xref: /linux/include/linux/dcache.h (revision 592329e5e94e26080f4815c6cc6cd0f487a91064)
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(13)
207      /* Parent inode is watched by some fsnotify listener */
208 
209 #define DCACHE_DENTRY_KILLED		BIT(14)
210 
211 #define DCACHE_MOUNTED			BIT(15) /* is a mountpoint */
212 #define DCACHE_NEED_AUTOMOUNT		BIT(16) /* handle automount on this dir */
213 #define DCACHE_MANAGE_TRANSIT		BIT(17) /* 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(18)
218 
219 #define DCACHE_ENTRY_TYPE		(7 << 19) /* bits 19..21 are for storing type: */
220 #define DCACHE_MISS_TYPE		(0 << 19) /* Negative dentry */
221 #define DCACHE_WHITEOUT_TYPE		(1 << 19) /* Whiteout dentry (stop pathwalk) */
222 #define DCACHE_DIRECTORY_TYPE		(2 << 19) /* Normal directory */
223 #define DCACHE_AUTODIR_TYPE		(3 << 19) /* Lookupless directory (presumed automount) */
224 #define DCACHE_REGULAR_TYPE		(4 << 19) /* Regular file type */
225 #define DCACHE_SPECIAL_TYPE		(5 << 19) /* Other file type */
226 #define DCACHE_SYMLINK_TYPE		(6 << 19) /* Symlink */
227 
228 #define DCACHE_NOKEY_NAME		BIT(22) /* Encrypted name encoded without key */
229 #define DCACHE_OP_REAL			BIT(23)
230 
231 #define DCACHE_PAR_LOOKUP		BIT(24) /* being looked up (with parent locked shared) */
232 #define DCACHE_DENTRY_CURSOR		BIT(25)
233 #define DCACHE_NORCU			BIT(26) /* 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_find_any_alias(struct inode *inode);
257 extern struct dentry * d_obtain_alias(struct inode *);
258 extern struct dentry * d_obtain_root(struct inode *);
259 extern void shrink_dcache_sb(struct super_block *);
260 extern void shrink_dcache_parent(struct dentry *);
261 extern void d_invalidate(struct dentry *);
262 
263 /* only used at mount-time */
264 extern struct dentry * d_make_root(struct inode *);
265 
266 extern void d_mark_tmpfile(struct file *, struct inode *);
267 extern void d_tmpfile(struct file *, struct inode *);
268 
269 extern struct dentry *d_find_alias(struct inode *);
270 extern void d_prune_aliases(struct inode *);
271 
272 extern struct dentry *d_find_alias_rcu(struct inode *);
273 
274 /* test whether we have any submounts in a subdir tree */
275 extern int path_has_submounts(const struct path *);
276 
277 /*
278  * This adds the entry to the hash queues.
279  */
280 extern void d_rehash(struct dentry *);
281 
282 extern void d_add(struct dentry *, struct inode *);
283 
284 /* used for rename() and baskets */
285 extern void d_move(struct dentry *, struct dentry *);
286 extern void d_exchange(struct dentry *, struct dentry *);
287 extern struct dentry *d_ancestor(struct dentry *, struct dentry *);
288 
289 extern struct dentry *d_lookup(const struct dentry *, const struct qstr *);
290 extern struct dentry *d_hash_and_lookup(struct dentry *, struct qstr *);
291 
d_count(const struct dentry * dentry)292 static inline unsigned d_count(const struct dentry *dentry)
293 {
294 	return dentry->d_lockref.count;
295 }
296 
297 ino_t d_parent_ino(struct dentry *dentry);
298 
299 /*
300  * helper function for dentry_operations.d_dname() members
301  */
302 extern __printf(3, 4)
303 char *dynamic_dname(char *, int, const char *, ...);
304 
305 extern char *__d_path(const struct path *, const struct path *, char *, int);
306 extern char *d_absolute_path(const struct path *, char *, int);
307 extern char *d_path(const struct path *, char *, int);
308 extern char *dentry_path_raw(const struct dentry *, char *, int);
309 extern char *dentry_path(const struct dentry *, char *, int);
310 
311 /* Allocation counts.. */
312 
313 /**
314  * dget_dlock -	get a reference to a dentry
315  * @dentry: dentry to get a reference to
316  *
317  * Given a live dentry, increment the reference count and return the dentry.
