From adca4767821e54c72d4a2f467af77923f2c87e07 Mon Sep 17 00:00:00 2001 From: Andrew Lutomirski Date: Tue, 4 Mar 2014 17:24:10 -0800 Subject: [PATCH] net: Improve SO_TIMESTAMPING documentation and fix a minor code bug 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 Acked-by: Richard Cochran Signed-off-by: David S. Miller --- Documentation/networking/timestamping.txt | 52 ++++++++++++++--------- include/net/sock.h | 1 - 2 files changed, 32 insertions(+), 21 deletions(-) diff --git a/Documentation/networking/timestamping.txt b/Documentation/networking/timestamping.txt index 661d3c316a17..048c92b487f6 100644 --- a/Documentation/networking/timestamping.txt +++ b/Documentation/networking/timestamping.txt @@ -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. - -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 - -SOF_TIMESTAMPING_TX/RX determine how time stamps are generated. -SOF_TIMESTAMPING_RAW/SYS determine how they are reported in the -following control message: +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. + +Four of the bits are requests to the stack to try to generate +timestamps. Any combination of them is valid. + +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; diff --git a/include/net/sock.h b/include/net/sock.h index 5c3f7c3624aa..7c4167bc8266 100644 --- a/include/net/sock.h +++ b/include/net/sock.h @@ -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)) -- 2.20.1