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Linux/fs/kernfs/dir.c

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  1 /*
  2  * fs/kernfs/dir.c - kernfs directory implementation
  3  *
  4  * Copyright (c) 2001-3 Patrick Mochel
  5  * Copyright (c) 2007 SUSE Linux Products GmbH
  6  * Copyright (c) 2007, 2013 Tejun Heo <tj@kernel.org>
  7  *
  8  * This file is released under the GPLv2.
  9  */
 10 
 11 #include <linux/sched.h>
 12 #include <linux/fs.h>
 13 #include <linux/namei.h>
 14 #include <linux/idr.h>
 15 #include <linux/slab.h>
 16 #include <linux/security.h>
 17 #include <linux/hash.h>
 18 
 19 #include "kernfs-internal.h"
 20 
 21 DEFINE_MUTEX(kernfs_mutex);
 22 static DEFINE_SPINLOCK(kernfs_rename_lock);     /* kn->parent and ->name */
 23 static char kernfs_pr_cont_buf[PATH_MAX];       /* protected by rename_lock */
 24 static DEFINE_SPINLOCK(kernfs_idr_lock);        /* root->ino_idr */
 25 
 26 #define rb_to_kn(X) rb_entry((X), struct kernfs_node, rb)
 27 
 28 static bool kernfs_active(struct kernfs_node *kn)
 29 {
 30         lockdep_assert_held(&kernfs_mutex);
 31         return atomic_read(&kn->active) >= 0;
 32 }
 33 
 34 static bool kernfs_lockdep(struct kernfs_node *kn)
 35 {
 36 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 37         return kn->flags & KERNFS_LOCKDEP;
 38 #else
 39         return false;
 40 #endif
 41 }
 42 
 43 static int kernfs_name_locked(struct kernfs_node *kn, char *buf, size_t buflen)
 44 {
 45         if (!kn)
 46                 return strlcpy(buf, "(null)", buflen);
 47 
 48         return strlcpy(buf, kn->parent ? kn->name : "/", buflen);
 49 }
 50 
 51 /* kernfs_node_depth - compute depth from @from to @to */
 52 static size_t kernfs_depth(struct kernfs_node *from, struct kernfs_node *to)
 53 {
 54         size_t depth = 0;
 55 
 56         while (to->parent && to != from) {
 57                 depth++;
 58                 to = to->parent;
 59         }
 60         return depth;
 61 }
 62 
 63 static struct kernfs_node *kernfs_common_ancestor(struct kernfs_node *a,
 64                                                   struct kernfs_node *b)
 65 {
 66         size_t da, db;
 67         struct kernfs_root *ra = kernfs_root(a), *rb = kernfs_root(b);
 68 
 69         if (ra != rb)
 70                 return NULL;
 71 
 72         da = kernfs_depth(ra->kn, a);
 73         db = kernfs_depth(rb->kn, b);
 74 
 75         while (da > db) {
 76                 a = a->parent;
 77                 da--;
 78         }
 79         while (db > da) {
 80                 b = b->parent;
 81                 db--;
 82         }
 83 
 84         /* worst case b and a will be the same at root */
 85         while (b != a) {
 86                 b = b->parent;
 87                 a = a->parent;
 88         }
 89 
 90         return a;
 91 }
 92 
 93 /**
 94  * kernfs_path_from_node_locked - find a pseudo-absolute path to @kn_to,
 95  * where kn_from is treated as root of the path.
 96  * @kn_from: kernfs node which should be treated as root for the path
 97  * @kn_to: kernfs node to which path is needed
 98  * @buf: buffer to copy the path into
 99  * @buflen: size of @buf
100  *
101  * We need to handle couple of scenarios here:
102  * [1] when @kn_from is an ancestor of @kn_to at some level
103  * kn_from: /n1/n2/n3
104  * kn_to:   /n1/n2/n3/n4/n5
105  * result:  /n4/n5
106  *
107  * [2] when @kn_from is on a different hierarchy and we need to find common
108  * ancestor between @kn_from and @kn_to.
109  * kn_from: /n1/n2/n3/n4
110  * kn_to:   /n1/n2/n5
111  * result:  /../../n5
112  * OR
113  * kn_from: /n1/n2/n3/n4/n5   [depth=5]
114  * kn_to:   /n1/n2/n3         [depth=3]
115  * result:  /../..
116  *
117  * [3] when @kn_to is NULL result will be "(null)"
118  *
119  * Returns the length of the full path.  If the full length is equal to or
120  * greater than @buflen, @buf contains the truncated path with the trailing
121  * '\0'.  On error, -errno is returned.
