itimer.c

Go to the documentation of this file.

/*
 * linux/kernel/itimer.c
 *
 * Copyright (C) 1992 Darren Senn
 */

/* These are all the functions necessary to implement itimers */

#include <linux/mm.h>
#include <linux/interrupt.h>
#include <linux/syscalls.h>
#include <linux/time.h>
#include <linux/posix-timers.h>
#include <linux/hrtimer.h>
#include <trace/events/timer.h>

#include <asm/uaccess.h>

static struct timeval itimer_get_remtime(struct hrtimer *timer)
{
    ktime_t rem = hrtimer_get_remaining(timer);

    /*
     * Racy but safe: if the itimer expires after the above
     * hrtimer_get_remtime() call but before this condition
     * then we return 0 - which is correct.
     */
    if (hrtimer_active(timer)) {
        if (rem.tv64 <= 0)
            rem.tv64 = NSEC_PER_USEC;
    } else
        rem.tv64 = 0;

    return ktime_to_timeval(rem);
}

static void get_cpu_itimer(struct task_struct *tsk, unsigned int clock_id,
               struct itimerval *const value)
{
    cputime_t cval, cinterval;
    struct cpu_itimer *it = &tsk->signal->it[clock_id];

    spin_lock_irq(&tsk->sighand->siglock);

    cval = it->expires;
    cinterval = it->incr;
    if (cval) {
        struct task_cputime cputime;
        cputime_t t;

        thread_group_cputimer(tsk, &cputime);
        if (clock_id == CPUCLOCK_PROF)
            t = cputime.utime + cputime.stime;
        else
            /* CPUCLOCK_VIRT */
            t = cputime.utime;

        if (cval < t)
            /* about to fire */
            cval = cputime_one_jiffy;
        else
            cval = cval - t;
    }

    spin_unlock_irq(&tsk->sighand->siglock);

    cputime_to_timeval(cval, &value->it_value);
    cputime_to_timeval(cinterval, &value->it_interval);
}

int do_getitimer(int which, struct itimerval *value)
{
    struct task_struct *tsk = current;

    switch (which) {
    case ITIMER_REAL:
        spin_lock_irq(&tsk->sighand->siglock);
        value->it_value = itimer_get_remtime(&tsk->signal->real_timer);
        value->it_interval =
            ktime_to_timeval(tsk->signal->it_real_incr);
        spin_unlock_irq(&tsk->sighand->siglock);
        break;
    case ITIMER_VIRTUAL:
        get_cpu_itimer(tsk, CPUCLOCK_VIRT, value);
        break;
    case ITIMER_PROF:
        get_cpu_itimer(tsk, CPUCLOCK_PROF, value);
        break;
    default:
        return(-EINVAL);
    }
    return 0;
}

SYSCALL_DEFINE2(getitimer, int, which, struct itimerval __user *, value)
{
    int error = -EFAULT;
    struct itimerval get_buffer;

    if (value) {
        error = do_getitimer(which, &get_buffer);
        if (!error &&
            copy_to_user(value, &get_buffer, sizeof(get_buffer)))
            error = -EFAULT;
    }
    return error;
}


/*
 * The timer is automagically restarted, when interval != 0
 */
enum hrtimer_restart it_real_fn(struct hrtimer *timer)
{
    struct signal_struct *sig =
        container_of(timer, struct signal_struct, real_timer);

    trace_itimer_expire(ITIMER_REAL, sig->leader_pid, 0);
    kill_pid_info(SIGALRM, SEND_SIG_PRIV, sig->leader_pid);

    return HRTIMER_NORESTART;
}

static inline u32 cputime_sub_ns(cputime_t ct, s64 real_ns)
{
    struct timespec ts;
    s64 cpu_ns;

    cputime_to_timespec(ct, &ts);
    cpu_ns = timespec_to_ns(&ts);

    return (cpu_ns <= real_ns) ? 0 : cpu_ns - real_ns;
}

static void set_cpu_itimer(struct task_struct *tsk, unsigned int clock_id,
               const struct itimerval *const value,
               struct itimerval *const ovalue)
{
    cputime_t cval, nval, cinterval, ninterval;
    s64 ns_ninterval, ns_nval;
    u32 error, incr_error;
    struct cpu_itimer *it = &tsk->signal->it[clock_id];

    nval = timeval_to_cputime(&value->it_value);
    ns_nval = timeval_to_ns(&value->it_value);
    ninterval = timeval_to_cputime(&value->it_interval);
    ns_ninterval = timeval_to_ns(&value->it_interval);

