On Wed, Aug 04, 2010 at 03:48:28PM +0300, Alexander Shishkin wrote: > Certain userspace applications (like "clock" desktop applets or ntpd) might > want to be notified when some other application changes the system time. It > might also be important for an application to be able to distinguish between > its own and somebody else's time changes. > > This patch implements a notification interface via eventfd mechanism. Proccess > wishing to be notified about time changes should create an eventfd and echo > its file descriptor to /sys/kernel/time_notify. After that, any calls to > settimeofday()/stime()/adjtimex() made by other processes will be signalled > to this eventfd. Credits for suggesting the eventfd mechanism for this > purpose go te Kirill Shutemov. > > So far, this implementation can only filter out notifications caused by > time change calls made by the process that wrote the eventfd descriptor to > sysfs, but not its children which (might) have inherited the eventfd. It > is so far not clear to me whether this is bad and more confusing than > excluding such children as well. I think it's a bad idea to filter notifications. Let's leave it for userspace. Userspace always can check eventfd counter and understand who touch time based on its own activity. > Similar mechanism can also be used for signalling other (all?) system calls > made by certain (all?) processes without resorting to ptrace (which won't > help if you don't know what processes you'd like to look after), given > proper permission checks etc. > > Signed-off-by: Alexander Shishkin <virtuoso@xxxxxxxxx> > CC: Kirill A. Shutemov <kirill@xxxxxxxxxxxxx> > CC: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > CC: John Stultz <johnstul@xxxxxxxxxx> > CC: Martin Schwidefsky <schwidefsky@xxxxxxxxxx> > CC: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > CC: Jon Hunter <jon-hunter@xxxxxx> > CC: Ingo Molnar <mingo@xxxxxxx> > CC: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> > CC: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx> > CC: David Howells <dhowells@xxxxxxxxxx> > CC: Avi Kivity <avi@xxxxxxxxxx> > CC: "H. Peter Anvin" <hpa@xxxxxxxxx> > CC: John Kacur <jkacur@xxxxxxxxxx> > CC: Alexander Shishkin <virtuoso@xxxxxxxxx> > CC: linux-kernel@xxxxxxxxxxxxxxx > --- > include/linux/time.h | 7 ++ > init/Kconfig | 7 ++ > kernel/Makefile | 1 + > kernel/time.c | 11 +++- > kernel/time_notify.c | 158 ++++++++++++++++++++++++++++++++++++++++++++++++++ > 5 files changed, 182 insertions(+), 2 deletions(-) > create mode 100644 kernel/time_notify.c > > diff --git a/include/linux/time.h b/include/linux/time.h > index ea3559f..9fca62b 100644 > --- a/include/linux/time.h > +++ b/include/linux/time.h > @@ -237,6 +237,13 @@ static __always_inline void timespec_add_ns(struct timespec *a, u64 ns) > a->tv_sec += __iter_div_u64_rem(a->tv_nsec + ns, NSEC_PER_SEC, &ns); > a->tv_nsec = ns; > } > + > +#ifdef CONFIG_TIME_NOTIFY > +void time_notify_all(void); > +#else > +#define time_notify_all() do {} while (0) > +#endif > + > #endif /* __KERNEL__ */ > > #define NFDBITS __NFDBITS > diff --git a/init/Kconfig b/init/Kconfig > index 5cff9a9..f7271f8 100644 > --- a/init/Kconfig > +++ b/init/Kconfig > @@ -976,6 +976,13 @@ config PERF_USE_VMALLOC > help > See tools/perf/design.txt for details > > +config TIME_NOTIFY > + bool > + depends on EVENTFD > + help > + Enable time change notification events to userspace via > + eventfd. > + Do we really need config option? I think better just use CONFIG_EVENTFD. linux-api@xxxxxxxxxxxxxxx added to CC list. -- Kirill A. Shutemov -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html