signal/timer/event: timerfd core
This patch introduces a new system call for timers events delivered though
file descriptors. This allows timer event to be used with standard POSIX
poll(2), select(2) and read(2). As a consequence of supporting the Linux
f_op->poll subsystem, they can be used with epoll(2) too.
The system call is defined as:
int timerfd(int ufd, int clockid, int flags, const struct itimerspec *utmr);
The "ufd" parameter allows for re-use (re-programming) of an existing timerfd
w/out going through the close/open cycle (same as signalfd). If "ufd" is -1,
s new file descriptor will be created, otherwise the existing "ufd" will be
re-programmed.
The "clockid" parameter is either CLOCK_MONOTONIC or CLOCK_REALTIME. The time
specified in the "utmr->it_value" parameter is the expiry time for the timer.
If the TFD_TIMER_ABSTIME flag is set in "flags", this is an absolute time,
otherwise it's a relative time.
If the time specified in the "utmr->it_interval" is not zero (.tv_sec == 0,
tv_nsec == 0), this is the period at which the following ticks should be
generated.
The "utmr->it_interval" should be set to zero if only one tick is requested.
Setting the "utmr->it_value" to zero will disable the timer, or will create a
timerfd without the timer enabled.
The function returns the new (or same, in case "ufd" is a valid timerfd
descriptor) file, or -1 in case of error.
As stated before, the timerfd file descriptor supports poll(2), select(2) and
epoll(2). When a timer event happened on the timerfd, a POLLIN mask will be
returned.
The read(2) call can be used, and it will return a u32 variable holding the
number of "ticks" that happened on the interface since the last call to
read(2). The read(2) call supportes the O_NONBLOCK flag too, and EAGAIN will
be returned if no ticks happened.
A quick test program, shows timerfd working correctly on my amd64 box:
http://www.xmailserver.org/timerfd-test.c
[akpm@linux-foundation.org: add sys_timerfd to sys_ni.c]
Signed-off-by: Davide Libenzi <davidel@xmailserver.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/timerfd.c b/fs/timerfd.c
new file mode 100644
index 0000000..e329e37
--- /dev/null
+++ b/fs/timerfd.c
@@ -0,0 +1,227 @@
+/*
+ * 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;
+ spinlock_t lock;
+ 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->lock, flags);
+ ctx->expired = 1;
+ wake_up_locked(&ctx->wqh);
+ spin_unlock_irqrestore(&ctx->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->lock, flags);
+ if (ctx->expired)
+ events |= POLLIN;
+ spin_unlock_irqrestore(&ctx->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->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->lock);
+ schedule();
+ spin_lock_irq(&ctx->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->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);
+ spin_lock_init(&ctx->lock);
+
+ 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->lock);
+ if (hrtimer_try_to_cancel(&ctx->tmr) >= 0)
+ break;
+ spin_unlock_irq(&ctx->lock);
+ cpu_relax();
+ }
+ /*
+ * Re-program the timer to the new value ...
+ */
+ timerfd_setup(ctx, clockid, flags, &ktmr);
+
+ spin_unlock_irq(&ctx->lock);
+ fput(file);
+ }
+
+ return ufd;
+
+err_tmrcancel:
+ hrtimer_cancel(&ctx->tmr);
+ kfree(ctx);
+ return error;
+}
+