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/*
* 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;
}
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