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

[Darrick J. Wong]

On Wed, Apr 15, 2015 at 09:15:44AM +0200, Beata Michalska wrote:
> 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 a dedicated, for file system
> events, multicast group. The file systems might as
> well use this group to send their own custom messages.
> 
> The events have been split into four base categories:
> information, warnings, errors and threshold notifications,
> with some very basic event types like running out of space
> or file system being remounted as read-only.
> 
> Threshold notifications have been included to allow
> 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@xxxxxxxxxxx>
> ---
>  Documentation/filesystems/events.txt |  254 +++++++++++
>  fs/Makefile                          |    1 +
>  fs/events/Makefile                   |    6 +
>  fs/events/fs_event.c                 |  775 ++++++++++++++++++++++++++++++++++
>  fs/events/fs_event.h                 |   27 ++
>  fs/events/fs_event_netlink.c         |   94 +++++
>  fs/namespace.c                       |    1 +
>  include/linux/fs.h                   |    6 +-
>  include/linux/fs_event.h             |   69 +++
>  include/uapi/linux/fs_event.h        |   62 +++
>  include/uapi/linux/genetlink.h       |    1 +
>  net/netlink/genetlink.c              |    7 +-
>  12 files changed, 1301 insertions(+), 2 deletions(-)
>  create mode 100644 Documentation/filesystems/events.txt
>  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..c85dd88
> --- /dev/null
> +++ b/Documentation/filesystems/events.txt
> @@ -0,0 +1,254 @@
> +
> +	Generic file system event notification interface
> +
> +Document created 09 April 2015 by Beata Michalska <b.michalska@xxxxxxxxxxx>
> +
> +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 intreseting
> +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 file
> +system 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 : type of events to be enabled: info,warn,err,thr;
> +              at least one type needs to be specified;
> +              note the comma delimiter and lack of spaces between
> +	      those options
> + L1         : the threshold limit - lower range
> + L2         : the threshold limit - upper range
> + 	      case enabling threshold notifications the lower level is
> +	      mandatory, whereas the upper one remains optional;
> +	      note though, that as those refer to the number of available
> +	      blocks, the lower level needs to be higher than the upper one
> +
> +Sample request could look like the follwoing:
> +
> + echo /sample/mount/point warn,err,thr 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
> +particilar 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 eventy 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 thres 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 id of the entry (@see more on generic
> +netlink section), 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 disreagrded. 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 the purpose of
> +notifying any potential listeners of file system events. So in order to
> +receive such notifications, one should subscribe to this new mutlicast group.
> +
> +Each message type reflects the actual type of generated event (FS_EVENT_TYPE*)
> +Currently there are two supported message formats.
> +
> +There is a common message format representing an event generated by
> +a filesystem. The type of the event itself will be stored within
> +the generic netlink message header as the command filed. The messge
> +payload will provide more detailed info: the indentifier of the filesystem
> +trace (genereted upon registering the trace), the backing device major and
> +minor numbers, the event identifier and the id of the proccess which action
> +led to the event occurance. In case of threshold notifications, the current
> +number of available blocks will be included in the payload.
> +
> +
> +	 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 event type as genlmsghdr cdm field)		|
> +	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> +	| 	      Optional user specific message header		|
> +	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> +	| 		   GENERIC MESSAGE PAYLOAD:			|
> +	+---------------------------------------------------------------+
> +	|  		 FS_EVENT_ATR_FS_ID (NLA_U32)			|
> +	+---------------------------------------------------------------+
> +	|	  FS_EVENT_ATR_DEV_MAJOR (NLA_U32) (if available)	|
> +	+---------------------------------------------------------------+
> +	| 	  FS_EVENT_ATR_DEV_MINOR (NLA_U32) (if available)       |
> +	+---------------------------------------------------------------+
> +	| 		   FS_EVENT_ATR_ID (NLA_U32)			|
> +	+---------------------------------------------------------------+
> +	|  		FS_EVENT_ATR_CAUSED_ID (NLA_U32)		|
> +	+---------------------------------------------------------------+
> +	|  		  FS_EVENT_ATR_DATA (NLA_U64)			|
> +	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> +
> +
> +The second supported message format represents an event of a new trace being
> +registered. It contains two attributes within the payload: the trace id and the
> +mount point for which the trace has been registered. This message is of type
> +FS_EVENT_TYPE_NEW_TRACE and is being sent regardless the actual event types
> +being watched whenever new etnry for the 'config' file is being created. This
> +is supposed to ease parsing the messages by userpsace applications and to help
> +to identify the origin of the event. It also reduces the size of the payload
> +as there is no need to send additional data such as mount point and the file
> +system type for each possible event.
