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SubjectRe: [PATCHv6 0/7] system time changes notification
On Thu, Nov 11, 2010 at 11:50:38PM +0100, Thomas Gleixner wrote:
> B1;2401;0cOn Thu, 11 Nov 2010, Kyle Moffett wrote:
> > On Thu, Nov 11, 2010 at 16:16, Thomas Gleixner <tglx@linutronix.de> wrote:
> > > The notification itself is pointless unless your application is
> > > dealing with timers which need to be adjusted the one way or the
> > > other.
> > >
> > > That said, I'm still not convinced that this usecase justifies a new
> > > systemcall.
> > >
> > > 1) We can make timers wake up when a clock change happens
> > > 2) Can't we use existing notification stuff like uevents or such ?
> >
> > What about maybe adding device nodes for various kinds of "clock"
> > devices? You could then do:
> >
> > #define CLOCK_FD 0x80000000
> > fd = open("/dev/clock/realtime", O_RDWR);
> > poll(fd);
> > clock_gettime(CLOCK_FD|fd, &ts);
>
> That won't work due to the posix-cputimers occupying the negative
> number space already.
>
> > [...]
> >
> > This would also enable the folks who want to support things like PHY
> > hardware clocks (for very-low-latency ethernet timestamping). It
> > would resolve the enumeration problem; instead of 0, 1, 2, ... as
> > constants, they would show up in sysfs and be open()able. Ideally you
> > would be able to set up ntpd to slew the "realtime" clock by following
> > a particular hardware clock, or vice versa.
>
> There are other plans for the various interesting clocks floating
> around which look pretty good.
>
> But what you folks really want for this stuff is an extension to
> timerfd as you want to be able to poll, right?
>
> So what about the following:
>
> Add a new flag TDF_NOTIFY_CLOCK_WAS_SET to the timerfd flags. Now this
> flag adds the timer to a separate list, which gets woken up when the
> clock is set.
>
> No new syscall, just a few lines of code in fs/timerfd.c and
> clock_was_set().
>
> Thoughts ?

Something like this (sans ugliness)?

Signed-off-by: Alexander Shishkin <virtuoso@slind.org>
---
fs/timerfd.c | 52 +++++++++++++++++++++++++++++++++++++++++++++-
include/linux/timerfd.h | 3 +-
kernel/hrtimer.c | 2 +
3 files changed, 54 insertions(+), 3 deletions(-)
diff --git a/fs/timerfd.c b/fs/timerfd.c
index 8c4fc14..51a033e 100644
--- a/fs/timerfd.c
+++ b/fs/timerfd.c
@@ -30,8 +30,14 @@ struct timerfd_ctx {
u64 ticks;
int expired;
int clockid;
+ int clock_notifier; /* list_empty()? */
+ struct list_head notifiers_list;
};

+/* TFD_NOTIFY_CLOCK_SET timers go here */
+static DEFINE_SPINLOCK(notifiers_lock);
+static LIST_HEAD(notifiers_list);
+
/*
* 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,
@@ -51,6 +57,21 @@ static enum hrtimer_restart timerfd_tmrproc(struct hrtimer *htmr)
return HRTIMER_NORESTART;
}

+void timerfd_clock_was_set(void)
+{
+ struct timerfd_ctx *ctx;
+ unsigned long flags;
+
+ spin_lock(&notifiers_lock);
+ list_for_each_entry(ctx, &notifiers_list, notifiers_list) {
+ spin_lock_irqsave(&ctx->wqh.lock, flags);
+ ctx->ticks++;
+ wake_up_locked(&ctx->wqh);
+ spin_unlock_irqrestore(&ctx->wqh.lock, flags);
+ }
+ spin_unlock(&notifiers_lock);
+}
+
static ktime_t timerfd_get_remaining(struct timerfd_ctx *ctx)
{
ktime_t remaining;
@@ -65,6 +86,14 @@ static void timerfd_setup(struct timerfd_ctx *ctx, int flags,
enum hrtimer_mode htmode;
ktime_t texp;

+ if (flags & TFD_NOTIFY_CLOCK_SET) {
+ ctx->clock_notifier = 1;
+ ctx->ticks = 0;
+ INIT_LIST_HEAD(&ctx->notifiers_list);
+ list_add(&ctx->notifiers_list, &notifiers_list);
+ return;
+ }
+
htmode = (flags & TFD_TIMER_ABSTIME) ?
HRTIMER_MODE_ABS: HRTIMER_MODE_REL;

