1  /* SPDX-License-Identifier: GPL-2.0 */
2  #ifndef __LINUX_DCACHE_H
3  #define __LINUX_DCACHE_H
4  
5  #include <linux/atomic.h>
6  #include <linux/list.h>
7  #include <linux/math.h>
8  #include <linux/rculist.h>
9  #include <linux/rculist_bl.h>
10  #include <linux/spinlock.h>
11  #include <linux/seqlock.h>
12  #include <linux/cache.h>
13  #include <linux/rcupdate.h>
14  #include <linux/lockref.h>
15  #include <linux/stringhash.h>
16  #include <linux/wait.h>
17  
18  struct path;
19  struct file;
20  struct vfsmount;
21  
22  /*
23   * linux/include/linux/dcache.h
24   *
25   * Dirent cache data structures
26   *
27   * (C) Copyright 1997 Thomas Schoebel-Theuer,
28   * with heavy changes by Linus Torvalds
29   */
30  
31  #define IS_ROOT(x) ((x) == (x)->d_parent)
32  
33  /* The hash is always the low bits of hash_len */
34  #ifdef __LITTLE_ENDIAN
35   #define HASH_LEN_DECLARE u32 hash; u32 len
36   #define bytemask_from_count(cnt)	(~(~0ul << (cnt)*8))
37  #else
38   #define HASH_LEN_DECLARE u32 len; u32 hash
39   #define bytemask_from_count(cnt)	(~(~0ul >> (cnt)*8))
40  #endif
41  
42  /*
43   * "quick string" -- eases parameter passing, but more importantly
44   * saves "metadata" about the string (ie length and the hash).
45   *
46   * hash comes first so it snuggles against d_parent in the
47   * dentry.
48   */
49  struct qstr {
50  	union {
51  		struct {
52  			HASH_LEN_DECLARE;
53  		};
54  		u64 hash_len;
55  	};
56  	const unsigned char *name;
57  };
58  
59  #define QSTR_INIT(n,l) { { { .len = l } }, .name = n }
60  #define QSTR(n) (struct qstr)QSTR_INIT(n, strlen(n))
61  
62  extern const struct qstr empty_name;
63  extern const struct qstr slash_name;
64  extern const struct qstr dotdot_name;
65  
66  /*
67   * Try to keep struct dentry aligned on 64 byte cachelines (this will
68   * give reasonable cacheline footprint with larger lines without the
69   * large memory footprint increase).
70   */
71  #ifdef CONFIG_64BIT
72  # define DNAME_INLINE_WORDS 5 /* 192 bytes */
73  #else
74  # ifdef CONFIG_SMP
75  #  define DNAME_INLINE_WORDS 9 /* 128 bytes */
76  # else
77  #  define DNAME_INLINE_WORDS 11 /* 128 bytes */
78  # endif
79  #endif
80  
81  #define DNAME_INLINE_LEN (DNAME_INLINE_WORDS*sizeof(unsigned long))
82  
83  union shortname_store {
84  	unsigned char string[DNAME_INLINE_LEN];
85  	unsigned long words[DNAME_INLINE_WORDS];
86  };
87  
88  #define d_lock	d_lockref.lock
89  #define d_iname d_shortname.string
90  
91  struct dentry {
92  	/* RCU lookup touched fields */
93  	unsigned int d_flags;		/* protected by d_lock */
94  	seqcount_spinlock_t d_seq;	/* per dentry seqlock */
95  	struct hlist_bl_node d_hash;	/* lookup hash list */
96  	struct dentry *d_parent;	/* parent directory */
97  	struct qstr d_name;
98  	struct inode *d_inode;		/* Where the name belongs to - NULL is
99  					 * negative */
100  	union shortname_store d_shortname;
101  	/* --- cacheline 1 boundary (64 bytes) was 32 bytes ago --- */
102  
103  	/* Ref lookup also touches following */
104  	const struct dentry_operations *d_op;
105  	struct super_block *d_sb;	/* The root of the dentry tree */
106  	unsigned long d_time;		/* used by d_revalidate */
107  	void *d_fsdata;			/* fs-specific data */
108  	/* --- cacheline 2 boundary (128 bytes) --- */
109  	struct lockref d_lockref;	/* per-dentry lock and refcount
110  					 * keep separate from RCU lookup area if
111  					 * possible!
