Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755722AbaFJUDh (ORCPT ); Tue, 10 Jun 2014 16:03:37 -0400 Received: from mail-qa0-f44.google.com ([209.85.216.44]:37901 "EHLO mail-qa0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753636AbaFJUDe (ORCPT ); Tue, 10 Jun 2014 16:03:34 -0400 MIME-Version: 1.0 Reply-To: mtk.manpages@gmail.com In-Reply-To: <20140610163530.GF2243@moon> References: <20140428212517.200264067@openvz.org> <20140428213301.507657833@openvz.org> <20140610163530.GF2243@moon> From: "Michael Kerrisk (man-pages)" Date: Tue, 10 Jun 2014 22:03:12 +0200 Message-ID: Subject: Re: [patch 3/3] timerfd: Implement write method To: Cyrill Gorcunov Cc: Thomas Gleixner , LKML , Andrew Morton , Andrey Vagin , Pavel Emelyanov , vdavydov@parallels.com, Linux API Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org [CC += linux-api@] On Tue, Jun 10, 2014 at 6:35 PM, Cyrill Gorcunov wrote: > On Thu, May 22, 2014 at 06:58:19AM +0900, Thomas Gleixner wrote: >> > >> > So what wakes a potential waiter in read/poll? >> >> And who is updating timerfd_create(2) ? > > Thomas, could you please take a look if the approach below is acceptable? > If it will be fine I update manpage then. > --- > From: Cyrill Gorcunov > Subject: timerfd: Implement timerfd_ioctl method to restore timerfd_ctx::ticks > > The read() of timerfd files allows to fetch the number of timer ticks > while there is no way to set it back from userspace. > > To restore the timer's state as it was at checkpoint moment we need > a path to bring @ticks back. Initially I thought about writing ticks > back via write() interface but it seems such API is somehow obscure. > > Instead implement timerfd_ioctl() method with TFD_IOC_SET_TICKS > command which requires CAP_SYS_RESOURCE capability to be able to > set @ticks into arbitrary value. Note this command doesn't wake > up readers/waiters and its purpose only to serve C/R needs > (for same sake I wrapped code with CONFIG_CHECKPOINT_RESTORE). > Still if needed the ioctl may be extended for new commands > and CONFIG_CHECKPOINT_RESTORE dropped off. > > CC: Thomas Gleixner > CC: Andrew Morton > CC: Andrey Vagin > CC: Pavel Emelyanov > CC: Vladimir Davydov > Signed-off-by: Cyrill Gorcunov > --- > fs/timerfd.c | 31 +++++++++++++++++++++++++++++++ > include/linux/timerfd.h | 5 +++++ > 2 files changed, 36 insertions(+) > > Index: linux-2.6.git/fs/timerfd.c > =================================================================== > --- linux-2.6.git.orig/fs/timerfd.c > +++ linux-2.6.git/fs/timerfd.c > @@ -313,11 +313,42 @@ static int timerfd_show(struct seq_file > } > #endif > > +#ifdef CONFIG_CHECKPOINT_RESTORE > +static long timerfd_ioctl(struct file *file, unsigned int cmd, unsigned long arg) > +{ > + struct timerfd_ctx *ctx = file->private_data; > + int ret = 0; > + > + switch (cmd) { > + case TFD_IOC_SET_TICKS: { > + u64 ticks; > + > + if (!capable(CAP_SYS_RESOURCE)) > + return -EPERM; > + if (get_user(ticks, (u64 __user *)arg)) > + return -EFAULT; > + spin_lock_irq(&ctx->wqh.lock); > + ctx->ticks = ticks; > + spin_unlock_irq(&ctx->wqh.lock); > + break; > + } > + default: > + ret = -ENOTTY; > + break; > + } > + > + return ret; > +} > +#endif > + > static const struct file_operations timerfd_fops = { > .release = timerfd_release, > .poll = timerfd_poll, > .read = timerfd_read, > .llseek = noop_llseek, > +#ifdef CONFIG_CHECKPOINT_RESTORE > + .unlocked_ioctl = timerfd_ioctl, > +#endif > #ifdef CONFIG_PROC_FS > .show_fdinfo = timerfd_show, > #endif > Index: linux-2.6.git/include/linux/timerfd.h > =================================================================== > --- linux-2.6.git.orig/include/linux/timerfd.h > +++ linux-2.6.git/include/linux/timerfd.h > @@ -11,6 +11,9 @@ > /* For O_CLOEXEC and O_NONBLOCK */ > #include > > +/* For _IO helpers */ > +#include > + > /* > * CAREFUL: Check include/asm-generic/fcntl.h when defining > * new flags, since they might collide with O_* ones. We want > @@ -29,4 +32,6 @@ > /* Flags for timerfd_settime. */ > #define TFD_SETTIME_FLAGS (TFD_TIMER_ABSTIME | TFD_TIMER_CANCEL_ON_SET) > > +#define TFD_IOC_SET_TICKS _IOW('T', 0, u64) > + > #endif /* _LINUX_TIMERFD_H */ -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/ -- 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/