    error = cputime_sub_ns(nval, ns_nval);
    incr_error = cputime_sub_ns(ninterval, ns_ninterval);

    spin_lock_irq(&tsk->sighand->siglock);

    cval = it->expires;
    cinterval = it->incr;
    if (cval || nval) {
        if (nval > 0)
            nval += cputime_one_jiffy;
        set_process_cpu_timer(tsk, clock_id, &nval, &cval);
    }
    it->expires = nval;
    it->incr = ninterval;
    it->error = error;
    it->incr_error = incr_error;
    trace_itimer_state(clock_id == CPUCLOCK_VIRT ?
               ITIMER_VIRTUAL : ITIMER_PROF, value, nval);

    spin_unlock_irq(&tsk->sighand->siglock);

    if (ovalue) {
        cputime_to_timeval(cval, &ovalue->it_value);
        cputime_to_timeval(cinterval, &ovalue->it_interval);
    }
}

/*
 * Returns true if the timeval is in canonical form
 */
#define timeval_valid(t) \
    (((t)->tv_sec >= 0) && (((unsigned long) (t)->tv_usec) < USEC_PER_SEC))

int do_setitimer(int which, struct itimerval *value, struct itimerval *ovalue)
{
    struct task_struct *tsk = current;
    struct hrtimer *timer;
    ktime_t expires;

    /*
     * Validate the timevals in value.
     */
    if (!timeval_valid(&value->it_value) ||
        !timeval_valid(&value->it_interval))
        return -EINVAL;

    switch (which) {
    case ITIMER_REAL:
again:
        spin_lock_irq(&tsk->sighand->siglock);
        timer = &tsk->signal->real_timer;
        if (ovalue) {
            ovalue->it_value = itimer_get_remtime(timer);
            ovalue->it_interval
                = ktime_to_timeval(tsk->signal->it_real_incr);
        }
        /* We are sharing ->siglock with it_real_fn() */
        if (hrtimer_try_to_cancel(timer) < 0) {
            spin_unlock_irq(&tsk->sighand->siglock);
            goto again;
        }
        expires = timeval_to_ktime(value->it_value);
        if (expires.tv64 != 0) {
            tsk->signal->it_real_incr =
                timeval_to_ktime(value->it_interval);
            hrtimer_start(timer, expires, HRTIMER_MODE_REL);
        } else
            tsk->signal->it_real_incr.tv64 = 0;

        trace_itimer_state(ITIMER_REAL, value, 0);
        spin_unlock_irq(&tsk->sighand->siglock);
        break;
    case ITIMER_VIRTUAL:
        set_cpu_itimer(tsk, CPUCLOCK_VIRT, value, ovalue);
        break;
    case ITIMER_PROF:
        set_cpu_itimer(tsk, CPUCLOCK_PROF, value, ovalue);
        break;
    default:
        return -EINVAL;
    }
    return 0;
}

unsigned int alarm_setitimer(unsigned int seconds)
{
    struct itimerval it_new, it_old;

#if BITS_PER_LONG < 64
    if (seconds > INT_MAX)
        seconds = INT_MAX;
#endif
    it_new.it_value.tv_sec = seconds;
    it_new.it_value.tv_usec = 0;
    it_new.it_interval.tv_sec = it_new.it_interval.tv_usec = 0;

    do_setitimer(ITIMER_REAL, &it_new, &it_old);

    /*
     * We can't return 0 if we have an alarm pending ...  And we'd
     * better return too much than too little anyway
     */
    if ((!it_old.it_value.tv_sec && it_old.it_value.tv_usec) ||
          it_old.it_value.tv_usec >= 500000)
        it_old.it_value.tv_sec++;

    return it_old.it_value.tv_sec;
}

SYSCALL_DEFINE3(setitimer, int, which, struct itimerval __user *, value,
        struct itimerval __user *, ovalue)
{
    struct itimerval set_buffer, get_buffer;
    int error;

    if (value) {
        if(copy_from_user(&set_buffer, value, sizeof(set_buffer)))
            return -EFAULT;
    } else {
        memset(&set_buffer, 0, sizeof(set_buffer));
        printk_once(KERN_WARNING "%s calls setitimer() with new_value NULL pointer."
                " Misfeature support will be removed\n",
                current->comm);
    }

    error = do_setitimer(which, &set_buffer, ovalue ? &get_buffer : NULL);
    if (error || !ovalue)
        return error;

    if (copy_to_user(ovalue, &get_buffer, sizeof(get_buffer)))
        return -EFAULT;
    return 0;
}