112  					 */
113  
114  	union {
115  		struct list_head d_lru;		/* LRU list */
116  		wait_queue_head_t *d_wait;	/* in-lookup ones only */
117  	};
118  	struct hlist_node d_sib;	/* child of parent list */
119  	struct hlist_head d_children;	/* our children */
120  	/*
121  	 * d_alias and d_rcu can share memory
122  	 */
123  	union {
124  		struct hlist_node d_alias;	/* inode alias list */
125  		struct hlist_bl_node d_in_lookup_hash;	/* only for in-lookup ones */
126  	 	struct rcu_head d_rcu;
127  	} d_u;
128  };
129  
130  /*
131   * dentry->d_lock spinlock nesting subclasses:
132   *
133   * 0: normal
134   * 1: nested
135   */
136  enum dentry_d_lock_class
137  {
138  	DENTRY_D_LOCK_NORMAL, /* implicitly used by plain spin_lock() APIs. */
139  	DENTRY_D_LOCK_NESTED
140  };
141  
142  enum d_real_type {
143  	D_REAL_DATA,
144  	D_REAL_METADATA,
145  };
146  
147  struct dentry_operations {
148  	int (*d_revalidate)(struct inode *, const struct qstr *,
149  			    struct dentry *, unsigned int);
150  	int (*d_weak_revalidate)(struct dentry *, unsigned int);
151  	int (*d_hash)(const struct dentry *, struct qstr *);
152  	int (*d_compare)(const struct dentry *,
153  			unsigned int, const char *, const struct qstr *);
154  	int (*d_delete)(const struct dentry *);
155  	int (*d_init)(struct dentry *);
156  	void (*d_release)(struct dentry *);
157  	void (*d_prune)(struct dentry *);
158  	void (*d_iput)(struct dentry *, struct inode *);
159  	char *(*d_dname)(struct dentry *, char *, int);
160  	struct vfsmount *(*d_automount)(struct path *);
161  	int (*d_manage)(const struct path *, bool);
162  	struct dentry *(*d_real)(struct dentry *, enum d_real_type type);
163  	bool (*d_unalias_trylock)(const struct dentry *);
164  	void (*d_unalias_unlock)(const struct dentry *);
165  } ____cacheline_aligned;
166  
167  /*
168   * Locking rules for dentry_operations callbacks are to be found in
169   * Documentation/filesystems/locking.rst. Keep it updated!
170   *
171   * FUrther descriptions are found in Documentation/filesystems/vfs.rst.
172   * Keep it updated too!
173   */
174  
175  /* d_flags entries */
176  #define DCACHE_OP_HASH			BIT(0)
177  #define DCACHE_OP_COMPARE		BIT(1)
178  #define DCACHE_OP_REVALIDATE		BIT(2)
179  #define DCACHE_OP_DELETE		BIT(3)
180  #define DCACHE_OP_PRUNE			BIT(4)
181  
182  #define	DCACHE_DISCONNECTED		BIT(5)
183       /* This dentry is possibly not currently connected to the dcache tree, in
184        * which case its parent will either be itself, or will have this flag as
185        * well.  nfsd will not use a dentry with this bit set, but will first
186        * endeavour to clear the bit either by discovering that it is connected,
187        * or by performing lookup operations.   Any filesystem which supports
188        * nfsd_operations MUST have a lookup function which, if it finds a
189        * directory inode with a DCACHE_DISCONNECTED dentry, will d_move that
190        * dentry into place and return that dentry rather than the passed one,
191        * typically using d_splice_alias. */
192  
193  #define DCACHE_REFERENCED		BIT(6) /* Recently used, don't discard. */
194  
195  #define DCACHE_DONTCACHE		BIT(7) /* Purge from memory on final dput() */
196  
197  #define DCACHE_CANT_MOUNT		BIT(8)
198  #define DCACHE_GENOCIDE			BIT(9)
199  #define DCACHE_SHRINK_LIST		BIT(10)
200  
201  #define DCACHE_OP_WEAK_REVALIDATE	BIT(11)
202  
203  #define DCACHE_NFSFS_RENAMED		BIT(12)
204       /* this dentry has been "silly renamed" and has to be deleted on the last