> +
> +	 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 event type as genlmsghdr cdm field)		|
> +	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> +	| 	      Optional user specific message header		|
> +	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> +	| 		   GENERIC MESSAGE PAYLOAD:			|
> +	+ ------------------------------------------------------------- +
> +	|  		 FS_EVENT_ATR_FS_ID (NLA_U32)			|
> +	+ ------------------------------------------------------------- +
> +	|  	        FS_EVENT_ATR_MOUNT (NLA_STRING)			|
> +	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> +
> +The above figures are based on:
> + http://www.linuxfoundation.org/collaborate/workgroups/networking/generic_netlink_howto#Message_Format
> +
> +
> +
> +4. API Reference:
> +=================
> +
> + 4.1 Generic file system event interface operations
> +
> + #include <linux/fs_event.h>
> +
> + struct fs_trace_operations {
> +	 int (*fs_trace_query)(struct super_block *, struct fs_trace_sdata *);
> + };
> +
> + Each filesystem supporting the event notifications should register its
> + file system trace operations. This can be done through new entry in
> + the super_block structure: the s_trace_ops. The fs_trace_query shall
> + be called whenever new trace entry for given filesystem is being created
> + or when threshold notifications are being requested for the first time.
> + The filesystem should specify then, which event types are being supported.
> + In case of threshold notifications the current number of avaialble blocks
> + should be provided.
> +
> + 4.2 Event notification:
> +
> + #include <linux/fs_event.h>
> + void fs_event_notify(struct super_block *sb, unsigned int event_type,
> +  			unsigned int event_id);
> +
> + Notify the generic FS event interface of an occuring event.
> + This shall be used by any file system that wishes to inform any potenial
> + listeners/watchers of a particular event.
> + - sb:         the filesystem's super block
> + - event_type: the type of an event (one of the FS_EVENT_*)
> + - 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 treshold notifiactions should call
> + fs_event_alloc_space/fs_event_free_space repsectively whenever the
> + ammount of availbale blocks changes.
> + - sb:     the filesystem's super block
> + - ncount: number of blocks being acquired/released
> +
> + Note that to properly handle the treshold notifiactions the fs events
> + interface needs to be keept up to date by the filesystems. Each should
> + register fs_trace_operations to enable querying the basic trace data,
> + among which, is the current number of the available blocks (fs_trace_query).
> +
> + 4.4 Sending message through generic netlink interface
> +
> + #include <linux/fs_event.h>
> + int fs_netlink_send_event(size_t size, unsigned int event_type,
> + 	int (*compose_msg)(struct sk_buff *skb, unsigned int event_id,
> +		void *data),
> +	unsigned int event_id, void *data);
> +
> + Although the fs event interface is fully responsible for sending the messages
> + over the netlink, filesystems might use the FS_EVENT mutlicast group to send
> + their own custom messages.
> + - size:        the size of the message payload
> + - event_type:  the type of an event: stored as message header's command
> + - compose_msg: a custom callback handling composing the message payload
> + - event_id:    the event identifier
> + - data:        message custom data
> +
> + Calling fs_netlink_send_event will result in a message being sent through
> + the FS_EVENT muslicast 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.
> +
> +
> diff --git a/fs/Makefile b/fs/Makefile
> index a88ac48..798021d 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-$(CONFIG_EFIVAR_FS)		+= efivarfs/
> +obj-y				+= events/
> diff --git a/fs/events/Makefile b/fs/events/Makefile
> new file mode 100644
> index 0000000..58d1454
> --- /dev/null
> +++ b/fs/events/Makefile
> @@ -0,0 +1,6 @@
> +#
> +# Makefile for the Linux Generic File System Event Interface
> +#
> +
> +obj-y := fs_event.o
> +obj-$(CONFIG_NET) += fs_event_netlink.o
> diff --git a/fs/events/fs_event.c b/fs/events/fs_event.c
> new file mode 100644
> index 0000000..8ebe371
> --- /dev/null
> +++ b/fs/events/fs_event.c
> @@ -0,0 +1,775 @@
> +/*
> + * 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.
> + */
> +#include <linux/fs.h>
> +#include <linux/hashtable.h>
> +#include <linux/idr.h>
> +#include <linux/module.h>
> +#include <linux/mount.h>
> +#include <linux/namei.h>
> +#include <linux/parser.h>
> +#include <linux/seq_file.h>
> +#include <linux/slab.h>
> +#include <net/genetlink.h>
> +#include "../mount.h"
> +#include "fs_event.h"
> +
> +#define FS_HASHTB_BITS		8
> +#define FS_HASHTB_SIZE		(1 << FS_HASHTB_BITS)
> +
> +/**
> + * The FS event trace entries are being stored in a hashtable
> + * for fast entry look-up, and in a doubly-linked list
> + * to ease all the paths that need to go through all
> + * the entries.
