include/linux/fsnotify_backend.h - kernel/msm-4.19 - Gitiles

 /*
  * Filesystem access notification for Linux
  *
  *  Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com>
  */

 #ifndef __LINUX_FSNOTIFY_BACKEND_H
 #define __LINUX_FSNOTIFY_BACKEND_H

 #ifdef __KERNEL__

 #include <linux/idr.h> /* inotify uses this */
 #include <linux/fs.h> /* struct inode */
 #include <linux/list.h>
 #include <linux/path.h> /* struct path */
 #include <linux/spinlock.h>
 #include <linux/types.h>
 #include <linux/atomic.h>

 /*
  * IN_* from inotfy.h lines up EXACTLY with FS_*, this is so we can easily
  * convert between them.  dnotify only needs conversion at watch creation
  * so no perf loss there.  fanotify isn't defined yet, so it can use the
  * wholes if it needs more events.
  */
 #define FS_ACCESS		0x00000001	/* File was accessed */
 #define FS_MODIFY		0x00000002	/* File was modified */
 #define FS_ATTRIB		0x00000004	/* Metadata changed */
 #define FS_CLOSE_WRITE		0x00000008	/* Writtable file was closed */
 #define FS_CLOSE_NOWRITE	0x00000010	/* Unwrittable file closed */
 #define FS_OPEN			0x00000020	/* File was opened */
 #define FS_MOVED_FROM		0x00000040	/* File was moved from X */
 #define FS_MOVED_TO		0x00000080	/* File was moved to Y */
 #define FS_CREATE		0x00000100	/* Subfile was created */
 #define FS_DELETE		0x00000200	/* Subfile was deleted */
 #define FS_DELETE_SELF		0x00000400	/* Self was deleted */
 #define FS_MOVE_SELF		0x00000800	/* Self was moved */

 #define FS_UNMOUNT		0x00002000	/* inode on umount fs */
 #define FS_Q_OVERFLOW		0x00004000	/* Event queued overflowed */
 #define FS_IN_IGNORED		0x00008000	/* last inotify event here */

 #define FS_OPEN_PERM		0x00010000	/* open event in an permission hook */
 #define FS_ACCESS_PERM		0x00020000	/* access event in a permissions hook */

 #define FS_EXCL_UNLINK		0x04000000	/* do not send events if object is unlinked */
 #define FS_ISDIR		0x40000000	/* event occurred against dir */
 #define FS_IN_ONESHOT		0x80000000	/* only send event once */

 #define FS_DN_RENAME		0x10000000	/* file renamed */
 #define FS_DN_MULTISHOT		0x20000000	/* dnotify multishot */

 /* This inode cares about things that happen to its children.  Always set for
  * dnotify and inotify. */
 #define FS_EVENT_ON_CHILD	0x08000000

 /* This is a list of all events that may get sent to a parernt based on fs event
  * happening to inodes inside that directory */
 #define FS_EVENTS_POSS_ON_CHILD   (FS_ACCESS | FS_MODIFY | FS_ATTRIB |\
 				   FS_CLOSE_WRITE | FS_CLOSE_NOWRITE | FS_OPEN |\
 				   FS_MOVED_FROM | FS_MOVED_TO | FS_CREATE |\
 				   FS_DELETE | FS_OPEN_PERM | FS_ACCESS_PERM)

 #define FS_MOVE			(FS_MOVED_FROM | FS_MOVED_TO)

 #define ALL_FSNOTIFY_PERM_EVENTS (FS_OPEN_PERM | FS_ACCESS_PERM)

 #define ALL_FSNOTIFY_EVENTS (FS_ACCESS | FS_MODIFY | FS_ATTRIB | \
 			     FS_CLOSE_WRITE | FS_CLOSE_NOWRITE | FS_OPEN | \
 			     FS_MOVED_FROM | FS_MOVED_TO | FS_CREATE | \
 			     FS_DELETE | FS_DELETE_SELF | FS_MOVE_SELF | \
 			     FS_UNMOUNT | FS_Q_OVERFLOW | FS_IN_IGNORED | \
 			     FS_OPEN_PERM | FS_ACCESS_PERM | FS_EXCL_UNLINK | \
 			     FS_ISDIR | FS_IN_ONESHOT | FS_DN_RENAME | \
 			     FS_DN_MULTISHOT | FS_EVENT_ON_CHILD)

 struct fsnotify_group;
 struct fsnotify_event;
 struct fsnotify_mark;
 struct fsnotify_event_private_data;
 struct fsnotify_fname;