205        * dput() */
206  #define DCACHE_FSNOTIFY_PARENT_WATCHED	BIT(14)
207       /* Parent inode is watched by some fsnotify listener */
208  
209  #define DCACHE_DENTRY_KILLED		BIT(15)
210  
211  #define DCACHE_MOUNTED			BIT(16) /* is a mountpoint */
212  #define DCACHE_NEED_AUTOMOUNT		BIT(17) /* handle automount on this dir */
213  #define DCACHE_MANAGE_TRANSIT		BIT(18) /* manage transit from this dirent */
214  #define DCACHE_MANAGED_DENTRY \
215  	(DCACHE_MOUNTED|DCACHE_NEED_AUTOMOUNT|DCACHE_MANAGE_TRANSIT)
216  
217  #define DCACHE_LRU_LIST			BIT(19)
218  
219  #define DCACHE_ENTRY_TYPE		(7 << 20) /* bits 20..22 are for storing type: */
220  #define DCACHE_MISS_TYPE		(0 << 20) /* Negative dentry */
221  #define DCACHE_WHITEOUT_TYPE		(1 << 20) /* Whiteout dentry (stop pathwalk) */
222  #define DCACHE_DIRECTORY_TYPE		(2 << 20) /* Normal directory */
223  #define DCACHE_AUTODIR_TYPE		(3 << 20) /* Lookupless directory (presumed automount) */
224  #define DCACHE_REGULAR_TYPE		(4 << 20) /* Regular file type */
225  #define DCACHE_SPECIAL_TYPE		(5 << 20) /* Other file type */
226  #define DCACHE_SYMLINK_TYPE		(6 << 20) /* Symlink */
227  
228  #define DCACHE_NOKEY_NAME		BIT(25) /* Encrypted name encoded without key */
229  #define DCACHE_OP_REAL			BIT(26)
230  
231  #define DCACHE_PAR_LOOKUP		BIT(28) /* being looked up (with parent locked shared) */
232  #define DCACHE_DENTRY_CURSOR		BIT(29)
233  #define DCACHE_NORCU			BIT(30) /* No RCU delay for freeing */
234  
235  extern seqlock_t rename_lock;
236  
237  /*
238   * These are the low-level FS interfaces to the dcache..
239   */
240  extern void d_instantiate(struct dentry *, struct inode *);
241  extern void d_instantiate_new(struct dentry *, struct inode *);
242  extern void __d_drop(struct dentry *dentry);
243  extern void d_drop(struct dentry *dentry);
244  extern void d_delete(struct dentry *);
245  extern void d_set_d_op(struct dentry *dentry, const struct dentry_operations *op);
246  
247  /* allocate/de-allocate */
248  extern struct dentry * d_alloc(struct dentry *, const struct qstr *);
249  extern struct dentry * d_alloc_anon(struct super_block *);
250  extern struct dentry * d_alloc_parallel(struct dentry *, const struct qstr *,
251  					wait_queue_head_t *);
252  extern struct dentry * d_splice_alias(struct inode *, struct dentry *);
253  extern struct dentry * d_add_ci(struct dentry *, struct inode *, struct qstr *);
254  extern bool d_same_name(const struct dentry *dentry, const struct dentry *parent,
255  			const struct qstr *name);
256  extern struct dentry * d_exact_alias(struct dentry *, struct inode *);
257  extern struct dentry *d_find_any_alias(struct inode *inode);
258  extern struct dentry * d_obtain_alias(struct inode *);
259  extern struct dentry * d_obtain_root(struct inode *);
260  extern void shrink_dcache_sb(struct super_block *);
261  extern void shrink_dcache_parent(struct dentry *);
262  extern void d_invalidate(struct dentry *);
263  
264  /* only used at mount-time */
265  extern struct dentry * d_make_root(struct inode *);
266  
267  extern void d_mark_tmpfile(struct file *, struct inode *);
268  extern void d_tmpfile(struct file *, struct inode *);
269  
270  extern struct dentry *d_find_alias(struct inode *);
271  extern void d_prune_aliases(struct inode *);
272  
273  extern struct dentry *d_find_alias_rcu(struct inode *);
274  
275  /* test whether we have any submounts in a subdir tree */
276  extern int path_has_submounts(const struct path *);
277  
278  /*
279   * This adds the entry to the hash queues.