> + */
> +static DEFINE_HASHTABLE(fs_trace_hashtbl, FS_HASHTB_BITS);
> +static LIST_HEAD(fs_trace_list);
> +static DEFINE_SPINLOCK(fs_trace_lock);
> +
> +static struct kmem_cache *fs_trace_cachep __read_mostly;
> +
> +/*
> + * Each registered FS event trace is being marked with
> + * a unique identifier managed by IDR
> + */
> +static struct idr fs_trace_idr;
> +static DEFINE_SPINLOCK(fs_trace_idr_lock);
> +
> +/*
> + * 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 list_head	node;
> +	struct hlist_node	hnode;
> +	struct path		path;
> +	struct fs_trace_sdata	data;
> +	int			mark;
> +	unsigned int		notify_mask;
> +	struct fs_event_thresh {
> +		u64		lrange;
> +		u64		urange;
> +		unsigned int	state;
> +	}			thresh;
> +	spinlock_t		lock;
> +};
> +
> +static const match_table_t fs_etypes = {
> +	{ FS_EVENT_INFO,    "info"  },
> +	{ FS_EVENT_WARN,    "warn"  },
> +	{ FS_EVENT_THRESH,  "thr"   },
> +	{ FS_EVENT_ERR,     "err"   },
> +	{ 0, NULL },
> +};
> +
> +#define fs_trace_sb(en) ((en)->path.mnt->mnt_sb)
> +
> +#define fs_trace_query_data(sb, arg)				 \
> +	(((sb)->s_trace_ops && (sb)->s_trace_ops->fs_trace_query) ? \
> +	(sb)->s_trace_ops->fs_trace_query((sb), arg) : -EINVAL)
> +
> +#define fs_event_type_cast(event_type)  (ffs(event_type))
> +
> +static inline unsigned int fs_trace_hasfn(const struct super_block *sb)
> +{
> +	return ((unsigned long)sb >> L1_CACHE_SHIFT) & (FS_HASHTB_SIZE - 1);
> +}
> +
> +static struct fs_trace_entry *fs_find_trace_entry(struct super_block *sb)
> +{
> +	struct fs_trace_entry *en;
> +	unsigned long hash;
> +
> +	if (list_empty(&fs_trace_list))
> +		return ERR_PTR(-EINVAL);
> +	hash = fs_trace_hasfn(sb);
> +	hash_for_each_possible(fs_trace_hashtbl, en, hnode, hash)
> +		if (fs_trace_sb(en) == sb)
> +			return en;
> +	return ERR_PTR(-EINVAL);
> +}
> +
> +static inline void fs_trace_entry_list_del(struct fs_trace_entry *en)
> +{
> +	spin_lock(&en->lock);
> +	list_del(&en->node);
> +	hash_del(&en->hnode);
> +	spin_unlock(&en->lock);
> +}
> +
> +static inline void fs_trace_entry_idr_remove(struct fs_trace_entry *en)
> +{
> +	spin_lock(&fs_trace_idr_lock);
> +	idr_remove(&fs_trace_idr, en->mark);
> +	spin_unlock(&fs_trace_idr_lock);
> +}
> +
> +static inline void fs_trace_entry_free(struct fs_trace_entry *en)
> +{
> +	kmem_cache_free(fs_trace_cachep, en);
> +}
> +
> +static inline void fs_destroy_trace_entry(struct fs_trace_entry *en)
> +{
> +	fs_trace_entry_list_del(en);
> +	fs_trace_entry_idr_remove(en);
> +	fs_trace_entry_free(en);
> +}
> +
> +static int fs_remove_trace_entry(struct super_block *sb)
> +{
> +	struct fs_trace_entry *en;
> +	int ret = -EINVAL;
> +
> +	spin_lock(&fs_trace_lock);
> +	en = fs_find_trace_entry(sb);
> +	if (!IS_ERR(en)) {
> +		fs_destroy_trace_entry(en);
> +		ret = 0;
> +	}
> +	spin_unlock(&fs_trace_lock);
> +	return ret;
> +}
> +
> +static void fs_remove_all_traces(void)
> +{
> +	struct fs_trace_entry *en, *guard;
> +
> +	spin_lock(&fs_trace_lock);
> +	list_for_each_entry_safe(en, guard, &fs_trace_list, node)
> +		fs_destroy_trace_entry(en);
> +	spin_unlock(&fs_trace_lock);
> +}
> +
> +static int fs_event_new_trace_create_msg(struct sk_buff *skb,
> +				unsigned int event_id, void *data)
> +{
> +	struct fs_trace_entry *en = (struct fs_trace_entry *)data;
> +	char *path, *mount_dir;
> +	int ret;
> +
> +	path = kzalloc(PATH_MAX, GFP_KERNEL);
> +	if (!path)
> +		return -EINVAL;
> +	mount_dir = d_path(&en->path, path, PATH_MAX - 1);
> +	if (IS_ERR(mount_dir))
> +		mount_dir = "unknown";
> +
> +	ret = nla_put_u32(skb, FS_EVENT_ATR_FS_ID, en->mark);
> +	if (ret)
> +		goto leave;
> +	ret = nla_put_string(skb, FS_EVENT_ATR_MOUNT, mount_dir);
> +
> +leave:
> +	kfree(path);
> +	return ret;
> +}
> +
> +static int fs_event_common_create_msg(struct sk_buff *skb,