 /*
  * Each group much define these ops.  The fsnotify infrastructure will call
  * these operations for each relevant group.
  *
  * should_send_event - given a group, inode, and mask this function determines
  *		if the group is interested in this event.
  * handle_event - main call for a group to handle an fs event
  * free_group_priv - called when a group refcnt hits 0 to clean up the private union
  * freeing_mark - called when a mark is being destroyed for some reason.  The group
  * 		MUST be holding a reference on each mark and that reference must be
  * 		dropped in this function.  inotify uses this function to send
  * 		userspace messages that marks have been removed.
  */
 struct fsnotify_ops {
 	int (*handle_event)(struct fsnotify_group *group,
 			    struct inode *inode,
 			    struct fsnotify_mark *inode_mark,
 			    struct fsnotify_mark *vfsmount_mark,
 			    u32 mask, void *data, int data_type,
 			    const unsigned char *file_name, u32 cookie);
 	void (*free_group_priv)(struct fsnotify_group *group);
 	void (*freeing_mark)(struct fsnotify_mark *mark, struct fsnotify_group *group);
 	void (*free_event)(struct fsnotify_event *event);
 };

 /*
  * all of the information about the original object we want to now send to
  * a group.  If you want to carry more info from the accessing task to the
  * listener this structure is where you need to be adding fields.
  */
 struct fsnotify_event {
 	struct list_head list;
 	/* inode may ONLY be dereferenced during handle_event(). */
 	struct inode *inode;	/* either the inode the event happened to or its parent */
 	u32 mask;		/* the type of access, bitwise OR for FS_* event types */
 };

 /*
  * A group is a "thing" that wants to receive notification about filesystem
  * events.  The mask holds the subset of event types this group cares about.
  * refcnt on a group is up to the implementor and at any moment if it goes 0
  * everything will be cleaned up.
  */
 struct fsnotify_group {
 	/*
 	 * How the refcnt is used is up to each group.  When the refcnt hits 0
 	 * fsnotify will clean up all of the resources associated with this group.
 	 * As an example, the dnotify group will always have a refcnt=1 and that
 	 * will never change.  Inotify, on the other hand, has a group per
 	 * inotify_init() and the refcnt will hit 0 only when that fd has been
 	 * closed.
 	 */
 	atomic_t refcnt;		/* things with interest in this group */

 	const struct fsnotify_ops *ops;	/* how this group handles things */

 	/* needed to send notification to userspace */
 	struct mutex notification_mutex;	/* protect the notification_list */
 	struct list_head notification_list;	/* list of event_holder this group needs to send to userspace */
 	wait_queue_head_t notification_waitq;	/* read() on the notification file blocks on this waitq */
 	unsigned int q_len;			/* events on the queue */
 	unsigned int max_events;		/* maximum events allowed on the list */
 	/*
 	 * Valid fsnotify group priorities.  Events are send in order from highest
 	 * priority to lowest priority.  We default to the lowest priority.
 	 */
 	#define FS_PRIO_0	0 /* normal notifiers, no permissions */
 	#define FS_PRIO_1	1 /* fanotify content based access control */
 	#define FS_PRIO_2	2 /* fanotify pre-content access */
 	unsigned int priority;

 	/* stores all fastpath marks assoc with this group so they can be cleaned on unregister */
 	struct mutex mark_mutex;	/* protect marks_list */
 	atomic_t num_marks;		/* 1 for each mark and 1 for not being
 					 * past the point of no return when freeing
 					 * a group */
 	struct list_head marks_list;	/* all inode marks for this group */

 	struct fasync_struct *fsn_fa;    /* async notification */

 	struct fsnotify_event *overflow_event;	/* Event we queue when the
 						 * notification list is too
 						 * full */

 	/* groups can define private fields here or use the void *private */
 	union {
 		void *private;
 #ifdef CONFIG_INOTIFY_USER
 		struct inotify_group_private_data {
 			spinlock_t	idr_lock;
 			struct idr      idr;
 			struct user_struct      *user;
 		} inotify_data;
 #endif
 #ifdef CONFIG_FANOTIFY
 		struct fanotify_group_private_data {
 #ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
 			/* allows a group to block waiting for a userspace response */
 			spinlock_t access_lock;
 			struct list_head access_list;
 			wait_queue_head_t access_waitq;
 			atomic_t bypass_perm;
 #endif /* CONFIG_FANOTIFY_ACCESS_PERMISSIONS */
 			int f_flags;
 			unsigned int max_marks;
 			struct user_struct *user;
 		} fanotify_data;
 #endif /* CONFIG_FANOTIFY */
 	};
 };

 /* when calling fsnotify tell it if the data is a path or inode */
 #define FSNOTIFY_EVENT_NONE	0
 #define FSNOTIFY_EVENT_PATH	1
 #define FSNOTIFY_EVENT_INODE	2

