/* * 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/list.h> #include <linux/spinlock.h> #include <linux/time.h> #include <linux/hrtimer.h> #include <linux/anon_inodes.h> #include <linux/timerfd.h> struct timerfd_ctx { struct hrtimer tmr; ktime_t tintv; wait_queue_head_t wqh; int expired; }; /* * 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 read. */ 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; wake_up_locked(&ctx->wqh); spin_unlock_irqrestore(&ctx->wqh.lock, flags); return HRTIMER_NORESTART; } static void timerfd_setup(struct timerfd_ctx *ctx, int clockid, 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->tintv = timespec_to_ktime(ktmr->it_interval); hrtimer_init(&ctx->tmr, clockid, htmode); ctx->tmr.expires = 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->expired) 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; u32 ticks = 0; DECLARE_WAITQUEUE(wait, current); if (count < sizeof(ticks)) return -EINVAL; spin_lock_irq(&ctx->wqh.lock); res = -EAGAIN; if (!ctx->expired && !(file->f_flags & O_NONBLOCK)) { __add_wait_queue(&ctx->wqh, &wait); for (res = 0;;) { set_current_state(TASK_INTERRUPTIBLE); if (ctx->expired) { res = 0; break; } if (signal_pending(current)) { res = -ERESTARTSYS; break; } spin_unlock_irq(&ctx->wqh.lock); schedule(); spin_lock_irq(&ctx->wqh.lock); } __remove_wait_queue(&ctx->wqh, &wait); __set_current_state(TASK_RUNNING); } if (ctx->expired) { ctx->expired = 0; if (ctx->tintv.tv64 != 0) { /* * 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 = (u32) hrtimer_forward(&ctx->tmr, hrtimer_cb_get_time(&ctx->tmr), ctx->tintv); hrtimer_restart(&ctx->tmr); } else ticks = 1; } spin_unlock_irq(&ctx->wqh.lock); if (ticks) res = put_user(ticks, buf) ? -EFAULT: sizeof(ticks); return res; } static const struct file_operations timerfd_fops = { .release = timerfd_release, .poll = timerfd_poll, .read = timerfd_read, }; asmlinkage long sys_timerfd(int ufd, int clockid, int flags, const struct itimerspec __user *utmr) { int error; struct timerfd_ctx *ctx; struct file *file; struct inode *inode; struct itimerspec ktmr; if (copy_from_user(&ktmr, utmr, sizeof(ktmr))) return -EFAULT; if (clockid != CLOCK_MONOTONIC && clockid != CLOCK_REALTIME) return -EINVAL; if (!timespec_valid(&ktmr.it_value) || !timespec_valid(&ktmr.it_interval)) return -EINVAL; if (ufd == -1) { ctx = kmalloc(sizeof(*ctx), GFP_KERNEL); if (!ctx) return -ENOMEM; init_waitqueue_head(&ctx->wqh); timerfd_setup(ctx, clockid, flags, &ktmr); /* * When we call this, the initialization must be complete, since * anon_inode_getfd() will install the fd. */ error = anon_inode_getfd(&ufd, &inode, &file, "[timerfd]", &timerfd_fops, ctx); if (error) goto err_tmrcancel; } else { file = fget(ufd); if (!file) return -EBADF; ctx = file->private_data; if (file->f_op != &timerfd_fops) { fput(file); return -EINVAL; } /* * 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(); } /* * Re-program the timer to the new value ... */ timerfd_setup(ctx, clockid, flags, &ktmr); spin_unlock_irq(&ctx->wqh.lock); fput(file); } return ufd; err_tmrcancel: hrtimer_cancel(&ctx->tmr); kfree(ctx); return error; }