318  * Caller must hold @dentry->d_lock.  Making sure that dentry is alive is
319  * caller's resonsibility.  There are many conditions sufficient to guarantee
320  * that; e.g. anything with non-negative refcount is alive, so's anything
321  * hashed, anything positive, anyone's parent, etc.
322  */
dget_dlock(struct dentry * dentry)323 static inline struct dentry *dget_dlock(struct dentry *dentry)
324 {
325 	dentry->d_lockref.count++;
326 	return dentry;
327 }
328 
329 
330 /**
331  * dget - get a reference to a dentry
332  * @dentry: dentry to get a reference to
333  *
334  * Given a dentry or %NULL pointer increment the reference count
335  * if appropriate and return the dentry.  A dentry will not be
336  * destroyed when it has references.  Conversely, a dentry with
337  * no references can disappear for any number of reasons, starting
338  * with memory pressure.  In other words, that primitive is
339  * used to clone an existing reference; using it on something with
340  * zero refcount is a bug.
341  *
342  * NOTE: it will spin if @dentry->d_lock is held.  From the deadlock
343  * avoidance point of view it is equivalent to spin_lock()/increment
344  * refcount/spin_unlock(), so calling it under @dentry->d_lock is
345  * always a bug; so's calling it under ->d_lock on any of its descendents.
346  *
347  */
dget(struct dentry * dentry)348 static inline struct dentry *dget(struct dentry *dentry)
349 {
350 	if (dentry)
351 		lockref_get(&dentry->d_lockref);
352 	return dentry;
353 }
354 
355 extern struct dentry *dget_parent(struct dentry *dentry);
356 
357 /**
358  * d_unhashed - is dentry hashed
359  * @dentry: entry to check
360  *
361  * Returns true if the dentry passed is not currently hashed.
362  */
d_unhashed(const struct dentry * dentry)363 static inline int d_unhashed(const struct dentry *dentry)
364 {
365 	return hlist_bl_unhashed(&dentry->d_hash);
366 }
367 
d_unlinked(const struct dentry * dentry)368 static inline int d_unlinked(const struct dentry *dentry)
369 {
370 	return d_unhashed(dentry) && !IS_ROOT(dentry);
371 }
372 
cant_mount(const struct dentry * dentry)373 static inline int cant_mount(const struct dentry *dentry)
374 {
375 	return (dentry->d_flags & DCACHE_CANT_MOUNT);
376 }
377 
dont_mount(struct dentry * dentry)378 static inline void dont_mount(struct dentry *dentry)
379 {
380 	spin_lock(&dentry->d_lock);
381 	dentry->d_flags |= DCACHE_CANT_MOUNT;
382 	spin_unlock(&dentry->d_lock);
383 }
384 
385 extern void __d_lookup_unhash_wake(struct dentry *dentry);
386 
d_in_lookup(const struct dentry * dentry)387 static inline int d_in_lookup(const struct dentry *dentry)
388 {
389 	return dentry->d_flags & DCACHE_PAR_LOOKUP;
390 }
391 
d_lookup_done(struct dentry * dentry)392 static inline void d_lookup_done(struct dentry *dentry)
393 {
394 	if (unlikely(d_in_lookup(dentry)))
395 		__d_lookup_unhash_wake(dentry);
396 }
397 
398 extern void dput(struct dentry *);
399 
d_managed(const struct dentry * dentry)400 static inline bool d_managed(const struct dentry *dentry)
401 {
402 	return dentry->d_flags & DCACHE_MANAGED_DENTRY;
403 }
404 
d_mountpoint(const struct dentry * dentry)405 static inline bool d_mountpoint(const struct dentry *dentry)
406 {
407 	return dentry->d_flags & DCACHE_MOUNTED;
408 }
409 
410 /*
411  * Directory cache entry type accessor functions.
