text: /* SPDX-License-Identifier: GPL-2.0 */
  #ifndef __LINUX_DCACHE_H
  #define __LINUX_DCACHE_H
  
  #include <linux/atomic.h>
  #include <linux/list.h>
  #include <linux/rculist.h>
  #include <linux/rculist_bl.h>
  #include <linux/spinlock.h>
  #include <linux/seqlock.h>
  #include <linux/cache.h>
  #include <linux/rcupdate.h>
  #include <linux/lockref.h>
  #include <linux/stringhash.h>
  #include <linux/wait.h>
  
  struct path;
  struct vfsmount;
  
  /*
   * linux/include/linux/dcache.h
   *
   * Dirent cache data structures
   *
   * (C) Copyright 1997 Thomas Schoebel-Theuer,
   * with heavy changes by Linus Torvalds
   */
  
  #define IS_ROOT(x) ((x) == (x)->d_parent)
  
  /* The hash is always the low bits of hash_len */
  #ifdef __LITTLE_ENDIAN
   #define HASH_LEN_DECLARE u32 hash; u32 len
   #define bytemask_from_count(cnt)	(~(~0ul << (cnt)*8))
  #else
   #define HASH_LEN_DECLARE u32 len; u32 hash
   #define bytemask_from_count(cnt)	(~(~0ul >> (cnt)*8))
  #endif
  
  /*
   * "quick string" -- eases parameter passing, but more importantly
   * saves "metadata" about the string (ie length and the hash).
   *
   * hash comes first so it snuggles against d_parent in the
   * dentry.
   */
  struct qstr {
  	union {
  		struct {
  			HASH_LEN_DECLARE;
  		};
  		u64 hash_len;
  	};
  	const unsigned char *name;
  };
  
  #define QSTR_INIT(n,l) { { { .len = l } }, .name = n }
  
  extern const struct qstr empty_name;
  extern const struct qstr slash_name;
  
  struct dentry_stat_t {
  	long nr_dentry;
  	long nr_unused;
  	long age_limit;		/* age in seconds */
  	long want_pages;	/* pages requested by system */
  	long nr_negative;	/* # of unused negative dentries */
  	long dummy;		/* Reserved for future use */
  };
  extern struct dentry_stat_t dentry_stat;
  
  /*
   * Try to keep struct dentry aligned on 64 byte cachelines (this will
   * give reasonable cacheline footprint with larger lines without the
   * large memory footprint increase).
   */
  #ifdef CONFIG_64BIT
  # define DNAME_INLINE_LEN 32 /* 192 bytes */
  #else
  # ifdef CONFIG_SMP
  #  define DNAME_INLINE_LEN 36 /* 128 bytes */
  # else
  #  define DNAME_INLINE_LEN 40 /* 128 bytes */
  # endif
  #endif
  
  #define d_lock	d_lockref.lock
  
  struct dentry {
  	/* RCU lookup touched fields */
  	unsigned int d_flags;		/* protected by d_lock */
  	seqcount_t d_seq;		/* per dentry seqlock */
  	struct hlist_bl_node d_hash;	/* lookup hash list */
  	struct dentry *d_parent;	/* parent directory */
  	struct qstr d_name;
  	struct inode *d_inode;		/* Where the name belongs to - NULL is
  					 * negative */
  	unsigned char d_iname[DNAME_INLINE_LEN];	/* small names */
  
  	/* Ref lookup also touches following */
  	struct lockref d_lockref;	/* per-dentry lock and refcount */
  	const struct dentry_operations *d_op;
  	struct super_block *d_sb;	/* The root of the dentry tree */
  	unsigned long d_time;		/* used by d_revalidate */
  	void *d_fsdata;			/* fs-specific data */
  
  	union {
  		struct list_head d_lru;		/* LRU list */
  		wait_queue_head_t *d_wait;	/* in-lookup ones only */
  	};
  	struct list_head d_child;	/* child of parent list */
  	struct list_head d_subdirs;	/* our children */
  	/*
  	 * d_alias and d_rcu can share memory
  	 */
  	union {
  		struct hlist_node d_alias;	/* inode alias list */
  		struct hlist_bl_node d_in_lookup_hash;	/* only for in-lookup ones */
  	 	struct rcu_head d_rcu;
  	} d_u;
  } __randomize_layout;
  
