timerfd: Implement timerfd_ioctl method to restore timerfd_ctx::ticks, v3

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 allows to adjust @ticks into non-zero value waking
up the waiters.

I wrapped code with CONFIG_CHECKPOINT_RESTORE which can be
dropped off if there users except c/r camp appear.

v2 (by akpm@):
 - Use define timerfd_ioctl NULL for non c/r config

v3:
 - Use copy_from_user for @ticks fetching since
   not all arch support get_user for 8 byte argument

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Andrey Vagin <avagin@openvz.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Christopher Covington <cov@codeaurora.org>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Vladimir Davydov <vdavydov@parallels.com>
Link: http://lkml.kernel.org/r/20140715215703.285617923@openvz.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

diff --git a/fs/timerfd.c b/fs/timerfd.c
index 77183f047f65cb885153a15771b691ff0d25355f..709603cac9e6173b9837b3d111aedc66a2f6b843 100644 (file)
--- a/fs/timerfd.c
+++ b/fs/timerfd.c
@@ -315,12 +315,49 @@ static int timerfd_show(struct seq_file *m, struct file *file)
 #define timerfd_show NULL
 #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 (copy_from_user(&ticks, (u64 __user *)arg, sizeof(ticks)))
+                       return -EFAULT;
+               if (!ticks)
+                       return -EINVAL;
+
+               spin_lock_irq(&ctx->wqh.lock);
+               if (!timerfd_canceled(ctx)) {
+                       ctx->ticks = ticks;
+                       if (ticks)
+                               wake_up_locked(&ctx->wqh);
+               } else
+                       ret = -ECANCELED;
+               spin_unlock_irq(&ctx->wqh.lock);
+               break;
+       }
+       default:
+               ret = -ENOTTY;
+               break;
+       }
+
+       return ret;
+}
+#else
+#define timerfd_ioctl NULL
+#endif
+
 static const struct file_operations timerfd_fops = {
        .release        = timerfd_release,
        .poll           = timerfd_poll,
        .read           = timerfd_read,
        .llseek         = noop_llseek,
        .show_fdinfo    = timerfd_show,
+       .unlocked_ioctl = timerfd_ioctl,
 };
 
 static int timerfd_fget(int fd, struct fd *p)

diff --git a/include/linux/timerfd.h b/include/linux/timerfd.h
index d3b57fa1222557d90fa41f6325ad8d1f5daac100..bd36ce431e32cbb57a1ec4e97964b78774787a2e 100644 (file)
--- a/include/linux/timerfd.h
+++ b/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 */