/* * fs/timerfd.c * * Copyright (C) 2007 Davide Libenzi <davidel@xmailserver.org> * * * Thanks to Thomas Gleixner for code reviews and useful comments. * */ #include <linux/file.h> #include <linux/poll.h> #include <linux/init.h> #include <linux/fs.h> #include <linux/sched.h> #include <linux/kernel.h> #include <linux/slab.h> #include <linux/list.h> #include <linux/spinlock.h> #include <linux/time.h> #include <linux/hrtimer.h> #include <linux/anon_inodes.h> #include <linux/timerfd.h> #include <linux/syscalls.h> struct timerfd_ctx { struct hrtimer tmr; ktime_t tintv; wait_queue_head_t wqh; u64 ticks; int expired; int clockid; }; /* * This gets called when the timer event triggers. We set the "expired" * flag, but we do not re-arm the timer (in case it's necessary, * tintv.tv64 != 0) until the timer is accessed. */ static enum hrtimer_restart timerfd_tmrproc(struct hrtimer *htmr) { struct timerfd_ctx *ctx = container_of(htmr, struct timerfd_ctx, tmr); unsigned long flags; spin_lock_irqsave(&ctx->wqh.lock, flags); ctx->expired = 1; ctx->ticks++; wake_up_locked(&ctx->wqh); spin_unlock_irqrestore(&ctx->wqh.lock, flags); return HRTIMER_NORESTART; } static ktime_t timerfd_get_remaining(struct timerfd_ctx *ctx) { ktime_t remaining; remaining = hrtimer_expires_remaining(&ctx->tmr); return remaining.tv64 < 0 ? ktime_set(0, 0): remaining; } static void timerfd_setup(struct timerfd_ctx *ctx, int flags, const struct itimerspec *ktmr) { enum hrtimer_mode htmode; ktime_t texp; htmode = (flags & TFD_TIMER_ABSTIME) ? HRTIMER_MODE_ABS: HRTIMER_MODE_REL; texp = timespec_to_ktime(ktmr->it_value); ctx->expired = 0; ctx->ticks = 0; ctx->tintv = timespec_to_ktime(ktmr->it_interval); hrtimer_init(&ctx->tmr, ctx->clockid, htmode); hrtimer_set_expires(&ctx->tmr, texp); ctx->tmr.function = timerfd_tmrproc; if (texp.tv64 != 0) hrtimer_start(&ctx->tmr, texp, htmode); } static int timerfd_release(struct inode *inode, struct file *file) { struct timerfd_ctx *ctx = file->private_data; hrtimer_cancel(&ctx->tmr); kfree(ctx); return 0; } static unsigned int timerfd_poll(struct file *file, poll_table *wait) { struct timerfd_ctx *ctx = file->private_data; unsigned int events = 0; unsigned long flags; poll_wait(file, &ctx->wqh, wait); spin_lock_irqsave(&ctx->wqh.lock, flags); if (ctx->ticks) events |= POLLIN; spin_unlock_irqrestore(&ctx->wqh.lock, flags); return events; } static ssize_t timerfd_read(struct file *file, char __user *buf, size_t count, loff_t *ppos) { struct timerfd_ctx *ctx = file->private_data; ssize_t res; u64 ticks = 0; if (count < sizeof(ticks)) return -EINVAL; spin_lock_irq(&ctx->wqh.lock); if (file->f_flags & O_NONBLOCK) res = -EAGAIN; else res = wait_event_interruptible_locked_irq(ctx->wqh, ctx->ticks); if (ctx->ticks) { ticks = ctx->ticks; if (ctx->expired && ctx->tintv.tv64) { /* * If tintv.tv64 != 0, this is a periodic timer that * needs to be re-armed. We avoid doing it in the timer * callback to avoid DoS attacks specifying a very * short timer period. */ ticks += hrtimer_forward_now(&ctx->tmr, ctx->tintv) - 1; hrtimer_restart(&ctx->tmr); } ctx->expired = 0; ctx->ticks = 