  /*
   * dentry->d_lock spinlock nesting subclasses:
   *
   * 0: normal
   * 1: nested
   */
  enum dentry_d_lock_class
  {
  	DENTRY_D_LOCK_NORMAL, /* implicitly used by plain spin_lock() APIs. */
  	DENTRY_D_LOCK_NESTED
  };
  
  struct dentry_operations {
  	int (*d_revalidate)(struct dentry *, unsigned int);
  	int (*d_weak_revalidate)(struct dentry *, unsigned int);
  	int (*d_hash)(const struct dentry *, struct qstr *);
  	int (*d_compare)(const struct dentry *,
  			unsigned int, const char *, const struct qstr *);
  	int (*d_delete)(const struct dentry *);
  	int (*d_init)(struct dentry *);
  	void (*d_release)(struct dentry *);
  	void (*d_prune)(struct dentry *);
  	void (*d_iput)(struct dentry *, struct inode *);
  	char *(*d_dname)(struct dentry *, char *, int);
  	struct vfsmount *(*d_automount)(struct path *);
  	int (*d_manage)(const struct path *, bool);
  	struct dentry *(*d_real)(struct dentry *, const struct inode *);
  } ____cacheline_aligned;
  
  /*
   * Locking rules for dentry_operations callbacks are to be found in
   * Documentation/filesystems/locking.rst. Keep it updated!
   *
   * FUrther descriptions are found in Documentation/filesystems/vfs.rst.
   * Keep it updated too!
   */
  
  /* d_flags entries */
  #define DCACHE_OP_HASH			0x00000001
  #define DCACHE_OP_COMPARE		0x00000002
  #define DCACHE_OP_REVALIDATE		0x00000004
  #define DCACHE_OP_DELETE		0x00000008
  #define DCACHE_OP_PRUNE			0x00000010
  
  #define	DCACHE_DISCONNECTED		0x00000020
       /* This dentry is possibly not currently connected to the dcache tree, in
        * which case its parent will either be itself, or will have this flag as
        * well.  nfsd will not use a dentry with this bit set, but will first
        * endeavour to clear the bit either by discovering that it is connected,
        * or by performing lookup operations.   Any filesystem which supports
        * nfsd_operations MUST have a lookup function which, if it finds a
        * directory inode with a DCACHE_DISCONNECTED dentry, will d_move that
        * dentry into place and return that dentry rather than the passed one,
        * typically using d_splice_alias. */
  
  #define DCACHE_REFERENCED		0x00000040 /* Recently used, don't discard. */
  
  #define DCACHE_DONTCACHE		0x00000080 /* Purge from memory on final dput() */
  
  #define DCACHE_CANT_MOUNT		0x00000100
  #define DCACHE_GENOCIDE			0x00000200
  #define DCACHE_SHRINK_LIST		0x00000400
  
  #define DCACHE_OP_WEAK_REVALIDATE	0x00000800
  
  #define DCACHE_NFSFS_RENAMED		0x00001000
       /* this dentry has been "silly renamed" and has to be deleted on the last
        * dput() */
  #define DCACHE_COOKIE			0x00002000 /* For use by dcookie subsystem */
  #define DCACHE_FSNOTIFY_PARENT_WATCHED	0x00004000
       /* Parent inode is watched by some fsnotify listener */
  
