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Subject[patch 6/9] signalfd/timerfd - 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 tmrtype, const struct timespec *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 "tmrtype" parameter allows to specify the timer type. The following
values are supported:

TFD_TIMER_REL
The time specified in the "utmr" parameter is a relative time
from NOW.

TFD_TIMER_ABS
The timer specified in the "utmr" parameter is an absolute time.

TFD_TIMER_SEQ
The time specified in the "utmr" parameter is an interval at
which a continuous clock rate will be generated.

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




Signed-off-by: Davide Libenzi <davidel@xmailserver.org>



- Davide



Index: linux-2.6.20.ep2/fs/timerfd.c
===================================================================
--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6.20.ep2/fs/timerfd.c 2007-03-10 15:58:05.000000000 -0800
@@ -0,0 +1,268 @@
+/*
+ * fs/timerfd.c
+ *
+ * Copyright (C) 2007 Davide Libenzi <davidel@xmailserver.org>
+ *
+ */
+
+#include <linux/file.h>
+#include <linux/poll.h>
+#include <linux/slab.h>
+#include <linux/init.h>
+#include <linux/fs.h>
+#include <linux/mount.h>
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/signal.h>
+#include <linux/list.h>
+#include <linux/spinlock.h>
+#include <linux/time.h>
+#include <linux/hrtimer.h>
+#include <linux/jiffies.h>
+#include <linux/anon_inodes.h>
+#include <linux/timerfd.h>
+
+#include <asm/uaccess.h>
+
+
+
+struct timerfd_ctx {
+ struct hrtimer tmr;
+ int clockid;
+ ktime_t tval;
+ int tmrtype;
+ spinlock_t lock;
+ wait_queue_head_t wqh;
+ unsigned long ticks;
+};
+
+
+static int timerfd_tmrproc(struct hrtimer *htmr);
+static void timerfd_cleanup(struct timerfd_ctx *ctx);
+static int timerfd_close(struct inode *inode, struct file *file);
+static unsigned int timerfd_poll(struct file *file, poll_table *wait);
+static ssize_t timerfd_read(struct file *file, char __user *buf, size_t count,
+ loff_t *ppos);
+
+
+
+static const struct file_operations timerfd_fops = {
+ .release = timerfd_close,
+ .poll = timerfd_poll,
+ .read = timerfd_read,
+};
+static struct kmem_cache *timerfd_ctx_cachep;
+
+
+
+static int timerfd_tmrproc(struct hrtimer *htmr)
+{
+ struct timerfd_ctx *ctx = container_of(htmr, struct timerfd_ctx, tmr);
+ int rval = HRTIMER_NORESTART;
+ unsigned long flags;
+
+ spin_lock_irqsave(&ctx->lock, flags);
+ ctx->ticks++;
+ wake_up_locked(&ctx->wqh);
+ if (ctx->tmrtype == TFD_TIMER_SEQ) {
+ hrtimer_forward(htmr, htmr->base->softirq_time, ctx->tval);
+ rval = HRTIMER_RESTART;
+ }
+ spin_unlock_irqrestore(&ctx->lock, flags);
+
+ return rval;
+}
+
+
+asmlinkage long sys_timerfd(int ufd, int clockid, int tmrtype,
+ const struct timespec __user *utmr)
+{
+ int error;
+ struct timerfd_ctx *ctx;
+ struct file *file;
+ struct inode *inode;
+ ktime_t tval, tnow;
+ struct timespec ktmr, tmrnow;
+
+ error = -EFAULT;
+ if (copy_from_user(&ktmr, utmr, sizeof(ktmr)))
+ goto err_exit;
+
+ tval = timespec_to_ktime(ktmr);
+ error = -EINVAL;
+ if (clockid != CLOCK_MONOTONIC &&
+ clockid != CLOCK_REALTIME)
+ goto err_exit;
+ switch (tmrtype) {
+ case TFD_TIMER_REL:
+ case TFD_TIMER_SEQ:
+ break;
+ case TFD_TIMER_ABS:
+ getnstimeofday(&tmrnow);
+ tnow = timespec_to_ktime(tmrnow);
+ if (ktime_to_ns(tval) <= ktime_to_ns(tnow))
+ goto err_exit;
+ tval = ktime_sub(tval, tnow);
+ break;
+ default:
+ goto err_exit;
+ }
+
+ if (ufd == -1) {
+ error = -ENOMEM;
+ ctx = kmem_cache_alloc(timerfd_ctx_cachep, GFP_KERNEL);
+ if (!ctx)
+ goto err_exit;
+
+ init_waitqueue_head(&ctx->wqh);
+ spin_lock_init(&ctx->lock);
+ ctx->ticks = 0;
+ ctx->tmrtype = tmrtype;
+ ctx->clockid = clockid;
+ ctx->tval = tval;
+ hrtimer_init(&ctx->tmr, ctx->clockid, HRTIMER_REL);
+ ctx->tmr.expires = ctx->tval;
+ ctx->tmr.function = timerfd_tmrproc;
+
+ hrtimer_start(&ctx->tmr, ctx->tval, HRTIMER_REL);
+
+ /*
+ * When we call this, the initialization must be complete, since
+ * aino_getfd() will install the fd.
+ */
+ error = aino_getfd(&ufd, &inode, &file, "[timerfd]",
+ &timerfd_fops, ctx);
+ if (error)
+ goto err_fdalloc;
+ } else {
+ error = -EBADF;
+ file = fget(ufd);