122  */
123 static int kernfs_path_from_node_locked(struct kernfs_node *kn_to,
124                                         struct kernfs_node *kn_from,
125                                         char *buf, size_t buflen)
126 {
127         struct kernfs_node *kn, *common;
128         const char parent_str[] = "/..";
129         size_t depth_from, depth_to, len = 0;
130         int i, j;
131 
132         if (!kn_to)
133                 return strlcpy(buf, "(null)", buflen);
134 
135         if (!kn_from)
136                 kn_from = kernfs_root(kn_to)->kn;
137 
138         if (kn_from == kn_to)
139                 return strlcpy(buf, "/", buflen);
140 
141         common = kernfs_common_ancestor(kn_from, kn_to);
142         if (WARN_ON(!common))
143                 return -EINVAL;
144 
145         depth_to = kernfs_depth(common, kn_to);
146         depth_from = kernfs_depth(common, kn_from);
147 
148         if (buf)
149                 buf[0] = '\0';
150 
151         for (i = 0; i < depth_from; i++)
152                 len += strlcpy(buf + len, parent_str,
153                                len < buflen ? buflen - len : 0);
154 
155         /* Calculate how many bytes we need for the rest */
156         for (i = depth_to - 1; i >= 0; i--) {
157                 for (kn = kn_to, j = 0; j < i; j++)
158                         kn = kn->parent;
159                 len += strlcpy(buf + len, "/",
160                                len < buflen ? buflen - len : 0);
161                 len += strlcpy(buf + len, kn->name,
162                                len < buflen ? buflen - len : 0);
163         }
164 
165         return len;
166 }
167 
168 /**
169  * kernfs_name - obtain the name of a given node
170  * @kn: kernfs_node of interest
171  * @buf: buffer to copy @kn's name into
172  * @buflen: size of @buf
173  *
174  * Copies the name of @kn into @buf of @buflen bytes.  The behavior is
175  * similar to strlcpy().  It returns the length of @kn's name and if @buf
176  * isn't long enough, it's filled upto @buflen-1 and nul terminated.
177  *
178  * Fills buffer with "(null)" if @kn is NULL.
179  *
180  * This function can be called from any context.
181  */
182 int kernfs_name(struct kernfs_node *kn, char *buf, size_t buflen)
183 {
184         unsigned long flags;
185         int ret;
186 
187         spin_lock_irqsave(&kernfs_rename_lock, flags);
188         ret = kernfs_name_locked(kn, buf, buflen);
189         spin_unlock_irqrestore(&kernfs_rename_lock, flags);
190         return ret;
191 }
192 
193 /**
194  * kernfs_path_from_node - build path of node @to relative to @from.
195  * @from: parent kernfs_node relative to which we need to build the path
196  * @to: kernfs_node of interest
197  * @buf: buffer to copy @to's path into
198  * @buflen: size of @buf
199  *
200  * Builds @to's path relative to @from in @buf. @from and @to must
201  * be on the same kernfs-root. If @from is not parent of @to, then a relative
202  * path (which includes '..'s) as needed to reach from @from to @to is
203  * returned.
204  *
205  * Returns the length of the full path.  If the full length is equal to or
206  * greater than @buflen, @buf contains the truncated path with the trailing
207  * '\0'.  On error, -errno is returned.
208  */
209 int kernfs_path_from_node(struct kernfs_node *to, struct kernfs_node *from,
210                           char *buf, size_t buflen)
211 {
212         unsigned long flags;
213         int ret;
214 
215         spin_lock_irqsave(&kernfs_rename_lock, flags);
216         ret = kernfs_path_from_node_locked(to, from, buf, buflen);
217         spin_unlock_irqrestore(&kernfs_rename_lock, flags);
218         return ret;
219 }
220 EXPORT_SYMBOL_GPL(kernfs_path_from_node);
221 
222 /**
223  * pr_cont_kernfs_name - pr_cont name of a kernfs_node
224  * @kn: kernfs_node of interest
225  *
226  * This function can be called from any context.
227  */
228 void pr_cont_kernfs_name(struct kernfs_node *kn)
229 {
230         unsigned long flags;
231 
232         spin_lock_irqsave(&kernfs_rename_lock, flags);
233 
234         kernfs_name_locked(kn, kernfs_pr_cont_buf, sizeof(kernfs_pr_cont_buf));
235         pr_cont("%s", kernfs_pr_cont_buf);
236 
237         spin_unlock_irqrestore(&kernfs_rename_lock, flags);
238 }
239 
240 /**
241  * pr_cont_kernfs_path - pr_cont path of a kernfs_node
242  * @kn: kernfs_node of interest
243  *
244  * This function can be called from any context.
245  */
246 void pr_cont_kernfs_path(struct kernfs_node *kn)
247 {
248         unsigned long flags;
249         int sz;
250 
251         spin_lock_irqsave(&kernfs_rename_lock, flags);
252 
253         sz = kernfs_path_from_node_locked(kn, NULL, kernfs_pr_cont_buf,
254                                           sizeof(kernfs_pr_cont_buf));
255         if (sz < 0) {
256                 pr_cont("(error)");
257                 goto out;
258         }
259 
260         if (sz >= sizeof(kernfs_pr_cont_buf)) {
261                 pr_cont("(name too long)");
262                 goto out;
263         }
264 
265         pr_cont("%s", kernfs_pr_cont_buf);
266 
267 out:
268         spin_unlock_irqrestore(&kernfs_rename_lock, flags);
269 }
270 
271 /**
272  * kernfs_get_parent - determine the parent node and pin it
273  * @kn: kernfs_node of interest
274  *
275  * Determines @kn's parent, pins and returns it.  This function can be
276  * called from any context.
