time.c

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/*
 *  linux/kernel/time.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *
 *  This file contains the interface functions for the various
 *  time related system calls: time, stime, gettimeofday, settimeofday,
 *                 adjtime
 */
/*
 * Modification history kernel/time.c
 *
 * 1993-09-02    Philip Gladstone
 *      Created file with time related functions from sched.c and adjtimex()
 * 1993-10-08    Torsten Duwe
 *      adjtime interface update and CMOS clock write code
 * 1995-08-13    Torsten Duwe
 *      kernel PLL updated to 1994-12-13 specs (rfc-1589)
 * 1999-01-16    Ulrich Windl
 *  Introduced error checking for many cases in adjtimex().
 *  Updated NTP code according to technical memorandum Jan '96
 *  "A Kernel Model for Precision Timekeeping" by Dave Mills
 *  Allow time_constant larger than MAXTC(6) for NTP v4 (MAXTC == 10)
 *  (Even though the technical memorandum forbids it)
 * 2004-07-14    Christoph Lameter
 *  Added getnstimeofday to allow the posix timer functions to return
 *  with nanosecond accuracy
 */

#include <linux/export.h>
#include <linux/timex.h>
#include <linux/capability.h>
#include <linux/timekeeper_internal.h>
#include <linux/errno.h>
#include <linux/syscalls.h>
#include <linux/security.h>
#include <linux/fs.h>
#include <linux/math64.h>
#include <linux/ptrace.h>

#include <asm/uaccess.h>
#include <asm/unistd.h>

#include "timeconst.h"

/*
 * The timezone where the local system is located.  Used as a default by some
 * programs who obtain this value by using gettimeofday.
 */
struct timezone sys_tz;

EXPORT_SYMBOL(sys_tz);

#ifdef __ARCH_WANT_SYS_TIME

/*
 * sys_time() can be implemented in user-level using
 * sys_gettimeofday().  Is this for backwards compatibility?  If so,
 * why not move it into the appropriate arch directory (for those
 * architectures that need it).
 */
SYSCALL_DEFINE1(time, time_t __user *, tloc)
{
    time_t i = get_seconds();

    if (tloc) {
        if (put_user(i,tloc))
            return -EFAULT;
    }
    force_successful_syscall_return();
    return i;
}

/*
 * sys_stime() can be implemented in user-level using
 * sys_settimeofday().  Is this for backwards compatibility?  If so,
 * why not move it into the appropriate arch directory (for those
 * architectures that need it).
 */

SYSCALL_DEFINE1(stime, time_t __user *, tptr)
{
    struct timespec tv;
    int err;

    if (get_user(tv.tv_sec, tptr))
        return -EFAULT;

    tv.tv_nsec = 0;

    err = security_settime(&tv, NULL);
    if (err)
        return err;

    do_settimeofday(&tv);
    return 0;
}

#endif /* __ARCH_WANT_SYS_TIME */

SYSCALL_DEFINE2(gettimeofday, struct timeval __user *, tv,
        struct timezone __user *, tz)
{
    if (likely(tv != NULL)) {
        struct timeval ktv;
        do_gettimeofday(&ktv);
        if (copy_to_user(tv, &ktv, sizeof(ktv)))
            return -EFAULT;
    }
    if (unlikely(tz != NULL)) {
        if (copy_to_user(tz, &sys_tz, sizeof(sys_tz)))
            return -EFAULT;
    }
    return 0;
}

/*
 * Adjust the time obtained from the CMOS to be UTC time instead of
 * local time.
 *
 * This is ugly, but preferable to the alternatives.  Otherwise we
 * would either need to write a program to do it in /etc/rc (and risk
 * confusion if the program gets run more than once; it would also be
 * hard to make the program warp the clock precisely n hours)  or
 * compile in the timezone information into the kernel.  Bad, bad....
 *
 *                      - TYT, 1992-01-01
 *
 * The best thing to do is to keep the CMOS clock in universal time (UTC)
 * as real UNIX machines always do it. This avoids all headaches about
 * daylight saving times and warping kernel clocks.
 */
static inline void warp_clock(void)
{
    struct timespec adjust;

    adjust = current_kernel_time();
    adjust.tv_sec += sys_tz.tz_minuteswest * 60;
    do_settimeofday(&adjust);
}

