[patch 0/4] timerfd c/r support, v5

Hi, sorry for spamming, but in v4 I simply messed up in the series,
doing reply-to-reply with updated variants. So here are all patches
up to date on top of -rc5. Sorry again for resend.

ioctl(2)
	The following commands are supported: TFD_IOC_SET_TICKS to adjust
	the number of the timer expirations that have occurred.
	It take a pointer to nonzero 8-byte integer (uint64_t*) containing
	new number of expirations. Once the number is set any waiter on
	the timer is woken up. The only purpose of this command is to restore
	the expirations in a sake of checkpoint/restore procedure.
	It requires the kernel to be built with CONFIG_CHECKPOINT_RESTORE
	support.

Signed-off-by: Cyrill Gorcunov <redacted>
CC: Michael Kerrisk <redacted>
CC: Thomas Gleixner <redacted>
CC: Andrew Morton <akpm@linux-foundation.org>
CC: Andrey Vagin <redacted>
CC: Pavel Emelyanov <redacted>
CC: Vladimir Davydov <redacted>
CC: linux-api@vger.kernel.org
---
 man2/timerfd_create.2 |   14 ++++++++++++++
 1 file changed, 14 insertions(+)

Index: man-pages/man2/timerfd_create.2
===================================================================

--- man-pages.orig/man2/timerfd_create.2
+++ man-pages/man2/timerfd_create.2

@@ -260,6 +260,20 @@ multiplexing APIs:
 and
 .BR epoll (7).
 .TP
+.BR ioctl "(2)"
+The following commands are supported:
+.B TFD_IOC_SET_TICKS
+to adjust the number of the timer expirations that have occurred.
+It take a pointer to nonzero 8-byte integer
+.RI ( uint64_t *)
+containing the new number of expirations.
+Once the number is set any waiter on the timer is woken up.
+The only purpose of this command is to restore the expirations
+in a sake of checkpoint/restore procedure.
+It requires the kernel to be built with
+.BR CONFIG_CHECKPOINT_RESTORE
+support.
+.TP
 .BR close (2)
 When the file descriptor is no longer required it should be closed.
 When all file descriptors associated with the same timer object

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

CC: Thomas Gleixner <redacted>
CC: Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>
CC: Andrey Vagin <redacted>
CC: Arnd Bergmann <redacted>
CC: Christopher Covington <redacted>
CC: Pavel Emelyanov <redacted>
CC: Vladimir Davydov <redacted>
Signed-off-by: Cyrill Gorcunov <redacted>
---
 fs/timerfd.c            |   37 +++++++++++++++++++++++++++++++++++++
 include/linux/timerfd.h |    5 +++++
 2 files changed, 42 insertions(+)

Index: linux-2.6.git/fs/timerfd.c
===================================================================

--- linux-2.6.git.orig/fs/timerfd.c
+++ linux-2.6.git/fs/timerfd.c

@@ -315,12 +315,49 @@ static int timerfd_show(struct seq_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)

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 */

CC: Thomas Gleixner <redacted>
CC: Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>
CC: Andrey Vagin <redacted>
CC: Pavel Emelyanov <redacted>
CC: Vladimir Davydov <redacted>
Signed-off-by: Cyrill Gorcunov <redacted>
---
 Documentation/filesystems/proc.txt |   19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

Index: linux-2.6.git/Documentation/filesystems/proc.txt
===================================================================

--- linux-2.6.git.orig/Documentation/filesystems/proc.txt
+++ linux-2.6.git/Documentation/filesystems/proc.txt

@@ -1743,6 +1743,25 @@ pair provide additional information part
 	While the first three lines are mandatory and always printed, the rest is
 	optional and may be omitted if no marks created yet.
 
