root/include/linux/dcache.h

INCLUDED FROM

DEFINITIONS

1. d_count
2. __printf
3. dget
4. d_unhashed
5. d_unlinked
6. cant_mount
7. dont_mount
8. d_in_lookup
9. d_lookup_done
10. d_managed
11. d_mountpoint
12. __d_entry_type
13. d_is_miss
14. d_is_whiteout
15. d_can_lookup
16. d_is_autodir
17. d_is_dir
18. d_is_symlink
19. d_is_reg
20. d_is_special
21. d_is_file
22. d_is_negative
23. d_is_positive
24. d_really_is_negative
25. d_really_is_positive
26. simple_positive
27. d_is_fallthru
28. vfs_pressure_ratio
29. d_inode
30. d_inode_rcu
31. d_backing_inode
32. d_backing_dentry
33. d_real
34. d_real_inode

   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/rculist.h>
   8 #include <linux/rculist_bl.h>
   9 #include <linux/spinlock.h>
  10 #include <linux/seqlock.h>
  11 #include <linux/cache.h>
  12 #include <linux/rcupdate.h>
  13 #include <linux/lockref.h>
  14 #include <linux/stringhash.h>
  15 #include <linux/wait.h>
  16 
  17 struct path;
  18 struct vfsmount;
  19 
  20 /*
  21  * linux/include/linux/dcache.h
  22  *
  23  * Dirent cache data structures
  24  *
  25  * (C) Copyright 1997 Thomas Schoebel-Theuer,
  26  * with heavy changes by Linus Torvalds
  27  */
  28 
  29 #define IS_ROOT(x) ((x) == (x)->d_parent)
  30 
  31 /* The hash is always the low bits of hash_len */
  32 #ifdef __LITTLE_ENDIAN
  33  #define HASH_LEN_DECLARE u32 hash; u32 len
  34  #define bytemask_from_count(cnt)       (~(~0ul << (cnt)*8))
  35 #else
  36  #define HASH_LEN_DECLARE u32 len; u32 hash
  37  #define bytemask_from_count(cnt)       (~(~0ul >> (cnt)*8))
  38 #endif
  39 
  40 /*
  41  * "quick string" -- eases parameter passing, but more importantly
  42  * saves "metadata" about the string (ie length and the hash).
  43  *
  44  * hash comes first so it snuggles against d_parent in the
  45  * dentry.
  46  */
  47 struct qstr {
  48         union {
  49                 struct {
  50                         HASH_LEN_DECLARE;
  51                 };
  52                 u64 hash_len;
  53         };
  54         const unsigned char *name;
  55 };
  56 
  57 #define QSTR_INIT(n,l) { { { .len = l } }, .name = n }
  58 
  59 extern const struct qstr empty_name;
  60 extern const struct qstr slash_name;
  61 
  62 struct dentry_stat_t {
  63         long nr_dentry;
  64         long nr_unused;
  65         long age_limit;         /* age in seconds */
  66         long want_pages;        /* pages requested by system */
  67         long nr_negative;       /* # of unused negative dentries */
  68         long dummy;             /* Reserved for future use */
  69 };
  70 extern struct dentry_stat_t dentry_stat;
  71 
  72 /*
  73  * Try to keep struct dentry aligned on 64 byte cachelines (this will
  74  * give reasonable cacheline footprint with larger lines without the
  75  * large memory footprint increase).