> +				unsigned int event_id, void *data)
> +{
> +	struct fs_trace_entry *en = (struct fs_trace_entry *)data;
> +	struct super_block *sb = fs_trace_sb(en);
> +
> +	if (nla_put_u32(skb, FS_EVENT_ATR_FS_ID, en->mark))
> +		return -EINVAL;
> +
> +	/* In case there is no backing dev, so skip the followng */
> +	if (sb->s_bdev && MAJOR(sb->s_dev))
> +		if (nla_put_u32(skb, FS_EVENT_ATR_DEV_MAJOR, MAJOR(sb->s_dev))
> +		||  nla_put_u32(skb, FS_EVENT_ATR_DEV_MINOR, MINOR(sb->s_dev)))
> +			return -EINVAL;
> +
> +	if (nla_put_u32(skb, FS_EVENT_ATR_ID, event_id))
> +		return -EINVAL;
> +	if (nla_put_u64(skb, FS_EVENT_ATR_CAUSED_ID, pid_nr(task_pid(current))))
> +		return -EINVAL;
> +
> +	if (event_id & (FS_THRESH_LR_REACHED | FS_THRESH_UR_REACHED))
> +		return nla_put_u64(skb, FS_EVENT_ATR_DATA,
> +					en->data.available_blks);
> +
> +	return 0;
> +}
> +
> +static void fs_event_new_trace(struct fs_trace_entry *en)
> +{
> +	fs_netlink_send_event(GENLMSG_DEFAULT_SIZE, FS_EVENT_TYPE_NEW_TRACE,
> +				fs_event_new_trace_create_msg, 0, en);
> +}
> +
> +static void fs_event_send(struct fs_trace_entry *en,
> +			  unsigned int event_type, unsigned int event_id)
> +{
> +	size_t size = nla_total_size(sizeof(u32)) * 4 +
> +		      nla_total_size(sizeof(u64)) * 2;
> +
> +	fs_netlink_send_event(size, fs_event_type_cast(event_type),
> +				fs_event_common_create_msg, event_id, en);
> +}
> +
> +void fs_event_notify(struct super_block *sb, unsigned int event_type,
> +				unsigned int event_id)
> +{
> +	struct fs_trace_entry *en;
> +
> +	spin_lock(&fs_trace_lock);
> +	en = fs_find_trace_entry(sb);
> +	if (IS_ERR(en)) {
> +		spin_unlock(&fs_trace_lock);
> +		return;
> +	}
> +
> +	spin_lock(&en->lock);
> +	/* Relase the main lock - it's enough to keep the entry lock here */
> +	spin_unlock(&fs_trace_lock);
> +	if (en->notify_mask & event_type)
> +		fs_event_send(en, event_type, event_id);
> +	spin_unlock(&en->lock);
> +}
> +EXPORT_SYMBOL(fs_event_notify);
> +
> +void fs_event_alloc_space(struct super_block *sb, u64 ncount)
> +{
> +	struct fs_trace_entry *en;
> +	s64 count;
> +
> +	spin_lock(&fs_trace_lock);
> +	en = fs_find_trace_entry(sb);
> +	if (IS_ERR(en)) {
> +		spin_unlock(&fs_trace_lock);
> +		return;
> +	}
> +
> +	spin_lock(&en->lock);
> +	spin_unlock(&fs_trace_lock);
> +
> +	if (!(en->notify_mask & FS_EVENT_THRESH))
> +		goto leave;
> +	/* we shouldn't drop below 0 here, unless there is a sync issue
> +	  somewhere (?) */
> +	count = en->data.available_blks - ncount;
> +	en->data.available_blks = count < 0 ? 0 : count;
> +
> +	if (en->data.available_blks > en->thresh.lrange)
> +		/* Not 'even' close - leave */
> +		goto leave;
> +
> +	if (en->data.available_blks > en->thresh.urange) {
> +		/* Close enough - the lower range has been reached */
> +		if (!(en->thresh.state & THRESH_LR_BEYOND)) {
> +			/* Send notificaton */
> +			fs_event_send(en, FS_EVENT_THRESH,
> +				FS_THRESH_LR_REACHED);
> +			en->thresh.state &= ~THRESH_LR_BELOW;
> +			en->thresh.state |= THRESH_LR_BEYOND;
> +		}
> +		goto leave;
> +	}
> +	if (!(en->thresh.state & THRESH_UR_BEYOND)) {
> +		fs_event_send(en, FS_EVENT_THRESH, FS_THRESH_UR_REACHED);
> +		en->thresh.state &=  ~THRESH_UR_BELOW;
> +		en->thresh.state |= THRESH_UR_BEYOND;
> +	}
> +
> +leave:
> +	spin_unlock(&en->lock);
> +}
> +EXPORT_SYMBOL(fs_event_alloc_space);
> +
> +void fs_event_free_space(struct super_block *sb, u64 ncount)
> +{
> +	struct fs_trace_entry *en;
> +
> +	spin_lock(&fs_trace_lock);
> +	en = fs_find_trace_entry(sb);
> +	if (IS_ERR(en)) {
> +		spin_unlock(&fs_trace_lock);
> +		return;
> +	}
> +
> +	spin_lock(&en->lock);
> +	spin_unlock(&fs_trace_lock);
> +
> +	if (!(en->notify_mask & FS_EVENT_THRESH))
> +		goto leave;
> +
> +	en->data.available_blks += ncount;
> +