/*
 * In case for some reason the CMOS clock has not already been running
 * in UTC, but in some local time: The first time we set the timezone,
 * we will warp the clock so that it is ticking UTC time instead of
 * local time. Presumably, if someone is setting the timezone then we
 * are running in an environment where the programs understand about
 * timezones. This should be done at boot time in the /etc/rc script,
 * as soon as possible, so that the clock can be set right. Otherwise,
 * various programs will get confused when the clock gets warped.
 */

int do_sys_settimeofday(const struct timespec *tv, const struct timezone *tz)
{
    static int firsttime = 1;
    int error = 0;

    if (tv && !timespec_valid(tv))
        return -EINVAL;

    error = security_settime(tv, tz);
    if (error)
        return error;

    if (tz) {
        sys_tz = *tz;
        update_vsyscall_tz();
        if (firsttime) {
            firsttime = 0;
            if (!tv)
                warp_clock();
        }
    }
    if (tv)
        return do_settimeofday(tv);
    return 0;
}

SYSCALL_DEFINE2(settimeofday, struct timeval __user *, tv,
        struct timezone __user *, tz)
{
    struct timeval user_tv;
    struct timespec new_ts;
    struct timezone new_tz;

    if (tv) {
        if (copy_from_user(&user_tv, tv, sizeof(*tv)))
            return -EFAULT;
        new_ts.tv_sec = user_tv.tv_sec;
        new_ts.tv_nsec = user_tv.tv_usec * NSEC_PER_USEC;
    }
    if (tz) {
        if (copy_from_user(&new_tz, tz, sizeof(*tz)))
            return -EFAULT;
    }

    return do_sys_settimeofday(tv ? &new_ts : NULL, tz ? &new_tz : NULL);
}

SYSCALL_DEFINE1(adjtimex, struct timex __user *, txc_p)
{
    struct timex txc;       /* Local copy of parameter */
    int ret;

    /* Copy the user data space into the kernel copy
     * structure. But bear in mind that the structures
     * may change
     */
    if(copy_from_user(&txc, txc_p, sizeof(struct timex)))
        return -EFAULT;
    ret = do_adjtimex(&txc);
    return copy_to_user(txc_p, &txc, sizeof(struct timex)) ? -EFAULT : ret;
}

struct timespec current_fs_time(struct super_block *sb)
{
    struct timespec now = current_kernel_time();
    return timespec_trunc(now, sb->s_time_gran);
}
EXPORT_SYMBOL(current_fs_time);

/*
 * Convert jiffies to milliseconds and back.
 *
 * Avoid unnecessary multiplications/divisions in the
 * two most common HZ cases:
 */
inline unsigned int jiffies_to_msecs(const unsigned long j)
{
#if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
    return (MSEC_PER_SEC / HZ) * j;
#elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
    return (j + (HZ / MSEC_PER_SEC) - 1)/(HZ / MSEC_PER_SEC);
#else
# if BITS_PER_LONG == 32
    return (HZ_TO_MSEC_MUL32 * j) >> HZ_TO_MSEC_SHR32;
# else
    return (j * HZ_TO_MSEC_NUM) / HZ_TO_MSEC_DEN;
# endif
#endif
}
EXPORT_SYMBOL(jiffies_to_msecs);

inline unsigned int jiffies_to_usecs(const unsigned long j)
{
#if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ)
    return (USEC_PER_SEC / HZ) * j;
#elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
    return (j + (HZ / USEC_PER_SEC) - 1)/(HZ / USEC_PER_SEC);
#else
# if BITS_PER_LONG == 32
    return (HZ_TO_USEC_MUL32 * j) >> HZ_TO_USEC_SHR32;
# else
    return (j * HZ_TO_USEC_NUM) / HZ_TO_USEC_DEN;
# endif
#endif
}
EXPORT_SYMBOL(jiffies_to_usecs);

struct timespec timespec_trunc(struct timespec t, unsigned gran)
{
    /*
     * Division is pretty slow so avoid it for common cases.
     * Currently current_kernel_time() never returns better than
     * jiffies resolution. Exploit that.
     */
    if (gran <= jiffies_to_usecs(1) * 1000) {
        /* nothing */
    } else if (gran == 1000000000) {
        t.tv_nsec = 0;
    } else {
        t.tv_nsec -= t.tv_nsec % gran;
    }
    return t;
}
EXPORT_SYMBOL(timespec_trunc);

