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time: add ADJ_OFFSET_SS_READ

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Michael Kerrisk reported that a long standing bug in the adjtimex()
system call causes glibc's adjtime(3) function to deliver the wrong
results if 'delta' is NULL.

add the ADJ_OFFSET_SS_READ API detail, which will be used by glibc
to fix this API compatibility bug.

Also see: http://bugzilla.kernel.org/show_bug.cgi?id=6761

[ mingo@elte.hu: added patch description and made it backwards compatible ]

NOTE: the new flag is defined 0xa001 so that it returns -EINVAL on
older kernels - this way glibc can use it safely. Suggested by Ulrich
Drepper.

Acked-by: Ulrich Drepper <drepper@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
John Stultz 2007-11-26 20:42:19 +01:00 committed by Ingo Molnar
parent 8232fd6252
commit 52bfb36050
2 changed files with 7 additions and 3 deletions
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1
include/linux/timex.h
View File

@ -137,6 +137,7 @@ struct timex {
#define ADJ_TIMECONST 0x0020 /* pll time constant */
#define ADJ_TICK 0x4000 /* tick value */
#define ADJ_OFFSET_SINGLESHOT 0x8001 /* old-fashioned adjtime */
#define ADJ_OFFSET_SS_READ 0xa001 /* read-only adjtime */
/* xntp 3.4 compatibility names */
#define MOD_OFFSET ADJ_OFFSET

9
kernel/time/ntp.c
View File

@ -249,10 +249,12 @@ int do_adjtimex(struct timex *txc)
/* Now we validate the data before disabling interrupts */
if ((txc->modes & ADJ_OFFSET_SINGLESHOT) == ADJ_OFFSET_SINGLESHOT)
if ((txc->modes & ADJ_OFFSET_SINGLESHOT) == ADJ_OFFSET_SINGLESHOT) {
/* singleshot must not be used with any other mode bits */
if (txc->modes != ADJ_OFFSET_SINGLESHOT)
if (txc->modes != ADJ_OFFSET_SINGLESHOT &&
txc->modes != ADJ_OFFSET_SS_READ)
return -EINVAL;
}
if (txc->modes != ADJ_OFFSET_SINGLESHOT && (txc->modes & ADJ_OFFSET))
/* adjustment Offset limited to +- .512 seconds */
@ -372,7 +374,8 @@ int do_adjtimex(struct timex *txc)
leave: if ((time_status & (STA_UNSYNC|STA_CLOCKERR)) != 0)
result = TIME_ERROR;
if ((txc->modes & ADJ_OFFSET_SINGLESHOT) == ADJ_OFFSET_SINGLESHOT)
if ((txc->modes == ADJ_OFFSET_SINGLESHOT) ||
(txc->modes == ADJ_OFFSET_SS_READ))
txc->offset = save_adjust;
else
txc->offset = ((long)shift_right(time_offset, SHIFT_UPDATE)) *