Messages in this thread | | | Date | Wed, 11 Jun 2014 11:27:43 +0400 | From | Andrew Vagin <> | Subject | Re: [patch 3/3] timerfd: Implement write method |
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On Tue, Jun 10, 2014 at 08:35:30PM +0400, 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 <gorcunov@openvz.org> > 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 <tglx@linutronix.de> > CC: Andrew Morton <akpm@linux-foundation.org> > CC: Andrey Vagin <avagin@openvz.org> > CC: Pavel Emelyanov <xemul@parallels.com> > CC: Vladimir Davydov <vdavydov@parallels.com> > Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org> > --- > 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;
I think it is too strong. It will not work in userns.
Why do we need to check CAP_SYS_RESOURCE here? Can we replace capable on ns_capable?
> + if (get_user(ticks, (u64 __user *)arg)) > + return -EFAULT; > + spin_lock_irq(&ctx->wqh.lock); > + ctx->ticks = ticks;
I think we need to wakt up readers here if ctx->ticks isn't zero.
> + 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 <linux/fcntl.h> > > +/* For _IO helpers */ > +#include <linux/ioctl.h> > + > /* > * 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 */
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