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net: Improve SO_TIMESTAMPING documentation and fix a minor code bug

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The original documentation was very unclear.

The code fix is presumably related to the formerly unclear
documentation: SOCK_TIMESTAMPING_RX_SOFTWARE has no effect on
__sock_recv_timestamp's behavior, so calling __sock_recv_ts_and_drops
from sock_recv_ts_and_drops if only SOCK_TIMESTAMPING_RX_SOFTWARE is
set is pointless.  This should have no user-observable effect.

Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Andrew Lutomirski 2014-03-04 17:24:10 -08:00 committed by David S. Miller
parent 4ae6e50c76
commit adca476782
2 changed files with 30 additions and 19 deletions
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48
Documentation/networking/timestamping.txt
View File

@ -21,26 +21,38 @@ has such a feature).
SO_TIMESTAMPING:
Instructs the socket layer which kind of information is wanted. The
parameter is an integer with some of the following bits set. Setting
other bits is an error and doesn't change the current state.
Instructs the socket layer which kind of information should be collected
and/or reported. The parameter is an integer with some of the following
bits set. Setting other bits is an error and doesn't change the current
state.
SOF_TIMESTAMPING_TX_HARDWARE: try to obtain send time stamp in hardware
SOF_TIMESTAMPING_TX_SOFTWARE: if SOF_TIMESTAMPING_TX_HARDWARE is off or
fails, then do it in software
SOF_TIMESTAMPING_RX_HARDWARE: return the original, unmodified time stamp
as generated by the hardware
SOF_TIMESTAMPING_RX_SOFTWARE: if SOF_TIMESTAMPING_RX_HARDWARE is off or
fails, then do it in software
SOF_TIMESTAMPING_RAW_HARDWARE: return original raw hardware time stamp
SOF_TIMESTAMPING_SYS_HARDWARE: return hardware time stamp transformed to
the system time base
SOF_TIMESTAMPING_SOFTWARE: return system time stamp generated in
software
Four of the bits are requests to the stack to try to generate
timestamps. Any combination of them is valid.
SOF_TIMESTAMPING_TX/RX determine how time stamps are generated.
SOF_TIMESTAMPING_RAW/SYS determine how they are reported in the
following control message:
SOF_TIMESTAMPING_TX_HARDWARE: try to obtain send time stamps in hardware
SOF_TIMESTAMPING_TX_SOFTWARE: try to obtain send time stamps in software
SOF_TIMESTAMPING_RX_HARDWARE: try to obtain receive time stamps in hardware
SOF_TIMESTAMPING_RX_SOFTWARE: try to obtain receive time stamps in software
The other three bits control which timestamps will be reported in a
generated control message. If none of these bits are set or if none of
the set bits correspond to data that is available, then the control
message will not be generated:
SOF_TIMESTAMPING_SOFTWARE: report systime if available
SOF_TIMESTAMPING_SYS_HARDWARE: report hwtimetrans if available
SOF_TIMESTAMPING_RAW_HARDWARE: report hwtimeraw if available
It is worth noting that timestamps may be collected for reasons other
than being requested by a particular socket with
SOF_TIMESTAMPING_[TR]X_(HARD|SOFT)WARE. For example, most drivers that
can generate hardware receive timestamps ignore
SOF_TIMESTAMPING_RX_HARDWARE. It is still a good idea to set that flag
in case future drivers pay attention.
If timestamps are reported, they will appear in a control message with
cmsg_level==SOL_SOCKET, cmsg_type==SO_TIMESTAMPING, and a payload like
this:
struct scm_timestamping {
struct timespec systime;

1
include/net/sock.h
View File

@ -2186,7 +2186,6 @@ static inline void sock_recv_ts_and_drops(struct msghdr *msg, struct sock *sk,
{
#define FLAGS_TS_OR_DROPS ((1UL << SOCK_RXQ_OVFL) | \
(1UL << SOCK_RCVTSTAMP) | \
(1UL << SOCK_TIMESTAMPING_RX_SOFTWARE) | \
(1UL << SOCK_TIMESTAMPING_SOFTWARE) | \
(1UL << SOCK_TIMESTAMPING_RAW_HARDWARE) | \
(1UL << SOCK_TIMESTAMPING_SYS_HARDWARE))