  #define DCACHE_DENTRY_KILLED		0x00008000
  
  #define DCACHE_MOUNTED			0x00010000 /* is a mountpoint */
  #define DCACHE_NEED_AUTOMOUNT		0x00020000 /* handle automount on this dir */
  #define DCACHE_MANAGE_TRANSIT		0x00040000 /* manage transit from this dirent */
  #define DCACHE_MANAGED_DENTRY \
  	(DCACHE_MOUNTED|DCACHE_NEED_AUTOMOUNT|DCACHE_MANAGE_TRANSIT)
  
  #define DCACHE_LRU_LIST			0x00080000
  
  #define DCACHE_ENTRY_TYPE		0x00700000
  #define DCACHE_MISS_TYPE		0x00000000 /* Negative dentry (maybe fallthru to nowhere) */
  #define DCACHE_WHITEOUT_TYPE		0x00100000 /* Whiteout dentry (stop pathwalk) */
  #define DCACHE_DIRECTORY_TYPE		0x00200000 /* Normal directory */
  #define DCACHE_AUTODIR_TYPE		0x00300000 /* Lookupless directory (presumed automount) */
  #define DCACHE_REGULAR_TYPE		0x00400000 /* Regular file type (or fallthru to such) */
  #define DCACHE_SPECIAL_TYPE		0x00500000 /* Other file type (or fallthru to such) */
  #define DCACHE_SYMLINK_TYPE		0x00600000 /* Symlink (or fallthru to such) */
  
  #define DCACHE_MAY_FREE			0x00800000
  #define DCACHE_FALLTHRU			0x01000000 /* Fall through to lower layer */
  #define DCACHE_ENCRYPTED_NAME		0x02000000 /* Encrypted name (dir key was unavailable) */
  #define DCACHE_OP_REAL			0x04000000
  
  #define DCACHE_PAR_LOOKUP		0x10000000 /* being looked up (with parent locked shared) */
  #define DCACHE_DENTRY_CURSOR		0x20000000
  #define DCACHE_NORCU			0x40000000 /* No RCU delay for freeing */
  
  extern seqlock_t rename_lock;
  
  /*
   * These are the low-level FS interfaces to the dcache..
   */
  extern void d_instantiate(struct dentry *, struct inode *);
  extern void d_instantiate_new(struct dentry *, struct inode *);
  extern struct dentry * d_instantiate_unique(struct dentry *, struct inode *);
  extern struct dentry * d_instantiate_anon(struct dentry *, struct inode *);
  extern void __d_drop(struct dentry *dentry);
  extern void d_drop(struct dentry *dentry);
  extern void d_delete(struct dentry *);
  extern void d_set_d_op(struct dentry *dentry, const struct dentry_operations *op);
  
  /* allocate/de-allocate */
  extern struct dentry * d_alloc(struct dentry *, const struct qstr *);
  extern struct dentry * d_alloc_anon(struct super_block *);
  extern struct dentry * d_alloc_parallel(struct dentry *, const struct qstr *,
  					wait_queue_head_t *);
  extern struct dentry * d_splice_alias(struct inode *, struct dentry *);
  extern struct dentry * d_add_ci(struct dentry *, struct inode *, struct qstr *);
  extern struct dentry * d_exact_alias(struct dentry *, struct inode *);
  extern struct dentry *d_find_any_alias(struct inode *inode);
  extern struct dentry * d_obtain_alias(struct inode *);
  extern struct dentry * d_obtain_root(struct inode *);
  extern void shrink_dcache_sb(struct super_block *);
  extern void shrink_dcache_parent(struct dentry *);
  extern void shrink_dcache_for_umount(struct super_block *);
  extern void d_invalidate(struct dentry *);
  
  /* only used at mount-time */
  extern struct dentry * d_make_root(struct inode *);
  
  /* <clickety>-<click> the ramfs-type tree */
  extern void d_genocide(struct dentry *);
  
  extern void d_tmpfile(struct dentry *, struct inode *);
  
  extern struct dentry *d_find_alias(struct inode *);
  extern void d_prune_aliases(struct inode *);
  