277  */
278 struct kernfs_node *kernfs_get_parent(struct kernfs_node *kn)
279 {
280         struct kernfs_node *parent;
281         unsigned long flags;
282 
283         spin_lock_irqsave(&kernfs_rename_lock, flags);
284         parent = kn->parent;
285         kernfs_get(parent);
286         spin_unlock_irqrestore(&kernfs_rename_lock, flags);
287 
288         return parent;
289 }
290 
291 /**
292  *      kernfs_name_hash
293  *      @name: Null terminated string to hash
294  *      @ns:   Namespace tag to hash
295  *
296  *      Returns 31 bit hash of ns + name (so it fits in an off_t )
297  */
298 static unsigned int kernfs_name_hash(const char *name, const void *ns)
299 {
300         unsigned long hash = init_name_hash(ns);
301         unsigned int len = strlen(name);
302         while (len--)
303                 hash = partial_name_hash(*name++, hash);
304         hash = end_name_hash(hash);
305         hash &= 0x7fffffffU;
306         /* Reserve hash numbers 0, 1 and INT_MAX for magic directory entries */
307         if (hash < 2)
308                 hash += 2;
309         if (hash >= INT_MAX)
310                 hash = INT_MAX - 1;
311         return hash;
312 }
313 
314 static int kernfs_name_compare(unsigned int hash, const char *name,
315                                const void *ns, const struct kernfs_node *kn)
316 {
317         if (hash < kn->hash)
318                 return -1;
319         if (hash > kn->hash)
320                 return 1;
321         if (ns < kn->ns)
322                 return -1;
323         if (ns > kn->ns)
324                 return 1;
325         return strcmp(name, kn->name);
326 }
327 
328 static int kernfs_sd_compare(const struct kernfs_node *left,
329                              const struct kernfs_node *right)
330 {
331         return kernfs_name_compare(left->hash, left->name, left->ns, right);
332 }
333 
334 /**
335  *      kernfs_link_sibling - link kernfs_node into sibling rbtree
336  *      @kn: kernfs_node of interest
337  *
338  *      Link @kn into its sibling rbtree which starts from
339  *      @kn->parent->dir.children.
340  *
341  *      Locking:
342  *      mutex_lock(kernfs_mutex)
343  *
344  *      RETURNS:
345  *      0 on susccess -EEXIST on failure.
346  */
347 static int kernfs_link_sibling(struct kernfs_node *kn)
348 {
349         struct rb_node **node = &kn->parent->dir.children.rb_node;
350         struct rb_node *parent = NULL;
351 
352         while (*node) {
353                 struct kernfs_node *pos;
354                 int result;
355 
356                 pos = rb_to_kn(*node);
357                 parent = *node;
358                 result = kernfs_sd_compare(kn, pos);
359                 if (result < 0)
360                         node = &pos->rb.rb_left;
361                 else if (result > 0)
362                         node = &pos->rb.rb_right;
363                 else
364                         return -EEXIST;
365         }
366 
367         /* add new node and rebalance the tree */
368         rb_link_node(&kn->rb, parent, node);
369         rb_insert_color(&kn->rb, &kn->parent->dir.children);
370 
371         /* successfully added, account subdir number */
372         if (kernfs_type(kn) == KERNFS_DIR)
373                 kn->parent->dir.subdirs++;
374 
375         return 0;
376 }
377 
378 /**
379  *      kernfs_unlink_sibling - unlink kernfs_node from sibling rbtree
380  *      @kn: kernfs_node of interest
381  *
382  *      Try to unlink @kn from its sibling rbtree which starts from
383  *      kn->parent->dir.children.  Returns %true if @kn was actually
384  *      removed, %false if @kn wasn't on the rbtree.
385  *
386  *      Locking:
387  *      mutex_lock(kernfs_mutex)
388  */
389 static bool kernfs_unlink_sibling(struct kernfs_node *kn)
390 {
391         if (RB_EMPTY_NODE(&kn->rb))
392                 return false;
393 
394         if (kernfs_type(kn) == KERNFS_DIR)
395                 kn->parent->dir.subdirs--;
396 
397         rb_erase(&kn->rb, &kn->parent->dir.children);
398         RB_CLEAR_NODE(&kn->rb);
399         return true;
400 }
401 
402 /**
403  *      kernfs_get_active - get an active reference to kernfs_node
404  *      @kn: kernfs_node to get an active reference to
405  *
406  *      Get an active reference of @kn.  This function is noop if @kn
407  *      is NULL.
408  *
409  *      RETURNS:
410  *      Pointer to @kn on success, NULL on failure.
