception,
timestamps might either be available in-band (through metadata in the
DSA header, or attached in other ways to the packet), or out-of-band
(through another RX timestamping FIFO). Deferral on RX is typically
necessary when retrieving the timestamp needs a sleepable context. In
that case, it is the responsibility of the DSA driver to call
”…””}”(hj  hžhhŸNh Nubjt
  )”}”(hŒ``netif_rx()``”h]”hŒ
netif_rx()”…””}”(hj*  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1js
  hj  ubhŒ  on the freshly timestamped skb.”…””}”(hj  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h Mæhj  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j—  hjŸ  hžhhŸh³h Nubeh}”(h]”h ]”h"]”h$]”h&]”j  j  uh1j’  hŸh³h MÍhjD  hžhubeh}”(h]”Œ,dsa-distributed-switch-architecture-switches”ah ]”h"]”Œ43.2.1 dsa (distributed switch architecture) switches”ah$]”h&]”uh1h´hj%  hžhhŸh³h M®ubhµ)”}”(hhh]”(hº)”}”(hŒ3.2.2 Ethernet PHYs”h]”hŒ3.2.2 Ethernet PHYs”…””}”(hjY  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hjV  hžhhŸh³h MóubhÛ)”}”(hXz  These are devices that typically fulfill a Layer 1 role in the network stack,
hence they do not have a representation in terms of a network interface as DSA
switches do. However, PHYs may be able to detect and timestamp PTP packets, for
performance reasons: timestamps taken as close as possible to the wire have the
potential to yield a more stable and precise synchronization.”h]”hXz  These are devices that typically fulfill a Layer 1 role in the network stack,
hence they do not have a representation in terms of a network interface as DSA
switches do. However, PHYs may be able to detect and timestamp PTP packets, for
performance reasons: timestamps taken as close as possible to the wire have the
potential to yield a more stable and precise synchronization.”…””}”(hjg  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h MõhjV  hžhubhÛ)”}”(hŒÉA PHY driver that supports PTP timestamping must create a ``struct
mii_timestamper`` and add a pointer to it in ``phydev->mii_ts``. The presence
of this pointer will be checked by the networking stack.”h]”(hŒ:A PHY driver that supports PTP timestamping must create a ”…””}”(hju  hžhhŸNh Nubjt
  )”}”(hŒ``struct
mii_timestamper``”h]”hŒstruct
mii_timestamper”…””}”(hj}  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1js
  hju  ubhŒ and add a pointer to it in ”…””}”(hju  hžhhŸNh Nubjt
  )”}”(hŒ``phydev->mii_ts``”h]”hŒphydev->mii_ts”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1js
  hju  ubhŒG. The presence
of this pointer will be checked by the networking stack.”…””}”(hju  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h MûhjV  hžhubhÛ)”}”(hX4  Since PHYs do not have network interface representations, the timestamping and
ethtool ioctl operations for them need to be mediated by their respective MAC
driver.  Therefore, as opposed to DSA switches, modifications need to be done
to each individual MAC driver for PHY timestamping support. This entails:”h]”hX4  Since PHYs do not have network interface representations, the timestamping and
ethtool ioctl operations for them need to be mediated by their respective MAC
driver.  Therefore, as opposed to DSA switches, modifications need to be done
to each individual MAC driver for PHY timestamping support. This entails:”…””}”(hj§  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h MÿhjV  hžhubj“  )”}”(hhh]”(j˜  )”}”(hŒÙChecking, in ``.ndo_eth_ioctl``, whether ``phy_has_hwtstamp(netdev->phydev)``
is true or not. If it is, then the MAC driver should not process this request
but instead pass it on to the PHY using ``phy_mii_ioctl()``.
