inittodr(9): introduce dedicated flag to enable writes from resettodr(9)

We don't want resettodr(9) to write the RTC until inittodr(9) has
actually run.  Until inittodr(9) calls tc_setclock() the system UTC
clock will contain a meaningless value and there's no sense in
overwriting a good value with a value we know is nonsense.

This is not an uncommon problem if you're debugging a problem in early
boot, e.g. a panic that occurs prior to inittodr(9).

Currently we use the following logic in resettodr(9) to inhibit writes:

	if (time_second == 1)
		return;

... this is too magical.

A better way to accomplish the same thing is to introduce a dedicated
flag set from inittodr(9).  Hence, "inittodr_done".

Suggested by visa@.

ok kettenis@

1 files changed, 9 insertions, 2 deletions

diff --git a/sys/kern/kern_time.c b/sys/kern/kern_time.c
index 6be556ecf2a..741bc2b9650 100644
--- a/sys/kern/kern_time.c
+++ b/sys/kern/kern_time.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: kern_time.c,v 1.130 2020/05/20 17:23:01 cheloha Exp $	*/
+/*	$OpenBSD: kern_time.c,v 1.131 2020/06/22 18:25:57 cheloha Exp $	*/
 /*	$NetBSD: kern_time.c,v 1.20 1996/02/18 11:57:06 fvdl Exp $	*/
 
 /*
@@ -778,6 +778,7 @@ ppsratecheck(struct timeval *lasttime, int *curpps, int maxpps)
 }
 
 todr_chip_handle_t todr_handle;
+int inittodr_done;
 
 #define MINYEAR		((OpenBSD / 100) - 1)	/* minimum plausible year */
 
@@ -794,6 +795,8 @@ inittodr(time_t base)
 	struct timespec ts;
 	int badbase;
 
+	inittodr_done = 1;
+
 	if (base < (MINYEAR - 1970) * SECYR) {
 		printf("WARNING: preposterous time in file system\n");
 		/* read the system clock anyway */
@@ -856,7 +859,11 @@ resettodr(void)
 {
 	struct timeval rtctime;
 
-	if (time_second == 1)
+	/*
+	 * Skip writing the RTC if inittodr(9) never ran.  We don't
+	 * want to overwrite a reasonable value with a nonsense value.
+	 */
+	if (!inittodr_done)
 		return;
 
 	microtime(&rtctime);