/* Converts Gregorian date to seconds since 1970-01-01 00:00:00.
 * Assumes input in normal date format, i.e. 1980-12-31 23:59:59
 * => year=1980, mon=12, day=31, hour=23, min=59, sec=59.
 *
 * [For the Julian calendar (which was used in Russia before 1917,
 * Britain & colonies before 1752, anywhere else before 1582,
 * and is still in use by some communities) leave out the
 * -year/100+year/400 terms, and add 10.]
 *
 * This algorithm was first published by Gauss (I think).
 *
 * WARNING: this function will overflow on 2106-02-07 06:28:16 on
 * machines where long is 32-bit! (However, as time_t is signed, we
 * will already get problems at other places on 2038-01-19 03:14:08)
 */
unsigned long
mktime(const unsigned int year0, const unsigned int mon0,
       const unsigned int day, const unsigned int hour,
       const unsigned int min, const unsigned int sec)
{
    unsigned int mon = mon0, year = year0;

    /* 1..12 -> 11,12,1..10 */
    if (0 >= (int) (mon -= 2)) {
        mon += 12;  /* Puts Feb last since it has leap day */
        year -= 1;
    }

    return ((((unsigned long)
          (year/4 - year/100 + year/400 + 367*mon/12 + day) +
          year*365 - 719499
        )*24 + hour /* now have hours */
      )*60 + min /* now have minutes */
    )*60 + sec; /* finally seconds */
}

EXPORT_SYMBOL(mktime);

void set_normalized_timespec(struct timespec *ts, time_t sec, s64 nsec)
{
    while (nsec >= NSEC_PER_SEC) {
        /*
         * The following asm() prevents the compiler from
         * optimising this loop into a modulo operation. See
         * also __iter_div_u64_rem() in include/linux/time.h
         */
        asm("" : "+rm"(nsec));
        nsec -= NSEC_PER_SEC;
        ++sec;
    }
    while (nsec < 0) {
        asm("" : "+rm"(nsec));
        nsec += NSEC_PER_SEC;
        --sec;
    }
    ts->tv_sec = sec;
    ts->tv_nsec = nsec;
}
EXPORT_SYMBOL(set_normalized_timespec);

struct timespec ns_to_timespec(const s64 nsec)
{
    struct timespec ts;
    s32 rem;

    if (!nsec)
        return (struct timespec) {0, 0};

    ts.tv_sec = div_s64_rem(nsec, NSEC_PER_SEC, &rem);
    if (unlikely(rem < 0)) {
        ts.tv_sec--;
        rem += NSEC_PER_SEC;
    }
    ts.tv_nsec = rem;

    return ts;
}
EXPORT_SYMBOL(ns_to_timespec);

struct timeval ns_to_timeval(const s64 nsec)
{
    struct timespec ts = ns_to_timespec(nsec);
    struct timeval tv;

    tv.tv_sec = ts.tv_sec;
    tv.tv_usec = (suseconds_t) ts.tv_nsec / 1000;

    return tv;
}
EXPORT_SYMBOL(ns_to_timeval);

/*
 * When we convert to jiffies then we interpret incoming values
 * the following way:
 *
 * - negative values mean 'infinite timeout' (MAX_JIFFY_OFFSET)
 *
 * - 'too large' values [that would result in larger than
 *   MAX_JIFFY_OFFSET values] mean 'infinite timeout' too.
 *
 * - all other values are converted to jiffies by either multiplying
 *   the input value by a factor or dividing it with a factor
 *
 * We must also be careful about 32-bit overflows.
 */
unsigned long msecs_to_jiffies(const unsigned int m)
{
    /*
     * Negative value, means infinite timeout:
     */
    if ((int)m < 0)
        return MAX_JIFFY_OFFSET;

