On Wed, 2007-05-02 at 02:22 -0300, Davi Arnaut wrote:
> plain text document attachment (pollfs-timer.patch)
> Per file descriptor high-resolution timers. A classic unix file interface for
> the POSIX timer_(create|settime|gettime|delete) family of functions.
>
> Signed-off-by: Davi E. M. Arnaut <[EMAIL PROTECTED]>
Nacked-by-me.
Aside of the fact, that it is a bad clone of the timerfd code, it is
simply broken and untested.
> +
> +struct hrtimerspec {
> + int flags;
> + clockid_t clock;
> + struct itimerspec expr;
> +};
How exactly knows userspace what a struct hrtimerspec is ? Is the c file
exported as a header ?
> +static ssize_t read(struct pfs_timer *evs, struct itimerspec __user *uspec)
> +{
> + int ret = -EAGAIN;
> + ktime_t remaining = {};
> + unsigned long overruns = 0;
> + struct itimerspec spec = {};
> + struct hrtimer *timer = &evs->timer;
> +
> + spin_lock_irq(&evs->lock);
> +
> + if (!evs->overruns)
> + goto out_unlock;
> +
> + if (hrtimer_active(timer))
> + remaining = hrtimer_get_remaining(timer);
> + else if (evs->interval.tv64 > 0)
> + overruns = hrtimer_forward(timer, hrtimer_cb_get_time(timer),
> + evs->interval);
Where is the logic here ?
If no overrun, return remaining time = 0
If active, return the real remaining time. This path is never hit, as
the timer is nowhere restarted.
If not active, return remanining time = 0. How does the caller know how
many events are missed ?
> + ret = -EOVERFLOW;
> + if (overruns > (ULONG_MAX - evs->overruns))
> + goto out_unlock;
> + else
> + evs->overruns += overruns;
Interesting feature. evs->overruns is adding up forever and then limited
to ULONG_MAX
> +static enum hrtimer_restart timer_fn(struct hrtimer *timer)
> +{
> + struct pfs_timer *evs = container_of(timer, struct pfs_timer, timer);
> + unsigned long flags;
> +
> + spin_lock_irqsave(&evs->lock, flags);
> + /* timer tick, interval has elapsed */
> + if (!evs->overruns++)
> + wake_up_all(&evs->wait);
Cool. Waiters, which came after the first event are stuck. Simply
because there is no second event.
> +static ssize_t write(struct pfs_timer *evs,
> + const struct hrtimerspec __user *uspec)
> +{
> + struct hrtimerspec spec;
See first comment !
> + if (copy_from_user(&spec, uspec, sizeof(spec)))
> + return -EFAULT;
> +
> + if (spec_invalid(&spec))
> + return -EINVAL;
> +
> + rearm_timer(evs, &spec);
> +
> + return 0;
> +}
> +
> +static int poll(struct pfs_timer *evs)
> +{
> + int ret;
> +
> + ret = evs->overruns ? POLLIN : 0;
> +
> + return ret;
> +}
Creative lockless programming style with 4 lines overhead and a
guaranteed return POLLIN after the first timer event. This is really
cute as it covers the missing timer restart and guarantees 100% CPU load
for ever. Hmm, maybe it's correct: polling should loop for ever,
shouldn't it ?
> +static const struct pfs_operations timer_ops = {
> + .read = PFS_READ(read, struct pfs_timer, struct itimerspec),
> + .write = PFS_WRITE(write, struct pfs_timer, struct hrtimerspec),
> + .poll = PFS_POLL(poll, struct pfs_timer),
> + .release = PFS_RELEASE(release, struct pfs_timer),
> + .rsize = sizeof(struct itimerspec),
> + .wsize = sizeof(struct hrtimerspec),
See first comment !
tglx
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