412  */
__d_entry_type(const struct dentry * dentry)413 static inline unsigned __d_entry_type(const struct dentry *dentry)
414 {
415 	return dentry->d_flags & DCACHE_ENTRY_TYPE;
416 }
417 
d_is_miss(const struct dentry * dentry)418 static inline bool d_is_miss(const struct dentry *dentry)
419 {
420 	return __d_entry_type(dentry) == DCACHE_MISS_TYPE;
421 }
422 
d_is_whiteout(const struct dentry * dentry)423 static inline bool d_is_whiteout(const struct dentry *dentry)
424 {
425 	return __d_entry_type(dentry) == DCACHE_WHITEOUT_TYPE;
426 }
427 
d_can_lookup(const struct dentry * dentry)428 static inline bool d_can_lookup(const struct dentry *dentry)
429 {
430 	return __d_entry_type(dentry) == DCACHE_DIRECTORY_TYPE;
431 }
432 
d_is_autodir(const struct dentry * dentry)433 static inline bool d_is_autodir(const struct dentry *dentry)
434 {
435 	return __d_entry_type(dentry) == DCACHE_AUTODIR_TYPE;
436 }
437 
d_is_dir(const struct dentry * dentry)438 static inline bool d_is_dir(const struct dentry *dentry)
439 {
440 	return d_can_lookup(dentry) || d_is_autodir(dentry);
441 }
442 
d_is_symlink(const struct dentry * dentry)443 static inline bool d_is_symlink(const struct dentry *dentry)
444 {
445 	return __d_entry_type(dentry) == DCACHE_SYMLINK_TYPE;
446 }
447 
d_is_reg(const struct dentry * dentry)448 static inline bool d_is_reg(const struct dentry *dentry)
449 {
450 	return __d_entry_type(dentry) == DCACHE_REGULAR_TYPE;
451 }
452 
d_is_special(const struct dentry * dentry)453 static inline bool d_is_special(const struct dentry *dentry)
454 {
455 	return __d_entry_type(dentry) == DCACHE_SPECIAL_TYPE;
456 }
457 
d_is_file(const struct dentry * dentry)458 static inline bool d_is_file(const struct dentry *dentry)
459 {
460 	return d_is_reg(dentry) || d_is_special(dentry);
461 }
462 
d_is_negative(const struct dentry * dentry)463 static inline bool d_is_negative(const struct dentry *dentry)
464 {
465 	// TODO: check d_is_whiteout(dentry) also.
466 	return d_is_miss(dentry);
467 }
468 
d_flags_negative(unsigned flags)469 static inline bool d_flags_negative(unsigned flags)
470 {
471 	return (flags & DCACHE_ENTRY_TYPE) == DCACHE_MISS_TYPE;
472 }
473 
d_is_positive(const struct dentry * dentry)474 static inline bool d_is_positive(const struct dentry *dentry)
475 {
476 	return !d_is_negative(dentry);
477 }
478 
479 /**
480  * d_really_is_negative - Determine if a dentry is really negative (ignoring fallthroughs)
481  * @dentry: The dentry in question
482  *
483  * Returns true if the dentry represents either an absent name or a name that
484  * doesn't map to an inode (ie. ->d_inode is NULL).  The dentry could represent
485  * a true miss, a whiteout that isn't represented by a 0,0 chardev or a
486  * fallthrough marker in an opaque directory.
487  *
488  * Note!  (1) This should be used *only* by a filesystem to examine its own
489  * dentries.  It should not be used to look at some other filesystem's
490  * dentries.  (2) It should also be used in combination with d_inode() to get
491  * the inode.  (3) The dentry may have something attached to ->d_lower and the
492  * type field of the flags may be set to something other than miss or whiteout.
493  */
d_really_is_negative(const struct dentry * dentry)494 static inline bool d_really_is_negative(const struct dentry *dentry)
495 {
496 	return dentry->d_inode == NULL;
497 }
498 
499 /**
500  * d_really_is_positive - Determine if a dentry is really positive (ignoring fallthroughs)
501  * @dentry: The dentry in question
502  *
503  * Returns true if the dentry represents a name that maps to an inode
504  * (ie. ->d_inode is not NULL).  The dentry might still represent a whiteout if
505  * that is represented on medium as a 0,0 chardev.
