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Subject[patch 09/22] pollfs: pollable hrtimers
Per file descriptor high-resolution timers. A classic unix file interface for
the POSIX timer_(create|settime|gettime|delete) family of functions.
Signed-off-by: Davi E. M. Arnaut <davi@haxent.com.br>

---
fs/pollfs/Makefile | 1
fs/pollfs/timer.c | 198 +++++++++++++++++++++++++++++++++++++++++++++++++++++
init/Kconfig | 7 +
3 files changed, 206 insertions(+)
Index: linux-2.6/fs/pollfs/timer.c
===================================================================
--- /dev/null
+++ linux-2.6/fs/pollfs/timer.c
@@ -0,0 +1,198 @@
+/*
+ * pollable timers
+ *
+ * Copyright (C) 2007 Davi E. M. Arnaut
+ *
+ * Licensed under the GNU GPL. See the file COPYING for details.
+ */
+
+#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/err.h>
+#include <linux/wait.h>
+#include <linux/poll.h>
+#include <linux/pollfs_fs.h>
+#include <linux/hrtimer.h>
+
+struct pfs_timer {
+ wait_queue_head_t wait;
+ ktime_t interval;
+ spinlock_t lock;
+ unsigned long overruns;
+ struct hrtimer timer;
+ struct pfs_file file;
+};
+
+struct hrtimerspec {
+ int flags;
+ clockid_t clock;
+ struct itimerspec expr;
+};
+
+static ssize_t read(struct pfs_timer *evs, struct itimerspec __user *uspec)
+{
+ int ret = -EAGAIN;
+ ktime_t remaining = {};
+ unsigned long overruns = 0;
+ struct itimerspec spec = {};
+ struct hrtimer *timer = &evs->timer;
+
+ spin_lock_irq(&evs->lock);
+
+ if (!evs->overruns)
+ goto out_unlock;
+
+ if (hrtimer_active(timer))
+ remaining = hrtimer_get_remaining(timer);
+ else if (evs->interval.tv64 > 0)
+ overruns = hrtimer_forward(timer, hrtimer_cb_get_time(timer),
+ evs->interval);
+
+ ret = -EOVERFLOW;
+ if (overruns > (ULONG_MAX - evs->overruns))
+ goto out_unlock;
+ else
+ evs->overruns += overruns;
+
+ if (remaining.tv64 > 0)
+ spec.it_value = ktime_to_timespec(remaining);
+
+ spec.it_interval = ktime_to_timespec(evs->interval);
+
+ ret = 0;
+
+out_unlock:
+ spin_unlock_irq(&evs->lock);
+
+ if (ret)
+ return ret;
+
+ if (copy_to_user(uspec, &spec, sizeof(spec)))
+ return -EFAULT;
+
+ return 0;
+}
+
+static enum hrtimer_restart timer_fn(struct hrtimer *timer)
+{
+ struct pfs_timer *evs = container_of(timer, struct pfs_timer, timer);
+ unsigned long flags;
+
+ spin_lock_irqsave(&evs->lock, flags);
+ /* timer tick, interval has elapsed */
+ if (!evs->overruns++)
+ wake_up_all(&evs->wait);
+ spin_unlock_irqrestore(&evs->lock, flags);
+
+ return HRTIMER_NORESTART;
+}
+
+static inline void rearm_timer(struct pfs_timer *evs, struct hrtimerspec *spec)
+{
+ struct hrtimer *timer = &evs->timer;
+ enum hrtimer_mode mode = HRTIMER_MODE_REL;
+
+ if (spec->flags & TIMER_ABSTIME)
+ mode = HRTIMER_MODE_ABS;
+
+ do {
+ spin_lock_irq(&evs->lock);
+ if (hrtimer_try_to_cancel(timer) >= 0)
+ break;
+ spin_unlock_irq(&evs->lock);
+ cpu_relax();
+ } while (1);
+
+ hrtimer_init(timer, spec->clock, mode);
+
+ timer->function = timer_fn;
+ timer->expires = timespec_to_ktime(spec->expr.it_value);
+ evs->interval = timespec_to_ktime(spec->expr.it_interval);
+
+ if (timer->expires.tv64)
+ hrtimer_start(timer, timer->expires, mode);
+
+ spin_unlock_irq(&evs->lock);
+}
+
+static inline int spec_invalid(const struct hrtimerspec *spec)
+{
+ if (spec->clock != CLOCK_REALTIME && spec->clock != CLOCK_MONOTONIC)
+ return 1;
+
+ if (!timespec_valid(&spec->expr.it_value) ||
+ !timespec_valid(&spec->expr.it_interval))
+ return 1;
+
+ return 0;
+}
+
+static ssize_t write(struct pfs_timer *evs,
+ const struct hrtimerspec __user *uspec)
+{
+ struct hrtimerspec spec;
+
+ if (copy_from_user(&spec, uspec, sizeof(spec)))
+ return -EFAULT;
+
+ if (spec_invalid(&spec))
+ return -EINVAL;
+
+ rearm_timer(evs, &spec);
+
+ return 0;
+}
+
+static int poll(struct pfs_timer *evs)
+{
+ int ret;
+
+ ret = evs->overruns ? POLLIN : 0;
+
+ return ret;
+}
+
+static int release(struct pfs_timer *evs)
+{
+ hrtimer_cancel(&evs->timer);
+ kfree(evs);
+
+ return 0;
+}
+
+static const struct pfs_operations timer_ops = {
+ .read = PFS_READ(read, struct pfs_timer, struct itimerspec),
+ .write = PFS_WRITE(write, struct pfs_timer, struct hrtimerspec),
+ .poll = PFS_POLL(poll, struct pfs_timer),
+ .release = PFS_RELEASE(release, struct pfs_timer),
+ .rsize = sizeof(struct itimerspec),
+ .wsize = sizeof(struct hrtimerspec),
+};
+
+asmlinkage long sys_pltimer(void)
+{
+ long error;
+ struct pfs_timer *evs;
+
+ evs = kmalloc(sizeof(*evs), GFP_KERNEL);
+ if (!evs)
+ return -ENOMEM;
+
+ evs->overruns = 0;
+ spin_lock_init(&evs->lock);
+ init_waitqueue_head(&evs->wait);
+ hrtimer_init(&evs->timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
+
+ evs->file.data = evs;
+ evs->file.fops = &timer_ops;
+ evs->file.wait = &evs->wait;
+
+ error = pfs_open(&evs->file);
+
+ if (error < 0)
+ release(evs);
+
+ return error;
+}
Index: linux-2.6/fs/pollfs/Makefile
===================================================================
--- linux-2.6.orig/fs/pollfs/Makefile
+++ linux-2.6/fs/pollfs/Makefile
@@ -2,3 +2,4 @@ obj-$(CONFIG_POLLFS) += pollfs.o
pollfs-y := file.o

pollfs-$(CONFIG_POLLFS_SIGNAL) += signal.o
+pollfs-$(CONFIG_POLLFS_TIMER) += timer.o
Index: linux-2.6/init/Kconfig
===================================================================
--- linux-2.6.orig/init/Kconfig
+++ linux-2.6/init/Kconfig
@@ -476,6 +476,13 @@ config POLLFS_SIGNAL
help
Pollable signal support

+config POLLFS_TIMER
+ bool "Enable pollfs timer" if EMBEDDED
+ default y
+ depends on POLLFS
+ help
+ Pollable timer support
+
config SHMEM
bool "Use full shmem filesystem" if EMBEDDED
default y
--
-
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