  /* test whether we have any submounts in a subdir tree */
  extern int path_has_submounts(const struct path *);
  
  /*
   * This adds the entry to the hash queues.
   */
  extern void d_rehash(struct dentry *);
   
  extern void d_add(struct dentry *, struct inode *);
  
  /* used for rename() and baskets */
  extern void d_move(struct dentry *, struct dentry *);
  extern void d_exchange(struct dentry *, struct dentry *);
  extern struct dentry *d_ancestor(struct dentry *, struct dentry *);
  
  /* appendix may either be NULL or be used for transname suffixes */
  extern struct dentry *d_lookup(const struct dentry *, const struct qstr *);
  extern struct dentry *d_hash_and_lookup(struct dentry *, struct qstr *);
  extern struct dentry *__d_lookup(const struct dentry *, const struct qstr *);
  extern struct dentry *__d_lookup_rcu(const struct dentry *parent,
  				const struct qstr *name, unsigned *seq);
  
  static inline unsigned d_count(const struct dentry *dentry)
  {
  	return dentry->d_lockref.count;
  }
  
  /*
   * helper function for dentry_operations.d_dname() members
   */
  extern __printf(4, 5)
  char *dynamic_dname(struct dentry *, char *, int, const char *, ...);
  
  extern char *__d_path(const struct path *, const struct path *, char *, int);
  extern char *d_absolute_path(const struct path *, char *, int);
  extern char *d_path(const struct path *, char *, int);
  extern char *dentry_path_raw(struct dentry *, char *, int);
  extern char *dentry_path(struct dentry *, char *, int);
  
  /* Allocation counts.. */
  
  /**
   *	dget, dget_dlock -	get a reference to a dentry
   *	@dentry: dentry to get a reference to
   *
   *	Given a dentry or %NULL pointer increment the reference count
   *	if appropriate and return the dentry. A dentry will not be 
   *	destroyed when it has references.
   */
  static inline struct dentry *dget_dlock(struct dentry *dentry)
  {
  	if (dentry)
  		dentry->d_lockref.count++;
  	return dentry;
  }
  
  static inline struct dentry *dget(struct dentry *dentry)
  {
  	if (dentry)
  		lockref_get(&dentry->d_lockref);
  	return dentry;
  }
  
  extern struct dentry *dget_parent(struct dentry *dentry);
  
  /**
   *	d_unhashed -	is dentry hashed
   *	@dentry: entry to check
   *
   *	Returns true if the dentry passed is not currently hashed.
   */
   
  static inline int d_unhashed(const struct dentry *dentry)
  {
  	return hlist_bl_unhashed(&dentry->d_hash);
  }
  
  static inline int d_unlinked(const struct dentry *dentry)
  {
  	return d_unhashed(dentry) && !IS_ROOT(dentry);
  }
  
  static inline int cant_mount(const struct dentry *dentry)
  {
  	return (dentry->d_flags & DCACHE_CANT_MOUNT);
  }
  
  static inline void dont_mount(struct dentry *dentry)
  {
  	spin_lock(&dentry->d_lock);
  	dentry->d_flags |= DCACHE_CANT_MOUNT;
  	spin_unlock(&dentry->d_lock);
  }
  
  extern void __d_lookup_done(struct dentry *);
  
  static inline int d_in_lookup(const struct dentry *dentry)
  {
  	return dentry->d_flags & DCACHE_PAR_LOOKUP;
  }
  
  static inline void d_lookup_done(struct dentry *dentry)
  {
  	if (unlikely(d_in_lookup(dentry))) {
  		spin_lock(&dentry->d_lock);
  		__d_lookup_done(dentry);
  		spin_unlock(&dentry->d_lock);
  	}
  }
  
  extern void dput(struct dentry *);
  
  static inline bool d_managed(const struct dentry *dentry)
  {
  	return dentry->d_flags & DCACHE_MANAGED_DENTRY;
  }
  
  static inline bool d_mountpoint(const struct dentry *dentry)
  {
  	return dentry->d_flags & DCACHE_MOUNTED;
  }
  