506  *
507  * Note!  (1) This should be used *only* by a filesystem to examine its own
508  * dentries.  It should not be used to look at some other filesystem's
509  * dentries.  (2) It should also be used in combination with d_inode() to get
510  * the inode.
511  */
d_really_is_positive(const struct dentry * dentry)512 static inline bool d_really_is_positive(const struct dentry *dentry)
513 {
514 	return dentry->d_inode != NULL;
515 }
516 
simple_positive(const struct dentry * dentry)517 static inline int simple_positive(const struct dentry *dentry)
518 {
519 	return d_really_is_positive(dentry) && !d_unhashed(dentry);
520 }
521 
522 unsigned long vfs_pressure_ratio(unsigned long val);
523 
524 /**
525  * d_inode - Get the actual inode of this dentry
526  * @dentry: The dentry to query
527  *
528  * This is the helper normal filesystems should use to get at their own inodes
529  * in their own dentries and ignore the layering superimposed upon them.
530  */
d_inode(const struct dentry * dentry)531 static inline struct inode *d_inode(const struct dentry *dentry)
532 {
533 	return dentry->d_inode;
534 }
535 
536 /**
537  * d_inode_rcu - Get the actual inode of this dentry with READ_ONCE()
538  * @dentry: The dentry to query
539  *
540  * This is the helper normal filesystems should use to get at their own inodes
541  * in their own dentries and ignore the layering superimposed upon them.
542  */
d_inode_rcu(const struct dentry * dentry)543 static inline struct inode *d_inode_rcu(const struct dentry *dentry)
544 {
545 	return READ_ONCE(dentry->d_inode);
546 }
547 
548 /**
549  * d_backing_inode - Get upper or lower inode we should be using
550  * @upper: The upper layer
551  *
552  * This is the helper that should be used to get at the inode that will be used
553  * if this dentry were to be opened as a file.  The inode may be on the upper
554  * dentry or it may be on a lower dentry pinned by the upper.
555  *
556  * Normal filesystems should not use this to access their own inodes.
557  */
d_backing_inode(const struct dentry * upper)558 static inline struct inode *d_backing_inode(const struct dentry *upper)
559 {
560 	struct inode *inode = upper->d_inode;
561 
562 	return inode;
563 }
564 
565 /**
566  * d_real - Return the real dentry
567  * @dentry: the dentry to query
568  * @type: the type of real dentry (data or metadata)
569  *
570  * If dentry is on a union/overlay, then return the underlying, real dentry.
571  * Otherwise return the dentry itself.
572  *
573  * See also: Documentation/filesystems/vfs.rst
574  */
d_real(struct dentry * dentry,enum d_real_type type)575 static inline struct dentry *d_real(struct dentry *dentry, enum d_real_type type)
576 {
577 	if (unlikely(dentry->d_flags & DCACHE_OP_REAL))
578 		return dentry->d_op->d_real(dentry, type);
579 	else
580 		return dentry;
581 }
582 
583 /**
584  * d_real_inode - Return the real inode hosting the data
585  * @dentry: The dentry to query
586  *
587  * If dentry is on a union/overlay, then return the underlying, real inode.
588  * Otherwise return d_inode().
589  */
d_real_inode(const struct dentry * dentry)590 static inline struct inode *d_real_inode(const struct dentry *dentry)
591 {
592 	/* This usage of d_real() results in const dentry */
593 	return d_inode(d_real((struct dentry *) dentry, D_REAL_DATA));
594 }
595 
596 struct name_snapshot {
597 	struct qstr name;
598 	union shortname_store inline_name;
599 };
600 void take_dentry_name_snapshot(struct name_snapshot *, struct dentry *);
601 void release_dentry_name_snapshot(struct name_snapshot *);
602 
d_first_child(const struct dentry * dentry)603 static inline struct dentry *d_first_child(const struct dentry *dentry)
604 {
605 	return hlist_entry_safe(dentry->d_children.first, struct dentry, d_sib);
606 }
607 
d_next_sibling(const struct dentry * dentry)608 static inline struct dentry *d_next_sibling(const struct dentry *dentry)
609 {
610 	return hlist_entry_safe(dentry->d_sib.next, struct dentry, d_sib);
611 }
612 
613 #endif	/* __LINUX_DCACHE_H */
614