”h]”hÛ)”}”(hŒØChecking, in ``.ndo_eth_ioctl``, whether ``phy_has_hwtstamp(netdev->phydev)``
is true or not. If it is, then the MAC driver should not process this request
but instead pass it on to the PHY using ``phy_mii_ioctl()``.”h]”(hŒChecking, in ”…””}”(hj¼  hžhhŸNh Nubjt
  )”}”(hŒ``.ndo_eth_ioctl``”h]”hŒ.ndo_eth_ioctl”…””}”(hjÄ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1js
  hj¼  ubhŒ
, whether ”…””}”(hj¼  hžhhŸNh Nubjt
  )”}”(hŒ$``phy_has_hwtstamp(netdev->phydev)``”h]”hŒ phy_has_hwtstamp(netdev->phydev)”…””}”(hjÖ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1js
  hj¼  ubhŒw
is true or not. If it is, then the MAC driver should not process this request
but instead pass it on to the PHY using ”…””}”(hj¼  hžhhŸNh Nubjt
  )”}”(hŒ``phy_mii_ioctl()``”h]”hŒphy_mii_ioctl()”…””}”(hjè  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1js
  hj¼  ubhŒ.”…””}”(hj¼  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h Mhj¸  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j—  hjµ  hžhhŸh³h Nubj˜  )”}”(hX{  On RX, special intervention may or may not be needed, depending on the
function used to deliver skb's up the network stack. In the case of plain
``netif_rx()`` and similar, MAC drivers must check whether
``skb_defer_rx_timestamp(skb)`` is necessary or not - and if it is, don't
call ``netif_rx()`` at all.  If ``CONFIG_NETWORK_PHY_TIMESTAMPING`` is
enabled, and ``skb->dev->phydev->mii_ts`` exists, its ``.rxtstamp()`` hook
will be called now, to determine, using logic very similar to DSA, whether
deferral for RX timestamping is necessary.  Again like DSA, it becomes the
responsibility of the PHY driver to send the packet up the stack when the
timestamp is available.

For other skb receive functions, such as ``napi_gro_receive`` and
``netif_receive_skb``, the stack automatically checks whether
``skb_defer_rx_timestamp()`` is necessary, so this check is not needed inside
the driver.
”h]”(hÛ)”}”(hXŸ  On RX, special intervention may or may not be needed, depending on the
function used to deliver skb's up the network stack. In the case of plain
``netif_rx()`` and similar, MAC drivers must check whether
``skb_defer_rx_timestamp(skb)`` is necessary or not - and if it is, don't
call ``netif_rx()`` at all.  If ``CONFIG_NETWORK_PHY_TIMESTAMPING`` is
enabled, and ``skb->dev->phydev->mii_ts`` exists, its ``.rxtstamp()`` hook
will be called now, to determine, using logic very similar to DSA, whether
deferral for RX timestamping is necessary.  Again like DSA, it becomes the
responsibility of the PHY driver to send the packet up the stack when the
timestamp is available.”h]”(hŒ“On RX, special intervention may or may not be needed, depending on the
function used to deliver skbâ€™s up the network stack. In the case of plain
”…””}”(hj
  hžhhŸNh Nubjt
  )”}”(hŒ``netif_rx()``”h]”hŒ
netif_rx()”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1js
  hj
  ubhŒ- and similar, MAC drivers must check whether
”…””}”(hj
  hžhhŸNh Nubjt
  )”}”(hŒ``skb_defer_rx_timestamp(skb)``”h]”hŒskb_defer_rx_timestamp(skb)”…””}”(hj$  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1js
  hj
  ubhŒ2 is necessary or not - and if it is, donâ€™t
call ”…””}”(hj
  hžhhŸNh Nubjt
  )”}”(hŒ``netif_rx()``”h]”hŒ
netif_rx()”…””}”(hj6  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1js
  hj
  ubhŒ at all.  If ”…””}”(hj
  hžhhŸNh Nubjt
  )”}”(hŒ#``CONFIG_NETWORK_PHY_TIMESTAMPING``”h]”hŒCONFIG_NETWORK_PHY_TIMESTAMPING”…””}”(hjH  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1js
  hj
  ubhŒ is
enabled, and ”…””}”(hj
  hžhhŸNh Nubjt
  )”}”(hŒ``skb->dev->phydev->mii_ts``”h]”hŒskb->dev->phydev->mii_ts”…””}”(hjZ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1js
  hj
  ubhŒ exists, its ”…””}”(hj
  hžhhŸNh Nubjt
  )”}”(hŒ``.rxtstamp()``”h]”hŒ.rxtstamp()”…””}”(hjl  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1js
  hj
  ubhŒý hook