  /*
   * Directory cache entry type accessor functions.
   */
  static inline unsigned __d_entry_type(const struct dentry *dentry)
  {
  	return dentry->d_flags & DCACHE_ENTRY_TYPE;
  }
  
  static inline bool d_is_miss(const struct dentry *dentry)
  {
  	return __d_entry_type(dentry) == DCACHE_MISS_TYPE;
  }
  
  static inline bool d_is_whiteout(const struct dentry *dentry)
  {
  	return __d_entry_type(dentry) == DCACHE_WHITEOUT_TYPE;
  }
  
  static inline bool d_can_lookup(const struct dentry *dentry)
  {
  	return __d_entry_type(dentry) == DCACHE_DIRECTORY_TYPE;
  }
  
  static inline bool d_is_autodir(const struct dentry *dentry)
  {
  	return __d_entry_type(dentry) == DCACHE_AUTODIR_TYPE;
  }
  
  static inline bool d_is_dir(const struct dentry *dentry)
  {
  	return d_can_lookup(dentry) || d_is_autodir(dentry);
  }
  
  static inline bool d_is_symlink(const struct dentry *dentry)
  {
  	return __d_entry_type(dentry) == DCACHE_SYMLINK_TYPE;
  }
  
  static inline bool d_is_reg(const struct dentry *dentry)
  {
  	return __d_entry_type(dentry) == DCACHE_REGULAR_TYPE;
  }
  
  static inline bool d_is_special(const struct dentry *dentry)
  {
  	return __d_entry_type(dentry) == DCACHE_SPECIAL_TYPE;
  }
  
  static inline bool d_is_file(const struct dentry *dentry)
  {
  	return d_is_reg(dentry) || d_is_special(dentry);
  }
  
  static inline bool d_is_negative(const struct dentry *dentry)
  {
  	// TODO: check d_is_whiteout(dentry) also.
  	return d_is_miss(dentry);
  }
  
  static inline bool d_flags_negative(unsigned flags)
  {
  	return (flags & DCACHE_ENTRY_TYPE) == DCACHE_MISS_TYPE;
  }
  
  static inline bool d_is_positive(const struct dentry *dentry)
  {
  	return !d_is_negative(dentry);
  }
  
  /**
   * d_really_is_negative - Determine if a dentry is really negative (ignoring fallthroughs)
   * @dentry: The dentry in question
   *
   * Returns true if the dentry represents either an absent name or a name that
   * doesn't map to an inode (ie. ->d_inode is NULL).  The dentry could represent
   * a true miss, a whiteout that isn't represented by a 0,0 chardev or a
   * fallthrough marker in an opaque directory.
   *
   * Note!  (1) This should be used *only* by a filesystem to examine its own
   * dentries.  It should not be used to look at some other filesystem's
   * dentries.  (2) It should also be used in combination with d_inode() to get
   * the inode.  (3) The dentry may have something attached to ->d_lower and the
   * type field of the flags may be set to something other than miss or whiteout.
   */
  static inline bool d_really_is_negative(const struct dentry *dentry)
  {
  	return dentry->d_inode == NULL;
  }
  