+ if (!file)
+ goto err_exit;
+ ctx = file->private_data;
+ error = -EINVAL;
+ if (file->f_op != &timerfd_fops) {
+ fput(file);
+ goto err_exit;
+ }
+
+ /*
+ * We need to stop the exiting timer before. We call
+ * hrtimer_cancel() w/out holding our lock.
+ */
+ spin_lock_irq(&ctx->lock);
+ while (hrtimer_active(&ctx->tmr)) {
+ spin_unlock_irq(&ctx->lock);
+ hrtimer_cancel(&ctx->tmr);
+ spin_lock_irq(&ctx->lock);
+ }
+ /*
+ * Re-program the timer to the new value ...
+ */
+ ctx->ticks = 0;
+ ctx->tmrtype = tmrtype;
+ ctx->clockid = clockid;
+ ctx->tval = tval;
+ hrtimer_init(&ctx->tmr, ctx->clockid, HRTIMER_REL);
+ ctx->tmr.expires = ctx->tval;
+ ctx->tmr.function = timerfd_tmrproc;
+
+ hrtimer_start(&ctx->tmr, ctx->tval, HRTIMER_REL);
+
+ spin_unlock_irq(&ctx->lock);
+
+ fput(file);
+ }
+
+ return ufd;
+
+err_fdalloc:
+ timerfd_cleanup(ctx);
+err_exit:
+ return error;
+}
+
+
+static void timerfd_cleanup(struct timerfd_ctx *ctx)
+{
+ hrtimer_cancel(&ctx->tmr);
+ kmem_cache_free(timerfd_ctx_cachep, ctx);
+}
+
+
+static int timerfd_close(struct inode *inode, struct file *file)
+{
+ timerfd_cleanup(file->private_data);
+ return 0;
+}
+
+
+static unsigned int timerfd_poll(struct file *file, poll_table *wait)
+{
+ struct timerfd_ctx *ctx = file->private_data;
+
+ poll_wait(file, &ctx->wqh, wait);
+
+ return ctx->ticks ? POLLIN: 0;
+}
+
+
+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;
+ DECLARE_WAITQUEUE(wait, current);
+
+ if (count < sizeof(ticks))
+ return -EINVAL;
+ spin_lock_irq(&ctx->lock);
+ res = -EAGAIN;
+ if ((ticks = (u32) ctx->ticks) == 0 &&
+ !(file->f_flags & O_NONBLOCK)) {
+ __add_wait_queue(&ctx->wqh, &wait);
+ for (res = 0;;) {
+ set_current_state(TASK_INTERRUPTIBLE);
+ if ((ticks = (u32) ctx->ticks) != 0) {
+ 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 (ticks)
+ ctx->ticks = 0;
+ spin_unlock_irq(&ctx->lock);
+ if (ticks)
+ res = put_user(ticks, buf) ? -EFAULT: sizeof(ticks);
+ return res;
+}
+
+
+static int __init timerfd_init(void)
+{
+ timerfd_ctx_cachep = kmem_cache_create("timerfd_ctx_cache",
+ sizeof(struct timerfd_ctx),
+ 0, SLAB_PANIC, NULL, NULL);
+ return 0;
+}
+
+
+static void __exit timerfd_exit(void)
+{
+ kmem_cache_destroy(timerfd_ctx_cachep);
+}
+
+module_init(timerfd_init);
+module_exit(timerfd_exit);
+
+MODULE_LICENSE("GPL");
Index: linux-2.6.20.ep2/include/linux/timerfd.h
===================================================================
--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6.20.ep2/include/linux/timerfd.h 2007-03-10 15:58:05.000000000 -0800
@@ -0,0 +1,20 @@
+/*
+ * include/linux/timerfd.h
+ *
+ * Copyright (C) 2007 Davide Libenzi <davidel@xmailserver.org>
+ *
+ */
+
+#ifndef _LINUX_TIMERFD_H
+#define _LINUX_TIMERFD_H
+
+
+#define TFD_TIMER_REL 1
+#define TFD_TIMER_ABS 2
+#define TFD_TIMER_SEQ 3
+
+
+
+
+#endif /* _LINUX_TIMERFD_H */
+
Index: linux-2.6.20.ep2/fs/Makefile
===================================================================
--- linux-2.6.20.ep2.orig/fs/Makefile 2007-03-10 15:57:51.000000000 -0800
+++ linux-2.6.20.ep2/fs/Makefile 2007-03-10 15:58:05.000000000 -0800
@@ -11,7 +11,7 @@
attr.o bad_inode.o file.o filesystems.o namespace.o aio.o \
seq_file.o xattr.o libfs.o fs-writeback.o \
pnode.o drop_caches.o splice.o sync.o utimes.o \
- stack.o anon_inodes.o signalfd.o
+ stack.o anon_inodes.o signalfd.o timerfd.o

ifeq ($(CONFIG_BLOCK),y)
obj-y += buffer.o bio.o block_dev.o direct-io.o mpage.o ioprio.o
Index: linux-2.6.20.ep2/include/linux/syscalls.h
===================================================================
--- linux-2.6.20.ep2.orig/include/linux/syscalls.h 2007-03-10 15:57:51.000000000 -0800
+++ linux-2.6.20.ep2/include/linux/syscalls.h 2007-03-10 15:58:05.000000000 -0800
@@ -603,6 +603,8 @@
size_t len);
asmlinkage long sys_getcpu(unsigned __user *cpu, unsigned __user *node, struct getcpu_cache __user *cache);
asmlinkage long sys_signalfd(int ufd, sigset_t __user *user_mask, size_t sizemask);
+asmlinkage long sys_timerfd(int ufd, int clockid, int tmrtype,
+ const struct timespec __user *utmr);

int kernel_execve(const char *filename, char *const argv[], char *const envp[]);

-
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