 /*
  * a mark is simply an object attached to an in core inode which allows an
  * fsnotify listener to indicate they are either no longer interested in events
  * of a type matching mask or only interested in those events.
  *
  * these are flushed when an inode is evicted from core and may be flushed
  * when the inode is modified (as seen by fsnotify_access).  Some fsnotify users
  * (such as dnotify) will flush these when the open fd is closed and not at
  * inode eviction or modification.
  */
 struct fsnotify_mark {
 	__u32 mask;			/* mask this mark is for */
 	/* we hold ref for each i_list and g_list.  also one ref for each 'thing'
 	 * in kernel that found and may be using this mark. */
 	atomic_t refcnt;		/* active things looking at this mark */
 	struct fsnotify_group *group;	/* group this mark is for */
 	struct list_head g_list;	/* list of marks by group->i_fsnotify_marks
 					 * Also reused for queueing mark into
 					 * destroy_list when it's waiting for
 					 * the end of SRCU period before it can
 					 * be freed */
 	spinlock_t lock;		/* protect group and inode */
 	struct hlist_node obj_list;	/* list of marks for inode / vfsmount */
 	struct list_head free_list;	/* tmp list used when freeing this mark */
 	union {
 		struct inode *inode;	/* inode this mark is associated with */
 		struct vfsmount *mnt;	/* vfsmount this mark is associated with */
 	};
 	__u32 ignored_mask;		/* events types to ignore */
 #define FSNOTIFY_MARK_FLAG_INODE		0x01
 #define FSNOTIFY_MARK_FLAG_VFSMOUNT		0x02
 #define FSNOTIFY_MARK_FLAG_OBJECT_PINNED	0x04
 #define FSNOTIFY_MARK_FLAG_IGNORED_SURV_MODIFY	0x08
 #define FSNOTIFY_MARK_FLAG_ALIVE		0x10
 	unsigned int flags;		/* vfsmount or inode mark? */
 	void (*free_mark)(struct fsnotify_mark *mark); /* called on final put+free */
 };

 #ifdef CONFIG_FSNOTIFY

 /* called from the vfs helpers */

 /* main fsnotify call to send events */
 extern int fsnotify(struct inode *to_tell, __u32 mask, void *data, int data_is,
 		    const unsigned char *name, u32 cookie);
 extern int __fsnotify_parent(struct path *path, struct dentry *dentry, __u32 mask);
 extern void __fsnotify_inode_delete(struct inode *inode);
 extern void __fsnotify_vfsmount_delete(struct vfsmount *mnt);
 extern u32 fsnotify_get_cookie(void);

 static inline int fsnotify_inode_watches_children(struct inode *inode)
 {
 	/* FS_EVENT_ON_CHILD is set if the inode may care */
 	if (!(inode->i_fsnotify_mask & FS_EVENT_ON_CHILD))
 		return 0;
 	/* this inode might care about child events, does it care about the
 	 * specific set of events that can happen on a child? */
 	return inode->i_fsnotify_mask & FS_EVENTS_POSS_ON_CHILD;
 }

 /*
  * Update the dentry with a flag indicating the interest of its parent to receive
  * filesystem events when those events happens to this dentry->d_inode.
  */
 static inline void __fsnotify_update_dcache_flags(struct dentry *dentry)
 {
 	struct dentry *parent;

 	assert_spin_locked(&dentry->d_lock);

 	/*
 	 * Serialisation of setting PARENT_WATCHED on the dentries is provided
 	 * by d_lock. If inotify_inode_watched changes after we have taken
 	 * d_lock, the following __fsnotify_update_child_dentry_flags call will
 	 * find our entry, so it will spin until we complete here, and update
 	 * us with the new state.
 	 */
 	parent = dentry->d_parent;
 	if (parent->d_inode && fsnotify_inode_watches_children(parent->d_inode))
 		dentry->d_flags |= DCACHE_FSNOTIFY_PARENT_WATCHED;
 	else
 		dentry->d_flags &= ~DCACHE_FSNOTIFY_PARENT_WATCHED;
 }

 /*
  * fsnotify_d_instantiate - instantiate a dentry for inode
  */
 static inline void __fsnotify_d_instantiate(struct dentry *dentry, struct inode *inode)
 {
 	if (!inode)
 		return;

 	spin_lock(&dentry->d_lock);
 	__fsnotify_update_dcache_flags(dentry);
 	spin_unlock(&dentry->d_lock);
 }