@@ -83,7 +112,12 @@ static int timerfd_release(struct inode *inode, struct file *file)
{
struct timerfd_ctx *ctx = file->private_data;

- hrtimer_cancel(&ctx->tmr);
+ if (ctx->clock_notifier) {
+ spin_lock(&notifiers_lock);
+ list_del(&ctx->notifiers_list);
+ spin_unlock(&notifiers_lock);
+ } else
+ hrtimer_cancel(&ctx->tmr);
kfree(ctx);
return 0;
}
@@ -113,6 +147,7 @@ static ssize_t timerfd_read(struct file *file, char __user *buf, size_t count,

if (count < sizeof(ticks))
return -EINVAL;
+
spin_lock_irq(&ctx->wqh.lock);
if (file->f_flags & O_NONBLOCK)
res = -EAGAIN;
@@ -120,7 +155,7 @@ static ssize_t timerfd_read(struct file *file, char __user *buf, size_t count,
res = wait_event_interruptible_locked_irq(ctx->wqh, ctx->ticks);
if (ctx->ticks) {
ticks = ctx->ticks;
- if (ctx->expired && ctx->tintv.tv64) {
+ if (ctx->expired && ctx->tintv.tv64 && !ctx->clock_notifier) {
/*
* If tintv.tv64 != 0, this is a periodic timer that
* needs to be re-armed. We avoid doing it in the timer
@@ -218,13 +253,20 @@ SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
* it to the new values.
*/
for (;;) {
+ spin_lock(&notifiers_lock);
spin_lock_irq(&ctx->wqh.lock);
if (hrtimer_try_to_cancel(&ctx->tmr) >= 0)
break;
spin_unlock_irq(&ctx->wqh.lock);
+ spin_unlock(&notifiers_lock);
cpu_relax();
}

+ if (ctx->clock_notifier) {
+ ctx->clock_notifier = 0;
+ list_del(&ctx->notifiers_list);
+ }
+
/*
* If the timer is expired and it's periodic, we need to advance it
* because the caller may want to know the previous expiration time.
@@ -243,6 +285,7 @@ SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
timerfd_setup(ctx, flags, &ktmr);

spin_unlock_irq(&ctx->wqh.lock);
+ spin_unlock(&notifiers_lock);
fput(file);
if (otmr && copy_to_user(otmr, &kotmr, sizeof(kotmr)))
return -EFAULT;
@@ -262,6 +305,11 @@ SYSCALL_DEFINE2(timerfd_gettime, int, ufd, struct itimerspec __user *, otmr)
ctx = file->private_data;

spin_lock_irq(&ctx->wqh.lock);
+ if (ctx->clock_notifier) {
+ spin_unlock_irq(&ctx->wqh.lock);
+ return -EINVAL;
+ }
+
if (ctx->expired && ctx->tintv.tv64) {
ctx->expired = 0;
ctx->ticks +=
diff --git a/include/linux/timerfd.h b/include/linux/timerfd.h
index 2d07929..c3ddad9 100644
--- a/include/linux/timerfd.h
+++ b/include/linux/timerfd.h
@@ -19,6 +19,7 @@
* shared O_* flags.
*/
#define TFD_TIMER_ABSTIME (1 << 0)
+#define TFD_NOTIFY_CLOCK_SET (1 << 1)
#define TFD_CLOEXEC O_CLOEXEC
#define TFD_NONBLOCK O_NONBLOCK

@@ -26,6 +27,6 @@
/* Flags for timerfd_create. */
#define TFD_CREATE_FLAGS TFD_SHARED_FCNTL_FLAGS
/* Flags for timerfd_settime. */
-#define TFD_SETTIME_FLAGS TFD_TIMER_ABSTIME
+#define TFD_SETTIME_FLAGS (TFD_TIMER_ABSTIME | TFD_NOTIFY_CLOCK_SET)

#endif /* _LINUX_TIMERFD_H */
diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index 72206cf..a779e0f 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -642,8 +642,10 @@ static void retrigger_next_event(void *arg)
* resolution timer interrupts. On UP we just disable interrupts and
* call the high resolution interrupt code.
*/
+void timerfd_clock_was_set(clockid_t clockid);
void clock_was_set(void)
{
+ timerfd_clock_was_set(CLOCK_REALTIME);
/* Retrigger the CPU local events everywhere */
on_each_cpu(retrigger_next_event, NULL, 1);
}
--
1.7.2.1.45.gb66c2


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