  /**
   * d_really_is_positive - Determine if a dentry is really positive (ignoring fallthroughs)
   * @dentry: The dentry in question
   *
   * Returns true if the dentry represents a name that maps to an inode
   * (ie. ->d_inode is not NULL).  The dentry might still represent a whiteout if
   * that is represented on medium as a 0,0 chardev.
   *
   * Note!  (1) This should be used *only* by a filesystem to examine its own
   * dentries.  It should not be used to look at some other filesystem's
   * dentries.  (2) It should also be used in combination with d_inode() to get
   * the inode.
   */
  static inline bool d_really_is_positive(const struct dentry *dentry)
  {
  	return dentry->d_inode != NULL;
  }
  
  static inline int simple_positive(const struct dentry *dentry)
  {
  	return d_really_is_positive(dentry) && !d_unhashed(dentry);
  }
  
  extern void d_set_fallthru(struct dentry *dentry);
  
  static inline bool d_is_fallthru(const struct dentry *dentry)
  {
  	return dentry->d_flags & DCACHE_FALLTHRU;
  }
  
  
  extern int sysctl_vfs_cache_pressure;
  
  static inline unsigned long vfs_pressure_ratio(unsigned long val)
  {
  	return mult_frac(val, sysctl_vfs_cache_pressure, 100);
  }
  
  /**
   * d_inode - Get the actual inode of this dentry
   * @dentry: The dentry to query
   *
   * This is the helper normal filesystems should use to get at their own inodes
   * in their own dentries and ignore the layering superimposed upon them.
   */
  static inline struct inode *d_inode(const struct dentry *dentry)
  {
  	return dentry->d_inode;
  }
  
  /**
   * d_inode_rcu - Get the actual inode of this dentry with READ_ONCE()
   * @dentry: The dentry to query
   *
   * This is the helper normal filesystems should use to get at their own inodes
   * in their own dentries and ignore the layering superimposed upon them.
   */
  static inline struct inode *d_inode_rcu(const struct dentry *dentry)
  {
  	return READ_ONCE(dentry->d_inode);
  }
  
  /**
   * d_backing_inode - Get upper or lower inode we should be using
   * @upper: The upper layer
   *
   * This is the helper that should be used to get at the inode that will be used
   * if this dentry were to be opened as a file.  The inode may be on the upper
   * dentry or it may be on a lower dentry pinned by the upper.
   *
   * Normal filesystems should not use this to access their own inodes.
   */
  static inline struct inode *d_backing_inode(const struct dentry *upper)
  {
  	struct inode *inode = upper->d_inode;
  
  	return inode;
  }
  
  /**
   * d_backing_dentry - Get upper or lower dentry we should be using
   * @upper: The upper layer
   *
   * This is the helper that should be used to get the dentry of the inode that
   * will be used if this dentry were opened as a file.  It may be the upper
   * dentry or it may be a lower dentry pinned by the upper.
   *
   * Normal filesystems should not use this to access their own dentries.
   */
  static inline struct dentry *d_backing_dentry(struct dentry *upper)
  {
  	return upper;
  }
  
  /**
   * d_real - Return the real dentry
   * @dentry: the dentry to query
   * @inode: inode to select the dentry from multiple layers (can be NULL)
   *
   * If dentry is on a union/overlay, then return the underlying, real dentry.
   * Otherwise return the dentry itself.
   *
   * See also: Documentation/filesystems/vfs.rst
   */
  static inline struct dentry *d_real(struct dentry *dentry,
  				    const struct inode *inode)
  {
  	if (unlikely(dentry->d_flags & DCACHE_OP_REAL))
  		return dentry->d_op->d_real(dentry, inode);
  	else
  		return dentry;
  }
  
  /**
   * d_real_inode - Return the real inode
   * @dentry: The dentry to query
   *
   * If dentry is on a union/overlay, then return the underlying, real inode.
   * Otherwise return d_inode().
   */
  static inline struct inode *d_real_inode(const struct dentry *dentry)
  {
  	/* This usage of d_real() results in const dentry */
  	return d_backing_inode(d_real((struct dentry *) dentry, NULL));
  }
  
  struct name_snapshot {
  	struct qstr name;
  	unsigned char inline_name[DNAME_INLINE_LEN];
  };
  void take_dentry_name_snapshot(struct name_snapshot *, struct dentry *);
  void release_dentry_name_snapshot(struct name_snapshot *);
  
  #endif	/* __LINUX_DCACHE_H */
  