 /* called from fsnotify listeners, such as fanotify or dnotify */

 /* create a new group */
 extern struct fsnotify_group *fsnotify_alloc_group(const struct fsnotify_ops *ops);
 /* get reference to a group */
 extern void fsnotify_get_group(struct fsnotify_group *group);
 /* drop reference on a group from fsnotify_alloc_group */
 extern void fsnotify_put_group(struct fsnotify_group *group);
 /* destroy group */
 extern void fsnotify_destroy_group(struct fsnotify_group *group);
 /* fasync handler function */
 extern int fsnotify_fasync(int fd, struct file *file, int on);
 /* Free event from memory */
 extern void fsnotify_destroy_event(struct fsnotify_group *group,
 				   struct fsnotify_event *event);
 /* attach the event to the group notification queue */
 extern int fsnotify_add_event(struct fsnotify_group *group,
 			      struct fsnotify_event *event,
 			      int (*merge)(struct list_head *,
 					   struct fsnotify_event *));
 /* Remove passed event from groups notification queue */
 extern void fsnotify_remove_event(struct fsnotify_group *group, struct fsnotify_event *event);
 /* true if the group notification queue is empty */
 extern bool fsnotify_notify_queue_is_empty(struct fsnotify_group *group);
 /* return, but do not dequeue the first event on the notification queue */
 extern struct fsnotify_event *fsnotify_peek_first_event(struct fsnotify_group *group);
 /* return AND dequeue the first event on the notification queue */
 extern struct fsnotify_event *fsnotify_remove_first_event(struct fsnotify_group *group);

 /* functions used to manipulate the marks attached to inodes */

 /* run all marks associated with a vfsmount and update mnt->mnt_fsnotify_mask */
 extern void fsnotify_recalc_vfsmount_mask(struct vfsmount *mnt);
 /* run all marks associated with an inode and update inode->i_fsnotify_mask */
 extern void fsnotify_recalc_inode_mask(struct inode *inode);
 extern void fsnotify_init_mark(struct fsnotify_mark *mark, void (*free_mark)(struct fsnotify_mark *mark));
 /* find (and take a reference) to a mark associated with group and inode */
 extern struct fsnotify_mark *fsnotify_find_inode_mark(struct fsnotify_group *group, struct inode *inode);
 /* find (and take a reference) to a mark associated with group and vfsmount */
 extern struct fsnotify_mark *fsnotify_find_vfsmount_mark(struct fsnotify_group *group, struct vfsmount *mnt);
 /* copy the values from old into new */
 extern void fsnotify_duplicate_mark(struct fsnotify_mark *new, struct fsnotify_mark *old);
 /* set the ignored_mask of a mark */
 extern void fsnotify_set_mark_ignored_mask_locked(struct fsnotify_mark *mark, __u32 mask);
 /* set the mask of a mark (might pin the object into memory */
 extern void fsnotify_set_mark_mask_locked(struct fsnotify_mark *mark, __u32 mask);
 /* attach the mark to both the group and the inode */
 extern int fsnotify_add_mark(struct fsnotify_mark *mark, struct fsnotify_group *group,
 			     struct inode *inode, struct vfsmount *mnt, int allow_dups);
 extern int fsnotify_add_mark_locked(struct fsnotify_mark *mark, struct fsnotify_group *group,
 				    struct inode *inode, struct vfsmount *mnt, int allow_dups);
 /* given a group and a mark, flag mark to be freed when all references are dropped */
 extern void fsnotify_destroy_mark(struct fsnotify_mark *mark,
 				  struct fsnotify_group *group);
 extern void fsnotify_destroy_mark_locked(struct fsnotify_mark *mark,
 					 struct fsnotify_group *group);
 /* run all the marks in a group, and clear all of the vfsmount marks */
 extern void fsnotify_clear_vfsmount_marks_by_group(struct fsnotify_group *group);
 /* run all the marks in a group, and clear all of the inode marks */
 extern void fsnotify_clear_inode_marks_by_group(struct fsnotify_group *group);
 /* run all the marks in a group, and clear all of the marks where mark->flags & flags is true*/
 extern void fsnotify_clear_marks_by_group_flags(struct fsnotify_group *group, unsigned int flags);
 /* run all the marks in a group, and flag them to be freed */
 extern void fsnotify_clear_marks_by_group(struct fsnotify_group *group);
 extern void fsnotify_get_mark(struct fsnotify_mark *mark);
 extern void fsnotify_put_mark(struct fsnotify_mark *mark);
 extern void fsnotify_unmount_inodes(struct list_head *list);

 /* put here because inotify does some weird stuff when destroying watches */
 extern void fsnotify_init_event(struct fsnotify_event *event,
 				struct inode *to_tell, u32 mask);

 #else

 static inline int fsnotify(struct inode *to_tell, __u32 mask, void *data, int data_is,
 			   const unsigned char *name, u32 cookie)
 {
 	return 0;
 }

 static inline int __fsnotify_parent(struct path *path, struct dentry *dentry, __u32 mask)
 {
 	return 0;
 }

 static inline void __fsnotify_inode_delete(struct inode *inode)
 {}

 static inline void __fsnotify_vfsmount_delete(struct vfsmount *mnt)
 {}

 static inline void __fsnotify_update_dcache_flags(struct dentry *dentry)
 {}

 static inline void __fsnotify_d_instantiate(struct dentry *dentry, struct inode *inode)
 {}

 static inline u32 fsnotify_get_cookie(void)
 {
 	return 0;
 }

 static inline void fsnotify_unmount_inodes(struct list_head *list)
 {}

 #endif	/* CONFIG_FSNOTIFY */

 #endif	/* __KERNEL __ */

 #endif	/* __LINUX_FSNOTIFY_BACKEND_H */
	/*
	* Filesystem access notification for Linux
	*
	* Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com>
	*/