411  */
412 struct kernfs_node *kernfs_get_active(struct kernfs_node *kn)
413 {
414         if (unlikely(!kn))
415                 return NULL;
416 
417         if (!atomic_inc_unless_negative(&kn->active))
418                 return NULL;
419 
420         if (kernfs_lockdep(kn))
421                 rwsem_acquire_read(&kn->dep_map, 0, 1, _RET_IP_);
422         return kn;
423 }
424 
425 /**
426  *      kernfs_put_active - put an active reference to kernfs_node
427  *      @kn: kernfs_node to put an active reference to
428  *
429  *      Put an active reference to @kn.  This function is noop if @kn
430  *      is NULL.
431  */
432 void kernfs_put_active(struct kernfs_node *kn)
433 {
434         struct kernfs_root *root = kernfs_root(kn);
435         int v;
436 
437         if (unlikely(!kn))
438                 return;
439 
440         if (kernfs_lockdep(kn))
441                 rwsem_release(&kn->dep_map, 1, _RET_IP_);
442         v = atomic_dec_return(&kn->active);
443         if (likely(v != KN_DEACTIVATED_BIAS))
444                 return;
445 
446         wake_up_all(&root->deactivate_waitq);
447 }
448 
449 /**
450  * kernfs_drain - drain kernfs_node
451  * @kn: kernfs_node to drain
452  *
453  * Drain existing usages and nuke all existing mmaps of @kn.  Mutiple
454  * removers may invoke this function concurrently on @kn and all will
455  * return after draining is complete.
456  */
457 static void kernfs_drain(struct kernfs_node *kn)
458         __releases(&kernfs_mutex) __acquires(&kernfs_mutex)
459 {
460         struct kernfs_root *root = kernfs_root(kn);
461 
462         lockdep_assert_held(&kernfs_mutex);
463         WARN_ON_ONCE(kernfs_active(kn));
464 
465         mutex_unlock(&kernfs_mutex);
466 
467         if (kernfs_lockdep(kn)) {
468                 rwsem_acquire(&kn->dep_map, 0, 0, _RET_IP_);
469                 if (atomic_read(&kn->active) != KN_DEACTIVATED_BIAS)
470                         lock_contended(&kn->dep_map, _RET_IP_);
471         }
472 
473         /* but everyone should wait for draining */
474         wait_event(root->deactivate_waitq,
475                    atomic_read(&kn->active) == KN_DEACTIVATED_BIAS);
476 
477         if (kernfs_lockdep(kn)) {
478                 lock_acquired(&kn->dep_map, _RET_IP_);
479                 rwsem_release(&kn->dep_map, 1, _RET_IP_);
480         }
481 
482         kernfs_drain_open_files(kn);
483 
484         mutex_lock(&kernfs_mutex);
485 }
486 
487 /**
488  * kernfs_get - get a reference count on a kernfs_node
489  * @kn: the target kernfs_node
490  */
491 void kernfs_get(struct kernfs_node *kn)
492 {
493         if (kn) {
494                 WARN_ON(!atomic_read(&kn->count));
495                 atomic_inc(&kn->count);
496         }
497 }
498 EXPORT_SYMBOL_GPL(kernfs_get);
499 
500 /**
501  * kernfs_put - put a reference count on a kernfs_node
502  * @kn: the target kernfs_node
503  *
504  * Put a reference count of @kn and destroy it if it reached zero.
505  */
506 void kernfs_put(struct kernfs_node *kn)
507 {
508         struct kernfs_node *parent;
509         struct kernfs_root *root;
510 
511         /*
512          * kernfs_node is freed with ->count 0, kernfs_find_and_get_node_by_ino
513          * depends on this to filter reused stale node
514          */
515         if (!kn || !atomic_dec_and_test(&kn->count))
516                 return;
517         root = kernfs_root(kn);
518  repeat:
519         /*
520          * Moving/renaming is always done while holding reference.
521          * kn->parent won't change beneath us.