> +	if (en->data.available_blks > en->thresh.lrange) {
> +		if (!(en->thresh.state & THRESH_LR_BELOW)
> +		&& en->thresh.state & THRESH_LR_BEYOND) {
> +			/* Send notificaton */
> +			fs_event_send(en, FS_EVENT_THRESH,
> +				FS_THRESH_LR_REACHED);
> +			en->thresh.state &= ~THRESH_LR_BEYOND;
> +			en->thresh.state |= THRESH_LR_BELOW;
> +			goto leave;
> +		}
> +	}
> +	if (en->data.available_blks > en->thresh.urange) {
> +		if (!(en->thresh.state & THRESH_UR_BELOW)
> +		&& en->thresh.state & THRESH_UR_BEYOND) {
> +			/* Notify */
> +			fs_event_send(en, FS_EVENT_THRESH,
> +					FS_THRESH_UR_REACHED);
> +			en->thresh.state &= ~THRESH_UR_BEYOND;
> +			en->thresh.state |= THRESH_UR_BELOW;
> +		}
> +	}
> +leave:
> +	spin_unlock(&en->lock);
> +}
> +EXPORT_SYMBOL(fs_event_free_space);
> +
> +void fs_event_mount_dropped(struct vfsmount *mnt)
> +{
> +	struct fs_trace_entry *en;
> +
> +	spin_lock(&fs_trace_lock);
> +	en = fs_find_trace_entry(mnt->mnt_sb);
> +	if (!IS_ERR(en)) {
> +		spin_lock(&en->lock);
> +		if (en->notify_mask & FS_EVENT_INFO)
> +			fs_event_send(en, FS_EVENT_TYPE_INFO, FS_INFO_UMOUNT);
> +		spin_unlock(&en->lock);
> +		fs_destroy_trace_entry(en);
> +	}
> +	spin_unlock(&fs_trace_lock);
> +}
> +
> +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 umount 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 send the event and perform appropraite clean-up
> +	 */
> +	r_mnt = real_mount(path->mnt);
> +	en->path.dentry = r_mnt->mnt.mnt_root;
> +	en->path.mnt = &r_mnt->mnt;
> +
> +	sb = fs_trace_sb(en);
> +	spin_lock_init(&en->lock);
> +
> +	spin_lock(&fs_trace_idr_lock);
> +	idr_preload(GFP_KERNEL);
> +	en->mark = idr_alloc_cyclic(&fs_trace_idr, en, 1, 0, GFP_KERNEL);
> +	idr_preload_end();
> +	spin_unlock(&fs_trace_idr_lock);
> +
> +	if (en->mark < 0)
> +		goto leave;
> +	if (fs_trace_query_data(sb, &en->data))
> +		goto leave;
> +
> +	nmask = en->data.events_cap_mask & nmask;
> +	if (!nmask)
> +		goto leave;
> +	en->notify_mask = nmask;
> +	memcpy(&en->thresh, thresh, offsetof(struct fs_event_thresh, state));
> +
> +	spin_lock(&fs_trace_lock);
> +	list_add(&en->node, &fs_trace_list);
> +	hash_add(fs_trace_hashtbl, &en->hnode, fs_trace_hasfn(sb));
> +	spin_unlock(&fs_trace_lock);
> +
> +	fs_event_new_trace(en);
> +	return 0;
> +leave:
> +	kmem_cache_free(fs_trace_cachep, en);
> +	return -EINVAL;
> +}
> +
> +static int fs_update_trace_entry_locked(struct fs_trace_entry *en,
> +				   struct fs_event_thresh *thresh,
> +				    unsigned int nmask)
> +{
> +	int extend = nmask & FS_TRACE_ADD;
> +
> +	nmask &= en->data.events_cap_mask;
> +	if (!nmask)
> +		return -EINVAL;
> +
> +	if (nmask & FS_EVENT_THRESH) {
> +		if (extend) {
> +			/* Get the current state */
> +			if (!(en->notify_mask & FS_EVENT_THRESH))
> +				fs_trace_query_data(fs_trace_sb(en),
> +						&en->data);
> +			if (thresh->state & THRESH_LR_ON) {
> +				en->thresh.lrange = thresh->lrange;
> +				en->thresh.state &= ~THRESH_LR_ON;
> +			}
> +			if (thresh->state & THRESH_UR_ON) {
> +				en->thresh.urange = thresh->urange;
> +				en->thresh.state &= ~THRESH_UR_ON;
> +			}
> +		} else {
> +			memset(&en->thresh, 0, sizeof(en->thresh));
> +		}
> +	}
> +
> +	if (extend)
> +		en->notify_mask |= nmask;
> +	else
> +		en->notify_mask &= ~nmask;
> +	return 0;
> +}
> +
> +static int fs_update_trace_entry(struct path *path,
> +				  struct fs_event_thresh *thresh,
> +				  unsigned int nmask)
> +{
> +	struct fs_trace_entry *en;
> +	int ret;
> +
> +	spin_lock(&fs_trace_lock);
> +	en = fs_find_trace_entry(path->mnt->mnt_sb);
> +	if (IS_ERR(en)) {
> +		spin_unlock(&fs_trace_lock);
> +		return (nmask & FS_TRACE_ADD)
> +			?  fs_new_trace_entry(path, thresh, nmask)
> +			: -EINVAL;
> +	}
> +	spin_lock(&en->lock);
> +	spin_unlock(&fs_trace_lock);
> +
> +	ret = fs_update_trace_entry_locked(en, thresh, nmask);