280   */
281  extern void d_rehash(struct dentry *);
282  
283  extern void d_add(struct dentry *, struct inode *);
284  
285  /* used for rename() and baskets */
286  extern void d_move(struct dentry *, struct dentry *);
287  extern void d_exchange(struct dentry *, struct dentry *);
288  extern struct dentry *d_ancestor(struct dentry *, struct dentry *);
289  
290  extern struct dentry *d_lookup(const struct dentry *, const struct qstr *);
291  extern struct dentry *d_hash_and_lookup(struct dentry *, struct qstr *);
292  
d_count(const struct dentry * dentry)293  static inline unsigned d_count(const struct dentry *dentry)
294  {
295  	return dentry->d_lockref.count;
296  }
297  
298  ino_t d_parent_ino(struct dentry *dentry);
299  
300  /*
301   * helper function for dentry_operations.d_dname() members
302   */
303  extern __printf(3, 4)
304  char *dynamic_dname(char *, int, const char *, ...);
305  
306  extern char *__d_path(const struct path *, const struct path *, char *, int);
307  extern char *d_absolute_path(const struct path *, char *, int);
308  extern char *d_path(const struct path *, char *, int);
309  extern char *dentry_path_raw(const struct dentry *, char *, int);
310  extern char *dentry_path(const struct dentry *, char *, int);
311  
312  /* Allocation counts.. */
313  
314  /**
315   * dget_dlock -	get a reference to a dentry
316   * @dentry: dentry to get a reference to
317   *
318   * Given a live dentry, increment the reference count and return the dentry.
319   * Caller must hold @dentry->d_lock.  Making sure that dentry is alive is
320   * caller's resonsibility.  There are many conditions sufficient to guarantee
321   * that; e.g. anything with non-negative refcount is alive, so's anything
322   * hashed, anything positive, anyone's parent, etc.
323   */
dget_dlock(struct dentry * dentry)324  static inline struct dentry *dget_dlock(struct dentry *dentry)
325  {
326  	dentry->d_lockref.count++;
327  	return dentry;
328  }
329  
330  
331  /**
332   * dget - get a reference to a dentry
333   * @dentry: dentry to get a reference to
334   *
335   * Given a dentry or %NULL pointer increment the reference count
336   * if appropriate and return the dentry.  A dentry will not be
337   * destroyed when it has references.  Conversely, a dentry with
338   * no references can disappear for any number of reasons, starting
339   * with memory pressure.  In other words, that primitive is
340   * used to clone an existing reference; using it on something with
341   * zero refcount is a bug.
342   *
343   * NOTE: it will spin if @dentry->d_lock is held.  From the deadlock
344   * avoidance point of view it is equivalent to spin_lock()/increment
345   * refcount/spin_unlock(), so calling it under @dentry->d_lock is
346   * always a bug; so's calling it under ->d_lock on any of its descendents.
347   *
348   */
dget(struct dentry * dentry)349  static inline struct dentry *dget(struct dentry *dentry)
350  {
351  	if (dentry)
352  		lockref_get(&dentry->d_lockref);
353  	return dentry;
354  }
355  
356  extern struct dentry *dget_parent(struct dentry *dentry);
357  
358  /**
359   * d_unhashed - is dentry hashed
360   * @dentry: entry to check
361   *
362   * Returns true if the dentry passed is not currently hashed.
363   */
d_unhashed(const struct dentry * dentry)364  static inline int d_unhashed(const struct dentry *dentry)
365  {
366  	return hlist_bl_unhashed(&dentry->d_hash);
367  }
368  
d_unlinked(const struct dentry * dentry)369  static inline int d_unlinked(const struct dentry *dentry)
370  {
371  	return d_unhashed(dentry) && !IS_ROOT(dentry);
372  }
373  
cant_mount(const struct dentry * dentry)374  static inline int cant_mount(const struct dentry *dentry)
375  {
376  	return (dentry->d_flags & DCACHE_CANT_MOUNT);
377  }
378  
dont_mount(struct dentry * dentry)379  static inline void dont_mount(struct dentry *dentry)
380  {
381  	spin_lock(&dentry->d_lock);
382  	dentry->d_flags |= DCACHE_CANT_MOUNT;
383  	spin_unlock(&dentry->d_lock);
384  }
385  
386  extern void __d_lookup_unhash_wake(struct dentry *dentry);
387  
d_in_lookup(const struct dentry * dentry)388  static inline int d_in_lookup(const struct dentry *dentry)
389  {
390  	return dentry->d_flags & DCACHE_PAR_LOOKUP;
391  }
392  
d_lookup_done(struct dentry * dentry)393  static inline void d_lookup_done(struct dentry *dentry)
394  {
395  	if (unlikely(d_in_lookup(dentry)))
396  		__d_lookup_unhash_wake(dentry);
397  }
398  
399  extern void dput(struct dentry *);
400  
d_managed(const struct dentry * dentry)401  static inline bool d_managed(const struct dentry *dentry)
402  {
403  	return dentry->d_flags & DCACHE_MANAGED_DENTRY;
404  }
405  
d_mountpoint(const struct dentry * dentry)406  static inline bool d_mountpoint(const struct dentry *dentry)
407  {
408  	return dentry->d_flags & DCACHE_MOUNTED;
409  }
410  
411  /*
412   * Directory cache entry type accessor functions.