	#ifndef __LINUX_FSNOTIFY_BACKEND_H
	#define __LINUX_FSNOTIFY_BACKEND_H

	#ifdef __KERNEL__

	#include <linux/idr.h> /* inotify uses this */
	#include <linux/fs.h> /* struct inode */
	#include <linux/list.h>
	#include <linux/path.h> /* struct path */
	#include <linux/spinlock.h>
	#include <linux/types.h>
	#include <linux/atomic.h>

	/*
	* IN_* from inotfy.h lines up EXACTLY with FS_*, this is so we can easily
	* convert between them. dnotify only needs conversion at watch creation
	* so no perf loss there. fanotify isn't defined yet, so it can use the
	* wholes if it needs more events.
	*/
	#define FS_ACCESS 0x00000001 /* File was accessed */
	#define FS_MODIFY 0x00000002 /* File was modified */
	#define FS_ATTRIB 0x00000004 /* Metadata changed */
	#define FS_CLOSE_WRITE 0x00000008 /* Writtable file was closed */
	#define FS_CLOSE_NOWRITE 0x00000010 /* Unwrittable file closed */
	#define FS_OPEN 0x00000020 /* File was opened */
	#define FS_MOVED_FROM 0x00000040 /* File was moved from X */
	#define FS_MOVED_TO 0x00000080 /* File was moved to Y */
	#define FS_CREATE 0x00000100 /* Subfile was created */
	#define FS_DELETE 0x00000200 /* Subfile was deleted */
	#define FS_DELETE_SELF 0x00000400 /* Self was deleted */
	#define FS_MOVE_SELF 0x00000800 /* Self was moved */

	#define FS_UNMOUNT 0x00002000 /* inode on umount fs */
	#define FS_Q_OVERFLOW 0x00004000 /* Event queued overflowed */
	#define FS_IN_IGNORED 0x00008000 /* last inotify event here */

	#define FS_OPEN_PERM 0x00010000 /* open event in an permission hook */
	#define FS_ACCESS_PERM 0x00020000 /* access event in a permissions hook */

	#define FS_EXCL_UNLINK 0x04000000 /* do not send events if object is unlinked */
	#define FS_ISDIR 0x40000000 /* event occurred against dir */
	#define FS_IN_ONESHOT 0x80000000 /* only send event once */

	#define FS_DN_RENAME 0x10000000 /* file renamed */
	#define FS_DN_MULTISHOT 0x20000000 /* dnotify multishot */

	/* This inode cares about things that happen to its children. Always set for
	* dnotify and inotify. */
	#define FS_EVENT_ON_CHILD 0x08000000

	/* This is a list of all events that may get sent to a parernt based on fs event
	* happening to inodes inside that directory */
	#define FS_EVENTS_POSS_ON_CHILD (FS_ACCESS \| FS_MODIFY \| FS_ATTRIB \|\
	FS_CLOSE_WRITE \| FS_CLOSE_NOWRITE \| FS_OPEN \|\
	FS_MOVED_FROM \| FS_MOVED_TO \| FS_CREATE \|\
	FS_DELETE \| FS_OPEN_PERM \| FS_ACCESS_PERM)

	#define FS_MOVE (FS_MOVED_FROM \| FS_MOVED_TO)

	#define ALL_FSNOTIFY_PERM_EVENTS (FS_OPEN_PERM \| FS_ACCESS_PERM)

	#define ALL_FSNOTIFY_EVENTS (FS_ACCESS \| FS_MODIFY \| FS_ATTRIB \| \
	FS_CLOSE_WRITE \| FS_CLOSE_NOWRITE \| FS_OPEN \| \
	FS_MOVED_FROM \| FS_MOVED_TO \| FS_CREATE \| \
	FS_DELETE \| FS_DELETE_SELF \| FS_MOVE_SELF \| \
	FS_UNMOUNT \| FS_Q_OVERFLOW \| FS_IN_IGNORED \| \
	FS_OPEN_PERM \| FS_ACCESS_PERM \| FS_EXCL_UNLINK \| \
	FS_ISDIR \| FS_IN_ONESHOT \| FS_DN_RENAME \| \
	FS_DN_MULTISHOT \| FS_EVENT_ON_CHILD)

	struct fsnotify_group;
	struct fsnotify_event;
	struct fsnotify_mark;
	struct fsnotify_event_private_data;
	struct fsnotify_fname;