> +
> +	spin_unlock(&en->lock);
> +	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;
> +	}
> +
> +	while ((s = strsep(argv, ",")) != NULL) {
> +		if (!*s)
> +			continue;
> +		args[0].to = args[0].from = NULL;
> +		token = match_token(s, fs_etypes, args);
> +		nmask |= (token & FS_EVENTS_ALL);
> +	}
> +
> +	if (!(nmask & (~FS_TRACE_ADD)) ||
> +	(!(--argc) && (nmask & FS_EVENT_THRESH && nmask & FS_TRACE_ADD)))
> +		goto leave;
> +
> +	if ((nmask & FS_EVENT_THRESH) && (nmask & FS_TRACE_ADD)) {
> +		/*
> +		 * Get the threshold config data:
> +		 * lower range
> +		 * upper range
> +		 */
> +		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;
> +		}
> +		/* The thresholds are based on number of available blocks */
> +		if (thresh.lrange < thresh.urange) {
> +			ret = -EINVAL;
> +			goto leave;
> +		}
> +
> +	}
> +	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)
> +{
> +	spin_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)
> +{
> +	spin_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);
> +	sb = fs_trace_sb(en);
> +
> +	seq_printf(m, "%d ", en->mark);
> +
> +	seq_path(m, &en->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->path.mnt->mnt_root);
> +	} else {
> +		r_mnt = real_mount(en->path.mnt);
> +		seq_escape(m, r_mnt->mnt_devname ? r_mnt->mnt_devname : "none",
> +				" \t\n\\");
> +	}
> +	seq_puts(m, " (");
> +
> +	nmask = en->notify_mask;
> +	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->thresh.lrange,
> +			en->thresh.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;
> +	if (!fs_event_netlink_register()) {
> +		idr_init(&fs_trace_idr);
> +		return 0;
> +	}
> +	kmem_cache_destroy(fs_trace_cachep);
> +	return -EINVAL;
> +}
> +
> +/* VFS support */
> +static int fs_trace_fill_super(struct super_block *sb, void *data, int silent)
> +{
> +	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)
> +{
> +	fs_remove_all_traces();
> +	idr_destroy(&fs_trace_idr);
> +	fs_event_netlink_unregister();
> +	kmem_cache_destroy(fs_trace_cachep);
> +	kill_litter_super(sb);
> +}
> +
> +static struct kset	*fs_trace_kset;
> +static struct vfsmount	*fs_trace_mount;
> +
> +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)) {
> +		fs_trace_mount = kern_mount(&fs_trace_fstype);
> +		if (!IS_ERR(fs_trace_mount))
> +			return;
> +
> +		unregister_filesystem(&fs_trace_fstype);
> +	}
> +	kset_unregister(fs_trace_kset);
> +}
> +
> +static int __init fs_trace_events_init(void)
> +{
> +	fs_trace_vfs_init();
> +	return 0;
> +};
> +module_init(fs_trace_events_init);
> +
> diff --git a/fs/events/fs_event.h b/fs/events/fs_event.h
> new file mode 100644
> index 0000000..4260ce5
> --- /dev/null
> +++ b/fs/events/fs_event.h
> @@ -0,0 +1,27 @@
> +/*
> + * 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
> +
> +#ifdef CONFIG_NET
> +int  fs_event_netlink_register(void);
> +void fs_event_netlink_unregister(void);
> +#else /* CONFIG_NET */
> +static inline int  fs_event_netlink_register(void) { return -ENOSYS; }
> +static inline void fs_event_netlink_unregister(void) {};
> +#endif /* CONFIG_NET */
> +
> +#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..9c56e35
> --- /dev/null
> +++ b/fs/events/fs_event_netlink.c
> @@ -0,0 +1,94 @@
> +/*
> + * 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>
> +
> +static const struct genl_multicast_group fs_event_mcgroups[] = {
> +	{ .name = "event", },
> +};
> +
> +static struct genl_family fs_event_family = {
> +	.id		= GENL_ID_FS_EVENT,
> +	.hdrsize	= 0,
> +	.name		= "FS_EVENT",
> +	.version	= 1,
> +	.maxattr	= FS_EVENT_ATR_MAX,
> +	.mcgrps		= fs_event_mcgroups,
> +	.n_mcgrps	= ARRAY_SIZE(fs_event_mcgroups),
> +};
> +
> +int fs_netlink_send_event(size_t size, unsigned int event_type,
> +		int (*compose_msg)(struct sk_buff *skb,