413   */
__d_entry_type(const struct dentry * dentry)414  static inline unsigned __d_entry_type(const struct dentry *dentry)
415  {
416  	return dentry->d_flags & DCACHE_ENTRY_TYPE;
417  }
418  
d_is_miss(const struct dentry * dentry)419  static inline bool d_is_miss(const struct dentry *dentry)
420  {
421  	return __d_entry_type(dentry) == DCACHE_MISS_TYPE;
422  }
423  
d_is_whiteout(const struct dentry * dentry)424  static inline bool d_is_whiteout(const struct dentry *dentry)
425  {
426  	return __d_entry_type(dentry) == DCACHE_WHITEOUT_TYPE;
427  }
428  
d_can_lookup(const struct dentry * dentry)429  static inline bool d_can_lookup(const struct dentry *dentry)
430  {
431  	return __d_entry_type(dentry) == DCACHE_DIRECTORY_TYPE;
432  }
433  
d_is_autodir(const struct dentry * dentry)434  static inline bool d_is_autodir(const struct dentry *dentry)
435  {
436  	return __d_entry_type(dentry) == DCACHE_AUTODIR_TYPE;
437  }
438  
d_is_dir(const struct dentry * dentry)439  static inline bool d_is_dir(const struct dentry *dentry)
440  {
441  	return d_can_lookup(dentry) || d_is_autodir(dentry);
442  }
443  
d_is_symlink(const struct dentry * dentry)444  static inline bool d_is_symlink(const struct dentry *dentry)
445  {
446  	return __d_entry_type(dentry) == DCACHE_SYMLINK_TYPE;
447  }
448  
d_is_reg(const struct dentry * dentry)449  static inline bool d_is_reg(const struct dentry *dentry)
450  {
451  	return __d_entry_type(dentry) == DCACHE_REGULAR_TYPE;
452  }
453  
d_is_special(const struct dentry * dentry)454  static inline bool d_is_special(const struct dentry *dentry)
455  {
456  	return __d_entry_type(dentry) == DCACHE_SPECIAL_TYPE;
457  }
458  
d_is_file(const struct dentry * dentry)459  static inline bool d_is_file(const struct dentry *dentry)
460  {
461  	return d_is_reg(dentry) || d_is_special(dentry);
462  }
463  
d_is_negative(const struct dentry * dentry)464  static inline bool d_is_negative(const struct dentry *dentry)
465  {
466  	// TODO: check d_is_whiteout(dentry) also.
467  	return d_is_miss(dentry);
468  }
469  
d_flags_negative(unsigned flags)470  static inline bool d_flags_negative(unsigned flags)
471  {
472  	return (flags & DCACHE_ENTRY_TYPE) == DCACHE_MISS_TYPE;
473  }
474  
d_is_positive(const struct dentry * dentry)475  static inline bool d_is_positive(const struct dentry *dentry)
476  {
477  	return !d_is_negative(dentry);
478  }
479  
480  /**
481   * d_really_is_negative - Determine if a dentry is really negative (ignoring fallthroughs)
482   * @dentry: The dentry in question
483   *
484   * Returns true if the dentry represents either an absent name or a name that
485   * doesn't map to an inode (ie. ->d_inode is NULL).  The dentry could represent
486   * a true miss, a whiteout that isn't represented by a 0,0 chardev or a
487   * fallthrough marker in an opaque directory.
488   *
489   * Note!  (1) This should be used *only* by a filesystem to examine its own
490   * dentries.  It should not be used to look at some other filesystem's
491   * dentries.  (2) It should also be used in combination with d_inode() to get
492   * the inode.  (3) The dentry may have something attached to ->d_lower and the
493   * type field of the flags may be set to something other than miss or whiteout.
494   */
d_really_is_negative(const struct dentry * dentry)495  static inline bool d_really_is_negative(const struct dentry *dentry)
496  {
497  	return dentry->d_inode == NULL;
498  }
499  
500  /**
501   * d_really_is_positive - Determine if a dentry is really positive (ignoring fallthroughs)
502   * @dentry: The dentry in question
503   *
504   * Returns true if the dentry represents a name that maps to an inode
505   * (ie. ->d_inode is not NULL).  The dentry might still represent a whiteout if
506   * that is represented on medium as a 0,0 chardev.