522          */
523         parent = kn->parent;
524 
525         WARN_ONCE(atomic_read(&kn->active) != KN_DEACTIVATED_BIAS,
526                   "kernfs_put: %s/%s: released with incorrect active_ref %d\n",
527                   parent ? parent->name : "", kn->name, atomic_read(&kn->active));
528 
529         if (kernfs_type(kn) == KERNFS_LINK)
530                 kernfs_put(kn->symlink.target_kn);
531 
532         kfree_const(kn->name);
533 
534         if (kn->iattr) {
535                 if (kn->iattr->ia_secdata)
536                         security_release_secctx(kn->iattr->ia_secdata,
537                                                 kn->iattr->ia_secdata_len);
538                 simple_xattrs_free(&kn->iattr->xattrs);
539         }
540         kfree(kn->iattr);
541         spin_lock(&kernfs_idr_lock);
542         idr_remove(&root->ino_idr, kn->id.ino);
543         spin_unlock(&kernfs_idr_lock);
544         kmem_cache_free(kernfs_node_cache, kn);
545 
546         kn = parent;
547         if (kn) {
548                 if (atomic_dec_and_test(&kn->count))
549                         goto repeat;
550         } else {
551                 /* just released the root kn, free @root too */
552                 idr_destroy(&root->ino_idr);
553                 kfree(root);
554         }
555 }
556 EXPORT_SYMBOL_GPL(kernfs_put);
557 
558 static int kernfs_dop_revalidate(struct dentry *dentry, unsigned int flags)
559 {
560         struct kernfs_node *kn;
561 
562         if (flags & LOOKUP_RCU)
563                 return -ECHILD;
564 
565         /* Always perform fresh lookup for negatives */
566         if (d_really_is_negative(dentry))
567                 goto out_bad_unlocked;
568 
569         kn = kernfs_dentry_node(dentry);
570         mutex_lock(&kernfs_mutex);
571 
572         /* The kernfs node has been deactivated */
573         if (!kernfs_active(kn))
574                 goto out_bad;
575 
576         /* The kernfs node has been moved? */
577         if (kernfs_dentry_node(dentry->d_parent) != kn->parent)
578                 goto out_bad;
579 
580         /* The kernfs node has been renamed */
581         if (strcmp(dentry->d_name.name, kn->name) != 0)
582                 goto out_bad;
583 
584         /* The kernfs node has been moved to a different namespace */
585         if (kn->parent && kernfs_ns_enabled(kn->parent) &&
586             kernfs_info(dentry->d_sb)->ns != kn->ns)
587                 goto out_bad;
588 
589         mutex_unlock(&kernfs_mutex);
590         return 1;
591 out_bad:
592         mutex_unlock(&kernfs_mutex);
593 out_bad_unlocked:
594         return 0;
595 }
596 
597 const struct dentry_operations kernfs_dops = {
598         .d_revalidate   = kernfs_dop_revalidate,
599 };
600 
601 /**
602  * kernfs_node_from_dentry - determine kernfs_node associated with a dentry
603  * @dentry: the dentry in question
604  *
605  * Return the kernfs_node associated with @dentry.  If @dentry is not a
606  * kernfs one, %NULL is returned.
607  *
608  * While the returned kernfs_node will stay accessible as long as @dentry
609  * is accessible, the returned node can be in any state and the caller is
610  * fully responsible for determining what's accessible.
611  */
612 struct kernfs_node *kernfs_node_from_dentry(struct dentry *dentry)
613 {
614         if (dentry->d_sb->s_op == &kernfs_sops &&
615             !d_really_is_negative(dentry))
616                 return kernfs_dentry_node(dentry);
617         return NULL;
618 }
619 
620 static struct kernfs_node *__kernfs_new_node(struct kernfs_root *root,
621                                              const char *name, umode_t mode,
622                                              unsigned flags)
623 {
624         struct kernfs_node *kn;
625         u32 gen;
626         int cursor;
627         int ret;
628 
629         name = kstrdup_const(name, GFP_KERNEL);
630         if (!name)
631                 return NULL;
632 
633         kn = kmem_cache_zalloc(kernfs_node_cache, GFP_KERNEL);
634         if (!kn)
635                 goto err_out1;
636 
637         idr_preload(GFP_KERNEL);
638         spin_lock(&kernfs_idr_lock);
639         cursor = idr_get_cursor(&root->ino_idr);
640         ret = idr_alloc_cyclic(&root->ino_idr, kn, 1, 0, GFP_ATOMIC);
641         if (ret >= 0 && ret < cursor)
642                 root->next_generation++;
643         gen = root->next_generation;
644         spin_unlock(&kernfs_idr_lock);
645         idr_preload_end();
646         if (ret < 0)
647                 goto err_out2;
648         kn->id.ino = ret;
649         kn->id.generation = gen;
650 
651         /*
652          * set ino first. This barrier is paired with atomic_inc_not_zero in
653          * kernfs_find_and_get_node_by_ino
654          */
655         smp_mb__before_atomic();
656         atomic_set(&kn->count, 1);
657         atomic_set(&kn->active, KN_DEACTIVATED_BIAS);
658         RB_CLEAR_NODE(&kn->rb);
659 
660         kn->name = name;
661         kn->mode = mode;
662         kn->flags = flags;
663 
664         return kn;
665 
666  err_out2:
667         kmem_cache_free(kernfs_node_cache, kn);
668  err_out1:
669         kfree_const(name);
670         return NULL;
671 }
672 
673 struct kernfs_node *kernfs_new_node(struct kernfs_node *parent,
674                                     const char *name, umode_t mode,
675                                     unsigned flags)
676 {
677         struct kernfs_node *kn;
678 
679         kn = __kernfs_new_node(kernfs_root(parent), name, mode, flags);
680         if (kn) {
681                 kernfs_get(parent);
682                 kn->parent = parent;
683         }
684         return kn;
685 }
686 
687 /*
688  * kernfs_find_and_get_node_by_ino - get kernfs_node from inode number
689  * @root: the kernfs root
690  * @ino: inode number
691  *
692  * RETURNS:
693  * NULL on failure. Return a kernfs node with reference counter incremented
694  */
695 struct kernfs_node *kernfs_find_and_get_node_by_ino(struct kernfs_root *root,
696                                                     unsigned int ino)
697 {
698         struct kernfs_node *kn;
699 
700         rcu_read_lock();
701         kn = idr_find(&root->ino_idr, ino);
702         if (!kn)
703                 goto out;
704 
705         /*
706          * Since kernfs_node is freed in RCU, it's possible an old node for ino
707          * is freed, but reused before RCU grace period. But a freed node (see
708          * kernfs_put) or an incompletedly initialized node (see
709          * __kernfs_new_node) should have 'count' 0. We can use this fact to
710          * filter out such node.