will be called now, to determine, using logic very similar to DSA, whether
deferral for RX timestamping is necessary.  Again like DSA, it becomes the
responsibility of the PHY driver to send the packet up the stack when the
timestamp is available.”…””}”(hj
  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h Mhj  ubhÛ)”}”(hŒÙFor other skb receive functions, such as ``napi_gro_receive`` and
``netif_receive_skb``, the stack automatically checks whether
``skb_defer_rx_timestamp()`` is necessary, so this check is not needed inside
the driver.”h]”(hŒ)For other skb receive functions, such as ”…””}”(hj„  hžhhŸNh Nubjt
  )”}”(hŒ``napi_gro_receive``”h]”hŒnapi_gro_receive”…””}”(hjŒ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1js
  hj„  ubhŒ and
”…””}”(hj„  hžhhŸNh Nubjt
  )”}”(hŒ``netif_receive_skb``”h]”hŒnetif_receive_skb”…””}”(hjž  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1js
  hj„  ubhŒ), the stack automatically checks whether
”…””}”(hj„  hžhhŸNh Nubjt
  )”}”(hŒ``skb_defer_rx_timestamp()``”h]”hŒskb_defer_rx_timestamp()”…””}”(hj°  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1js
  hj„  ubhŒ= is necessary, so this check is not needed inside
the driver.”…””}”(hj„  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h Mhj  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1j—  hjµ  hžhhŸh³h Nubj˜  )”}”(hX  On TX, again, special intervention might or might not be needed.  The
function that calls the ``mii_ts->txtstamp()`` hook is named
``skb_clone_tx_timestamp()``. This function can either be called directly
(case in which explicit MAC driver support is indeed needed), but the
function also piggybacks from the ``skb_tx_timestamp()`` call, which many MAC
drivers already perform for software timestamping purposes. Therefore, if a
MAC supports software timestamping, it does not need to do anything further
at this stage.
”h]”hÛ)”}”(hX  On TX, again, special intervention might or might not be needed.  The
function that calls the ``mii_ts->txtstamp()`` hook is named
``skb_clone_tx_timestamp()``. This function can either be called directly
(case in which explicit MAC driver support is indeed needed), but the
function also piggybacks from the ``skb_tx_timestamp()`` call, which many MAC
drivers already perform for software timestamping purposes. Therefore, if a
MAC supports software timestamping, it does not need to do anything further
at this stage.”h]”(hŒ^On TX, again, special intervention might or might not be needed.  The
function that calls the ”…””}”(hjÒ  hžhhŸNh Nubjt
  )”}”(hŒ``mii_ts->txtstamp()``”h]”hŒmii_ts->txtstamp()”…””}”(hjÚ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1js
  hjÒ  ubhŒ hook is named
”…””}”(hjÒ  hžhhŸNh Nubjt
  )”}”(hŒ``skb_clone_tx_timestamp()``”h]”hŒskb_clone_tx_timestamp()”…””}”(hjì  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1js
  hjÒ  ubhŒ–. This function can either be called directly
(case in which explicit MAC driver support is indeed needed), but the
function also piggybacks from the ”…””}”(hjÒ  hžhhŸNh Nubjt
  )”}”(hŒ``skb_tx_timestamp()``”h]”hŒskb_tx_timestamp()”…””}”(hjþ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1js
  hjÒ  ubhŒ¼ call, which many MAC
drivers already perform for software timestamping purposes. Therefore, if a
MAC supports software timestamping, it does not need to do anything further
at this stage.”…””}”(hjÒ  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h MhjÎ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j—  hjµ  hžhhŸh³h Nubeh}”(h]”h ]”h"]”h$]”h&]”j  j  uh1j’  hŸh³h MhjV  hžhubeh}”(h]”Œethernet-phys”ah ]”h"]”Œ3.2.2 ethernet phys”ah$]”h&]”uh1h´hj%  hžhhŸh³h Móubhµ)”}”(hhh]”(hº)”}”(hŒ3.2.3 MII bus snooping devices”h]”hŒ3.2.3 MII bus snooping devices”…””}”(hj-  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hj*  hžhhŸh³h M"ubhÛ)”}”(hX¹  These perform the same role as timestamping Ethernet PHYs, save for the fact