	/*
	* Each group much define these ops. The fsnotify infrastructure will call
	* these operations for each relevant group.
	*
	* should_send_event - given a group, inode, and mask this function determines
	* if the group is interested in this event.
	* handle_event - main call for a group to handle an fs event
	* free_group_priv - called when a group refcnt hits 0 to clean up the private union
	* freeing_mark - called when a mark is being destroyed for some reason. The group
	* MUST be holding a reference on each mark and that reference must be
	* dropped in this function. inotify uses this function to send
	* userspace messages that marks have been removed.
	*/
	struct fsnotify_ops {
	int (handle_event)(struct fsnotify_group group,
	struct inode *inode,
	struct fsnotify_mark *inode_mark,
	struct fsnotify_mark *vfsmount_mark,
	u32 mask, void *data, int data_type,
	const unsigned char *file_name, u32 cookie);
	void (free_group_priv)(struct fsnotify_group group);
	void (freeing_mark)(struct fsnotify_mark mark, struct fsnotify_group *group);
	void (free_event)(struct fsnotify_event event);
	};

	/*
	* all of the information about the original object we want to now send to
	* a group. If you want to carry more info from the accessing task to the
	* listener this structure is where you need to be adding fields.
	*/
	struct fsnotify_event {
	struct list_head list;
	/* inode may ONLY be dereferenced during handle_event(). */
	struct inode inode; / either the inode the event happened to or its parent */
	u32 mask; /* the type of access, bitwise OR for FS_* event types */
	};

	/*
	* A group is a "thing" that wants to receive notification about filesystem
	* events. The mask holds the subset of event types this group cares about.
	* refcnt on a group is up to the implementor and at any moment if it goes 0
	* everything will be cleaned up.
	*/
	struct fsnotify_group {
	/*
	* How the refcnt is used is up to each group. When the refcnt hits 0
	* fsnotify will clean up all of the resources associated with this group.
	* As an example, the dnotify group will always have a refcnt=1 and that
	* will never change. Inotify, on the other hand, has a group per
	* inotify_init() and the refcnt will hit 0 only when that fd has been
	* closed.
	*/
	atomic_t refcnt; /* things with interest in this group */

	const struct fsnotify_ops ops; / how this group handles things */

	/* needed to send notification to userspace */
	struct mutex notification_mutex; /* protect the notification_list */
	struct list_head notification_list; /* list of event_holder this group needs to send to userspace */
	wait_queue_head_t notification_waitq; /* read() on the notification file blocks on this waitq */
	unsigned int q_len; /* events on the queue */
	unsigned int max_events; /* maximum events allowed on the list */
	/*
	* Valid fsnotify group priorities. Events are send in order from highest
	* priority to lowest priority. We default to the lowest priority.
	*/
	#define FS_PRIO_0 0 /* normal notifiers, no permissions */
	#define FS_PRIO_1 1 /* fanotify content based access control */
	#define FS_PRIO_2 2 /* fanotify pre-content access */
	unsigned int priority;

	/* stores all fastpath marks assoc with this group so they can be cleaned on unregister */
	struct mutex mark_mutex; /* protect marks_list */
	atomic_t num_marks; /* 1 for each mark and 1 for not being
	* past the point of no return when freeing
	* a group */
	struct list_head marks_list; /* all inode marks for this group */

	struct fasync_struct fsn_fa; / async notification */

	struct fsnotify_event overflow_event; / Event we queue when the
	* notification list is too
	* full */

	/* groups can define private fields here or use the void private /
	union {
	void *private;
	#ifdef CONFIG_INOTIFY_USER
	struct inotify_group_private_data {
	spinlock_t idr_lock;
	struct idr idr;
	struct user_struct *user;
	} inotify_data;
	#endif
	#ifdef CONFIG_FANOTIFY
	struct fanotify_group_private_data {
	#ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
	/* allows a group to block waiting for a userspace response */
	spinlock_t access_lock;
	struct list_head access_list;
	wait_queue_head_t access_waitq;
	atomic_t bypass_perm;
	#endif /* CONFIG_FANOTIFY_ACCESS_PERMISSIONS */
	int f_flags;
	unsigned int max_marks;
	struct user_struct *user;
	} fanotify_data;
	#endif /* CONFIG_FANOTIFY */
	};
	};

	/* when calling fsnotify tell it if the data is a path or inode */
	#define FSNOTIFY_EVENT_NONE 0
	#define FSNOTIFY_EVENT_PATH 1
	#define FSNOTIFY_EVENT_INODE 2

