[RFC v3 0/4] fs: Add generic file system event notifications

@@ -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.
+
+

@@ -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"

@@ -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/

@@ -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

@@ -0,0 +1,5 @@
+#
+# Makefile for the Linux Generic File System Event Interface
+#
+
+obj-y := fs_event.o fs_event_netlink.o

@@ -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;
+
+	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);
+