Re: [RFC v3 1/4] fs: Add generic file system event notifications

[Dmitry Monakhov <dmonlist-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

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Beata Michalska <b.michalska-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org> writes:

> Introduce configurable generic interface for file
> system-wide event notifications, to provide file
> systems with a common way of reporting any potential
> issues as they emerge.
>
> The notifications are to be issued through generic
> netlink interface by newly introduced multicast group.
>
> Threshold notifications have been included, allowing
> triggering an event whenever the amount of free space drops
> below a certain level - or levels to be more precise as two
> of them are being supported: the lower and the upper range.
> The notifications work both ways: once the threshold level
> has been reached, an event shall be generated whenever
> the number of available blocks goes up again re-activating
> the threshold.
>
> The interface has been exposed through a vfs. Once mounted,
> it serves as an entry point for the set-up where one can
> register for particular file system events.
>
> Signed-off-by: Beata Michalska <b.michalska-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org>
> ---
>  Documentation/filesystems/events.txt |  232 ++++++++++
>  fs/Kconfig                           |    2 +
>  fs/Makefile                          |    1 +
>  fs/events/Kconfig                    |    7 +
>  fs/events/Makefile                   |    5 +
>  fs/events/fs_event.c                 |  809 ++++++++++++++++++++++++++++++++++
>  fs/events/fs_event.h                 |   22 +
>  fs/events/fs_event_netlink.c         |  104 +++++
>  fs/namespace.c                       |    1 +
>  include/linux/fs.h                   |    6 +-
>  include/linux/fs_event.h             |   72 +++
>  include/uapi/linux/Kbuild            |    1 +
>  include/uapi/linux/fs_event.h        |   58 +++
>  13 files changed, 1319 insertions(+), 1 deletion(-)
>  create mode 100644 Documentation/filesystems/events.txt
>  create mode 100644 fs/events/Kconfig
>  create mode 100644 fs/events/Makefile
>  create mode 100644 fs/events/fs_event.c
>  create mode 100644 fs/events/fs_event.h
>  create mode 100644 fs/events/fs_event_netlink.c
>  create mode 100644 include/linux/fs_event.h
>  create mode 100644 include/uapi/linux/fs_event.h
>
> diff --git a/Documentation/filesystems/events.txt b/Documentation/filesystems/events.txt
> new file mode 100644
> index 0000000..c2e6227
> --- /dev/null
> +++ b/Documentation/filesystems/events.txt
> @@ -0,0 +1,232 @@
> +
> +	Generic file system event notification interface
> +
> +Document created 23 April 2015 by Beata Michalska <b.michalska@samsung.com>
> +
> +1. The reason behind:
> +=====================
> +
> +There are many corner cases when things might get messy with the filesystems.
> +And it is not always obvious what and when went wrong. Sometimes you might
> +get some subtle hints that there is something going on - but by the time
> +you realise it, it might be too late as you are already out-of-space
> +or the filesystem has been remounted as read-only (i.e.). The generic
> +interface for the filesystem events fills the gap by providing a rather
> +easy way of real-time notifications triggered whenever something interesting
> +happens, allowing filesystems to report events in a common way, as they occur.
> +
> +2. How does it work:
> +====================
> +
> +The interface itself has been exposed as fstrace-type Virtual File System,
> +primarily to ease the process of setting up the configuration for the
> +notifications. So for starters, it needs to get mounted (obviously):
> +
> +	mount -t fstrace none /sys/fs/events
> +
> +This will unveil the single fstrace filesystem entry - the 'config' file,
> +through which the notification are being set-up.
> +
> +Activating notifications for particular filesystem is as straightforward
> +as writing into the 'config' file. Note that by default all events, despite
> +the actual filesystem type, are being disregarded.
> +
> +Synopsis of config:
> +------------------
> +
> +	MOUNT EVENT_TYPE [L1] [L2]
> +
> + MOUNT      : the filesystem's mount point
> + EVENT_TYPE : event types - currently two of them are being supported:
> +
> +	      * generic events ("G") covering most common warnings
> +	      and errors that might be reported by any filesystem;
> +	      this option does not take any arguments;
> +
> +	      * threshold notifications ("T") - events sent whenever
> +	      the amount of available space drops below certain level;
> +	      it is possible to specify two threshold levels though
> +	      only one is required to properly setup the notifications;
> +	      as those refer to the number of available blocks, the lower
> +	      level [L1] needs to be higher than the upper one [L2]
> +
> +Sample request could look like the following:
> +
> + echo /sample/mount/point G T 710000 500000 > /sys/fs/events/config
> +
> +Multiple request might be specified provided they are separated with semicolon.
> +
> +The configuration itself might be modified at any time. One can add/remove
> +particular event types for given fielsystem, modify the threshold levels,
> +and remove single or all entries from the 'config' file.
> +
> + - Adding new event type:
> +
> + $ echo MOUNT EVENT_TYPE > /sys/fs/events/config
> +
> +(Note that is is enough to provide the event type to be enabled without
> +the already set ones.)
> +
> + - Removing event type:
> +
> + $ echo '!MOUNT EVENT_TYPE' > /sys/fs/events/config
> +
> + - Updating threshold limits:
> +
> + $ echo MOUNT T L1 L2 > /sys/fs/events/config
> +
> + - Removing single entry:
> +
> + $ echo '!MOUNT' > /sys/fs/events/config
> +
> + - Removing all entries:
> +
> + $ echo > /sys/fs/events/config
> +
> +Reading the file will list all registered entries with their current set-up
> +along with some additional info like the filesystem type and the backing device
> +name if available.
> +
> +Final, though a very important note on the configuration: when and if the
> +actual events are being triggered falls way beyond the scope of the generic
> +filesystem events interface. It is up to a particular filesystem
> +implementation which events are to be supported - if any at all. So if
> +given filesystem does not support the event notifications, an attempt to
> +enable those through 'config' file will fail.
> +
> +
> +3. The generic netlink interface support:
> +=========================================
> +
> +Whenever an event notification is triggered (by given filesystem) the current
> +configuration is being validated to decide whether a userpsace notification
> +should be launched. If there has been no request (in a mean of 'config' file
> +entry) for given event, one will be silently disregarded. If, on the other
> +hand, someone is 'watching' given filesystem for specific events, a generic
> +netlink message will be sent. A dedicated multicast group has been provided
> +solely for this purpose so in order to receive such notifications, one should
> +subscribe to this new multicast group. As for now only the init network
> +namespace is being supported.
> +
> +3.1 Message format
> +
> +The FS_NL_C_EVENT shall be stored within the generic netlink message header
> +as the command field. The message payload will provide more detailed info:
> +the backing device major and minor numbers, the event code and the id of
> +the process which action led to the event occurrence. In case of threshold
> +notifications, the current number of available blocks will be included
> +in the payload as well.