	/*
	* a mark is simply an object attached to an in core inode which allows an
	* fsnotify listener to indicate they are either no longer interested in events
	* of a type matching mask or only interested in those events.
	*
	* these are flushed when an inode is evicted from core and may be flushed
	* when the inode is modified (as seen by fsnotify_access). Some fsnotify users
	* (such as dnotify) will flush these when the open fd is closed and not at
	* inode eviction or modification.
	*/
	struct fsnotify_mark {
	__u32 mask; /* mask this mark is for */
	/* we hold ref for each i_list and g_list. also one ref for each 'thing'
	* in kernel that found and may be using this mark. */
	atomic_t refcnt; /* active things looking at this mark */
	struct fsnotify_group group; / group this mark is for */
	struct list_head g_list; /* list of marks by group->i_fsnotify_marks
	* Also reused for queueing mark into
	* destroy_list when it's waiting for
	* the end of SRCU period before it can
	* be freed */
	spinlock_t lock; /* protect group and inode */
	struct hlist_node obj_list; /* list of marks for inode / vfsmount */
	struct list_head free_list; /* tmp list used when freeing this mark */
	union {
	struct inode inode; / inode this mark is associated with */
	struct vfsmount mnt; / vfsmount this mark is associated with */
	};
	__u32 ignored_mask; /* events types to ignore */
	#define FSNOTIFY_MARK_FLAG_INODE 0x01
	#define FSNOTIFY_MARK_FLAG_VFSMOUNT 0x02
	#define FSNOTIFY_MARK_FLAG_OBJECT_PINNED 0x04
	#define FSNOTIFY_MARK_FLAG_IGNORED_SURV_MODIFY 0x08
	#define FSNOTIFY_MARK_FLAG_ALIVE 0x10
	unsigned int flags; /* vfsmount or inode mark? */
	void (free_mark)(struct fsnotify_mark mark); /* called on final put+free */
	};

	#ifdef CONFIG_FSNOTIFY

	/* called from the vfs helpers */

	/* main fsnotify call to send events */
	extern int fsnotify(struct inode to_tell, __u32 mask, void data, int data_is,
	const unsigned char *name, u32 cookie);
	extern int __fsnotify_parent(struct path path, struct dentry dentry, __u32 mask);
	extern void __fsnotify_inode_delete(struct inode *inode);
	extern void __fsnotify_vfsmount_delete(struct vfsmount *mnt);
	extern u32 fsnotify_get_cookie(void);

	static inline int fsnotify_inode_watches_children(struct inode *inode)
	{
	/* FS_EVENT_ON_CHILD is set if the inode may care */
	if (!(inode->i_fsnotify_mask & FS_EVENT_ON_CHILD))
	return 0;
	/* this inode might care about child events, does it care about the
	* specific set of events that can happen on a child? */
	return inode->i_fsnotify_mask & FS_EVENTS_POSS_ON_CHILD;
	}

	/*
	* Update the dentry with a flag indicating the interest of its parent to receive
	* filesystem events when those events happens to this dentry->d_inode.
	*/
	static inline void __fsnotify_update_dcache_flags(struct dentry *dentry)
	{
	struct dentry *parent;

	assert_spin_locked(&dentry->d_lock);

	/*
	* Serialisation of setting PARENT_WATCHED on the dentries is provided
	* by d_lock. If inotify_inode_watched changes after we have taken
	* d_lock, the following __fsnotify_update_child_dentry_flags call will
	* find our entry, so it will spin until we complete here, and update
	* us with the new state.
	*/
	parent = dentry->d_parent;
	if (parent->d_inode && fsnotify_inode_watches_children(parent->d_inode))
	dentry->d_flags \|= DCACHE_FSNOTIFY_PARENT_WATCHED;
	else
	dentry->d_flags &= ~DCACHE_FSNOTIFY_PARENT_WATCHED;
	}

	/*
	* fsnotify_d_instantiate - instantiate a dentry for inode
	*/
	static inline void __fsnotify_d_instantiate(struct dentry dentry, struct inode inode)
	{
	if (!inode)
	return;

	spin_lock(&dentry->d_lock);
	__fsnotify_update_dcache_flags(dentry);
	spin_unlock(&dentry->d_lock);
	}

	/* called from fsnotify listeners, such as fanotify or dnotify */

	/* create a new group */
	extern struct fsnotify_group fsnotify_alloc_group(const struct fsnotify_ops ops);
	/* get reference to a group */
	extern void fsnotify_get_group(struct fsnotify_group *group);
	/* drop reference on a group from fsnotify_alloc_group */
	extern void fsnotify_put_group(struct fsnotify_group *group);
	/* destroy group */
	extern void fsnotify_destroy_group(struct fsnotify_group *group);
	/* fasync handler function */
	extern int fsnotify_fasync(int fd, struct file *file, int on);
	/* Free event from memory */
	extern void fsnotify_destroy_event(struct fsnotify_group *group,
	struct fsnotify_event *event);
	/* attach the event to the group notification queue */
	extern int fsnotify_add_event(struct fsnotify_group *group,
	struct fsnotify_event *event,
	int (merge)(struct list_head ,
	struct fsnotify_event *));
	/* Remove passed event from groups notification queue */
	extern void fsnotify_remove_event(struct fsnotify_group group, struct fsnotify_event event);
	/* true if the group notification queue is empty */
	extern bool fsnotify_notify_queue_is_empty(struct fsnotify_group *group);
	/* return, but do not dequeue the first event on the notification queue */
	extern struct fsnotify_event fsnotify_peek_first_event(struct fsnotify_group group);
	/* return AND dequeue the first event on the notification queue */
	extern struct fsnotify_event fsnotify_remove_first_event(struct fsnotify_group group);