> +			unsigned int event_id, void *data),
> +		unsigned int event_id, void *data)
> +{
> +	static atomic_t seq;
> +	struct sk_buff *skb;
> +	void *msg_head;
> +	int ret = 0;
> +
> +	if (!size || !compose_msg)
> +		return -EINVAL;
> +
> +	size += nla_total_size(sizeof(u64));
> +	skb = genlmsg_new(size, GFP_NOFS);
> +
> +	if (!skb) {
> +		pr_err("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, event_type);
> +	if (!msg_head)
> +		goto cleanup;
> +
> +	ret = compose_msg(skb, event_id, data);
> +	if (ret) {
> +		genlmsg_cancel(skb, msg_head);
> +		goto cleanup;
> +	}
> +
> +	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;
> +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..bb529af 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
> @@ -1233,6 +1237,7 @@ struct super_block {
>  	const struct dquot_operations	*dq_op;
>  	const struct quotactl_ops	*s_qcop;
>  	const struct export_operations *s_export_op;
> +	const struct fs_trace_operations *s_trace_ops;
>  	unsigned long		s_flags;
>  	unsigned long		s_magic;
>  	struct dentry		*s_root;
> @@ -1253,7 +1258,6 @@ 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 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..1e128d8
> --- /dev/null
> +++ b/include/linux/fs_event.h
> @@ -0,0 +1,69 @@
> +/*
> + * 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>
> +
> +/*
> + * Those event flags match the event types send though the netlink interface
> + * so mind in case making any modifications.
> + */
> +#define FS_EVENT_INFO	0x001
> +#define FS_EVENT_WARN	0x002
> +#define FS_EVENT_ERR	0x004
> +#define FS_EVENT_THRESH	0x008
> +
> +#define FS_EVENTS_ALL \
> +	(FS_EVENT_INFO | FS_EVENT_WARN | FS_EVENT_THRESH | FS_EVENT_ERR)
> +
> +struct fs_trace_sdata {
> +	/* Supported notification types */
> +	unsigned int	events_cap_mask;
> +	/* Number of available/reachable blocks */
> +	u64		available_blks;
> +};
> +
> +struct fs_trace_operations {
> +	int (*fs_trace_query)(struct super_block *, struct fs_trace_sdata *);
> +};
> +
> +
> +void fs_event_notify(struct super_block *sb, unsigned int event_type,
> +		     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);
> +
> +#ifdef CONFIG_NET
> +int fs_netlink_send_event(size_t size, unsigned int event_type,
> +		int (*compose_msg)(struct sk_buff *skb, unsigned int event_id,
> +		void *data),
> +		unsigned int event_id, void *data);
> +#else /* CONFIG_NET */
> +static inline
> +int fs_netlink_send_event(size_t size, unsigned int event_type,
> +		int (*compose_msg)(struct sk_buff *skb, unsigned int event_id,
> +		void *data),
> +		unsigned int event_idid, void *data)
> +{
> +	return -ENOSYS;
> +}
> +#endif /* CONFIG_NET */
> +
> +#endif /* _LINUX_GENERIC_FS_EVENTS_ */
> +
> diff --git a/include/uapi/linux/fs_event.h b/include/uapi/linux/fs_event.h
> new file mode 100644
> index 0000000..dd79953
> --- /dev/null
> +++ b/include/uapi/linux/fs_event.h
> @@ -0,0 +1,62 @@
> +/*
> + * 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_
> +/*
> + * Generic FS event types
> + */
> +enum {
> +	FS_EVENT_TYPE_NONE,
> +	FS_EVENT_TYPE_INFO,
> +	FS_EVENT_TYPE_WARN,
> +	FS_EVENT_TYPE_ERR,
> +	FS_EVENT_TYPE_THRESH,
> +	FS_EVENT_TYPE_NEW_TRACE,
> +	__FS_EVENT_TYPE_MAX,
> +};
> +#define FS_EVENT_TYPE_MAX (__FS_EVENT_TYPE_MAX - 1)
> +/*
> + * Generic netlink attribute types
> + */
> +enum {
> +	FS_EVENT_ATR_NONE,
> +	FS_EVENT_ATR_FS_ID,	/* An identifier of traced fs */
> +	FS_EVENT_ATR_MOUNT,	/* Mount point directory name */
> +	FS_EVENT_ATR_DEV_MAJOR,
> +	FS_EVENT_ATR_DEV_MINOR,
> +	FS_EVENT_ATR_ID,
> +	FS_EVENT_ATR_CAUSED_ID,
> +	FS_EVENT_ATR_DATA,
> +	__FS_EVENT_ATR_MAX,
> +};
> +#define FS_EVENT_ATR_MAX (__FS_EVENT_ATR_MAX - 1)

FS_EVENT_ATTR_ ?  Most of the time, the kernel seems to use "attr" as shorthand
for "attribute".

