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current_kernel_time

struct timespec current_kernel_time(void)
{
    struct timespec now;
    unsigned long seq;

    do {
        seq = read_seqbegin(&xtime_lock);

        now = xtime;
    } while (read_seqretry(&xtime_lock, seq));

    return now;
}

do_gettimeofday

struct timespec {
    __kernel_time_t tv_sec;         /* seconds */
    long        tv_nsec;        /* nanoseconds */
};

void do_gettimeofday(struct timeval *tv)
{
    struct timespec now;

    getnstimeofday(&now);
    tv->tv_sec = now.tv_sec;
    tv->tv_usec = now.tv_nsec/1000;
}

void getnstimeofday(struct timespec *ts)
{
    unsigned long seq;
    s64 nsecs;

    WARN_ON(timekeeping_suspended);

    do {
        seq = read_seqbegin(&xtime_lock);

        *ts = xtime;
        nsecs = timekeeping_get_ns();

        /* If arch requires, add in gettimeoffset() */
        nsecs += arch_gettimeoffset();

    } while (read_seqretry(&xtime_lock, seq));

    timespec_add_ns(ts, nsecs);
}

rtc_time_to_tm

struct rtc_time {
    int tm_sec;
    int tm_min;
    int tm_hour;
    int tm_mday;
    int tm_mon;
    int tm_year;
    int tm_wday;
    int tm_yday;
    int tm_isdst;
};

int rtc_tm_to_time(struct rtc_time *tm, unsigned long *time)
{
    *time = mktime(tm->tm_year + 1900, tm->tm_mon + 1, tm->tm_mday,
            tm->tm_hour, tm->tm_min, tm->tm_sec);
    return 0;
}

rtc_time_to_tm

void rtc_time_to_tm(unsigned long time, struct rtc_time *tm)
{
    unsigned int month, year;
    int days;

    days = time / 86400;
    time -= (unsigned int) days * 86400;

    /* day of the week, 1970-01-01 was a Thursday */
    tm->tm_wday = (days + 4) % 7;

    year = 1970 + days / 365;
    days -= (year - 1970) * 365
        + LEAPS_THRU_END_OF(year - 1)
        - LEAPS_THRU_END_OF(1970 - 1);
    if (days < 0) {
        year -= 1;
        days += 365 + is_leap_year(year);
    }
    tm->tm_year = year - 1900;
    tm->tm_yday = days + 1;

    for (month = 0; month < 11; month++) {
        int newdays;

        newdays = days - rtc_month_days(month, year);
        if (newdays < 0)
            break;
        days = newdays;
    }
    tm->tm_mon = month;
    tm->tm_mday = days + 1;

    tm->tm_hour = time / 3600;
    time -= tm->tm_hour * 3600;
    tm->tm_min = time / 60;
    tm->tm_sec = time - tm->tm_min * 60;
}