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Linux/include/linux/dcache.h

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  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. Keep it updated!
155  *
156  * FUrther descriptions are found in Documentation/filesystems/vfs.txt.
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 #define DCACHE_RCUACCESS                0x00000080 /* Entry has ever been RCU-visible */
180 
181 #define DCACHE_CANT_MOUNT               0x00000100
182 #define DCACHE_GENOCIDE                 0x00000200
183 #define DCACHE_SHRINK_LIST              0x00000400
184 
185 #define DCACHE_OP_WEAK_REVALIDATE       0x00000800
186 
187 #define DCACHE_NFSFS_RENAMED            0x00001000
188      /* this dentry has been "silly renamed" and has to be deleted on the last
189       * dput() */
190 #define DCACHE_COOKIE                   0x00002000 /* For use by dcookie subsystem */
191 #define DCACHE_FSNOTIFY_PARENT_WATCHED  0x00004000
192      /* Parent inode is watched by some fsnotify listener */
193 
194 #define DCACHE_DENTRY_KILLED            0x00008000
195 
196 #define DCACHE_MOUNTED                  0x00010000 /* is a mountpoint */
197 #define DCACHE_NEED_AUTOMOUNT           0x00020000 /* handle automount on this dir */
198 #define DCACHE_MANAGE_TRANSIT           0x00040000 /* manage transit from this dirent */
199 #define DCACHE_MANAGED_DENTRY \
200         (DCACHE_MOUNTED|DCACHE_NEED_AUTOMOUNT|DCACHE_MANAGE_TRANSIT)
201 
202 #define DCACHE_LRU_LIST                 0x00080000
203 
204 #define DCACHE_ENTRY_TYPE               0x00700000
205 #define DCACHE_MISS_TYPE                0x00000000 /* Negative dentry (maybe fallthru to nowhere) */
206 #define DCACHE_WHITEOUT_TYPE            0x00100000 /* Whiteout dentry (stop pathwalk) */
207 #define DCACHE_DIRECTORY_TYPE           0x00200000 /* Normal directory */
208 #define DCACHE_AUTODIR_TYPE             0x00300000 /* Lookupless directory (presumed automount) */
209 #define DCACHE_REGULAR_TYPE             0x00400000 /* Regular file type (or fallthru to such) */
210 #define DCACHE_SPECIAL_TYPE             0x00500000 /* Other file type (or fallthru to such) */
211 #define DCACHE_SYMLINK_TYPE             0x00600000 /* Symlink (or fallthru to such) */
212 
213 #define DCACHE_MAY_FREE                 0x00800000
214 #define DCACHE_FALLTHRU                 0x01000000 /* Fall through to lower layer */
215 #define DCACHE_ENCRYPTED_WITH_KEY       0x02000000 /* dir is encrypted with a valid key */
216 #define DCACHE_OP_REAL                  0x04000000
217 
218 #define DCACHE_PAR_LOOKUP               0x10000000 /* being looked up (with parent locked shared) */
219 #define DCACHE_DENTRY_CURSOR            0x20000000
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_pseudo(struct super_block *, const struct qstr *);
239 extern struct dentry * d_alloc_parallel(struct dentry *, const struct qstr *,
240                                         wait_queue_head_t *);
241 extern struct dentry * d_splice_alias(struct inode *, struct dentry *);
242 extern struct dentry * d_add_ci(struct dentry *, struct inode *, struct qstr *);
243 extern struct dentry * d_exact_alias(struct dentry *, struct inode *);
244 extern struct dentry *d_find_any_alias(struct inode *inode);
245 extern struct dentry * d_obtain_alias(struct inode *);
246 extern struct dentry * d_obtain_root(struct inode *);
247 extern void shrink_dcache_sb(struct super_block *);
248 extern void shrink_dcache_parent(struct dentry *);
249 extern void shrink_dcache_for_umount(struct super_block *);
250 extern void d_invalidate(struct dentry *);
251 
252 /* only used at mount-time */
253 extern struct dentry * d_make_root(struct inode *);
254 
255 /* <clickety>-<click> the ramfs-type tree */
256 extern void d_genocide(struct dentry *);
257 
258 extern void d_tmpfile(struct dentry *, struct inode *);
259 
260 extern struct dentry *d_find_alias(struct inode *);
261 extern void d_prune_aliases(struct inode *);
262 
263 /* test whether we have any submounts in a subdir tree */
264 extern int path_has_submounts(const struct path *);
265 
266 /*
267  * This adds the entry to the hash queues.