> +
> +/*
> + * Supported set of FS events ids
> + */
> +#define FS_INFO_UMOUNT		0x00000001	/* File system unmounted */
> +#define FS_WARN_UNKNOWN		0x00000004	/* Unknown warning */
> +#define FS_WARN_ENOSPC		0x00000008	/* No space left to reserve data blks */
> +#define FS_WANR_ENOSPC_META	0x00000010	/* No space left for metadata */

Why WANR, as opposed to WARN?

> +#define FS_THRESH_LR_REACHED	0x00000020	/* The lower range of threshold has been reached */
> +#define FS_THRESH_UR_REACHED	0x00000040	/* The upper range of threshold has been reached */
> +#define FS_ERR_UNKNOWN		0x00000080	/* Unknown error */
> +#define FS_ERR_RO_REMOUT	0x00000100	/* The file system has been remounted as red-only */

_REMOUNT... read-only...

> +#define FS_ERR_ITERNAL		0x00000200	/* File system's internal error */

_INTERNAL...

What does FS_ERR_ITERNAL mean?  "programming error"?

How about a separate FS_ERR_CORRUPTED to mean "go run fsck"?

Hmm, these are bit flags... it doesn't make sense that I can send things like
FS_INFO_UMOUNT | FS_ERR_RO_REMOUT.

> +
> +#endif /* _UAPI_LINUX_GENERIC_FS_EVENTS_ */
> +
> diff --git a/include/uapi/linux/genetlink.h b/include/uapi/linux/genetlink.h
> index c3363ba..6464129 100644
> --- a/include/uapi/linux/genetlink.h
> +++ b/include/uapi/linux/genetlink.h
> @@ -29,6 +29,7 @@ struct genlmsghdr {
>  #define GENL_ID_CTRL		NLMSG_MIN_TYPE
>  #define GENL_ID_VFS_DQUOT	(NLMSG_MIN_TYPE + 1)
>  #define GENL_ID_PMCRAID		(NLMSG_MIN_TYPE + 2)
> +#define GENL_ID_FS_EVENT	(NLMSG_MIN_TYPE + 3)
>  
>  /**************************************************************************
>   * Controller
> diff --git a/net/netlink/genetlink.c b/net/netlink/genetlink.c
> index 2ed5f96..e8e0bd68 100644
> --- a/net/netlink/genetlink.c
> +++ b/net/netlink/genetlink.c
> @@ -82,7 +82,8 @@ static struct list_head family_ht[GENL_FAM_TAB_SIZE];
>   */
>  static unsigned long mc_group_start = 0x3 | BIT(GENL_ID_CTRL) |
>  				      BIT(GENL_ID_VFS_DQUOT) |
> -				      BIT(GENL_ID_PMCRAID);
> +				      BIT(GENL_ID_PMCRAID) |
> +				      BIT(GENL_ID_FS_EVENT);
>  static unsigned long *mc_groups = &mc_group_start;
>  static unsigned long mc_groups_longs = 1;
>  
> @@ -146,6 +147,7 @@ static u16 genl_generate_id(void)
>  	for (i = 0; i <= GENL_MAX_ID - GENL_MIN_ID; i++) {
>  		if (id_gen_idx != GENL_ID_VFS_DQUOT &&
>  		    id_gen_idx != GENL_ID_PMCRAID &&
> +		    id_gen_idx != GENL_ID_FS_EVENT &&
>  		    !genl_family_find_byid(id_gen_idx))
>  			return id_gen_idx;
>  		if (++id_gen_idx > GENL_MAX_ID)
> @@ -249,6 +251,9 @@ static int genl_validate_assign_mc_groups(struct genl_family *family)
>  	} else if (family->id == GENL_ID_PMCRAID) {
>  		first_id = GENL_ID_PMCRAID;
>  		BUG_ON(n_groups != 1);
> +	} else if (family->id == GENL_ID_FS_EVENT) {
> +		first_id = GENL_ID_FS_EVENT;
> +		BUG_ON(n_groups != 1);
>  	} else {
>  		groups_allocated = true;
>  		err = genl_allocate_reserve_groups(n_groups, &first_id);
> -- 
> 1.7.9.5
> 
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