that they are discrete devices and can therefore be used in conjunction with
any PHY even if it doesn't support timestamping. In Linux, they are
discoverable and attachable to a ``struct phy_device`` through Device Tree, and
for the rest, they use the same mii_ts infrastructure as those. See
Documentation/devicetree/bindings/ptp/timestamper.txt for more details.”h]”(hX  These perform the same role as timestamping Ethernet PHYs, save for the fact
that they are discrete devices and can therefore be used in conjunction with
any PHY even if it doesnâ€™t support timestamping. In Linux, they are
discoverable and attachable to a ”…””}”(hj;  hžhhŸNh Nubjt
  )”}”(hŒ``struct phy_device``”h]”hŒstruct phy_device”…””}”(hjC  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1js
  hj;  ubhŒ¥ through Device Tree, and
for the rest, they use the same mii_ts infrastructure as those. See
Documentation/devicetree/bindings/ptp/timestamper.txt for more details.”…””}”(hj;  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h M$hj*  hžhubeh}”(h]”Œmii-bus-snooping-devices”ah ]”h"]”Œ3.2.3 mii bus snooping devices”ah$]”h&]”uh1h´hj%  hžhhŸh³h M"ubhµ)”}”(hhh]”(hº)”}”(hŒ#3.2.4 Other caveats for MAC drivers”h]”hŒ#3.2.4 Other caveats for MAC drivers”…””}”(hjf  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hjc  hžhhŸh³h M,ubhÛ)”}”(hXf  Stacked PHCs, especially DSA (but not only) - since that doesn't require any
modification to MAC drivers, so it is more difficult to ensure correctness of
all possible code paths - is that they uncover bugs which were impossible to
trigger before the existence of stacked PTP clocks.  One example has to do with
this line of code, already presented earlier::”h]”hXg  Stacked PHCs, especially DSA (but not only) - since that doesnâ€™t require any
modification to MAC drivers, so it is more difficult to ensure correctness of
all possible code paths - is that they uncover bugs which were impossible to
trigger before the existence of stacked PTP clocks.  One example has to do with
this line of code, already presented earlier:”…””}”(hjt  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h M.hjc  hžhubj  )”}”(hŒ/skb_shinfo(skb)->tx_flags |= SKBTX_IN_PROGRESS;”h]”hŒ/skb_shinfo(skb)->tx_flags |= SKBTX_IN_PROGRESS;”…””}”hj‚  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1j~  hŸh³h M4hjc  hžhubhÛ)”}”(hX  Any TX timestamping logic, be it a plain MAC driver, a DSA switch driver, a PHY
driver or a MII bus snooping device driver, should set this flag.
But a MAC driver that is unaware of PHC stacking might get tripped up by
somebody other than itself setting this flag, and deliver a duplicate
timestamp.
For example, a typical driver design for TX timestamping might be to split the
transmission part into 2 portions:”h]”hX  Any TX timestamping logic, be it a plain MAC driver, a DSA switch driver, a PHY
driver or a MII bus snooping device driver, should set this flag.
But a MAC driver that is unaware of PHC stacking might get tripped up by
somebody other than itself setting this flag, and deliver a duplicate
timestamp.
For example, a typical driver design for TX timestamping might be to split the
transmission part into 2 portions:”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h M6hjc  hžhubhŒenumerated_list”“”)”}”(hhh]”(j˜  )”}”(hX-  "TX": checks whether PTP timestamping has been previously enabled through
the ``.ndo_eth_ioctl`` ("``priv->hwtstamp_tx_enabled == true``") and the
current skb requires a TX timestamp ("``skb_shinfo(skb)->tx_flags &
SKBTX_HW_TSTAMP``"). If this is true, it sets the
"``skb_shinfo(skb)->tx_flags |= SKBTX_IN_PROGRESS``" flag. Note: as
described above, in the case of a stacked PHC system, this condition should
never trigger, as this MAC is certainly not the outermost PHC. But this is
not where the typical issue is.  Transmission proceeds with this packet.