268  */
269 extern void d_rehash(struct dentry *);
270  
271 extern void d_add(struct dentry *, struct inode *);
272 
273 /* used for rename() and baskets */
274 extern void d_move(struct dentry *, struct dentry *);
275 extern void d_exchange(struct dentry *, struct dentry *);
276 extern struct dentry *d_ancestor(struct dentry *, struct dentry *);
277 
278 /* appendix may either be NULL or be used for transname suffixes */
279 extern struct dentry *d_lookup(const struct dentry *, const struct qstr *);
280 extern struct dentry *d_hash_and_lookup(struct dentry *, struct qstr *);
281 extern struct dentry *__d_lookup(const struct dentry *, const struct qstr *);
282 extern struct dentry *__d_lookup_rcu(const struct dentry *parent,
283                                 const struct qstr *name, unsigned *seq);
284 
285 static inline unsigned d_count(const struct dentry *dentry)
286 {
287         return dentry->d_lockref.count;
288 }
289 
290 /*
291  * helper function for dentry_operations.d_dname() members
292  */
293 extern __printf(4, 5)
294 char *dynamic_dname(struct dentry *, char *, int, const char *, ...);
295 extern char *simple_dname(struct dentry *, char *, int);
296 
297 extern char *__d_path(const struct path *, const struct path *, char *, int);
298 extern char *d_absolute_path(const struct path *, char *, int);
299 extern char *d_path(const struct path *, char *, int);
300 extern char *dentry_path_raw(struct dentry *, char *, int);
301 extern char *dentry_path(struct dentry *, char *, int);
302 
303 /* Allocation counts.. */
304 
305 /**
306  *      dget, dget_dlock -      get a reference to a dentry
307  *      @dentry: dentry to get a reference to
308  *
309  *      Given a dentry or %NULL pointer increment the reference count
310  *      if appropriate and return the dentry. A dentry will not be 
311  *      destroyed when it has references.
312  */
313 static inline struct dentry *dget_dlock(struct dentry *dentry)
314 {
315         if (dentry)
316                 dentry->d_lockref.count++;
317         return dentry;
318 }
319 
320 static inline struct dentry *dget(struct dentry *dentry)
321 {
322         if (dentry)
323                 lockref_get(&dentry->d_lockref);
324         return dentry;
325 }
326 
327 extern struct dentry *dget_parent(struct dentry *dentry);
328 
329 /**
330  *      d_unhashed -    is dentry hashed
331  *      @dentry: entry to check
332  *
333  *      Returns true if the dentry passed is not currently hashed.
334  */
335  
336 static inline int d_unhashed(const struct dentry *dentry)
337 {
338         return hlist_bl_unhashed(&dentry->d_hash);
339 }
340 
341 static inline int d_unlinked(const struct dentry *dentry)
342 {
343         return d_unhashed(dentry) && !IS_ROOT(dentry);
344 }
345 
346 static inline int cant_mount(const struct dentry *dentry)
347 {
348         return (dentry->d_flags & DCACHE_CANT_MOUNT);
349 }
350 
351 static inline void dont_mount(struct dentry *dentry)
352 {
353         spin_lock(&dentry->d_lock);
354         dentry->d_flags |= DCACHE_CANT_MOUNT;
355         spin_unlock(&dentry->d_lock);
356 }
357 
358 extern void __d_lookup_done(struct dentry *);
359 
360 static inline int d_in_lookup(const struct dentry *dentry)
361 {
362         return dentry->d_flags & DCACHE_PAR_LOOKUP;
363 }
364 
365 static inline void d_lookup_done(struct dentry *dentry)
366 {
367         if (unlikely(d_in_lookup(dentry))) {
368                 spin_lock(&dentry->d_lock);
369                 __d_lookup_done(dentry);
370                 spin_unlock(&dentry->d_lock);
371         }
372 }
373 
374 extern void dput(struct dentry *);
375 
376 static inline bool d_managed(const struct dentry *dentry)
377 {
378         return dentry->d_flags & DCACHE_MANAGED_DENTRY;
379 }
380 
381 static inline bool d_mountpoint(const struct dentry *dentry)
382 {
383         return dentry->d_flags & DCACHE_MOUNTED;
384 }
385 
386 /*
387  * Directory cache entry type accessor functions.