> +
> +
> +	 0                   1                   2                   3
> +	 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
> +	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> +	|	            NETLINK MESSAGE HEADER			|
> +	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> +	| 		GENERIC NETLINK MESSAGE HEADER   		|
> +	| 	   (with FS_NL_C_EVENT as genlmsghdr cdm field)		|
> +	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> +	| 	      Optional user specific message header		|
> +	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> +	|		   GENERIC MESSAGE PAYLOAD:			|
> +	+---------------------------------------------------------------+
> +	| 		  FS_NL_A_EVENT_ID  (NLA_U32)			|
> +	+---------------------------------------------------------------+
> +	|	  	  FS_NL_A_DEV_MAJOR (NLA_U32)			|
> +	+---------------------------------------------------------------+
> +	| 	  	  FS_NL_A_DEV_MINOR (NLA_U32) 			|

> +	+---------------------------------------------------------------+
> +	|  		  FS_NL_A_CAUSED_ID (NLA_U32)			|
> +	+---------------------------------------------------------------+
> +	|  		    FS_NL_A_DATA (NLA_U64)			|
> +	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> +
> +
> +The above figure is based on:
> + http://www.linuxfoundation.org/collaborate/workgroups/networking/generic_netlink_howto#Message_Format
> +
> +
> +4. API Reference:
> +=================
> +
> + 4.1 Generic file system event interface data & operations
> +
> + #include <linux/fs_event.h>
> +
> + struct fs_trace_info {
> +	void	__rcu	*e_priv		 /* READ ONLY */
> +	unsigned int 	events_cap_mask; /* Supported notifications */
> +	const struct fs_trace_operations *ops;
> + };
> +
> + struct fs_trace_operations {
> +	void (*query)(struct super_block *, u64 *);
> + };
> +
> + In order to get the fireworks and stuff, each filesystem needs to setup
> + the events_cap_mask field of the fs_trace_info structure, which has been
> + embedded within the super_block structure. This should reflect the type of
> + events the filesystem wants to support. In case of threshold notifications,
> + apart from setting the FS_EVENT_THRESH flag, the 'query' callback should
> + be provided as this enables the events interface to get the up-to-date
> + state of the number of available blocks whenever those notifications are
> + being requested.
> +
> + The 'e_priv' field of the fs_trace_info structure should be completely ignored
> + as it's for INTERNAL USE ONLY. So don't even think of messing with it, if you
> + do not want to get yourself into some real trouble. If still, you are tempted
> + to do so - feel free, it's gonna be pure fun. Consider yourself warned.
> +
> +
> + 4.2 Event notification:
> +
> + #include <linux/fs_event.h>
> + void fs_event_notify(struct super_block *sb, unsigned int event_id);
> +
> + Notify the generic FS event interface of an occurring event.
> + This shall be used by any file system that wishes to inform any potential
> + listeners/watchers of a particular event.
> + - sb:         the filesystem's super block
> + - event_id:   an event identifier
> +
> + 4.3 Threshold notifications:
> +
> + #include <linux/fs_event.h>
> + void fs_event_alloc_space(struct super_block *sb, u64 ncount);
> + void fs_event_free_space(struct super_block *sb, u64 ncount);
> +
> + Each filesystme supporting the threshold notifications should call
> + fs_event_alloc_space/fs_event_free_space respectively whenever the
> + amount of available blocks changes.
> + - sb:     the filesystem's super block
> + - ncount: number of blocks being acquired/released
> +
> + Note that to properly handle the threshold notifications the fs events
> + interface needs to be kept up to date by the filesystems. Each should
> + register fs_trace_operations to enable querying the current number of
> + available blocks.
> +
> + 4.4 Sending message through generic netlink interface
> +
> + #include <linux/fs_event.h>
> +
> + int fs_netlink_send_event(size_t size, unsigned int event_id,
> +	int (*compose_msg)(struct sk_buff *skb, void *data), void *cbdata);
> +
> + Although the fs event interface is fully responsible for sending the messages
> + over the netlink, filesystems might use the FS_EVENT multicast group to send
> + their own custom messages.
> + - size:        the size of the message payload
> + - event_id:    the event identifier
> + - compose_msg: a callback responsible for filling-in the message payload
> + - cbdata:      message custom data
> +
> + Calling fs_netlink_send_event will result in a message being sent by
> + the FS_EVENT multicast group. Note that the body of the message should be
> + prepared (set-up )by the caller - through compose_msg callback. The message's
> + sk_buff will be allocated on behalf of the caller (thus the size parameter).
> + The compose_msg should only fill the payload with proper data. Unless
> + the event id is specified as FS_EVENT_NONE, it's value shall be added
> + to the payload prior to calling the compose_msg.
> +
> +
> diff --git a/fs/Kconfig b/fs/Kconfig
> index ec35851..a89e678 100644
> --- a/fs/Kconfig
> +++ b/fs/Kconfig
> @@ -69,6 +69,8 @@ config FILE_LOCKING
>            for filesystems like NFS and for the flock() system
>            call. Disabling this option saves about 11k.
>  
> +source "fs/events/Kconfig"
> +
>  source "fs/notify/Kconfig"
>  
>  source "fs/quota/Kconfig"
> diff --git a/fs/Makefile b/fs/Makefile
> index a88ac48..bcb3048 100644
> --- a/fs/Makefile
> +++ b/fs/Makefile
> @@ -126,3 +126,4 @@ obj-y				+= exofs/ # Multiple modules
>  obj-$(CONFIG_CEPH_FS)		+= ceph/
>  obj-$(CONFIG_PSTORE)		+= pstore/
>  obj-$(CONFIG_EFIVAR_FS)		+= efivarfs/
> +obj-$(CONFIG_FS_EVENTS)		+= events/
> diff --git a/fs/events/Kconfig b/fs/events/Kconfig
> new file mode 100644
> index 0000000..1c60195
> --- /dev/null
> +++ b/fs/events/Kconfig
> @@ -0,0 +1,7 @@
> +# Generic Files System events interface
> +config FS_EVENTS
> +	bool "Generic filesystem events"
> +	select NET
> +	default y
> +	help
> +	  Enable generic filesystem events interface
> diff --git a/fs/events/Makefile b/fs/events/Makefile
> new file mode 100644
> index 0000000..9c98337
> --- /dev/null
> +++ b/fs/events/Makefile
> @@ -0,0 +1,5 @@
> +#
> +# Makefile for the Linux Generic File System Event Interface
> +#
> +
> +obj-y := fs_event.o fs_event_netlink.o
> diff --git a/fs/events/fs_event.c b/fs/events/fs_event.c
> new file mode 100644
> index 0000000..1037311
> --- /dev/null
> +++ b/fs/events/fs_event.c
> @@ -0,0 +1,809 @@
> +/*
> + * Generic File System Evens Interface
> + *
> + * Copyright(c) 2015 Samsung Electronics. All rights reserved.
