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periodically save system time to hardware time-of-day clock

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This is done in kern_ntptime, perhaps not the best place.
This is done using resettodr().
Some features:
- make save period configurable via tunable and sysctl
- period of zero disables saving, setting a non-zero period re-enables
  it or reschedules it
- do saving only if system clock is ntp-synchronized
- save on shutdown

Discussed with:	des, Peter Jeremy <peterjeremy@acm.org>
X-Maybe:		save time near seconds boundary for better precision
MFC after:		2 weeks
This commit is contained in:
avg 2010-04-29 09:02:46 +00:00
parent cbff4850b6
commit cce2a4186b
1 changed files with 65 additions and 0 deletions
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65
sys/kern/kern_ntptime.c
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@ -38,6 +38,7 @@ __FBSDID("$FreeBSD$");
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/sysproto.h>
#include <sys/eventhandler.h>
#include <sys/kernel.h>
#include <sys/priv.h>
#include <sys/proc.h>
@ -976,3 +977,67 @@ kern_adjtime(struct thread *td, struct timeval *delta, struct timeval *olddelta)
return (0);
}
static struct callout resettodr_callout;
static int resettodr_period = 1800;
static void
periodic_resettodr(void *arg __unused)
{
if (!ntp_is_time_error()) {
mtx_lock(&Giant);
resettodr();
mtx_unlock(&Giant);
}
if (resettodr_period > 0)
callout_schedule(&resettodr_callout, resettodr_period * hz);
}
static void
shutdown_resettodr(void *arg __unused, int howto __unused)
{
callout_drain(&resettodr_callout);
if (resettodr_period > 0 && !ntp_is_time_error()) {
mtx_lock(&Giant);
resettodr();
mtx_unlock(&Giant);
}
}
static int
sysctl_resettodr_period(SYSCTL_HANDLER_ARGS)
{
int error;
error = sysctl_handle_int(oidp, oidp->oid_arg1, oidp->oid_arg2, req);
if (error || !req->newptr)
return (error);
if (resettodr_period == 0)
callout_stop(&resettodr_callout);
else
callout_reset(&resettodr_callout, resettodr_period * hz,
periodic_resettodr, NULL);
return (0);
}
SYSCTL_PROC(_machdep, OID_AUTO, rtc_save_period, CTLTYPE_INT|CTLFLAG_RW,
&resettodr_period, 1800, sysctl_resettodr_period, "I",
"Save system time to RTC with this period (in seconds)");
TUNABLE_INT("machdep.rtc_save_period", &resettodr_period);
static void
start_periodic_resettodr(void *arg __unused)
{
EVENTHANDLER_REGISTER(shutdown_pre_sync, shutdown_resettodr, NULL,
SHUTDOWN_PRI_FIRST);
callout_init(&resettodr_callout, 1);
if (resettodr_period == 0)
return;
callout_reset(&resettodr_callout, resettodr_period * hz,
periodic_resettodr, NULL);
}
SYSINIT(periodic_resettodr, SI_SUB_RUN_SCHEDULER, SI_ORDER_ANY - 1,
start_periodic_resettodr, NULL);