507   *
508   * Note!  (1) This should be used *only* by a filesystem to examine its own
509   * dentries.  It should not be used to look at some other filesystem's
510   * dentries.  (2) It should also be used in combination with d_inode() to get
511   * the inode.
512   */
d_really_is_positive(const struct dentry * dentry)513  static inline bool d_really_is_positive(const struct dentry *dentry)
514  {
515  	return dentry->d_inode != NULL;
516  }
517  
simple_positive(const struct dentry * dentry)518  static inline int simple_positive(const struct dentry *dentry)
519  {
520  	return d_really_is_positive(dentry) && !d_unhashed(dentry);
521  }
522  
523  extern int sysctl_vfs_cache_pressure;
524  
vfs_pressure_ratio(unsigned long val)525  static inline unsigned long vfs_pressure_ratio(unsigned long val)
526  {
527  	return mult_frac(val, sysctl_vfs_cache_pressure, 100);
528  }
529  
530  /**
531   * d_inode - Get the actual inode of this dentry
532   * @dentry: The dentry to query
533   *
534   * This is the helper normal filesystems should use to get at their own inodes
535   * in their own dentries and ignore the layering superimposed upon them.
536   */
d_inode(const struct dentry * dentry)537  static inline struct inode *d_inode(const struct dentry *dentry)
538  {
539  	return dentry->d_inode;
540  }
541  
542  /**
543   * d_inode_rcu - Get the actual inode of this dentry with READ_ONCE()
544   * @dentry: The dentry to query
545   *
546   * This is the helper normal filesystems should use to get at their own inodes
547   * in their own dentries and ignore the layering superimposed upon them.
548   */
d_inode_rcu(const struct dentry * dentry)549  static inline struct inode *d_inode_rcu(const struct dentry *dentry)
550  {
551  	return READ_ONCE(dentry->d_inode);
552  }
553  
554  /**
555   * d_backing_inode - Get upper or lower inode we should be using
556   * @upper: The upper layer
557   *
558   * This is the helper that should be used to get at the inode that will be used
559   * if this dentry were to be opened as a file.  The inode may be on the upper
560   * dentry or it may be on a lower dentry pinned by the upper.
561   *
562   * Normal filesystems should not use this to access their own inodes.
563   */
d_backing_inode(const struct dentry * upper)564  static inline struct inode *d_backing_inode(const struct dentry *upper)
565  {
566  	struct inode *inode = upper->d_inode;
567  
568  	return inode;
569  }
570  
571  /**
572   * d_real - Return the real dentry
573   * @dentry: the dentry to query
574   * @type: the type of real dentry (data or metadata)
575   *
576   * If dentry is on a union/overlay, then return the underlying, real dentry.
577   * Otherwise return the dentry itself.
578   *
579   * See also: Documentation/filesystems/vfs.rst
580   */
d_real(struct dentry * dentry,enum d_real_type type)581  static inline struct dentry *d_real(struct dentry *dentry, enum d_real_type type)
582  {
583  	if (unlikely(dentry->d_flags & DCACHE_OP_REAL))
584  		return dentry->d_op->d_real(dentry, type);
585  	else
586  		return dentry;
587  }
588  
589  /**
590   * d_real_inode - Return the real inode hosting the data
591   * @dentry: The dentry to query
592   *
593   * If dentry is on a union/overlay, then return the underlying, real inode.
594   * Otherwise return d_inode().
595   */
d_real_inode(const struct dentry * dentry)596  static inline struct inode *d_real_inode(const struct dentry *dentry)
597  {
598  	/* This usage of d_real() results in const dentry */
599  	return d_inode(d_real((struct dentry *) dentry, D_REAL_DATA));
600  }
601  
602  struct name_snapshot {
603  	struct qstr name;
604  	union shortname_store inline_name;
605  };
606  void take_dentry_name_snapshot(struct name_snapshot *, struct dentry *);
607  void release_dentry_name_snapshot(struct name_snapshot *);
608  
d_first_child(const struct dentry * dentry)609  static inline struct dentry *d_first_child(const struct dentry *dentry)
610  {
611  	return hlist_entry_safe(dentry->d_children.first, struct dentry, d_sib);
612  }
613  
d_next_sibling(const struct dentry * dentry)614  static inline struct dentry *d_next_sibling(const struct dentry *dentry)
615  {
616  	return hlist_entry_safe(dentry->d_sib.next, struct dentry, d_sib);
617  }
618  
619  #endif	/* __LINUX_DCACHE_H */
620