  76  */
  77 #ifdef CONFIG_64BIT
  78 # define DNAME_INLINE_LEN 32 /* 192 bytes */
  79 #else
  80 # ifdef CONFIG_SMP
  81 #  define DNAME_INLINE_LEN 36 /* 128 bytes */
  82 # else
  83 #  define DNAME_INLINE_LEN 40 /* 128 bytes */
  84 # endif
  85 #endif
  86 
  87 #define d_lock  d_lockref.lock
  88 
  89 struct dentry {
  90         /* RCU lookup touched fields */
  91         unsigned int d_flags;           /* protected by d_lock */
  92         seqcount_t d_seq;               /* per dentry seqlock */
  93         struct hlist_bl_node d_hash;    /* lookup hash list */
  94         struct dentry *d_parent;        /* parent directory */
  95         struct qstr d_name;
  96         struct inode *d_inode;          /* Where the name belongs to - NULL is
  97                                          * negative */
  98         unsigned char d_iname[DNAME_INLINE_LEN];        /* small names */
  99 
 100         /* Ref lookup also touches following */
 101         struct lockref d_lockref;       /* per-dentry lock and refcount */
 102         const struct dentry_operations *d_op;
 103         struct super_block *d_sb;       /* The root of the dentry tree */
 104         unsigned long d_time;           /* used by d_revalidate */
 105         void *d_fsdata;                 /* fs-specific data */
 106 
 107         union {
 108                 struct list_head d_lru;         /* LRU list */
 109                 wait_queue_head_t *d_wait;      /* in-lookup ones only */
 110         };
 111         struct list_head d_child;       /* child of parent list */
 112         struct list_head d_subdirs;     /* our children */
 113         /*
 114          * d_alias and d_rcu can share memory
 115          */
 116         union {
 117                 struct hlist_node d_alias;      /* inode alias list */
 118                 struct hlist_bl_node d_in_lookup_hash;  /* only for in-lookup ones */
 119                 struct rcu_head d_rcu;
 120         } d_u;
 121 } __randomize_layout;
 122 
 123 /*
 124  * dentry->d_lock spinlock nesting subclasses:
 125  *
 126  * 0: normal
 127  * 1: nested
 128  */
 129 enum dentry_d_lock_class
 130 {
 131         DENTRY_D_LOCK_NORMAL, /* implicitly used by plain spin_lock() APIs. */
 132         DENTRY_D_LOCK_NESTED
 133 };
 134 
 135 struct dentry_operations {
 136         int (*d_revalidate)(struct dentry *, unsigned int);
 137         int (*d_weak_revalidate)(struct dentry *, unsigned int);
 138         int (*d_hash)(const struct dentry *, struct qstr *);
 139         int (*d_compare)(const struct dentry *,
 140                         unsigned int, const char *, const struct qstr *);
 141         int (*d_delete)(const struct dentry *);
 142         int (*d_init)(struct dentry *);
 143         void (*d_release)(struct dentry *);
 144         void (*d_prune)(struct dentry *);
 145         void (*d_iput)(struct dentry *, struct inode *);
 146         char *(*d_dname)(struct dentry *, char *, int);
 147         struct vfsmount *(*d_automount)(struct path *);
 148         int (*d_manage)(const struct path *, bool);
 149         struct dentry *(*d_real)(struct dentry *, const struct inode *);
 150 } ____cacheline_aligned;
 151 
 152 /*
 153  * Locking rules for dentry_operations callbacks are to be found in
 154  * Documentation/filesystems/locking.rst. Keep it updated!
 155  *
 156  * FUrther descriptions are found in Documentation/filesystems/vfs.rst.
 157  * Keep it updated too!
 158  */
 159 
 160 /* d_flags entries */
 161 #define DCACHE_OP_HASH                  0x00000001
 162 #define DCACHE_OP_COMPARE               0x00000002
 163 #define DCACHE_OP_REVALIDATE            0x00000004
 164 #define DCACHE_OP_DELETE                0x00000008
 165 #define DCACHE_OP_PRUNE                 0x00000010
 166 
 167 #define DCACHE_DISCONNECTED             0x00000020
 168      /* This dentry is possibly not currently connected to the dcache tree, in
 169       * which case its parent will either be itself, or will have this flag as
 170       * well.  nfsd will not use a dentry with this bit set, but will first
 171       * endeavour to clear the bit either by discovering that it is connected,
 172       * or by performing lookup operations.   Any filesystem which supports
 173       * nfsd_operations MUST have a lookup function which, if it finds a
 174       * directory inode with a DCACHE_DISCONNECTED dentry, will d_move that
 175       * dentry into place and return that dentry rather than the passed one,
 176       * typically using d_splice_alias. */
 177 
 178 #define DCACHE_REFERENCED               0x00000040 /* Recently used, don't discard. */
