Re: [PATCH] man2: adjtimex.2 : add info about Clock source
From: Laurent Georget <hidden>
Date: 2015-09-01 07:53:51
Also in:
linux-man
Hello!
I'm not sure that this is what is meant by "Clock source" in struct timex.h.
STA_CLK can take only two values ("A" and "B"), and is read-only.
It was added in commit ee9851b218b8bafa22942b5404505ff3d2d34324
(kernel 2.6.25) at the same time MOD_CLKA and MOD_CLKB were removed.
tree 581f455e02ed3d03e543642b5d54b83dc75d47c7 parent ee9851b218b8bafa22942b5404505ff3d2d34324 author Roman Zippel [off-list ref] Thu May 1 04:34:33 2008 -0700 committer Linus Torvalds [off-list ref] Thu May 1 08:03:58 2008 -0700 ntp: NTP4 user space bits update This adds a few more things from the ntp nanokernel related to user space. It's now possible to select the resolution used of some values via STA_NANO and the kernel reports in which mode it works (pll/fll). If some values for adjtimex() are outside the acceptable range, they are now simply normalized instead of letting the syscall fail. I removed MOD_CLKA/MOD_CLKB as the mapping didn't really makes any sense, the kernel doesn't support setting the clock. Signed-off-by: Roman Zippel <redacted> Cc: john stultz <johnstul-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org> Cc: Thomas Gleixner <redacted> Signed-off-by: Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org> Signed-off-by: Linus Torvalds <torvalds-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>
Originally, A and B were present to distinguish two modes of functioning: whether an external clock is present or not. If an external clock system adjusts the local clock, then NTP is not used. In the case of Linux, I think this distinction between sources "A" and "B" is present for historical reasons, and because it was present in the reference implementation for ntp but I don't see where it's used in the kernel. See this for example of use of STA_CLK in another implementation: http://www.slac.stanford.edu/comp/unix/package/rtems/src/ssrlApps/ntpNanoclock/api.htm And this for the NTP standard, version 4: http://www.eecis.udel.edu/~mills/ntp/html/extern.html In Linux, there are two ways to adjust the clock. If it's not by NTP, then it can be through the use of system call clock_adjtime(2) (for which there is no man page yet, see clock_settime(2) to get an idea of the interface) which uses a function pointer clock_adj declared in a k_clock struct, which can be initialised to function posix_clock_realtime_adj. (Everything is in kernel/time/posix-timers.c.) Eventually, this boils down to using do_adjtimex, just as adjtimex(2) does. I guess STA_CLK should be set/reset with one of the method and not the other, if my understanding is correct, but it's not. Maybe because it's unused anyway? Laurent Le 30/08/2015 13:50, Punit Vara a écrit :
quoted hunk
This is a patch to the adjtimex.2 file that add more detail about clock source in man page which is asked to be fixed. I got this information from standard document RFC5909 which is available at https://tools.ietf.org/html/rfc5905#appendix-A.5.5.1 Signed-off-by: Punit Vara <redacted> --- man2/adjtimex.2 | 24 ++++++++++++++++++++++-- 1 file changed, 22 insertions(+), 2 deletions(-)diff --git a/man2/adjtimex.2 b/man2/adjtimex.2 index 04b53b1..77b4e30 100644 --- a/man2/adjtimex.2 +++ b/man2/adjtimex.2@@ -276,8 +276,28 @@ Mode (0 = Phase Locked Loop, 1 = Frequency Locked Loop; read-only). .\" commit eea83d896e318bda54be2d2770d2c5d6668d11db .\" Author: Roman Zippel <zippel-Td1EMuHUCqxL1ZNQvxDV9g@public.gmane.org> Clock source (0 = A, 1 = B; read-only). -.\" FIXME It would be helpful to have some explanation of what -.\" "Clock source" is. +Clock source is used to synchronized the time.It can be any standard clock +sources like : + +Geosynchronous Orbit Environment Satellite +Global Position System +Galileo Positioning System +Generic pulse-per-second +Inter-Range Instrumentation Group +LF Radio WWVB Ft. Collins, CO 60 kHz +LF Radio DCF77 Mainflingen, DE 77.5 kHz +LF Radio HBG Prangins, HB 75 kHz +LF Radio MSF Anthorn, UK 60 kHz +LF Radio JJY Fukushima, JP 40 kHz, Saga, JP 60 kHz +MF Radio LORAN C station, 100 kHz +MF Radio Allouis, FR 162 kHz +HF Radio CHU Ottawa, Ontario +HF Radio WWV Ft. Collins, CO +HF Radio WWVH Kauai, HI +NIST telephone modem +NIST telephone modem +USNO telephone modem +European telephone modem .PP Attempts to set read-only .I status
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