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select: add a timespec_add_safe() function

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For the select() rework, it's important to be able to add timespec
structures in an overflow-safe manner.

This patch adds a timespec_add_safe() function for this which is similar in
operation to ktime_add_safe(), but works on a struct timespec.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
This commit is contained in:
Thomas Gleixner 2008-08-31 08:09:53 -07:00 committed by Arjan van de Ven
parent 7bb67439bf
commit df0cc0539b
2 changed files with 22 additions and 0 deletions
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4
include/linux/time.h
View file

@ -38,6 +38,8 @@ struct timezone {
#define NSEC_PER_SEC 1000000000L
#define FSEC_PER_SEC 1000000000000000L
#define TIME_T_MAX (time_t)((1UL << ((sizeof(time_t) << 3) - 1)) - 1)
static inline int timespec_equal(const struct timespec *a,
const struct timespec *b)
{
@ -72,6 +74,8 @@ extern unsigned long mktime(const unsigned int year, const unsigned int mon,
const unsigned int min, const unsigned int sec);
extern void set_normalized_timespec(struct timespec *ts, time_t sec, long nsec);
extern struct timespec timespec_add_safe(const struct timespec lhs,
const struct timespec rhs);
/*
* sub = lhs - rhs, in normalized form

18
kernel/time.c
View file

@ -669,3 +669,21 @@ EXPORT_SYMBOL(get_jiffies_64);
#endif
EXPORT_SYMBOL(jiffies);
/*
* Add two timespec values and do a safety check for overflow.
* It's assumed that both values are valid (>= 0)
*/
struct timespec timespec_add_safe(const struct timespec lhs,
const struct timespec rhs)
{
struct timespec res;
set_normalized_timespec(&res, lhs.tv_sec + rhs.tv_sec,
lhs.tv_nsec + rhs.tv_nsec);
if (res.tv_sec < lhs.tv_sec || res.tv_sec < rhs.tv_sec)
res.tv_sec = TIME_T_MAX;
return res;
}