 179 
 180 #define DCACHE_CANT_MOUNT               0x00000100
 181 #define DCACHE_GENOCIDE                 0x00000200
 182 #define DCACHE_SHRINK_LIST              0x00000400
 183 
 184 #define DCACHE_OP_WEAK_REVALIDATE       0x00000800
 185 
 186 #define DCACHE_NFSFS_RENAMED            0x00001000
 187      /* this dentry has been "silly renamed" and has to be deleted on the last
 188       * dput() */
 189 #define DCACHE_COOKIE                   0x00002000 /* For use by dcookie subsystem */
 190 #define DCACHE_FSNOTIFY_PARENT_WATCHED  0x00004000
 191      /* Parent inode is watched by some fsnotify listener */
 192 
 193 #define DCACHE_DENTRY_KILLED            0x00008000
 194 
 195 #define DCACHE_MOUNTED                  0x00010000 /* is a mountpoint */
 196 #define DCACHE_NEED_AUTOMOUNT           0x00020000 /* handle automount on this dir */
 197 #define DCACHE_MANAGE_TRANSIT           0x00040000 /* manage transit from this dirent */
 198 #define DCACHE_MANAGED_DENTRY \
 199         (DCACHE_MOUNTED|DCACHE_NEED_AUTOMOUNT|DCACHE_MANAGE_TRANSIT)
 200 
 201 #define DCACHE_LRU_LIST                 0x00080000
 202 
 203 #define DCACHE_ENTRY_TYPE               0x00700000
 204 #define DCACHE_MISS_TYPE                0x00000000 /* Negative dentry (maybe fallthru to nowhere) */
 205 #define DCACHE_WHITEOUT_TYPE            0x00100000 /* Whiteout dentry (stop pathwalk) */
 206 #define DCACHE_DIRECTORY_TYPE           0x00200000 /* Normal directory */
 207 #define DCACHE_AUTODIR_TYPE             0x00300000 /* Lookupless directory (presumed automount) */
 208 #define DCACHE_REGULAR_TYPE             0x00400000 /* Regular file type (or fallthru to such) */
 209 #define DCACHE_SPECIAL_TYPE             0x00500000 /* Other file type (or fallthru to such) */
 210 #define DCACHE_SYMLINK_TYPE             0x00600000 /* Symlink (or fallthru to such) */
 211 
 212 #define DCACHE_MAY_FREE                 0x00800000
 213 #define DCACHE_FALLTHRU                 0x01000000 /* Fall through to lower layer */
 214 #define DCACHE_ENCRYPTED_NAME           0x02000000 /* Encrypted name (dir key was unavailable) */
 215 #define DCACHE_OP_REAL                  0x04000000
 216 
 217 #define DCACHE_PAR_LOOKUP               0x10000000 /* being looked up (with parent locked shared) */
 218 #define DCACHE_DENTRY_CURSOR            0x20000000
 219 #define DCACHE_NORCU                    0x40000000 /* No RCU delay for freeing */
 220 
 221 extern seqlock_t rename_lock;
 222 
 223 /*
 224  * These are the low-level FS interfaces to the dcache..
 225  */
 226 extern void d_instantiate(struct dentry *, struct inode *);
 227 extern void d_instantiate_new(struct dentry *, struct inode *);
 228 extern struct dentry * d_instantiate_unique(struct dentry *, struct inode *);
 229 extern struct dentry * d_instantiate_anon(struct dentry *, struct inode *);
 230 extern void __d_drop(struct dentry *dentry);
 231 extern void d_drop(struct dentry *dentry);
 232 extern void d_delete(struct dentry *);
 233 extern void d_set_d_op(struct dentry *dentry, const struct dentry_operations *op);
 234 
 235 /* allocate/de-allocate */
 236 extern struct dentry * d_alloc(struct dentry *, const struct qstr *);
 237 extern struct dentry * d_alloc_anon(struct super_block *);
 238 extern struct dentry * d_alloc_parallel(struct dentry *, const struct qstr *,
 239                                         wait_queue_head_t *);
 240 extern struct dentry * d_splice_alias(struct inode *, struct dentry *);
 241 extern struct dentry * d_add_ci(struct dentry *, struct inode *, struct qstr *);
 242 extern struct dentry * d_exact_alias(struct dentry *, struct inode *);
 243 extern struct dentry *d_find_any_alias(struct inode *inode);
 244 extern struct dentry * d_obtain_alias(struct inode *);
 245 extern struct dentry * d_obtain_root(struct inode *);
 246 extern void shrink_dcache_sb(struct super_block *);
 247 extern void shrink_dcache_parent(struct dentry *);
 248 extern void shrink_dcache_for_umount(struct super_block *);
 249 extern void d_invalidate(struct dentry *);
 250 
 251 /* only used at mount-time */
 252 extern struct dentry * d_make_root(struct inode *);
 253 
 254 /* <clickety>-<click> the ramfs-type tree */
 255 extern void d_genocide(struct dentry *);
 256 
 257 extern void d_tmpfile(struct dentry *, struct inode *);
 258 
 259 extern struct dentry *d_find_alias(struct inode *);
 260 extern void d_prune_aliases(struct inode *);
 261 
 262 /* test whether we have any submounts in a subdir tree */
 263 extern int path_has_submounts(const struct path *);
 264 
 265 /*
 266  * This adds the entry to the hash queues.