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms of the GNU General Public License version 2.
> + *
> + * The full GNU General Public License is included in this distribution in the
> + * file called COPYING.
> + *
> + * This program is distributed in the hope that it will be useful, but WITHOUT
> + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
> + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
> + * more details.
> + */
> +#include <linux/fs.h>
> +#include <linux/module.h>
> +#include <linux/mount.h>
> +#include <linux/namei.h>
> +#include <linux/nsproxy.h>
> +#include <linux/parser.h>
> +#include <linux/seq_file.h>
> +#include <linux/slab.h>
> +#include <linux/rcupdate.h>
> +#include <net/genetlink.h>
> +#include "../pnode.h"
> +#include "fs_event.h"
> +
> +static LIST_HEAD(fs_trace_list);
> +static DEFINE_MUTEX(fs_trace_lock);
> +
> +static struct kmem_cache *fs_trace_cachep __read_mostly;
> +
> +static atomic_t stray_traces = ATOMIC_INIT(0);
> +static DECLARE_WAIT_QUEUE_HEAD(trace_wq);
> +/*
> + * Threshold notification state bits.
> + * Note the reverse as this refers to the number
> + * of available blocks.
> + */
> +#define THRESH_LR_BELOW		0x0001 /* Falling below the lower range */
> +#define THRESH_LR_BEYOND	0x0002
> +#define THRESH_UR_BELOW		0x0004
> +#define THRESH_UR_BEYOND	0x0008 /* Going beyond the upper range */
> +
> +#define THRESH_LR_ON	(THRESH_LR_BELOW | THRESH_LR_BEYOND)
> +#define THRESH_UR_ON	(THRESH_UR_BELOW | THRESH_UR_BEYOND)
> +
> +#define FS_TRACE_ADD	0x100000
> +
> +struct fs_trace_entry {
> +	struct kref	 count;
> +	atomic_t	 active;
> +	struct super_block *sb;
> +	unsigned int	 notify;
> +	struct path	 mnt_path;
> +	struct list_head  node;
> +
> +	struct fs_event_thresh {
> +		u64		 avail_space;
> +		u64		 lrange;
> +		u64		 urange;
> +		unsigned int	 state;
> +	}		 th;
> +	struct rcu_head	 rcu_head;
> +	spinlock_t	 lock;
> +};
> +
> +static const match_table_t fs_etypes = {
> +	{ FS_EVENT_GENERIC, "G"   },
> +	{ FS_EVENT_THRESH,  "T"   },
> +	{ 0, NULL },
> +};
> +
> +static inline int fs_trace_query_data(struct super_block *sb,
> +				       struct fs_trace_entry *en)
> +{
> +	if (sb->s_etrace.ops && sb->s_etrace.ops->query) {
> +		sb->s_etrace.ops->query(sb, &en->th.avail_space);
> +		return 0;
> +	}
> +
> +	return -EINVAL;
> +}
> +
> +static inline void fs_trace_entry_free(struct fs_trace_entry *en)
> +{
> +	kmem_cache_free(fs_trace_cachep, en);
> +}
> +
> +static void fs_destroy_trace_entry(struct kref *en_ref)
> +{
> +	struct fs_trace_entry *en = container_of(en_ref,
> +					 struct fs_trace_entry, count);
> +
> +	/* Last reference has been dropped */
> +	fs_trace_entry_free(en);
> +	atomic_dec(&stray_traces);
> +}
> +
> +static void fs_trace_entry_put(struct fs_trace_entry *en)
> +{
> +	kref_put(&en->count, fs_destroy_trace_entry);
> +}
> +
> +static void fs_release_trace_entry(struct rcu_head *rcu_head)
> +{
> +	struct fs_trace_entry *en = container_of(rcu_head,
> +						 struct fs_trace_entry,
> +						 rcu_head);
> +	/*
> +	 * As opposed to typical reference drop, this one is being
> +	 * called from the rcu callback. This is to make sure all
> +	 * readers have managed to safely grab the reference before
> +	 * the change to rcu pointer is visible to all and before
> +	 * the reference is dropped here.
> +	 */
> +	fs_trace_entry_put(en);
> +}
> +
> +static void fs_drop_trace_entry(struct fs_trace_entry *en)
> +{
> +	struct super_block *sb;
> +
> +	lockdep_assert_held(&fs_trace_lock);
> +	/*
> +	 * The trace entry might have already been removed
> +	 * from the list of active traces with the proper
> +	 * ref drop, though it was still in use handling
> +	 * one of the fs events. This means that the object
> +	 * has been already scheduled for being released.
> +	 * So leave...
> +	 */
> +
> +	if (!atomic_add_unless(&en->active, -1, 0))
> +		return;
> +	/*
> +	 * At this point the trace entry is being marked as inactive
> +	 * so no new references will be allowed.
> +	 * Still it might be floating around somewhere
> +	 * so drop the reference when the rcu readers are done.