”h]”hÛ)”}”(hX,  "TX": checks whether PTP timestamping has been previously enabled through
the ``.ndo_eth_ioctl`` ("``priv->hwtstamp_tx_enabled == true``") and the
current skb requires a TX timestamp ("``skb_shinfo(skb)->tx_flags &
SKBTX_HW_TSTAMP``"). If this is true, it sets the
"``skb_shinfo(skb)->tx_flags |= SKBTX_IN_PROGRESS``" flag. Note: as
described above, in the case of a stacked PHC system, this condition should
never trigger, as this MAC is certainly not the outermost PHC. But this is
not where the typical issue is.  Transmission proceeds with this packet.”h]”(hŒRâ€œTXâ€: checks whether PTP timestamping has been previously enabled through
the ”…””}”(hj§  hžhhŸNh Nubjt
  )”}”(hŒ``.ndo_eth_ioctl``”h]”hŒ.ndo_eth_ioctl”…””}”(hj¯  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1js
  hj§  ubhŒ (â€”…””}”(hj§  hžhhŸNh Nubjt
  )”}”(hŒ%``priv->hwtstamp_tx_enabled == true``”h]”hŒ!priv->hwtstamp_tx_enabled == true”…””}”(hjÁ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1js
  hj§  ubhŒ5â€) and the
current skb requires a TX timestamp (â€”…””}”(hj§  hžhhŸNh Nubjt
  )”}”(hŒ/``skb_shinfo(skb)->tx_flags &
SKBTX_HW_TSTAMP``”h]”hŒ+skb_shinfo(skb)->tx_flags &
SKBTX_HW_TSTAMP”…””}”(hjÓ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1js
  hj§  ubhŒ&â€). If this is true, it sets the
â€œ”…””}”(hj§  hžhhŸNh Nubjt
  )”}”(hŒ2``skb_shinfo(skb)->tx_flags |= SKBTX_IN_PROGRESS``”h]”hŒ.skb_shinfo(skb)->tx_flags |= SKBTX_IN_PROGRESS”…””}”(hjå  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1js
  hj§  ubhŒòâ€ flag. Note: as
described above, in the case of a stacked PHC system, this condition should
never trigger, as this MAC is certainly not the outermost PHC. But this is
not where the typical issue is.  Transmission proceeds with this packet.”…””}”(hj§  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h M>hj£  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j—  hj   hžhhŸh³h Nubj˜  )”}”(hXÄ  "TX confirmation": Transmission has finished. The driver checks whether it
is necessary to collect any TX timestamp for it. Here is where the typical
issues are: the MAC driver takes a shortcut and only checks whether
"``skb_shinfo(skb)->tx_flags & SKBTX_IN_PROGRESS``" was set. With a stacked
PHC system, this is incorrect because this MAC driver is not the only entity
in the TX data path who could have enabled SKBTX_IN_PROGRESS in the first
place.
”h]”hÛ)”}”(hXÃ  "TX confirmation": Transmission has finished. The driver checks whether it
is necessary to collect any TX timestamp for it. Here is where the typical
issues are: the MAC driver takes a shortcut and only checks whether
"``skb_shinfo(skb)->tx_flags & SKBTX_IN_PROGRESS``" was set. With a stacked
PHC system, this is incorrect because this MAC driver is not the only entity
in the TX data path who could have enabled SKBTX_IN_PROGRESS in the first
place.”h]”(hŒáâ€œTX confirmationâ€: Transmission has finished. The driver checks whether it
is necessary to collect any TX timestamp for it. Here is where the typical
issues are: the MAC driver takes a shortcut and only checks whether
â€œ”…””}”(hj  hžhhŸNh Nubjt
  )”}”(hŒ1``skb_shinfo(skb)->tx_flags & SKBTX_IN_PROGRESS``”h]”hŒ-skb_shinfo(skb)->tx_flags & SKBTX_IN_PROGRESS”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1js
  hj  ubhŒ¹â€ was set. With a stacked
PHC system, this is incorrect because this MAC driver is not the only entity
in the TX data path who could have enabled SKBTX_IN_PROGRESS in the first
