text: /*
   * 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 */
  