 267  */
 268 extern void d_rehash(struct dentry *);
 269  
 270 extern void d_add(struct dentry *, struct inode *);
 271 
 272 /* used for rename() and baskets */
 273 extern void d_move(struct dentry *, struct dentry *);
 274 extern void d_exchange(struct dentry *, struct dentry *);
 275 extern struct dentry *d_ancestor(struct dentry *, struct dentry *);
 276 
 277 /* appendix may either be NULL or be used for transname suffixes */
 278 extern struct dentry *d_lookup(const struct dentry *, const struct qstr *);
 279 extern struct dentry *d_hash_and_lookup(struct dentry *, struct qstr *);
 280 extern struct dentry *__d_lookup(const struct dentry *, const struct qstr *);
 281 extern struct dentry *__d_lookup_rcu(const struct dentry *parent,
 282                                 const struct qstr *name, unsigned *seq);
 283 
 284 static inline unsigned d_count(const struct dentry *dentry)
 285 {
 286         return dentry->d_lockref.count;
 287 }
 288 
 289 /*
 290  * helper function for dentry_operations.d_dname() members
 291  */
 292 extern __printf(4, 5)
 293 char *dynamic_dname(struct dentry *, char *, int, const char *, ...);
 294 
 295 extern char *__d_path(const struct path *, const struct path *, char *, int);
 296 extern char *d_absolute_path(const struct path *, char *, int);
 297 extern char *d_path(const struct path *, char *, int);
 298 extern char *dentry_path_raw(struct dentry *, char *, int);
 299 extern char *dentry_path(struct dentry *, char *, int);
 300 
 301 /* Allocation counts.. */
 302 
 303 /**
 304  *      dget, dget_dlock -      get a reference to a dentry
 305  *      @dentry: dentry to get a reference to
 306  *
 307  *      Given a dentry or %NULL pointer increment the reference count
 308  *      if appropriate and return the dentry. A dentry will not be 
 309  *      destroyed when it has references.
 310  */
 311 static inline struct dentry *dget_dlock(struct dentry *dentry)
 312 {
 313         if (dentry)
 314                 dentry->d_lockref.count++;
 315         return dentry;
 316 }
 317 
 318 static inline struct dentry *dget(struct dentry *dentry)
 319 {
 320         if (dentry)
 321                 lockref_get(&dentry->d_lockref);
 322         return dentry;
 323 }
 324 
 325 extern struct dentry *dget_parent(struct dentry *dentry);
 326 
 327 /**
 328  *      d_unhashed -    is dentry hashed
 329  *      @dentry: entry to check
 330  *
 331  *      Returns true if the dentry passed is not currently hashed.
 332  */
 333  
 334 static inline int d_unhashed(const struct dentry *dentry)
 335 {
 336         return hlist_bl_unhashed(&dentry->d_hash);
 337 }
 338 
 339 static inline int d_unlinked(const struct dentry *dentry)
 340 {
 341         return d_unhashed(dentry) && !IS_ROOT(dentry);
 342 }
 343 
 344 static inline int cant_mount(const struct dentry *dentry)
 345 {
 346         return (dentry->d_flags & DCACHE_CANT_MOUNT);
 347 }
 348 
 349 static inline void dont_mount(struct dentry *dentry)
 350 {
 351         spin_lock(&dentry->d_lock);
 352         dentry->d_flags |= DCACHE_CANT_MOUNT;
 353         spin_unlock(&dentry->d_lock);
 354 }
 355 
 356 extern void __d_lookup_done(struct dentry *);
 357 
 358 static inline int d_in_lookup(const struct dentry *dentry)
 359 {
 360         return dentry->d_flags & DCACHE_PAR_LOOKUP;
 361 }
 362 
 363 static inline void d_lookup_done(struct dentry *dentry)
 364 {
 365         if (unlikely(d_in_lookup(dentry))) {
 366                 spin_lock(&dentry->d_lock);
 367                 __d_lookup_done(dentry);
 368                 spin_unlock(&dentry->d_lock);
 369         }
 370 }
 371 
 372 extern void dput(struct dentry *);
 373 
 374 static inline bool d_managed(const struct dentry *dentry)
 375 {
 376         return dentry->d_flags & DCACHE_MANAGED_DENTRY;
 377 }
 378 
 379 static inline bool d_mountpoint(const struct dentry *dentry)
 380 {
 381         return dentry->d_flags & DCACHE_MOUNTED;
 382 }
 383 
 384 /*
 385  * Directory cache entry type accessor functions.