0; } spin_unlock_irq(&ctx->wqh.lock); if (ticks) res = put_user(ticks, (u64 __user *) buf) ? -EFAULT: sizeof(ticks); return res; } static const struct file_operations timerfd_fops = { .release = timerfd_release, .poll = timerfd_poll, .read = timerfd_read, }; static struct file *timerfd_fget(int fd) { struct file *file; file = fget(fd); if (!file) return ERR_PTR(-EBADF); if (file->f_op != &timerfd_fops) { fput(file); return ERR_PTR(-EINVAL); } return file; } SYSCALL_DEFINE2(timerfd_create, int, clockid, int, flags) { int ufd; struct timerfd_ctx *ctx; /* Check the TFD_* constants for consistency. */ BUILD_BUG_ON(TFD_CLOEXEC != O_CLOEXEC); BUILD_BUG_ON(TFD_NONBLOCK != O_NONBLOCK); if ((flags & ~TFD_CREATE_FLAGS) || (clockid != CLOCK_MONOTONIC && clockid != CLOCK_REALTIME)) return -EINVAL; ctx = kzalloc(sizeof(*ctx), GFP_KERNEL); if (!ctx) return -ENOMEM; init_waitqueue_head(&ctx->wqh); ctx->clockid = clockid; hrtimer_init(&ctx->tmr, clockid, HRTIMER_MODE_ABS); ufd = anon_inode_getfd("[timerfd]", &timerfd_fops, ctx, O_RDWR | (flags & TFD_SHARED_FCNTL_FLAGS)); if (ufd < 0) kfree(ctx); return ufd; } SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags, const struct itimerspec __user *, utmr, struct itimerspec __user *, otmr) { struct file *file; struct timerfd_ctx *ctx; struct itimerspec ktmr, kotmr; if (copy_from_user(&ktmr, utmr, sizeof(ktmr))) return -EFAULT; if ((flags & ~TFD_SETTIME_FLAGS) || !timespec_valid(&ktmr.it_value) || !timespec_valid(&ktmr.it_interval)) return -EINVAL; file = timerfd_fget(ufd); if (IS_ERR(file)) return PTR_ERR(file); ctx = file->private_data; /* * We need to stop the existing timer before reprogramming * it to the new values. */ for (;;) { spin_lock_irq(&ctx->wqh.lock); if (hrtimer_try_to_cancel(&ctx->tmr) >= 0) break; spin_unlock_irq(&ctx->wqh.lock); cpu_relax(); } /* * If the timer is expired and it's periodic, we need to advance it * because the caller may want to know the previous expiration time. * We do not update "ticks" and "expired" since the timer will be * re-programmed again in the following timerfd_setup() call. */ if (ctx->expired && ctx->tintv.tv64) hrtimer_forward_now(&ctx->tmr, ctx->tintv); kotmr.it_value = ktime_to_timespec(timerfd_get_remaining(ctx)); kotmr.it_interval = ktime_to_timespec(ctx->tintv); /* * Re-program the timer to the new value ... */ timerfd_setup(ctx, flags, &ktmr); spin_unlock_irq(&ctx->wqh.lock); fput(file); if (otmr && copy_to_user(otmr, &kotmr, sizeof(kotmr))) return -EFAULT; return 0; } SYSCALL_DEFINE2(timerfd_gettime, int, ufd, struct itimerspec __user *, otmr) { struct file *file; struct timerfd_ctx *ctx; struct itimerspec kotmr; file = timerfd_fget(ufd); if (IS_ERR(file)) return PTR_ERR(file); ctx = file->private_data; spin_lock_irq(&ctx->wqh.lock); if (ctx->expired && ctx->tintv.tv64) { ctx->expired = 0; ctx->ticks += hrtimer_forward_now(&ctx->tmr, ctx->tintv) - 1; hrtimer_restart(&ctx->tmr); } kotmr.it_value = ktime_to_timespec(timerfd_get_remaining(ctx)); kotmr.it_interval = ktime_to_timespec(ctx->tintv); spin_unlock_irq(&ctx->wqh.lock); fput(file); return copy_to_user(otmr, &kotmr, sizeof(kotmr)) ? -EFAULT: 0; }