+	Timerfd files
+	~~~~~~~~~~~~~
+
+	pos:	0
+	flags:	02
+	mnt_id:	9
+	clockid: 0
+	ticks: 0
+	settime flags: 01
+	it_value: (0, 49406829)
+	it_interval: (1, 0)
+
+	where 'clockid' is the clock type and 'ticks' is the number of the timer expirations
+	that have occurred [see timerfd_create(2) for details]. 'settime flags' are
+	flags in octal form been used to setup the timer [see timerfd_settime(2) for
+	details]. 'it_value' is remaining time until the timer exiration.
+	'it_interval' is the interval for the timer. Note the timer might be set up
+	with TIMER_ABSTIME option which will be shown in 'settime flags', but 'it_value'
+	still exhibits timer's remaining time.
 
 ------------------------------------------------------------------------------
 Configuring procfs

For checkpoint/restore of timerfd files we need to know how exactly
the timer were armed, to be able to recreate it on restore stage.
Thus implement show_fdinfo method which provides enough information
for that.

One of significant changes I think is the addition of @settime_flags
member. Currently there are two flags TFD_TIMER_ABSTIME and
TFD_TIMER_CANCEL_ON_SET, and the second can be found from
@might_cancel variable but in case if the flags will be extended
in future we most probably will have to somehow remember them
explicitly anyway so I guss doing that right now won't hurt.

To not bloat the timerfd_ctx structure I've converted @expired
to short integer and defined @settime_flags as short too.

v2 (by avagin@, vdavydov@ and tglx@):

 - Add it_value/it_interval fields
 - Save flags being used in timerfd_setup in context

v3 (by tglx@):
 - don't forget to use CONFIG_PROC_FS

v4 (by akpm@):
 -Use define timerfd_show NULL for non c/r config

CC: Thomas Gleixner <redacted>
CC: Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>
CC: Andrey Vagin <redacted>
CC: Pavel Emelyanov <redacted>
CC: Vladimir Davydov <redacted>
Signed-off-by: Cyrill Gorcunov <redacted>
---
 fs/timerfd.c |   34 +++++++++++++++++++++++++++++++++-
 1 file changed, 33 insertions(+), 1 deletion(-)

Index: linux-2.6.git/fs/timerfd.c
===================================================================

--- linux-2.6.git.orig/fs/timerfd.c
+++ linux-2.6.git/fs/timerfd.c

@@ -35,8 +35,9 @@ struct timerfd_ctx {
 	ktime_t moffs;
 	wait_queue_head_t wqh;
 	u64 ticks;
-	int expired;
 	int clockid;
+	short unsigned expired;
+	short unsigned settime_flags;	/* to show in fdinfo */
 	struct rcu_head rcu;
 	struct list_head clist;
 	bool might_cancel;

@@ -196,6 +197,8 @@ static int timerfd_setup(struct timerfd_
 		if (timerfd_canceled(ctx))
 			return -ECANCELED;
 	}
+
+	ctx->settime_flags = flags & TFD_SETTIME_FLAGS;
 	return 0;
 }
 

@@ -284,11 +287,40 @@ static ssize_t timerfd_read(struct file
 	return res;
 }
 
+#ifdef CONFIG_PROC_FS
+static int timerfd_show(struct seq_file *m, struct file *file)
+{
+	struct timerfd_ctx *ctx = file->private_data;
+	struct itimerspec t;
+
+	spin_lock_irq(&ctx->wqh.lock);
+	t.it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
+	t.it_interval = ktime_to_timespec(ctx->tintv);
+	spin_unlock_irq(&ctx->wqh.lock);
+
+	return seq_printf(m,
+			  "clockid: %d\n"
+			  "ticks: %llu\n"
+			  "settime flags: 0%o\n"
+			  "it_value: (%llu, %llu)\n"
+			  "it_interval: (%llu, %llu)\n",
+			  ctx->clockid, (unsigned long long)ctx->ticks,
+			  ctx->settime_flags,
+			  (unsigned long long)t.it_value.tv_sec,
+			  (unsigned long long)t.it_value.tv_nsec,
+			  (unsigned long long)t.it_interval.tv_sec,
+			  (unsigned long long)t.it_interval.tv_nsec);
+}
+#else
+#define timerfd_show 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,
 };
 
 static int timerfd_fget(int fd, struct fd *p)

Hello Cyrill,

On 07/15/2014 11:54 PM, Cyrill Gorcunov wrote:

ioctl(2)
	The following commands are supported: TFD_IOC_SET_TICKS to adjust
	the number of the timer expirations that have occurred.
	It take a pointer to nonzero 8-byte integer (uint64_t*) containing
	new number of expirations. Once the number is set any waiter on
	the timer is woken up. The only purpose of this command is to restore
	the expirations in a sake of checkpoint/restore procedure.
	It requires the kernel to be built with CONFIG_CHECKPOINT_RESTORE
	support.

Late... but, patch applied. Thank you.

Cheers,

Michael

-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/

On Mon, Apr 13, 2015 at 09:56:20PM +0200, Michael Kerrisk (man-pages) wrote:

Hello Cyrill,

On 07/15/2014 11:54 PM, Cyrill Gorcunov wrote:

quoted

ioctl(2)
	The following commands are supported: TFD_IOC_SET_TICKS to adjust
	the number of the timer expirations that have occurred.
	It take a pointer to nonzero 8-byte integer (uint64_t*) containing
	new number of expirations. Once the number is set any waiter on
	the timer is woken up. The only purpose of this command is to restore
	the expirations in a sake of checkpoint/restore procedure.
	It requires the kernel to be built with CONFIG_CHECKPOINT_RESTORE
	support.

Late... but, patch applied. Thank you.

Sure thing! Ping me if anything else should be added.