 386  */
 387 static inline unsigned __d_entry_type(const struct dentry *dentry)
 388 {
 389         return dentry->d_flags & DCACHE_ENTRY_TYPE;
 390 }
 391 
 392 static inline bool d_is_miss(const struct dentry *dentry)
 393 {
 394         return __d_entry_type(dentry) == DCACHE_MISS_TYPE;
 395 }
 396 
 397 static inline bool d_is_whiteout(const struct dentry *dentry)
 398 {
 399         return __d_entry_type(dentry) == DCACHE_WHITEOUT_TYPE;
 400 }
 401 
 402 static inline bool d_can_lookup(const struct dentry *dentry)
 403 {
 404         return __d_entry_type(dentry) == DCACHE_DIRECTORY_TYPE;
 405 }
 406 
 407 static inline bool d_is_autodir(const struct dentry *dentry)
 408 {
 409         return __d_entry_type(dentry) == DCACHE_AUTODIR_TYPE;
 410 }
 411 
 412 static inline bool d_is_dir(const struct dentry *dentry)
 413 {
 414         return d_can_lookup(dentry) || d_is_autodir(dentry);
 415 }
 416 
 417 static inline bool d_is_symlink(const struct dentry *dentry)
 418 {
 419         return __d_entry_type(dentry) == DCACHE_SYMLINK_TYPE;
 420 }
 421 
 422 static inline bool d_is_reg(const struct dentry *dentry)
 423 {
 424         return __d_entry_type(dentry) == DCACHE_REGULAR_TYPE;
 425 }
 426 
 427 static inline bool d_is_special(const struct dentry *dentry)
 428 {
 429         return __d_entry_type(dentry) == DCACHE_SPECIAL_TYPE;
 430 }
 431 
 432 static inline bool d_is_file(const struct dentry *dentry)
 433 {
 434         return d_is_reg(dentry) || d_is_special(dentry);
 435 }
 436 
 437 static inline bool d_is_negative(const struct dentry *dentry)
 438 {
 439         // TODO: check d_is_whiteout(dentry) also.
 440         return d_is_miss(dentry);
 441 }
 442 
 443 static inline bool d_is_positive(const struct dentry *dentry)
 444 {
 445         return !d_is_negative(dentry);
 446 }
 447 
 448 /**
 449  * d_really_is_negative - Determine if a dentry is really negative (ignoring fallthroughs)
 450  * @dentry: The dentry in question
 451  *
 452  * Returns true if the dentry represents either an absent name or a name that
 453  * doesn't map to an inode (ie. ->d_inode is NULL).  The dentry could represent
 454  * a true miss, a whiteout that isn't represented by a 0,0 chardev or a
 455  * fallthrough marker in an opaque directory.
 456  *
 457  * Note!  (1) This should be used *only* by a filesystem to examine its own
 458  * dentries.  It should not be used to look at some other filesystem's
 459  * dentries.  (2) It should also be used in combination with d_inode() to get
 460  * the inode.  (3) The dentry may have something attached to ->d_lower and the
 461  * type field of the flags may be set to something other than miss or whiteout.
 462  */
 463 static inline bool d_really_is_negative(const struct dentry *dentry)
 464 {
 465         return dentry->d_inode == NULL;
 466 }
 467 
 468 /**
 469  * d_really_is_positive - Determine if a dentry is really positive (ignoring fallthroughs)
 470  * @dentry: The dentry in question
 471  *
 472  * Returns true if the dentry represents a name that maps to an inode
 473  * (ie. ->d_inode is not NULL).  The dentry might still represent a whiteout if
 474  * that is represented on medium as a 0,0 chardev.
 475  *
 476  * Note!  (1) This should be used *only* by a filesystem to examine its own
 477  * dentries.  It should not be used to look at some other filesystem's
 478  * dentries.  (2) It should also be used in combination with d_inode() to get
 479  * the inode.