#if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
    /*
     * HZ is equal to or smaller than 1000, and 1000 is a nice
     * round multiple of HZ, divide with the factor between them,
     * but round upwards:
     */
    return (m + (MSEC_PER_SEC / HZ) - 1) / (MSEC_PER_SEC / HZ);
#elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
    /*
     * HZ is larger than 1000, and HZ is a nice round multiple of
     * 1000 - simply multiply with the factor between them.
     *
     * But first make sure the multiplication result cannot
     * overflow:
     */
    if (m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
        return MAX_JIFFY_OFFSET;

    return m * (HZ / MSEC_PER_SEC);
#else
    /*
     * Generic case - multiply, round and divide. But first
     * check that if we are doing a net multiplication, that
     * we wouldn't overflow:
     */
    if (HZ > MSEC_PER_SEC && m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
        return MAX_JIFFY_OFFSET;

    return (MSEC_TO_HZ_MUL32 * m + MSEC_TO_HZ_ADJ32)
        >> MSEC_TO_HZ_SHR32;
#endif
}
EXPORT_SYMBOL(msecs_to_jiffies);

unsigned long usecs_to_jiffies(const unsigned int u)
{
    if (u > jiffies_to_usecs(MAX_JIFFY_OFFSET))
        return MAX_JIFFY_OFFSET;
#if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ)
    return (u + (USEC_PER_SEC / HZ) - 1) / (USEC_PER_SEC / HZ);
#elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
    return u * (HZ / USEC_PER_SEC);
#else
    return (USEC_TO_HZ_MUL32 * u + USEC_TO_HZ_ADJ32)
        >> USEC_TO_HZ_SHR32;
#endif
}
EXPORT_SYMBOL(usecs_to_jiffies);

/*
 * The TICK_NSEC - 1 rounds up the value to the next resolution.  Note
 * that a remainder subtract here would not do the right thing as the
 * resolution values don't fall on second boundries.  I.e. the line:
 * nsec -= nsec % TICK_NSEC; is NOT a correct resolution rounding.
 *
 * Rather, we just shift the bits off the right.
 *
 * The >> (NSEC_JIFFIE_SC - SEC_JIFFIE_SC) converts the scaled nsec
 * value to a scaled second value.
 */
unsigned long
timespec_to_jiffies(const struct timespec *value)
{
    unsigned long sec = value->tv_sec;
    long nsec = value->tv_nsec + TICK_NSEC - 1;

    if (sec >= MAX_SEC_IN_JIFFIES){
        sec = MAX_SEC_IN_JIFFIES;
        nsec = 0;
    }
    return (((u64)sec * SEC_CONVERSION) +
        (((u64)nsec * NSEC_CONVERSION) >>
         (NSEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC;

}
EXPORT_SYMBOL(timespec_to_jiffies);

void
jiffies_to_timespec(const unsigned long jiffies, struct timespec *value)
{
    /*
     * Convert jiffies to nanoseconds and separate with
     * one divide.
     */
    u32 rem;
    value->tv_sec = div_u64_rem((u64)jiffies * TICK_NSEC,
                    NSEC_PER_SEC, &rem);
    value->tv_nsec = rem;
}
EXPORT_SYMBOL(jiffies_to_timespec);

/* Same for "timeval"
 *
 * Well, almost.  The problem here is that the real system resolution is
 * in nanoseconds and the value being converted is in micro seconds.
 * Also for some machines (those that use HZ = 1024, in-particular),
 * there is a LARGE error in the tick size in microseconds.