711          */
712         if (!atomic_inc_not_zero(&kn->count)) {
713                 kn = NULL;
714                 goto out;
715         }
716 
717         /*
718          * The node could be a new node or a reused node. If it's a new node,
719          * we are ok. If it's reused because of RCU (because of
720          * SLAB_TYPESAFE_BY_RCU), the __kernfs_new_node always sets its 'ino'
721          * before 'count'. So if 'count' is uptodate, 'ino' should be uptodate,
722          * hence we can use 'ino' to filter stale node.
723          */
724         if (kn->id.ino != ino)
725                 goto out;
726         rcu_read_unlock();
727 
728         return kn;
729 out:
730         rcu_read_unlock();
731         kernfs_put(kn);
732         return NULL;
733 }
734 
735 /**
736  *      kernfs_add_one - add kernfs_node to parent without warning
737  *      @kn: kernfs_node to be added
738  *
739  *      The caller must already have initialized @kn->parent.  This
740  *      function increments nlink of the parent's inode if @kn is a
741  *      directory and link into the children list of the parent.
742  *
743  *      RETURNS:
744  *      0 on success, -EEXIST if entry with the given name already
745  *      exists.
746  */
747 int kernfs_add_one(struct kernfs_node *kn)
748 {
749         struct kernfs_node *parent = kn->parent;
750         struct kernfs_iattrs *ps_iattr;
751         bool has_ns;
752         int ret;
753 
754         mutex_lock(&kernfs_mutex);
755 
756         ret = -EINVAL;
757         has_ns = kernfs_ns_enabled(parent);
758         if (WARN(has_ns != (bool)kn->ns, KERN_WARNING "kernfs: ns %s in '%s' for '%s'\n",
759                  has_ns ? "required" : "invalid", parent->name, kn->name))
760                 goto out_unlock;
761 
762         if (kernfs_type(parent) != KERNFS_DIR)
763                 goto out_unlock;
764 
765         ret = -ENOENT;
766         if (parent->flags & KERNFS_EMPTY_DIR)
767                 goto out_unlock;
768 
769         if ((parent->flags & KERNFS_ACTIVATED) && !kernfs_active(parent))
770                 goto out_unlock;
771 
772         kn->hash = kernfs_name_hash(kn->name, kn->ns);
773 
774         ret = kernfs_link_sibling(kn);
775         if (ret)
776                 goto out_unlock;
777 
778         /* Update timestamps on the parent */
779         ps_iattr = parent->iattr;
780         if (ps_iattr) {
781                 struct iattr *ps_iattrs = &ps_iattr->ia_iattr;
782                 ktime_get_real_ts(&ps_iattrs->ia_ctime);
783                 ps_iattrs->ia_mtime = ps_iattrs->ia_ctime;
784         }
785 
786         mutex_unlock(&kernfs_mutex);
787 
788         /*
789          * Activate the new node unless CREATE_DEACTIVATED is requested.
790          * If not activated here, the kernfs user is responsible for
791          * activating the node with kernfs_activate().  A node which hasn't
792          * been activated is not visible to userland and its removal won't
793          * trigger deactivation.
794          */
795         if (!(kernfs_root(kn)->flags & KERNFS_ROOT_CREATE_DEACTIVATED))
796                 kernfs_activate(kn);
797         return 0;
798 
799 out_unlock:
800         mutex_unlock(&kernfs_mutex);
801         return ret;
802 }
803 
804 /**
805  * kernfs_find_ns - find kernfs_node with the given name
806  * @parent: kernfs_node to search under
807  * @name: name to look for
808  * @ns: the namespace tag to use
809  *
810  * Look for kernfs_node with name @name under @parent.  Returns pointer to
811  * the found kernfs_node on success, %NULL on failure.