 480  */
 481 static inline bool d_really_is_positive(const struct dentry *dentry)
 482 {
 483         return dentry->d_inode != NULL;
 484 }
 485 
 486 static inline int simple_positive(const struct dentry *dentry)
 487 {
 488         return d_really_is_positive(dentry) && !d_unhashed(dentry);
 489 }
 490 
 491 extern void d_set_fallthru(struct dentry *dentry);
 492 
 493 static inline bool d_is_fallthru(const struct dentry *dentry)
 494 {
 495         return dentry->d_flags & DCACHE_FALLTHRU;
 496 }
 497 
 498 
 499 extern int sysctl_vfs_cache_pressure;
 500 
 501 static inline unsigned long vfs_pressure_ratio(unsigned long val)
 502 {
 503         return mult_frac(val, sysctl_vfs_cache_pressure, 100);
 504 }
 505 
 506 /**
 507  * d_inode - Get the actual inode of this dentry
 508  * @dentry: The dentry to query
 509  *
 510  * This is the helper normal filesystems should use to get at their own inodes
 511  * in their own dentries and ignore the layering superimposed upon them.
 512  */
 513 static inline struct inode *d_inode(const struct dentry *dentry)
 514 {
 515         return dentry->d_inode;
 516 }
 517 
 518 /**
 519  * d_inode_rcu - Get the actual inode of this dentry with READ_ONCE()
 520  * @dentry: The dentry to query
 521  *
 522  * This is the helper normal filesystems should use to get at their own inodes
 523  * in their own dentries and ignore the layering superimposed upon them.
 524  */
 525 static inline struct inode *d_inode_rcu(const struct dentry *dentry)
 526 {
 527         return READ_ONCE(dentry->d_inode);
 528 }
 529 
 530 /**
 531  * d_backing_inode - Get upper or lower inode we should be using
 532  * @upper: The upper layer
 533  *
 534  * This is the helper that should be used to get at the inode that will be used
 535  * if this dentry were to be opened as a file.  The inode may be on the upper
 536  * dentry or it may be on a lower dentry pinned by the upper.
 537  *
 538  * Normal filesystems should not use this to access their own inodes.
 539  */
 540 static inline struct inode *d_backing_inode(const struct dentry *upper)
 541 {
 542         struct inode *inode = upper->d_inode;
 543 
 544         return inode;
 545 }
 546 
 547 /**
 548  * d_backing_dentry - Get upper or lower dentry we should be using
 549  * @upper: The upper layer
 550  *
 551  * This is the helper that should be used to get the dentry of the inode that
 552  * will be used if this dentry were opened as a file.  It may be the upper
 553  * dentry or it may be a lower dentry pinned by the upper.
 554  *
 555  * Normal filesystems should not use this to access their own dentries.
 556  */
 557 static inline struct dentry *d_backing_dentry(struct dentry *upper)
 558 {
 559         return upper;
 560 }
 561 
 562 /**
 563  * d_real - Return the real dentry
 564  * @dentry: the dentry to query
 565  * @inode: inode to select the dentry from multiple layers (can be NULL)
 566  *
 567  * If dentry is on a union/overlay, then return the underlying, real dentry.
 568  * Otherwise return the dentry itself.
 569  *
 570  * See also: Documentation/filesystems/vfs.rst
 571  */
 572 static inline struct dentry *d_real(struct dentry *dentry,
 573                                     const struct inode *inode)
 574 {
 575         if (unlikely(dentry->d_flags & DCACHE_OP_REAL))
 576                 return dentry->d_op->d_real(dentry, inode);
 577         else
 578                 return dentry;
 579 }
 580 
 581 /**
 582  * d_real_inode - Return the real inode
 583  * @dentry: The dentry to query
 584  *
 585  * If dentry is on a union/overlay, then return the underlying, real inode.
 586  * Otherwise return d_inode().
 587  */
 588 static inline struct inode *d_real_inode(const struct dentry *dentry)
 589 {
 590         /* This usage of d_real() results in const dentry */
 591         return d_backing_inode(d_real((struct dentry *) dentry, NULL));
 592 }
 593 
 594 struct name_snapshot {
 595         struct qstr name;
 596         unsigned char inline_name[DNAME_INLINE_LEN];
 597 };
 598 void take_dentry_name_snapshot(struct name_snapshot *, struct dentry *);
 599 void release_dentry_name_snapshot(struct name_snapshot *);
 600 
 601 #endif  /* __LINUX_DCACHE_H */