> +	 */
> +	spin_lock(&en->lock);
> +	list_del(&en->node);
> +	sb = en->sb;
> +	en->sb = NULL;
> +	spin_unlock(&en->lock);
> +
> +	rcu_assign_pointer(sb->s_etrace.e_priv, NULL);
> +	call_rcu(&en->rcu_head, fs_release_trace_entry);
> +	/* It's safe now to drop the reference to the super */
> +	deactivate_super(sb);
> +	atomic_inc(&stray_traces);
> +}
> +
> +static inline
> +struct fs_trace_entry *fs_trace_entry_get(struct fs_trace_entry *en)
> +{
> +	if (en) {
> +		if (!kref_get_unless_zero(&en->count))
> +			return NULL;
> +		/* Don't allow referencing inactive object */
> +		if (!atomic_read(&en->active)) {
> +			fs_trace_entry_put(en);
> +			return NULL;
> +		}
> +	}
> +	return en;
> +}
> +
> +static struct fs_trace_entry *fs_trace_entry_get_rcu(struct super_block *sb)
> +{
> +	struct fs_trace_entry *en;
> +
> +	if (!sb)
> +		return NULL;
> +
> +	rcu_read_lock();
> +	en = rcu_dereference(sb->s_etrace.e_priv);
> +	en = fs_trace_entry_get(en);
> +	rcu_read_unlock();
> +
> +	return en;
> +}
> +
> +static int fs_remove_trace_entry(struct super_block *sb)
> +{
> +	struct fs_trace_entry *en;
> +
> +	en = fs_trace_entry_get_rcu(sb);
> +	if (!en)
> +		return -EINVAL;
> +
> +	mutex_lock(&fs_trace_lock);
> +	fs_drop_trace_entry(en);
> +	mutex_unlock(&fs_trace_lock);
> +	fs_trace_entry_put(en);
> +	return 0;
> +}
> +
> +static void fs_remove_all_traces(void)
> +{
> +	struct fs_trace_entry *en, *guard;
> +
> +	mutex_lock(&fs_trace_lock);
> +	list_for_each_entry_safe(en, guard, &fs_trace_list, node)
> +		fs_drop_trace_entry(en);
> +	mutex_unlock(&fs_trace_lock);
> +}
> +
> +static int create_common_msg(struct sk_buff *skb, void *data)
> +{
> +	struct fs_trace_entry *en = (struct fs_trace_entry *)data;
> +	struct super_block *sb = en->sb;
> +
> +	if (nla_put_u32(skb, FS_NL_A_DEV_MAJOR, MAJOR(sb->s_dev))
> +	||  nla_put_u32(skb, FS_NL_A_DEV_MINOR, MINOR(sb->s_dev)))
> +		return -EINVAL;
What about diskless(nfs,cifs,etc) filesystem? btrfs also has no
valid sb->s_dev  
> +
> +	if (nla_put_u64(skb, FS_NL_A_CAUSED_ID, pid_vnr(task_pid(current))))
> +		return -EINVAL;
> +
> +	return 0;
> +}
> +
> +static int create_thresh_msg(struct sk_buff *skb, void *data)
> +{
> +	struct fs_trace_entry *en = (struct fs_trace_entry *)data;
> +	int ret;
> +
> +	ret = create_common_msg(skb, data);
> +	if (!ret)
> +		ret = nla_put_u64(skb, FS_NL_A_DATA, en->th.avail_space);
> +	return ret;
> +}
> +
> +static void fs_event_send(struct fs_trace_entry *en, unsigned int event_id)
> +{
> +	size_t size = nla_total_size(sizeof(u32)) * 2 +
> +		      nla_total_size(sizeof(u64));
> +
> +	fs_netlink_send_event(size, event_id, create_common_msg, en);
> +}
> +
> +static void fs_event_send_thresh(struct fs_trace_entry *en,
> +				  unsigned int event_id)
> +{
> +	size_t size = nla_total_size(sizeof(u32)) * 2 +
> +		      nla_total_size(sizeof(u64)) * 2;
> +
> +	fs_netlink_send_event(size, event_id, create_thresh_msg, en);
> +}
> +
> +void fs_event_notify(struct super_block *sb, unsigned int event_id)
> +{
> +	struct fs_trace_entry *en;
> +
> +	en = fs_trace_entry_get_rcu(sb);
> +	if (!en)
> +		return;
> +
> +	spin_lock(&en->lock);
> +	if (atomic_read(&en->active) && (en->notify & FS_EVENT_GENERIC))
> +		fs_event_send(en, event_id);
> +	spin_unlock(&en->lock);
> +	fs_trace_entry_put(en);
> +}
> +EXPORT_SYMBOL(fs_event_notify);
> +
> +void fs_event_alloc_space(struct super_block *sb, u64 ncount)
> +{
> +	struct fs_trace_entry *en;
> +	s64 count;
> +
> +	en = fs_trace_entry_get_rcu(sb);
> +	if (!en)
> +		return;
> +
> +	spin_lock(&en->lock);
> +
> +	if (!atomic_read(&en->active) || !(en->notify & FS_EVENT_THRESH))
> +		goto leave;
> +	/*
> +	 * we shouldn't drop below 0 here,
> +	 * unless there is a sync issue somewhere (?)
> +	 */
> +	count = en->th.avail_space - ncount;
> +	en->th.avail_space = count < 0 ? 0 : count;
> +
> +	if (en->th.avail_space > en->th.lrange)
> +		/* Not 'even' close - leave */
> +		goto leave;
> +
> +	if (en->th.avail_space > en->th.urange) {
> +		/* Close enough - the lower range has been reached */
> +		if (!(en->th.state & THRESH_LR_BEYOND)) {
> +			/* Send notification */
> +			fs_event_send_thresh(en, FS_THR_LRBELOW);
> +			en->th.state &= ~THRESH_LR_BELOW;
> +			en->th.state |= THRESH_LR_BEYOND;
> +		}
> +		goto leave;
> +	}
> +	if (!(en->th.state & THRESH_UR_BEYOND)) {
> +		fs_event_send_thresh(en, FS_THR_URBELOW);
> +		en->th.state &=  ~THRESH_UR_BELOW;
> +		en->th.state |= THRESH_UR_BEYOND;
> +	}
> +
> +leave:
> +	spin_unlock(&en->lock);
> +	fs_trace_entry_put(en);
> +}
> +EXPORT_SYMBOL(fs_event_alloc_space);
> +
> +void fs_event_free_space(struct super_block *sb, u64 ncount)
> +{
> +	struct fs_trace_entry *en;
> +
> +	en = fs_trace_entry_get_rcu(sb);
> +	if (!en)
> +		return;
> +
> +	spin_lock(&en->lock);
> +
> +	if (!atomic_read(&en->active) || !(en->notify & FS_EVENT_THRESH))
> +		goto leave;
> +
> +	en->th.avail_space += ncount;
> +
> +	if (en->th.avail_space > en->th.lrange) {
> +		if (!(en->th.state & THRESH_LR_BELOW)
> +		&& en->th.state & THRESH_LR_BEYOND) {
> +			/* Send notification */
> +			fs_event_send_thresh(en, FS_THR_LRABOVE);
> +			en->th.state &= ~(THRESH_LR_BEYOND|THRESH_UR_BEYOND);
> +			en->th.state |= THRESH_LR_BELOW;
> +			goto leave;
> +		}
> +	}
> +	if (en->th.avail_space > en->th.urange) {
> +		if (!(en->th.state & THRESH_UR_BELOW)
> +		&& en->th.state & THRESH_UR_BEYOND) {
> +			/* Notify */
> +			fs_event_send_thresh(en, FS_THR_URABOVE);
> +			en->th.state &= ~THRESH_UR_BEYOND;
> +			en->th.state |= THRESH_UR_BELOW;
> +		}
> +	}
> +leave:
> +	spin_unlock(&en->lock);
> +	fs_trace_entry_put(en);
> +}
> +EXPORT_SYMBOL(fs_event_free_space);
> +
> +void fs_event_mount_dropped(struct vfsmount *mnt)
> +{
> +	/*
> +	 * The mount is dropped but the super might not get released
> +	 * at once so there is very small chance some notifications
> +	 * will come through.
> +	 * Note that the mount being dropped here might belong to a different
> +	 * namespace - if this is the case, just ignore it.
> +	 */
> +	struct fs_trace_entry  *en = fs_trace_entry_get_rcu(mnt->mnt_sb);
> +	struct vfsmount *en_mnt;
> +
> +	if (!en || !atomic_read(&en->active))
> +		return;
> +	/*
> +	 * The entry once set, does not change the mountpoint it's being
> +	 * pinned to, so no need to take the lock here.