812  */
813 static struct kernfs_node *kernfs_find_ns(struct kernfs_node *parent,
814                                           const unsigned char *name,
815                                           const void *ns)
816 {
817         struct rb_node *node = parent->dir.children.rb_node;
818         bool has_ns = kernfs_ns_enabled(parent);
819         unsigned int hash;
820 
821         lockdep_assert_held(&kernfs_mutex);
822 
823         if (has_ns != (bool)ns) {
824                 WARN(1, KERN_WARNING "kernfs: ns %s in '%s' for '%s'\n",
825                      has_ns ? "required" : "invalid", parent->name, name);
826                 return NULL;
827         }
828 
829         hash = kernfs_name_hash(name, ns);
830         while (node) {
831                 struct kernfs_node *kn;
832                 int result;
833 
834                 kn = rb_to_kn(node);
835                 result = kernfs_name_compare(hash, name, ns, kn);
836                 if (result < 0)
837                         node = node->rb_left;
838                 else if (result > 0)
839                         node = node->rb_right;
840                 else
841                         return kn;
842         }
843         return NULL;
844 }
845 
846 static struct kernfs_node *kernfs_walk_ns(struct kernfs_node *parent,
847                                           const unsigned char *path,
848                                           const void *ns)
849 {
850         size_t len;
851         char *p, *name;
852 
853         lockdep_assert_held(&kernfs_mutex);
854 
855         /* grab kernfs_rename_lock to piggy back on kernfs_pr_cont_buf */
856         spin_lock_irq(&kernfs_rename_lock);
857 
858         len = strlcpy(kernfs_pr_cont_buf, path, sizeof(kernfs_pr_cont_buf));
859 
860         if (len >= sizeof(kernfs_pr_cont_buf)) {
861                 spin_unlock_irq(&kernfs_rename_lock);
862                 return NULL;
863         }
864 
865         p = kernfs_pr_cont_buf;
866 
867         while ((name = strsep(&p, "/")) && parent) {
868                 if (*name == '\0')
869                         continue;
870                 parent = kernfs_find_ns(parent, name, ns);
871         }
872 
873         spin_unlock_irq(&kernfs_rename_lock);
874 
875         return parent;
876 }
877 
878 /**
879  * kernfs_find_and_get_ns - find and get kernfs_node with the given name
880  * @parent: kernfs_node to search under
881  * @name: name to look for
882  * @ns: the namespace tag to use
883  *
884  * Look for kernfs_node with name @name under @parent and get a reference
885  * if found.  This function may sleep and returns pointer to the found
886  * kernfs_node on success, %NULL on failure.
887  */
888 struct kernfs_node *kernfs_find_and_get_ns(struct kernfs_node *parent,
889                                            const char *name, const void *ns)
890 {
891         struct kernfs_node *kn;
892 
893         mutex_lock(&kernfs_mutex);
894         kn = kernfs_find_ns(parent, name, ns);
895         kernfs_get(kn);
896         mutex_unlock(&kernfs_mutex);
897 
898         return kn;
899 }
900 EXPORT_SYMBOL_GPL(kernfs_find_and_get_ns);
901 
902 /**
903  * kernfs_walk_and_get_ns - find and get kernfs_node with the given path
904  * @parent: kernfs_node to search under
905  * @path: path to look for
906  * @ns: the namespace tag to use
907  *
908  * Look for kernfs_node with path @path under @parent and get a reference
909  * if found.  This function may sleep and returns pointer to the found
910  * kernfs_node on success, %NULL on failure.
911  */
912 struct kernfs_node *kernfs_walk_and_get_ns(struct kernfs_node *parent,
913                                            const char *path, const void *ns)
914 {
915         struct kernfs_node *kn;
916 
917         mutex_lock(&kernfs_mutex);
918         kn = kernfs_walk_ns(parent, path, ns);
919         kernfs_get(kn);
920         mutex_unlock(&kernfs_mutex);
921 
922         return kn;
923 }
924 
925 /**
926  * kernfs_create_root - create a new kernfs hierarchy
927  * @scops: optional syscall operations for the hierarchy
928  * @flags: KERNFS_ROOT_* flags
929  * @priv: opaque data associated with the new directory
930  *
931  * Returns the root of the new hierarchy on success, ERR_PTR() value on
932  * failure.
933  */
934 struct kernfs_root *kernfs_create_root(struct kernfs_syscall_ops *scops,
935                                        unsigned int flags, void *priv)
936 {
937         struct kernfs_root *root;
938         struct kernfs_node *kn;
939 
940         root = kzalloc(sizeof(*root), GFP_KERNEL);
941         if (!root)
942                 return ERR_PTR(-ENOMEM);
943 
944         idr_init(&root->ino_idr);
945         INIT_LIST_HEAD(&root->supers);
946         root->next_generation = 1;
947 
948         kn = __kernfs_new_node(root, "", S_IFDIR | S_IRUGO | S_IXUGO,
949                                KERNFS_DIR);
950         if (!kn) {
951                 idr_destroy(&root->ino_idr);
952                 kfree(root);
953                 return ERR_PTR(-ENOMEM);
954         }
955 
956         kn->priv = priv;
957         kn->dir.root = root;
958 
959         root->syscall_ops = scops;
960         root->flags = flags;
961         root->kn = kn;
962         init_waitqueue_head(&root->deactivate_waitq);
963 
964         if (!(root->flags & KERNFS_ROOT_CREATE_DEACTIVATED))
965                 kernfs_activate(kn);
966 
967         return root;
968 }
969 
970 /**
971  * kernfs_destroy_root - destroy a kernfs hierarchy
972  * @root: root of the hierarchy to destroy
973  *
974  * Destroy the hierarchy anchored at @root by removing all existing
975  * directories and destroying @root.
