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Rework VTIME calculations so that they don't hit numeric overflow (ok now

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for hz < ~200kHz).  Old code failed VTIME > 214 even with hz=100.
Fixes kern/12285.
This commit is contained in:
dsl 2003-08-11 10:49:06 +00:00
parent 9f987d0ac0
commit 3530472a3b
1 changed files with 16 additions and 10 deletions
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26
sys/kern/tty.c
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@ -1,4 +1,4 @@
/* $NetBSD: tty.c,v 1.155 2003/08/07 16:31:55 agc Exp $ */ /* $NetBSD: tty.c,v 1.156 2003/08/11 10:49:06 dsl Exp $ */
/*- /*-
* Copyright (c) 1982, 1986, 1990, 1991, 1993 * Copyright (c) 1982, 1986, 1990, 1991, 1993
@ -37,7 +37,7 @@
*/ */
#include <sys/cdefs.h> #include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: tty.c,v 1.155 2003/08/07 16:31:55 agc Exp $"); __KERNEL_RCSID(0, "$NetBSD: tty.c,v 1.156 2003/08/11 10:49:06 dsl Exp $");
#include <sys/param.h> #include <sys/param.h>
#include <sys/systm.h> #include <sys/systm.h>
@ -1596,9 +1596,13 @@ ttread(struct tty *tp, struct uio *uio, int flag)
goto sleep; goto sleep;
goto read; goto read;
} }
t *= 100000; /* time in us */ t *= hz; /* time in deca-ticks */
#define diff(t1, t2) (((t1).tv_sec - (t2).tv_sec) * 1000000 + \ /*
((t1).tv_usec - (t2).tv_usec)) * Time difference in deca-ticks, split division to avoid numeric overflow.
* Ok for hz < ~200kHz
*/
#define diff(t1, t2) (((t1).tv_sec - (t2).tv_sec) * 10 * hz + \
((t1).tv_usec - (t2).tv_usec) / 100 * hz / 1000)
if (m > 0) { if (m > 0) {
if (qp->c_cc <= 0) if (qp->c_cc <= 0)
goto sleep; goto sleep;
@ -1631,14 +1635,16 @@ ttread(struct tty *tp, struct uio *uio, int flag)
#undef diff #undef diff
if (slp > 0) { if (slp > 0) {
/* /*
* Convert deca-ticks back to ticks.
* Rounding down may make us wake up just short * Rounding down may make us wake up just short
* of the target, so we round up. * of the target, so we round up.
* The formula is ceiling(slp * hz/1000000). * Maybe we should do 'slp/10 + 1' because the
* 32-bit arithmetic is enough for hz < 169. * first tick maybe almost immediate.
* * However it is more useful for a program that sets
* Also, use plain wakeup() not ttwakeup(). * VTIME=10 to wakeup every second not every 1.01
* seconds (if hz=100).
*/ */
slp = (long) (((u_long)slp * hz) + 999999) / 1000000; slp = (slp + 9)/ 10;
goto sleep; goto sleep;
} }
} else if ((qp = &tp->t_canq)->c_cc <= 0) { } else if ((qp = &tp->t_canq)->c_cc <= 0) {