 * The solution we use is to do the rounding AFTER we convert the
 * microsecond part.  Thus the USEC_ROUND, the bits to be shifted off.
 * Instruction wise, this should cost only an additional add with carry
 * instruction above the way it was done above.
 */
unsigned long
timeval_to_jiffies(const struct timeval *value)
{
    unsigned long sec = value->tv_sec;
    long usec = value->tv_usec;

    if (sec >= MAX_SEC_IN_JIFFIES){
        sec = MAX_SEC_IN_JIFFIES;
        usec = 0;
    }
    return (((u64)sec * SEC_CONVERSION) +
        (((u64)usec * USEC_CONVERSION + USEC_ROUND) >>
         (USEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC;
}
EXPORT_SYMBOL(timeval_to_jiffies);

void jiffies_to_timeval(const unsigned long jiffies, struct timeval *value)
{
    /*
     * Convert jiffies to nanoseconds and separate with
     * one divide.
     */
    u32 rem;

    value->tv_sec = div_u64_rem((u64)jiffies * TICK_NSEC,
                    NSEC_PER_SEC, &rem);
    value->tv_usec = rem / NSEC_PER_USEC;
}
EXPORT_SYMBOL(jiffies_to_timeval);

/*
 * Convert jiffies/jiffies_64 to clock_t and back.
 */
clock_t jiffies_to_clock_t(unsigned long x)
{
#if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
# if HZ < USER_HZ
    return x * (USER_HZ / HZ);
# else
    return x / (HZ / USER_HZ);
# endif
#else
    return div_u64((u64)x * TICK_NSEC, NSEC_PER_SEC / USER_HZ);
#endif
}
EXPORT_SYMBOL(jiffies_to_clock_t);

unsigned long clock_t_to_jiffies(unsigned long x)
{
#if (HZ % USER_HZ)==0
    if (x >= ~0UL / (HZ / USER_HZ))
        return ~0UL;
    return x * (HZ / USER_HZ);
#else
    /* Don't worry about loss of precision here .. */
    if (x >= ~0UL / HZ * USER_HZ)
        return ~0UL;

    /* .. but do try to contain it here */
    return div_u64((u64)x * HZ, USER_HZ);
#endif
}
EXPORT_SYMBOL(clock_t_to_jiffies);

u64 jiffies_64_to_clock_t(u64 x)
{
#if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
# if HZ < USER_HZ
    x = div_u64(x * USER_HZ, HZ);
# elif HZ > USER_HZ
    x = div_u64(x, HZ / USER_HZ);
# else
    /* Nothing to do */
# endif
#else
    /*
     * There are better ways that don't overflow early,
     * but even this doesn't overflow in hundreds of years
     * in 64 bits, so..
     */
    x = div_u64(x * TICK_NSEC, (NSEC_PER_SEC / USER_HZ));
#endif
    return x;
}
EXPORT_SYMBOL(jiffies_64_to_clock_t);

u64 nsec_to_clock_t(u64 x)
{
#if (NSEC_PER_SEC % USER_HZ) == 0
    return div_u64(x, NSEC_PER_SEC / USER_HZ);
#elif (USER_HZ % 512) == 0
    return div_u64(x * USER_HZ / 512, NSEC_PER_SEC / 512);
#else
    /*
         * max relative error 5.7e-8 (1.8s per year) for USER_HZ <= 1024,
         * overflow after 64.99 years.
         * exact for HZ=60, 72, 90, 120, 144, 180, 300, 600, 900, ...
         */
    return div_u64(x * 9, (9ull * NSEC_PER_SEC + (USER_HZ / 2)) / USER_HZ);
#endif
}

u64 nsecs_to_jiffies64(u64 n)
{
#if (NSEC_PER_SEC % HZ) == 0
    /* Common case, HZ = 100, 128, 200, 250, 256, 500, 512, 1000 etc. */
    return div_u64(n, NSEC_PER_SEC / HZ);
#elif (HZ % 512) == 0
    /* overflow after 292 years if HZ = 1024 */
    return div_u64(n * HZ / 512, NSEC_PER_SEC / 512);
#else
    /*
     * Generic case - optimized for cases where HZ is a multiple of 3.
     * overflow after 64.99 years, exact for HZ = 60, 72, 90, 120 etc.
     */
    return div_u64(n * 9, (9ull * NSEC_PER_SEC + HZ / 2) / HZ);
#endif
}

unsigned long nsecs_to_jiffies(u64 n)
{
    return (unsigned long)nsecs_to_jiffies64(n);
}

/*
 * 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;
}