	/* functions used to manipulate the marks attached to inodes */

	/* run all marks associated with a vfsmount and update mnt->mnt_fsnotify_mask */
	extern void fsnotify_recalc_vfsmount_mask(struct vfsmount *mnt);
	/* run all marks associated with an inode and update inode->i_fsnotify_mask */
	extern void fsnotify_recalc_inode_mask(struct inode *inode);
	extern void fsnotify_init_mark(struct fsnotify_mark mark, void (free_mark)(struct fsnotify_mark *mark));
	/* find (and take a reference) to a mark associated with group and inode */
	extern struct fsnotify_mark fsnotify_find_inode_mark(struct fsnotify_group group, struct inode *inode);
	/* find (and take a reference) to a mark associated with group and vfsmount */
	extern struct fsnotify_mark fsnotify_find_vfsmount_mark(struct fsnotify_group group, struct vfsmount *mnt);
	/* copy the values from old into new */
	extern void fsnotify_duplicate_mark(struct fsnotify_mark new, struct fsnotify_mark old);
	/* set the ignored_mask of a mark */
	extern void fsnotify_set_mark_ignored_mask_locked(struct fsnotify_mark *mark, __u32 mask);
	/* set the mask of a mark (might pin the object into memory */
	extern void fsnotify_set_mark_mask_locked(struct fsnotify_mark *mark, __u32 mask);
	/* attach the mark to both the group and the inode */
	extern int fsnotify_add_mark(struct fsnotify_mark mark, struct fsnotify_group group,
	struct inode inode, struct vfsmount mnt, int allow_dups);
	extern int fsnotify_add_mark_locked(struct fsnotify_mark mark, struct fsnotify_group group,
	struct inode inode, struct vfsmount mnt, int allow_dups);
	/* given a group and a mark, flag mark to be freed when all references are dropped */
	extern void fsnotify_destroy_mark(struct fsnotify_mark *mark,
	struct fsnotify_group *group);
	extern void fsnotify_destroy_mark_locked(struct fsnotify_mark *mark,
	struct fsnotify_group *group);
	/* run all the marks in a group, and clear all of the vfsmount marks */
	extern void fsnotify_clear_vfsmount_marks_by_group(struct fsnotify_group *group);
	/* run all the marks in a group, and clear all of the inode marks */
	extern void fsnotify_clear_inode_marks_by_group(struct fsnotify_group *group);
	/* run all the marks in a group, and clear all of the marks where mark->flags & flags is true*/
	extern void fsnotify_clear_marks_by_group_flags(struct fsnotify_group *group, unsigned int flags);
	/* run all the marks in a group, and flag them to be freed */
	extern void fsnotify_clear_marks_by_group(struct fsnotify_group *group);
	extern void fsnotify_get_mark(struct fsnotify_mark *mark);
	extern void fsnotify_put_mark(struct fsnotify_mark *mark);
	extern void fsnotify_unmount_inodes(struct list_head *list);

	/* put here because inotify does some weird stuff when destroying watches */
	extern void fsnotify_init_event(struct fsnotify_event *event,
	struct inode *to_tell, u32 mask);

	#else

	static inline int fsnotify(struct inode to_tell, __u32 mask, void data, int data_is,
	const unsigned char *name, u32 cookie)
	{
	return 0;
	}

	static inline int __fsnotify_parent(struct path path, struct dentry dentry, __u32 mask)
	{
	return 0;
	}

	static inline void __fsnotify_inode_delete(struct inode *inode)
	{}

	static inline void __fsnotify_vfsmount_delete(struct vfsmount *mnt)
	{}

	static inline void __fsnotify_update_dcache_flags(struct dentry *dentry)
	{}

	static inline void __fsnotify_d_instantiate(struct dentry dentry, struct inode inode)
	{}

	static inline u32 fsnotify_get_cookie(void)
	{
	return 0;
	}

	static inline void fsnotify_unmount_inodes(struct list_head *list)
	{}

	#endif /* CONFIG_FSNOTIFY */

	#endif /* __KERNEL __ */

	#endif /* __LINUX_FSNOTIFY_BACKEND_H */