the time corrections must be interlocked.  also, there's no need to expose
the internal workings of time time mechanism.

todo: using two seperate locks is probablly not a good idea.

Reference: /n/atom/patch/applied2013/timclean
Date: Thu Oct  3 16:31:14 CES 2013
Signed-off-by: quanstro@quanstro.net

--- /sys/src/fs/port/time.c	Thu Oct  3 16:29:10 2013
+++ /sys/src/fs/port/time.c	Thu Oct  3 16:29:10 2013
@@ -1,6 +1,15 @@
 #include	"all.h"
 
-typedef struct Toy Toy;
+typedef	struct	Time	Time;
+typedef	struct	Toy	Toy;
+
+struct Time {
+	Lock;
+	Timet	lasttoy;
+	Timet	bias;
+	Timet	offset;
+};
+
 struct Toy {
 	Lock;
 	Timet	base;
@@ -8,6 +17,7 @@
 };
 
 static Toy toy;
+static Time tim;
 
 enum {
 	T	= 500000000,		/* needs to be 0 mod HZ */
@@ -147,9 +157,12 @@
 
 	t = toytime();
 	while(tim.bias != 0) {			/* adjust at rate 1 sec/min */
+		ilock(&tim);
 		dt = t - tim.lasttoy;
-		if(dt < MINUTE(1))
+		if(dt < MINUTE(1)){
+			iunlock(&tim);
 			break;
+		}
 		if(tim.bias >= 0) {
 			tim.bias -= SECOND(1);
 			tim.offset += SECOND(1);
@@ -158,6 +171,7 @@
 			tim.offset -= SECOND(1);
 		}
 		tim.lasttoy += MINUTE(1);
+		iunlock(&tim);
 	}
 	return t + tim.offset;
 }
@@ -165,15 +179,18 @@
 void
 settime(Timet nt)
 {
-	Timet dt;
+	Timet dt, toy;
 
 	dt = nt - time();
-	tim.lasttoy = toytime();
+	toy = toytime();
+	ilock(&tim);
+	tim.lasttoy = toy;
 	if(dt > MAXBIAS || dt < -MAXBIAS) {	/* too much, just set it */
 		tim.bias = 0;
 		tim.offset = nt - tim.lasttoy;
 	} else
 		tim.bias = dt;
+	iunlock(&tim);
 }
 
 void
--- /sys/src/fs/port/all.h	Thu Oct  3 16:29:11 2013
+++ /sys/src/fs/port/all.h	Thu Oct  3 16:29:11 2013
@@ -35,7 +35,6 @@
 Uid*	uid;
 Userid*	gidspace;
 Lock	printing;
-Time	tim;
 File*	files;
 Wpath*	wpaths;
 Lock	wpathlock;
--- /sys/src/fs/port/portdat.h	Thu Oct  3 16:29:13 2013
+++ /sys/src/fs/port/portdat.h	Thu Oct  3 16:29:14 2013
@@ -94,7 +94,6 @@
 typedef	struct	File	File;
 typedef	struct	Chan	Chan;
 typedef	struct	Cons	Cons;
-typedef	struct	Time	Time;
 typedef	struct	Tm	Tm;
 typedef	struct	Rtc	Rtc;
 typedef	struct	Hiob	Hiob;
@@ -326,13 +325,6 @@
 {
 	char*	name;
 	Off	startsb;
-};
-
-struct	Time
-{
-	Timet	lasttoy;
-	Timet	bias;
-	Timet	offset;
 };
 
 /*