388  */
389 static inline unsigned __d_entry_type(const struct dentry *dentry)
390 {
391         return dentry->d_flags & DCACHE_ENTRY_TYPE;
392 }
393 
394 static inline bool d_is_miss(const struct dentry *dentry)
395 {
396         return __d_entry_type(dentry) == DCACHE_MISS_TYPE;
397 }
398 
399 static inline bool d_is_whiteout(const struct dentry *dentry)
400 {
401         return __d_entry_type(dentry) == DCACHE_WHITEOUT_TYPE;
402 }
403 
404 static inline bool d_can_lookup(const struct dentry *dentry)
405 {
406         return __d_entry_type(dentry) == DCACHE_DIRECTORY_TYPE;
407 }
408 
409 static inline bool d_is_autodir(const struct dentry *dentry)
410 {
411         return __d_entry_type(dentry) == DCACHE_AUTODIR_TYPE;
412 }
413 
414 static inline bool d_is_dir(const struct dentry *dentry)
415 {
416         return d_can_lookup(dentry) || d_is_autodir(dentry);
417 }
418 
419 static inline bool d_is_symlink(const struct dentry *dentry)
420 {
421         return __d_entry_type(dentry) == DCACHE_SYMLINK_TYPE;
422 }
423 
424 static inline bool d_is_reg(const struct dentry *dentry)
425 {
426         return __d_entry_type(dentry) == DCACHE_REGULAR_TYPE;
427 }
428 
429 static inline bool d_is_special(const struct dentry *dentry)
430 {
431         return __d_entry_type(dentry) == DCACHE_SPECIAL_TYPE;
432 }
433 
434 static inline bool d_is_file(const struct dentry *dentry)
435 {
436         return d_is_reg(dentry) || d_is_special(dentry);
437 }
438 
439 static inline bool d_is_negative(const struct dentry *dentry)
440 {
441         // TODO: check d_is_whiteout(dentry) also.
442         return d_is_miss(dentry);
443 }
444 
445 static inline bool d_is_positive(const struct dentry *dentry)
446 {
447         return !d_is_negative(dentry);
448 }
449 
450 /**
451  * d_really_is_negative - Determine if a dentry is really negative (ignoring fallthroughs)
452  * @dentry: The dentry in question
453  *
454  * Returns true if the dentry represents either an absent name or a name that
455  * doesn't map to an inode (ie. ->d_inode is NULL).  The dentry could represent
456  * a true miss, a whiteout that isn't represented by a 0,0 chardev or a
457  * fallthrough marker in an opaque directory.
458  *
459  * Note!  (1) This should be used *only* by a filesystem to examine its own
460  * dentries.  It should not be used to look at some other filesystem's
461  * dentries.  (2) It should also be used in combination with d_inode() to get
462  * the inode.  (3) The dentry may have something attached to ->d_lower and the
463  * type field of the flags may be set to something other than miss or whiteout.
464  */
465 static inline bool d_really_is_negative(const struct dentry *dentry)
466 {
467         return dentry->d_inode == NULL;
468 }
469 
470 /**
471  * d_really_is_positive - Determine if a dentry is really positive (ignoring fallthroughs)
472  * @dentry: The dentry in question
473  *
474  * Returns true if the dentry represents a name that maps to an inode
475  * (ie. ->d_inode is not NULL).  The dentry might still represent a whiteout if
476  * that is represented on medium as a 0,0 chardev.
