Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932760Ab0HDMva (ORCPT ); Wed, 4 Aug 2010 08:51:30 -0400 Received: from smtp.nokia.com ([192.100.105.134]:57554 "EHLO mgw-mx09.nokia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932715Ab0HDMv1 (ORCPT ); Wed, 4 Aug 2010 08:51:27 -0400 From: Alexander Shishkin To: lkml@vger.kernel.org Cc: Alexander Shishkin , "Kirill A. Shutemov" , Thomas Gleixner , John Stultz , Martin Schwidefsky , Andrew Morton , Jon Hunter , Ingo Molnar , Peter Zijlstra , "Paul E. McKenney" , David Howells , Avi Kivity , "H. Peter Anvin" , John Kacur , linux-kernel@vger.kernel.org Subject: [PATCH] [RFC] notify userspace about time changes Date: Wed, 4 Aug 2010 15:48:28 +0300 Message-Id: <1280926108-24668-1-git-send-email-virtuoso@slind.org> X-Mailer: git-send-email 1.7.2.rc1.1.gb2842 X-OriginalArrivalTime: 04 Aug 2010 12:49:24.0513 (UTC) FILETIME=[776FE910:01CB33D3] X-Nokia-AV: Clean Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 8568 Lines: 304 Certain userspace applications (like "clock" desktop applets or ntpd) might want to be notified when some other application changes the system time. It might also be important for an application to be able to distinguish between its own and somebody else's time changes. This patch implements a notification interface via eventfd mechanism. Proccess wishing to be notified about time changes should create an eventfd and echo its file descriptor to /sys/kernel/time_notify. After that, any calls to settimeofday()/stime()/adjtimex() made by other processes will be signalled to this eventfd. Credits for suggesting the eventfd mechanism for this purpose go te Kirill Shutemov. So far, this implementation can only filter out notifications caused by time change calls made by the process that wrote the eventfd descriptor to sysfs, but not its children which (might) have inherited the eventfd. It is so far not clear to me whether this is bad and more confusing than excluding such children as well. Similar mechanism can also be used for signalling other (all?) system calls made by certain (all?) processes without resorting to ptrace (which won't help if you don't know what processes you'd like to look after), given proper permission checks etc. Signed-off-by: Alexander Shishkin CC: Kirill A. Shutemov CC: Thomas Gleixner CC: John Stultz CC: Martin Schwidefsky CC: Andrew Morton CC: Jon Hunter CC: Ingo Molnar CC: Peter Zijlstra CC: "Paul E. McKenney" CC: David Howells CC: Avi Kivity CC: "H. Peter Anvin" CC: John Kacur CC: Alexander Shishkin CC: linux-kernel@vger.kernel.org --- include/linux/time.h | 7 ++ init/Kconfig | 7 ++ kernel/Makefile | 1 + kernel/time.c | 11 +++- kernel/time_notify.c | 158 ++++++++++++++++++++++++++++++++++++++++++++++++++ 5 files changed, 182 insertions(+), 2 deletions(-) create mode 100644 kernel/time_notify.c diff --git a/include/linux/time.h b/include/linux/time.h index ea3559f..9fca62b 100644 --- a/include/linux/time.h +++ b/include/linux/time.h @@ -237,6 +237,13 @@ static __always_inline void timespec_add_ns(struct timespec *a, u64 ns) a->tv_sec += __iter_div_u64_rem(a->tv_nsec + ns, NSEC_PER_SEC, &ns); a->tv_nsec = ns; } + +#ifdef CONFIG_TIME_NOTIFY +void time_notify_all(void); +#else +#define time_notify_all() do {} while (0) +#endif + #endif /* __KERNEL__ */ #define NFDBITS __NFDBITS diff --git a/init/Kconfig b/init/Kconfig index 5cff9a9..f7271f8 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -976,6 +976,13 @@ config PERF_USE_VMALLOC help See tools/perf/design.txt for details +config TIME_NOTIFY + bool + depends on EVENTFD + help + Enable time change notification events to userspace via + eventfd. + menu "Kernel Performance Events And Counters" config PERF_EVENTS diff --git a/kernel/Makefile b/kernel/Makefile index 057472f..7a25ee4 100644 --- a/kernel/Makefile +++ b/kernel/Makefile @@ -105,6 +105,7 @@ obj-$(CONFIG_PERF_EVENTS) += perf_event.o obj-$(CONFIG_HAVE_HW_BREAKPOINT) += hw_breakpoint.o obj-$(CONFIG_USER_RETURN_NOTIFIER) += user-return-notifier.o obj-$(CONFIG_PADATA) += padata.o +obj-$(CONFIG_TIME_NOTIFY) += time_notify.o ifneq ($(CONFIG_SCHED_OMIT_FRAME_POINTER),y) # According to Alan Modra , the -fno-omit-frame-pointer is diff --git a/kernel/time.c b/kernel/time.c index 848b1c2..74d355e 100644 --- a/kernel/time.c +++ b/kernel/time.c @@ -92,7 +92,9 @@ SYSCALL_DEFINE1(stime, time_t __user *, tptr) if (err) return err; - do_settimeofday(&tv); + err = do_settimeofday(&tv); + if (!err) + time_notify_all(); return 0; } @@ -177,7 +179,10 @@ int do_sys_settimeofday(struct timespec *tv, struct timezone *tz) /* SMP safe, again the code in arch/foo/time.c should * globally block out interrupts when it runs. */ - return do_settimeofday(tv); + error = do_settimeofday(tv); + if (!error) + time_notify_all(); + return error; } return 0; } @@ -215,6 +220,8 @@ SYSCALL_DEFINE1(adjtimex, struct timex __user *, txc_p) if(copy_from_user(&txc, txc_p, sizeof(struct timex))) return -EFAULT; ret = do_adjtimex(&txc); + if (!ret) + time_notify_all(); return copy_to_user(txc_p, &txc, sizeof(struct timex)) ? -EFAULT : ret; } diff --git a/kernel/time_notify.c b/kernel/time_notify.c new file mode 100644 index 0000000..c674f25 --- /dev/null +++ b/kernel/time_notify.c @@ -0,0 +1,158 @@ +/* + * linux/kernel/time_notify.c + * + * Copyright (C) 2010 Nokia Corporation + * Alexander Shishkin + * + * This file implements an interface to communicate time changes to userspace. + */ + +#include +#include +#include +#include +#include +#include +#include +#include +#include + +/* + * A process can "subscribe" to receive a notification via eventfd that + * some other process has called stime/settimeofday/adjtimex. + */ +struct time_event { + struct eventfd_ctx *eventfd; + struct task_struct *watcher; + struct work_struct remove; + wait_queue_t wq; + wait_queue_head_t *wqh; + poll_table pt; + struct list_head list; +}; + +static LIST_HEAD(event_list); +static DEFINE_SPINLOCK(event_lock); + +/* + * Do the necessary cleanup when the eventfd is being closed + */ +static void time_event_remove(struct work_struct *work) +{ + struct time_event *evt = container_of(work, struct time_event, remove); + + kfree(evt); +} + +static int time_event_wakeup(wait_queue_t *wq, unsigned int mode, int sync, + void *key) +{ + struct time_event *evt = container_of(wq, struct time_event, wq); + unsigned long flags = (unsigned long)key; + + if (flags & POLLHUP) { + remove_wait_queue_locked(evt->wqh, &evt->wq); + spin_lock(&event_lock); + list_del(&evt->list); + spin_unlock(&event_lock); + + schedule_work(&evt->remove); + } + + return 0; +} + +static void time_event_ptable_queue_proc(struct file *file, + wait_queue_head_t *wqh, poll_table *pt) +{ + struct time_event *evt = container_of(pt, struct time_event, pt); + + evt->wqh = wqh; + add_wait_queue(wqh, &evt->wq); +} + +/* + * Process wishing to be notified about time changes should write its + * eventfd's descriptor to /sys/kernel/time_notify. This eventfd will + * then be signalled about any time changes made by any process *but* + * this one. + */ +static int time_notify_store(struct kobject *kobj, struct kobj_attribute *attr, + const char *buf, size_t n) +{ + int ret = n; + unsigned int fd; + struct file *file; + struct time_event *evt; + + evt = kmalloc(sizeof(*evt), GFP_KERNEL); + if (!evt) + return -ENOMEM; + + fd = strict_strtoul(buf, NULL, 10); + file = eventfd_fget(fd); + if (IS_ERR(file)) { + ret = -EINVAL; + goto out_free; + } + + evt->eventfd = eventfd_ctx_fileget(file); + if (!evt->eventfd) { + ret = PTR_ERR(evt->eventfd); + goto out_fput; + } + + INIT_LIST_HEAD(&evt->list); + INIT_WORK(&evt->remove, time_event_remove); + + init_waitqueue_func_entry(&evt->wq, time_event_wakeup); + init_poll_funcptr(&evt->pt, time_event_ptable_queue_proc); + + if (file->f_op->poll(file, &evt->pt) & POLLHUP) { + ret = 0; + goto out_fput; + } + + evt->watcher = current; + + spin_lock(&event_lock); + list_add(&event_list, &evt->list); + spin_unlock(&event_lock); + + fput(file); + + return ret; + +out_fput: + fput(file); + +out_free: + kfree(evt); + + return ret; +} + +void time_notify_all(void) +{ + struct list_head *tmp; + + spin_lock(&event_lock); + list_for_each(tmp, &event_list) { + struct time_event *e = container_of(tmp, struct time_event, + list); + + if (e->watcher != current) + eventfd_signal(e->eventfd, 1); + } + spin_unlock(&event_lock); +} + +static struct kobj_attribute time_notify_attr = + __ATTR(time_notify, S_IWUGO, NULL, time_notify_store); + +static int time_notify_init(void) +{ + return sysfs_create_file(kernel_kobj, &time_notify_attr.attr); +} + +core_initcall(time_notify_init); -- 1.7.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/