> +	 */
> +	en_mnt = en->mnt_path.mnt;
> +	if (!(real_mount(mnt)->mnt_ns != (real_mount(en_mnt))->mnt_ns))
> +		fs_remove_trace_entry(mnt->mnt_sb);
> +	fs_trace_entry_put(en);
> +}
> +
> +static int fs_new_trace_entry(struct path *path, struct fs_event_thresh *thresh,
> +				unsigned int nmask)
> +{
> +	struct fs_trace_entry *en;
> +	struct super_block *sb;
> +	struct mount *r_mnt;
> +
> +	en = kmem_cache_zalloc(fs_trace_cachep, GFP_KERNEL);
> +	if (unlikely(!en))
> +		return -ENOMEM;
> +	/*
> +	 * Note that no reference is being taken here for the path as it would
> +	 * make the unmount unnecessarily puzzling (due to an extra 'valid'
> +	 * reference for the mnt).
> +	 * This is *rather* safe as the notification on mount being dropped
> +	 * will get called prior to releasing the super block - so right
> +	 * in time to perform appropriate clean-up
> +	 */
> +	r_mnt = real_mount(path->mnt);
> +
> +	en->mnt_path.dentry = r_mnt->mnt.mnt_root;
> +	en->mnt_path.mnt = &r_mnt->mnt;
> +
> +	sb = path->mnt->mnt_sb;
> +	en->sb = sb;
> +	/*
> +	 * Increase the refcount for sb to mark it's being relied on.
> +	 * Note that the reference to path is taken by the caller, so it
> +	 * is safe to assume there is at least single active reference
> +	 * to super as well.
> +	 */
> +	atomic_inc(&sb->s_active);
> +
> +	nmask &= sb->s_etrace.events_cap_mask;
> +	if (!nmask)
> +		goto leave;
> +
> +	spin_lock_init(&en->lock);
> +	INIT_LIST_HEAD(&en->node);
> +
> +	en->notify = nmask;
> +	memcpy(&en->th, thresh, offsetof(struct fs_event_thresh, state));
> +	if (nmask & FS_EVENT_THRESH)
> +		fs_trace_query_data(sb, en);
> +
> +	kref_init(&en->count);
> +
> +	if (rcu_access_pointer(sb->s_etrace.e_priv) != NULL) {
> +		struct fs_trace_entry *prev_en;
> +
> +		prev_en = fs_trace_entry_get_rcu(sb);
> +		if (prev_en) {
> +			WARN_ON(prev_en);
> +			fs_trace_entry_put(prev_en);
> +			goto leave;
> +		}
> +	}
> +	atomic_set(&en->active, 1);
> +
> +	mutex_lock(&fs_trace_lock);
> +	list_add(&en->node, &fs_trace_list);
> +	mutex_unlock(&fs_trace_lock);
> +
> +	rcu_assign_pointer(sb->s_etrace.e_priv, en);
> +	synchronize_rcu();
> +
> +	return 0;
> +leave:
> +	deactivate_super(sb);
> +	kmem_cache_free(fs_trace_cachep, en);
> +	return -EINVAL;
> +}
> +
> +static int fs_update_trace_entry(struct path *path,
> +				  struct fs_event_thresh *thresh,
> +				  unsigned int nmask)
> +{
> +	struct fs_trace_entry *en;
> +	struct super_block *sb;
> +	int extend = nmask & FS_TRACE_ADD;
> +	int ret = -EINVAL;
> +
> +	en = fs_trace_entry_get_rcu(path->mnt->mnt_sb);
> +	if (!en)
> +		return (extend) ? fs_new_trace_entry(path, thresh, nmask)
> +				: -EINVAL;
> +
> +	if (!atomic_read(&en->active))
> +		return -EINVAL;
> +
> +	nmask &= ~FS_TRACE_ADD;
> +
> +	spin_lock(&en->lock);
> +	sb  = en->sb;
> +	if (!sb || !(nmask & sb->s_etrace.events_cap_mask))
> +		goto leave;
> +
> +	if (nmask & FS_EVENT_THRESH) {
> +		if (extend) {
> +			/* Get the current state */
> +			if (!(en->notify & FS_EVENT_THRESH))
> +				if (fs_trace_query_data(sb, en))
> +					goto leave;
> +
> +			if (thresh->state & THRESH_LR_ON) {
> +				en->th.lrange = thresh->lrange;
> +				en->th.state &= ~THRESH_LR_ON;
> +			}
> +
> +			if (thresh->state & THRESH_UR_ON) {
> +				en->th.urange = thresh->urange;
> +				en->th.state &= ~THRESH_UR_ON;
> +			}
> +		} else {
> +			memset(&en->th, 0, sizeof(en->th));
> +		}
> +	}
> +
> +	if (extend)
> +		en->notify |= nmask;
> +	else
> +		en->notify &= ~nmask;
> +	ret = 0;
> +leave:
> +	spin_unlock(&en->lock);
> +	fs_trace_entry_put(en);
> +	return ret;
> +}
> +
> +static int fs_parse_trace_request(int argc, char **argv)
> +{
> +	struct fs_event_thresh thresh = {0};
> +	struct path path;
> +	substring_t args[MAX_OPT_ARGS];
> +	unsigned int nmask = FS_TRACE_ADD;
> +	int token;
> +	char *s;
> +	int ret = -EINVAL;
> +
> +	if (!argc) {
> +		fs_remove_all_traces();
> +		return 0;
> +	}
> +
> +	s = *(argv);
> +	if (*s == '!') {
> +		/* Clear the trace entry */
> +		nmask &= ~FS_TRACE_ADD;
> +		++s;
> +	}
> +
> +	if (kern_path_mountpoint(AT_FDCWD, s, &path, LOOKUP_FOLLOW))
> +		return -EINVAL;
> +
> +	if (!(--argc)) {
> +		if (!(nmask & FS_TRACE_ADD))
> +			ret = fs_remove_trace_entry(path.mnt->mnt_sb);
> +		goto leave;
> +	}
> +
> +repeat:
> +	args[0].to = args[0].from = NULL;
> +	token = match_token(*(++argv), fs_etypes, args);
> +	if (!token && !nmask)
> +		goto leave;
> +
> +	nmask |= token & FS_EVENTS_ALL;
> +	--argc;
> +	if ((token & FS_EVENT_THRESH)  && (nmask & FS_TRACE_ADD)) {
> +		/*
> +		 * Get the threshold config data:
> +		 * lower range
> +		 * upper range
> +		 */
> +		if (!argc)
> +			goto leave;
> +
> +		ret = kstrtoull(*(++argv), 10, &thresh.lrange);
> +		if (ret)
> +			goto leave;
> +		thresh.state |= THRESH_LR_ON;
> +		if ((--argc)) {
> +			ret = kstrtoull(*(++argv), 10, &thresh.urange);
> +			if (ret)
> +				goto leave;
> +			thresh.state |= THRESH_UR_ON;
> +			--argc;
> +		}
