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authorThomas Gleixner <tglx@linutronix.de>2011-04-27 16:16:42 +0400
committerThomas Gleixner <tglx@linutronix.de>2011-05-02 23:39:15 +0400
commit99ee5315dac6211e972fa3f23bcc9a0343ff58c4 (patch)
tree6663d6ceaabcb9bac03193e2781cdbe6a139f70c /fs/timerfd.c
parentb12a03ce4880bd13786a98db6de494a3e0123129 (diff)
downloadlinux-99ee5315dac6211e972fa3f23bcc9a0343ff58c4.tar.xz
timerfd: Allow timers to be cancelled when clock was set
Some applications must be aware of clock realtime being set backward. A simple example is a clock applet which arms a timer for the next minute display. If clock realtime is set backward then the applet displays a stale time for the amount of time which the clock was set backwards. Due to that applications poll the time because we don't have an interface. Extend the timerfd interface by adding a flag which puts the timer onto a different internal realtime clock. All timers on this clock are expired whenever the clock was set. The timerfd core records the monotonic offset when the timer is created. When the timer is armed, then the current offset is compared to the previous recorded offset. When it has changed, then timerfd_settime returns -ECANCELED. When a timer is read the offset is compared and if it changed -ECANCELED returned to user space. Periodic timers are not rearmed in the cancelation case. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: John Stultz <johnstul@us.ibm.com> Cc: Chris Friesen <chris.friesen@genband.com> Tested-by: Kay Sievers <kay.sievers@vrfy.org> Cc: "Kirill A. Shutemov" <kirill@shutemov.name> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Davide Libenzi <davidel@xmailserver.org> Reviewed-by: Alexander Shishkin <virtuoso@slind.org> Link: http://lkml.kernel.org/r/%3Calpine.LFD.2.02.1104271359580.3323%40ionos%3E Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'fs/timerfd.c')
-rw-r--r--fs/timerfd.c57
1 files changed, 51 insertions, 6 deletions
diff --git a/fs/timerfd.c b/fs/timerfd.c
index 8c4fc1425b3e..7e14c9e7c4ee 100644
--- a/fs/timerfd.c
+++ b/fs/timerfd.c
@@ -26,10 +26,12 @@
struct timerfd_ctx {
struct hrtimer tmr;
ktime_t tintv;
+ ktime_t moffs;
wait_queue_head_t wqh;
u64 ticks;
int expired;
int clockid;
+ bool might_cancel;
};
/*
@@ -59,24 +61,52 @@ static ktime_t timerfd_get_remaining(struct timerfd_ctx *ctx)
return remaining.tv64 < 0 ? ktime_set(0, 0): remaining;
}
-static void timerfd_setup(struct timerfd_ctx *ctx, int flags,
- const struct itimerspec *ktmr)
+static bool timerfd_canceled(struct timerfd_ctx *ctx)
+{
+ ktime_t moffs;
+
+ if (!ctx->might_cancel)
+ return false;
+
+ moffs = ktime_get_monotonic_offset();
+
+ if (moffs.tv64 == ctx->moffs.tv64)
+ return false;
+
+ ctx->moffs = moffs;
+ return true;
+}
+
+static int timerfd_setup(struct timerfd_ctx *ctx, int flags,
+ const struct itimerspec *ktmr)
{
enum hrtimer_mode htmode;
ktime_t texp;
+ int clockid = ctx->clockid;
htmode = (flags & TFD_TIMER_ABSTIME) ?
HRTIMER_MODE_ABS: HRTIMER_MODE_REL;
+ ctx->might_cancel = false;
+ if (htmode == HRTIMER_MODE_ABS && ctx->clockid == CLOCK_REALTIME &&
+ (flags & TFD_TIMER_CANCELON_SET)) {
+ clockid = CLOCK_REALTIME_COS;
+ ctx->might_cancel = true;
+ }
+
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_init(&ctx->tmr, clockid, htmode);
hrtimer_set_expires(&ctx->tmr, texp);
ctx->tmr.function = timerfd_tmrproc;
- if (texp.tv64 != 0)
+ if (texp.tv64 != 0) {
hrtimer_start(&ctx->tmr, texp, htmode);
+ if (timerfd_canceled(ctx))
+ return -ECANCELED;
+ }
+ return 0;
}
static int timerfd_release(struct inode *inode, struct file *file)
@@ -118,8 +148,21 @@ static ssize_t timerfd_read(struct file *file, char __user *buf, size_t count,
res = -EAGAIN;
else
res = wait_event_interruptible_locked_irq(ctx->wqh, ctx->ticks);
+
if (ctx->ticks) {
ticks = ctx->ticks;
+
+ /*
+ * If clock has changed, we do not care about the
+ * ticks and we do not rearm the timer. Userspace must
+ * reevaluate anyway.
+ */
+ if (timerfd_canceled(ctx)) {
+ ticks = 0;
+ ctx->expired = 0;
+ res = -ECANCELED;
+ }
+
if (ctx->expired && ctx->tintv.tv64) {
/*
* If tintv.tv64 != 0, this is a periodic timer that
@@ -183,6 +226,7 @@ SYSCALL_DEFINE2(timerfd_create, int, clockid, int, flags)
init_waitqueue_head(&ctx->wqh);
ctx->clockid = clockid;
hrtimer_init(&ctx->tmr, clockid, HRTIMER_MODE_ABS);
+ ctx->moffs = ktime_get_monotonic_offset();
ufd = anon_inode_getfd("[timerfd]", &timerfd_fops, ctx,
O_RDWR | (flags & TFD_SHARED_FCNTL_FLAGS));
@@ -199,6 +243,7 @@ SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
struct file *file;
struct timerfd_ctx *ctx;
struct itimerspec ktmr, kotmr;
+ int ret;
if (copy_from_user(&ktmr, utmr, sizeof(ktmr)))
return -EFAULT;
@@ -240,14 +285,14 @@ SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
/*
* Re-program the timer to the new value ...
*/
- timerfd_setup(ctx, flags, &ktmr);
+ ret = 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;
+ return ret;
}
SYSCALL_DEFINE2(timerfd_gettime, int, ufd, struct itimerspec __user *, otmr)