477  *
478  * Note!  (1) This should be used *only* by a filesystem to examine its own
479  * dentries.  It should not be used to look at some other filesystem's
480  * dentries.  (2) It should also be used in combination with d_inode() to get
481  * the inode.
482  */
483 static inline bool d_really_is_positive(const struct dentry *dentry)
484 {
485         return dentry->d_inode != NULL;
486 }
487 
488 static inline int simple_positive(const struct dentry *dentry)
489 {
490         return d_really_is_positive(dentry) && !d_unhashed(dentry);
491 }
492 
493 extern void d_set_fallthru(struct dentry *dentry);
494 
495 static inline bool d_is_fallthru(const struct dentry *dentry)
496 {
497         return dentry->d_flags & DCACHE_FALLTHRU;
498 }
499 
500 
501 extern int sysctl_vfs_cache_pressure;
502 
503 static inline unsigned long vfs_pressure_ratio(unsigned long val)
504 {
505         return mult_frac(val, sysctl_vfs_cache_pressure, 100);
506 }
507 
508 /**
509  * d_inode - Get the actual inode of this dentry
510  * @dentry: The dentry to query
511  *
512  * This is the helper normal filesystems should use to get at their own inodes
513  * in their own dentries and ignore the layering superimposed upon them.
514  */
515 static inline struct inode *d_inode(const struct dentry *dentry)
516 {
517         return dentry->d_inode;
518 }
519 
520 /**
521  * d_inode_rcu - Get the actual inode of this dentry with READ_ONCE()
522  * @dentry: The dentry to query
523  *
524  * This is the helper normal filesystems should use to get at their own inodes
525  * in their own dentries and ignore the layering superimposed upon them.
526  */
527 static inline struct inode *d_inode_rcu(const struct dentry *dentry)
528 {
529         return READ_ONCE(dentry->d_inode);
530 }
531 
532 /**
533  * d_backing_inode - Get upper or lower inode we should be using
534  * @upper: The upper layer
535  *
536  * This is the helper that should be used to get at the inode that will be used
537  * if this dentry were to be opened as a file.  The inode may be on the upper
538  * dentry or it may be on a lower dentry pinned by the upper.
539  *
540  * Normal filesystems should not use this to access their own inodes.
541  */
542 static inline struct inode *d_backing_inode(const struct dentry *upper)
543 {
544         struct inode *inode = upper->d_inode;
545 
546         return inode;
547 }
548 
549 /**
550  * d_backing_dentry - Get upper or lower dentry we should be using
551  * @upper: The upper layer
552  *
553  * This is the helper that should be used to get the dentry of the inode that
554  * will be used if this dentry were opened as a file.  It may be the upper
555  * dentry or it may be a lower dentry pinned by the upper.
556  *
557  * Normal filesystems should not use this to access their own dentries.
558  */
559 static inline struct dentry *d_backing_dentry(struct dentry *upper)
560 {
561         return upper;
562 }
563 
564 /**
565  * d_real - Return the real dentry
566  * @dentry: the dentry to query
567  * @inode: inode to select the dentry from multiple layers (can be NULL)
568  *
569  * If dentry is on a union/overlay, then return the underlying, real dentry.
570  * Otherwise return the dentry itself.
571  *
572  * See also: Documentation/filesystems/vfs.txt
573  */
574 static inline struct dentry *d_real(struct dentry *dentry,
575                                     const struct inode *inode)
576 {
577         if (unlikely(dentry->d_flags & DCACHE_OP_REAL))
578                 return dentry->d_op->d_real(dentry, inode);
579         else
580                 return dentry;
581 }
582 
583 /**
584  * d_real_inode - Return the real inode
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  */
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_backing_inode(d_real((struct dentry *) dentry, NULL));
594 }
595 
596 struct name_snapshot {
597         const unsigned char *name;
598         unsigned char inline_name[DNAME_INLINE_LEN];
599 };
600 void take_dentry_name_snapshot(struct name_snapshot *, struct dentry *);
601 void release_dentry_name_snapshot(struct name_snapshot *);
602 
603 #endif  /* __LINUX_DCACHE_H */
604 

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