> +		/* The thresholds are based on number of available blocks */
> +		if (thresh.lrange < thresh.urange) {
> +			ret = -EINVAL;
> +			goto leave;
> +		}
> +	}
> +	if (argc)
> +		goto repeat;
> +
> +	ret = fs_update_trace_entry(&path, &thresh, nmask);
> +leave:
> +	path_put(&path);
> +	return ret;
> +}
> +
> +#define DEFAULT_BUF_SIZE PAGE_SIZE
> +
> +static ssize_t fs_trace_write(struct file *file, const char __user *buffer,
> +				size_t count, loff_t *ppos)
> +{
> +	char **argv;
> +	char *kern_buf, *next, *cfg;
> +	size_t size, dcount = 0;
> +	int argc;
> +
> +	if (!count)
> +		return 0;
> +
> +	kern_buf = kmalloc(DEFAULT_BUF_SIZE, GFP_KERNEL);
> +	if (!kern_buf)
> +		return -ENOMEM;
> +
> +	while (dcount < count) {
> +
> +		size = count - dcount;
> +		if (size >= DEFAULT_BUF_SIZE)
> +			size = DEFAULT_BUF_SIZE - 1;
> +		if (copy_from_user(kern_buf, buffer + dcount, size)) {
> +			dcount = -EINVAL;
> +			goto leave;
> +		}
> +
> +		kern_buf[size] = '\0';
> +
> +		next = cfg = kern_buf;
> +
> +		do {
> +			next = strchr(cfg, ';');
> +			if (next)
> +				*next = '\0';
> +
> +			argv = argv_split(GFP_KERNEL, cfg, &argc);
> +			if (!argv) {
> +				dcount = -ENOMEM;
> +				goto leave;
> +			}
> +
> +			if (fs_parse_trace_request(argc, argv)) {
> +				dcount = -EINVAL;
> +				argv_free(argv);
> +				goto leave;
> +			}
> +
> +			argv_free(argv);
> +			if (next)
> +				cfg = ++next;
> +
> +		} while (next);
> +		dcount += size;
> +	}
> +leave:
> +	kfree(kern_buf);
> +	return dcount;
> +}
> +
> +static void *fs_trace_seq_start(struct seq_file *m, loff_t *pos)
> +{
> +	mutex_lock(&fs_trace_lock);
> +	return seq_list_start(&fs_trace_list, *pos);
> +}
> +
> +static void *fs_trace_seq_next(struct seq_file *m, void *v, loff_t *pos)
> +{
> +	return seq_list_next(v, &fs_trace_list, pos);
> +}
> +
> +static void fs_trace_seq_stop(struct seq_file *m, void *v)
> +{
> +	mutex_unlock(&fs_trace_lock);
> +}
> +
> +static int fs_trace_seq_show(struct seq_file *m, void *v)
> +{
> +	struct fs_trace_entry *en;
> +	struct super_block *sb;
> +	struct mount *r_mnt;
> +	const struct match_token *match;
> +	unsigned int nmask;
> +
> +	en = list_entry(v, struct fs_trace_entry, node);
> +	/* Do not show the entries outside current mount namespace */
> +	r_mnt = real_mount(en->mnt_path.mnt);
> +	if (r_mnt->mnt_ns != current->nsproxy->mnt_ns) {
> +		if (!__is_local_mountpoint(r_mnt->mnt_mountpoint))
> +			return 0;
> +	}
> +
> +	sb = en->sb;
> +
> +	seq_path(m, &en->mnt_path, "\t\n\\");
> +	seq_putc(m, ' ');
> +
> +	seq_escape(m, sb->s_type->name, " \t\n\\");
> +	if (sb->s_subtype && sb->s_subtype[0]) {
> +		seq_putc(m, '.');
> +		seq_escape(m, sb->s_subtype, " \t\n\\");
> +	}
> +
> +	seq_putc(m, ' ');
> +	if (sb->s_op->show_devname) {
> +		sb->s_op->show_devname(m, en->mnt_path.mnt->mnt_root);
> +	} else {
> +		seq_escape(m, r_mnt->mnt_devname ? r_mnt->mnt_devname : "none",
> +				" \t\n\\");
> +	}
> +	seq_puts(m, " (");
> +
> +	nmask = en->notify;
> +	for (match = fs_etypes; match->pattern; ++match) {
> +		if (match->token & nmask) {
> +			seq_puts(m, match->pattern);
> +			nmask &= ~match->token;
> +			if (nmask)
> +				seq_putc(m, ',');
> +		}
> +	}
> +	seq_printf(m, " %llu %llu", en->th.lrange, en->th.urange);
> +	seq_puts(m, ")\n");
> +	return 0;
> +}
> +
> +static const struct seq_operations fs_trace_seq_ops = {
> +	.start	= fs_trace_seq_start,
> +	.next	= fs_trace_seq_next,
> +	.stop	= fs_trace_seq_stop,
> +	.show	= fs_trace_seq_show,
> +};
> +
> +static int fs_trace_open(struct inode *inode, struct file *file)
> +{
> +	return seq_open(file, &fs_trace_seq_ops);
> +}
> +
> +static const struct file_operations fs_trace_fops = {
> +	.owner		= THIS_MODULE,
> +	.open		= fs_trace_open,
> +	.write		= fs_trace_write,
> +	.read		= seq_read,
> +	.llseek		= seq_lseek,
> +	.release	= seq_release,
> +};
> +
> +static int fs_trace_init(void)
> +{
> +	fs_trace_cachep = KMEM_CACHE(fs_trace_entry, 0);
> +	if (!fs_trace_cachep)
> +		return -EINVAL;
> +	init_waitqueue_head(&trace_wq);
> +	return 0;
> +}
> +
> +/* VFS support */
> +static int fs_trace_fill_super(struct super_block *sb, void *data, int silen)
> +{
> +	int ret;
> +	static struct tree_descr desc[] = {
> +		[2] = {
> +			.name	= "config",
> +			.ops	= &fs_trace_fops,
> +			.mode	= S_IWUSR | S_IRUGO,
> +		},
> +		{""},
> +	};
> +
> +	ret = simple_fill_super(sb, 0x7246332, desc);
> +	return !ret ? fs_trace_init() : ret;
> +}
> +
> +static struct dentry *fs_trace_do_mount(struct file_system_type *fs_type,
> +		 int ntype, const char *dev_name, void *data)
> +{
> +	return mount_single(fs_type, ntype, data, fs_trace_fill_super);
> +}
> +
> +static void fs_trace_kill_super(struct super_block *sb)
> +{
> +	/*
> +	 * The rcu_barrier here will/should make sure all call_rcu
> +	 * callbacks are completed - still there might be some active
> +	 * trace objects in use which can make calling the
> +	 * kmem_cache_destroy unsafe. So we wait until all traces
> +	 * are finally released.