place.”…””}”(hj  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h MGhj  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j—  hj   hžhhŸh³h Nubeh}”(h]”h ]”h"]”h$]”h&]”Œenumtype”Œarabic”Œprefix”hŒsuffix”Œ.”uh1jž  hjc  hžhhŸh³h M>ubhÛ)”}”(hX·  The correct solution for this problem is for MAC drivers to have a compound
check in their "TX confirmation" portion, not only for
"``skb_shinfo(skb)->tx_flags & SKBTX_IN_PROGRESS``", but also for
"``priv->hwtstamp_tx_enabled == true``". Because the rest of the system ensures
that PTP timestamping is not enabled for anything other than the outermost PHC,
this enhanced check will avoid delivering a duplicated TX timestamp to user
space.”h]”(hŒŠThe correct solution for this problem is for MAC drivers to have a compound
check in their â€œTX confirmationâ€ portion, not only for
â€œ”…””}”(hj8  hžhhŸNh Nubjt
  )”}”(hŒ1``skb_shinfo(skb)->tx_flags & SKBTX_IN_PROGRESS``”h]”hŒ-skb_shinfo(skb)->tx_flags & SKBTX_IN_PROGRESS”…””}”(hj@  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1js
  hj8  ubhŒâ€, but also for
â€œ”…””}”(hj8  hžhhŸNh Nubjt
  )”}”(hŒ%``priv->hwtstamp_tx_enabled == true``”h]”hŒ!priv->hwtstamp_tx_enabled == true”…””}”(hjR  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1js
  hj8  ubhŒÎâ€. Because the rest of the system ensures
that PTP timestamping is not enabled for anything other than the outermost PHC,
this enhanced check will avoid delivering a duplicated TX timestamp to user
space.”…””}”(hj8  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h MOhjc  hžhubeh}”(h]”Œother-caveats-for-mac-drivers”ah ]”h"]”Œ#3.2.4 other caveats for mac drivers”ah$]”h&]”uh1h´hj%  hžhhŸh³h M,ubeh}”(h]”Œ6special-considerations-for-stacked-ptp-hardware-clocks”ah ]”h"]”Œ:3.2 special considerations for stacked ptp hardware clocks”ah$]”h&]”uh1h´hj>
  hžhhŸh³h M¤ubeh}”(h]”Œ@hardware-timestamping-configuration-ethtool-msg-tsconfig-set-get”ah ]”h"]”ŒD3. hardware timestamping configuration: ethtool_msg_tsconfig_set/get”ah$]”h&]”uh1h´hh¶hžhhŸh³h Mubeh}”(h]”Œtimestamping”ah ]”h"]”Œtimestamping”ah$]”h&]”uh1h´hhhžhhŸh³h Kubeh}”(h]”h ]”h"]”h$]”h&]”Œsource”h³uh1hŒcurrent_source”NŒcurrent_line”NŒsettings”Œdocutils.frontend”ŒValues”“”)”}”(h¹NŒ	generator”NŒ	datestamp”NŒsource_link”NŒ
source_url”NŒtoc_backlinks”Œentry”Œfootnote_backlinks”KŒsectnum_xform”KŒstrip_comments”NŒstrip_elements_with_classes”NŒstrip_classes”NŒreport_level”KŒ
halt_level”KŒexit_status_level”KŒdebug”NŒwarning_stream”NŒ	traceback”ˆŒinput_encoding”Œ	utf-8-sig”Œinput_encoding_error_handler”Œstrict”Œoutput_encoding”Œutf-8”Œoutput_encoding_error_handler”j­  Œerror_encoding”Œutf-8”Œerror_encoding_error_handler”Œbackslashreplace”Œlanguage_code”Œen”Œrecord_dependencies”NŒconfig”NŒ	id_prefix”hŒauto_id_prefix”Œid”Œdump_settings”NŒdump_internals”NŒdump_transforms”NŒdump_pseudo_xml”NŒexpose_internals”NŒstrict_visitor”NŒ_disable_config”NŒ_source”h³Œ_destination”NŒ_config_files”]”Œ7/var/lib/git/docbuild/linux/Documentation/docutils.conf”aŒfile_insertion_enabled”ˆŒraw_enabled”KŒline_length_limit”M'Œpep_references”NŒpep_base_url”Œhttps://peps.python.org/”Œpep_file_url_template”Œpep-%04d”Œrfc_references”NŒrfc_base_url”Œ&https://datatracker.ietf.org/doc/html/”Œ	tab_width”KŒtrim_footnote_reference_space”‰Œsyntax_highlight”Œlong”Œsmart_quotes”ˆŒsmartquotes_locales”]”Œcharacter_level_inline_markup”‰Œdoctitle_xform”‰Œdocinfo_xform”KŒsectsubtitle_xform”‰Œimage_loading”Œlink”Œembed_stylesheet”‰Œcloak_email_addresses”ˆŒsection_self_link”‰Œenv”NubŒreporter”NŒindirect_targets”]”Œsubstitution_defs”}”Œsubstitution_names”}”Œrefnames”}”Œrefids”}”Œnameids”}”(j‡  j„  j3  j0  j  j  j\  jY  j°  j­  j   j  jÝ  jÚ  jI  jF  j¨  j¥  j+  j(  j;
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