> +	 */
> +	fs_remove_all_traces();
> +	rcu_barrier();
> +	wait_event(trace_wq, !atomic_read(&stray_traces));
> +
> +	kmem_cache_destroy(fs_trace_cachep);
> +	kill_litter_super(sb);
> +}
> +
> +static struct kset	*fs_trace_kset;
> +
> +static struct file_system_type fs_trace_fstype = {
> +	.name		= "fstrace",
> +	.mount		= fs_trace_do_mount,
> +	.kill_sb	= fs_trace_kill_super,
> +};
> +
> +static void __init fs_trace_vfs_init(void)
> +{
> +	fs_trace_kset = kset_create_and_add("events", NULL, fs_kobj);
> +
> +	if (!fs_trace_kset)
> +		return;
> +
> +	if (!register_filesystem(&fs_trace_fstype)) {
> +		if (!fs_event_netlink_register())
> +			return;
> +		unregister_filesystem(&fs_trace_fstype);
> +	}
> +	kset_unregister(fs_trace_kset);
> +}
> +
> +static int __init fs_trace_evens_init(void)
> +{
> +	fs_trace_vfs_init();
> +	return 0;
> +};
> +module_init(fs_trace_evens_init);
> +
> diff --git a/fs/events/fs_event.h b/fs/events/fs_event.h
> new file mode 100644
> index 0000000..23f24c8
> --- /dev/null
> +++ b/fs/events/fs_event.h
> @@ -0,0 +1,22 @@
> +/*
> + * Copyright(c) 2015 Samsung Electronics. All rights reserved.
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms of the GNU General Public License version 2.
> + *
> + * The full GNU General Public License is included in this distribution in the
> + * file called COPYING.
> + *
> + * This program is distributed in the hope that it will be useful, but WITHOUT
> + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
> + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
> + * more details.
> + */
> +
> +#ifndef __GENERIC_FS_EVENTS_H
> +#define __GENERIC_FS_EVENTS_H
> +
> +int  fs_event_netlink_register(void);
> +void fs_event_netlink_unregister(void);
> +
> +#endif /* __GENERIC_FS_EVENTS_H */
> diff --git a/fs/events/fs_event_netlink.c b/fs/events/fs_event_netlink.c
> new file mode 100644
> index 0000000..0c97eb7
> --- /dev/null
> +++ b/fs/events/fs_event_netlink.c
> @@ -0,0 +1,104 @@
> +/*
> + * Copyright(c) 2015 Samsung Electronics. All rights reserved.
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms of the GNU General Public License version 2.
> + *
> + * The full GNU General Public License is included in this distribution in the
> + * file called COPYING.
> + *
> + * This program is distributed in the hope that it will be useful, but WITHOUT
> + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
> + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
> + * more details.
> + */
> +#include <linux/fs.h>
> +#include <linux/init.h>
> +#include <linux/kernel.h>
> +#include <linux/sched.h>
> +#include <linux/slab.h>
> +#include <net/netlink.h>
> +#include <net/genetlink.h>
> +#include "fs_event.h"
> +
> +static const struct genl_multicast_group fs_event_mcgroups[] = {
> +	{ .name = FS_EVENTS_MCAST_GRP_NAME, },
> +};
> +
> +static struct genl_family fs_event_family = {
> +	.id		= GENL_ID_GENERATE,
> +	.name		= FS_EVENTS_FAMILY_NAME,
> +	.version	= 1,
> +	.maxattr	= FS_NL_A_MAX,
> +	.mcgrps		= fs_event_mcgroups,
> +	.n_mcgrps	= ARRAY_SIZE(fs_event_mcgroups),
> +};
> +
> +int fs_netlink_send_event(size_t size, unsigned int event_id,
> +			  int (*compose_msg)(struct sk_buff *skb,  void *data),
> +			  void *cbdata)
> +{
> +	static atomic_t seq;
> +	struct sk_buff *skb;
> +	void *msg_head;
> +	int ret = 0;
> +
> +	if (!size || !compose_msg)
> +		return -EINVAL;
> +
> +	/* Skip if there are no listeners */
> +	if (!genl_has_listeners(&fs_event_family, &init_net, 0))
> +		return 0;
> +
> +	if (event_id != FS_EVENT_NONE)
> +		size += nla_total_size(sizeof(u32));
> +	size += nla_total_size(sizeof(u64));
> +	skb = genlmsg_new(size, GFP_NOWAIT);
> +
> +	if (!skb) {
> +		pr_debug("Failed to allocate new FS generic netlink message\n");
> +		return -ENOMEM;
> +	}
> +
> +	msg_head = genlmsg_put(skb, 0, atomic_add_return(1, &seq),
> +			&fs_event_family, 0, FS_NL_C_EVENT);
> +	if (!msg_head)
> +		goto cleanup;
> +
> +	if (event_id != FS_EVENT_NONE)
> +		if (nla_put_u32(skb, FS_NL_A_EVENT_ID, event_id))
> +			goto cancel;
> +
> +	ret = compose_msg(skb, cbdata);
> +	if (ret)
> +		goto cancel;
> +
> +	genlmsg_end(skb, msg_head);
> +	ret = genlmsg_multicast(&fs_event_family, skb, 0, 0, GFP_NOWAIT);
> +	if (ret && ret != -ENOBUFS && ret != -ESRCH)
> +		goto cleanup;
> +
> +	return ret;
> +
> +cancel:
> +	genlmsg_cancel(skb, msg_head);
> +cleanup:
> +	nlmsg_free(skb);
> +	return ret;
> +}
> +EXPORT_SYMBOL(fs_netlink_send_event);
> +
> +int fs_event_netlink_register(void)
> +{
> +	int ret;
> +
> +	ret = genl_register_family(&fs_event_family);
> +	if (ret)
> +		pr_err("Failed to register FS netlink interface\n");
> +	return ret;
> +}
> +
> +void fs_event_netlink_unregister(void)
> +{
> +	genl_unregister_family(&fs_event_family);
> +}
> diff --git a/fs/namespace.c b/fs/namespace.c
> index 82ef140..ec6e2ef 100644
> --- a/fs/namespace.c
> +++ b/fs/namespace.c
> @@ -1031,6 +1031,7 @@ static void cleanup_mnt(struct mount *mnt)
>  	if (unlikely(mnt->mnt_pins.first))
>  		mnt_pin_kill(mnt);
>  	fsnotify_vfsmount_delete(&mnt->mnt);
> +	fs_event_mount_dropped(&mnt->mnt);
>  	dput(mnt->mnt.mnt_root);
>  	deactivate_super(mnt->mnt.mnt_sb);
>  	mnt_free_id(mnt);
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index b4d71b5..b7dadd9 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -263,6 +263,10 @@ struct iattr {
>   * Includes for diskquotas.
>   */
>  #include <linux/quota.h>
> +/*
> + * Include for Generic File System Events Interface
> + */
> +#include <linux/fs_event.h>
>  
>  /*
>   * Maximum number of layers of fs stack.  Needs to be limited to
> @@ -1253,7 +1257,7 @@ struct super_block {
>  	struct hlist_node	s_instances;
>  	unsigned int		s_quota_types;	/* Bitmask of supported quota types */
>  	struct quota_info	s_dquot;	/* Diskquota specific options */
> -
> +	struct fs_trace_info	s_etrace;
>  	struct sb_writers	s_writers;
>  
>  	char s_id[32];				/* Informational name */
> diff --git a/include/linux/fs_event.h b/include/linux/fs_event.h
> new file mode 100644
> index 0000000..83e22dd
> --- /dev/null
> +++ b/include/linux/fs_event.h
> @@ -0,0 +1,72 @@
> +/*
> + * Generic File System Events Interface
> + *
> + * Copyright(c) 2015 Samsung Electronics. All rights reserved.
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms of the GNU General Public License version 2.
> + *
> + * The full GNU General Public License is included in this distribution in the
> + * file called COPYING.
> + *
> + * This program is distributed in the hope that it will be useful, but WITHOUT
> + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
> + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
> + * more details.
> + */
> +#ifndef _LINUX_GENERIC_FS_EVETS_
> +#define _LINUX_GENERIC_FS_EVETS_
> +#include <net/netlink.h>
> +#include <uapi/linux/fs_event.h>
> +
> +/*
> + * Currently supported event types
> + */
> +#define FS_EVENT_GENERIC 0x001
> +#define FS_EVENT_THRESH	 0x002
> +
> +#define FS_EVENTS_ALL  (FS_EVENT_GENERIC | FS_EVENT_THRESH)
> +
> +struct fs_trace_operations {
> +	void (*query)(struct super_block *, u64 *);
> +};
> +
> +struct fs_trace_info {
> +	void	__rcu	*e_priv;		 /* READ ONLY */
> +	unsigned int	events_cap_mask; /* Supported notifications */
> +	const struct fs_trace_operations *ops;
> +};
> +
> +#ifdef CONFIG_FS_EVENTS
> +
> +void fs_event_notify(struct super_block *sb, unsigned int event_id);
> +void fs_event_alloc_space(struct super_block *sb, u64 ncount);
> +void fs_event_free_space(struct super_block *sb, u64 ncount);
> +void fs_event_mount_dropped(struct vfsmount *mnt);
> +
> +int fs_netlink_send_event(size_t size, unsigned int event_id,
> +			  int (*compose_msg)(struct sk_buff *skb, void *data),
> +			  void *cbdata);
> +
> +#else /* CONFIG_FS_EVENTS */
> +
> +static inline
> +void fs_event_notify(struct super_block *sb, unsigned int event_id) {};
> +static inline
> +void fs_event_alloc_space(struct super_block *sb, u64 ncount) {};
> +static inline
> +void fs_event_free_space(struct super_block *sb, u64 ncount) {};
> +static inline
> +void fs_event_mount_dropped(struct vfsmount *mnt) {};
> +
> +static inline
> +int fs_netlink_send_event(size_t size, unsigned int event_id,
> +			  int (*compose_msig)(struct sk_buff *skb, void *data),
> +			  void *cbdata)
> +{
> +	return -ENOSYS;
> +}
> +#endif /* CONFIG_FS_EVENTS */
> +
> +#endif /* _LINUX_GENERIC_FS_EVENTS_ */
> +
> diff --git a/include/uapi/linux/Kbuild b/include/uapi/linux/Kbuild
> index 68ceb97..dae0fab 100644
> --- a/include/uapi/linux/Kbuild
> +++ b/include/uapi/linux/Kbuild
> @@ -129,6 +129,7 @@ header-y += firewire-constants.h
>  header-y += flat.h
>  header-y += fou.h
>  header-y += fs.h
> +header-y += fs_event.h
>  header-y += fsl_hypervisor.h
>  header-y += fuse.h
>  header-y += futex.h
> diff --git a/include/uapi/linux/fs_event.h b/include/uapi/linux/fs_event.h
> new file mode 100644
> index 0000000..d8b07da
> --- /dev/null
> +++ b/include/uapi/linux/fs_event.h
> @@ -0,0 +1,58 @@
> +/*
> + * Generic netlink support for Generic File System Events Interface
> + *
> + * Copyright(c) 2015 Samsung Electronics. All rights reserved.
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms of the GNU General Public License version 2.
> + *
> + * The full GNU General Public License is included in this distribution in the
> + * file called COPYING.
> + *
> + * This program is distributed in the hope that it will be useful, but WITHOUT
> + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
> + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
> + * more details.
> + */
> +#ifndef _UAPI_LINUX_GENERIC_FS_EVENTS_
> +#define _UAPI_LINUX_GENERIC_FS_EVENTS_
> +
> +#define FS_EVENTS_FAMILY_NAME	 "fs_event"
> +#define FS_EVENTS_MCAST_GRP_NAME "fs_event_mc_grp"
> +
> +/*
> + * Generic netlink attribute types
> + */
> +enum {
> +	FS_NL_A_NONE,
> +	FS_NL_A_EVENT_ID,
> +	FS_NL_A_DEV_MAJOR,
> +	FS_NL_A_DEV_MINOR,
> +	FS_NL_A_CAUSED_ID,
> +	FS_NL_A_DATA,
> +	__FS_NL_A_MAX,
> +};
> +#define FS_NL_A_MAX (__FS_NL_A_MAX - 1)
> +/*
> + * Generic netlink commands
> + */
> +#define FS_NL_C_EVENT		1
> +
> +/*
> + * Supported set of FS events
> + */
> +enum {
> +	FS_EVENT_NONE,
> +	FS_WARN_ENOSPC,		/* No space left to reserve data blks */
> +	FS_WARN_ENOSPC_META,	/* No space left for metadata */
> +	FS_THR_LRBELOW,		/* The threshold lower range has been reached */
> +	FS_THR_LRABOVE,		/* The threshold lower range re-activcated*/
> +	FS_THR_URBELOW,
> +	FS_THR_URABOVE,
> +	FS_ERR_REMOUNT_RO,	/* The file system has been remounted as RO */
> +	FS_ERR_CORRUPTED	/* Critical error - fs corrupted */
> +
> +};
> +
> +#endif /* _UAPI_LINUX_GENERIC_FS_EVENTS_ */
> +
> -- 
> 1.7.9.5
>
> --
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