976  */
977 void kernfs_destroy_root(struct kernfs_root *root)
978 {
979         kernfs_remove(root->kn);        /* will also free @root */
980 }
981 
982 /**
983  * kernfs_create_dir_ns - create a directory
984  * @parent: parent in which to create a new directory
985  * @name: name of the new directory
986  * @mode: mode of the new directory
987  * @priv: opaque data associated with the new directory
988  * @ns: optional namespace tag of the directory
989  *
990  * Returns the created node on success, ERR_PTR() value on failure.
991  */
992 struct kernfs_node *kernfs_create_dir_ns(struct kernfs_node *parent,
993                                          const char *name, umode_t mode,
994                                          void *priv, const void *ns)
995 {
996         struct kernfs_node *kn;
997         int rc;
998 
999         /* allocate */
1000         kn = kernfs_new_node(parent, name, mode | S_IFDIR, KERNFS_DIR);
1001         if (!kn)
1002                 return ERR_PTR(-ENOMEM);
1003 
1004         kn->dir.root = parent->dir.root;
1005         kn->ns = ns;
1006         kn->priv = priv;
1007 
1008         /* link in */
1009         rc = kernfs_add_one(kn);
1010         if (!rc)
1011                 return kn;
1012 
1013         kernfs_put(kn);
1014         return ERR_PTR(rc);
1015 }
1016 
1017 /**
1018  * kernfs_create_empty_dir - create an always empty directory
1019  * @parent: parent in which to create a new directory
1020  * @name: name of the new directory
1021  *
1022  * Returns the created node on success, ERR_PTR() value on failure.
1023  */
1024 struct kernfs_node *kernfs_create_empty_dir(struct kernfs_node *parent,
1025                                             const char *name)
1026 {
1027         struct kernfs_node *kn;
1028         int rc;
1029 
1030         /* allocate */
1031         kn = kernfs_new_node(parent, name, S_IRUGO|S_IXUGO|S_IFDIR, KERNFS_DIR);
1032         if (!kn)
1033                 return ERR_PTR(-ENOMEM);
1034 
1035         kn->flags |= KERNFS_EMPTY_DIR;
1036         kn->dir.root = parent->dir.root;
1037         kn->ns = NULL;
1038         kn->priv = NULL;
1039 
1040         /* link in */
1041         rc = kernfs_add_one(kn);
1042         if (!rc)
1043                 return kn;
1044 
1045         kernfs_put(kn);
1046         return ERR_PTR(rc);
1047 }
1048 
1049 static struct dentry *kernfs_iop_lookup(struct inode *dir,
1050                                         struct dentry *dentry,
1051                                         unsigned int flags)
1052 {
1053         struct dentry *ret;
1054         struct kernfs_node *parent = dir->i_private;
1055         struct kernfs_node *kn;
1056         struct inode *inode;
1057         const void *ns = NULL;
1058 
1059         mutex_lock(&kernfs_mutex);
1060 
1061         if (kernfs_ns_enabled(parent))
1062                 ns = kernfs_info(dir->i_sb)->ns;
1063 
1064         kn = kernfs_find_ns(parent, dentry->d_name.name, ns);
1065 
1066         /* no such entry */
1067         if (!kn || !kernfs_active(kn)) {
1068                 ret = NULL;
1069                 goto out_unlock;
1070         }
1071 
1072         /* attach dentry and inode */
1073         inode = kernfs_get_inode(dir->i_sb, kn);
1074         if (!inode) {
1075                 ret = ERR_PTR(-ENOMEM);
1076                 goto out_unlock;
1077         }
1078 
1079         /* instantiate and hash dentry */
1080         ret = d_splice_alias(inode, dentry);
1081  out_unlock:
1082         mutex_unlock(&kernfs_mutex);
1083         return ret;
1084 }
1085 
1086 static int kernfs_iop_mkdir(struct inode *dir, struct dentry *dentry,
1087                             umode_t mode)
1088 {
1089         struct kernfs_node *parent = dir->i_private;
1090         struct kernfs_syscall_ops *scops = kernfs_root(parent)->syscall_ops;
1091         int ret;
1092 
1093         if (!scops || !scops->mkdir)
1094                 return -EPERM;
1095 
1096         if (!kernfs_get_active(parent))
1097                 return -ENODEV;
1098 
1099         ret = scops->mkdir(parent, dentry->d_name.name, mode);
1100 
1101         kernfs_put_active(parent);
1102         return ret;
1103 }
1104 
1105 static int kernfs_iop_rmdir(struct inode *dir, struct dentry *dentry)
1106 {
1107         struct kernfs_node *kn  = kernfs_dentry_node(dentry);
1108         struct kernfs_syscall_ops *scops = kernfs_root(kn)->syscall_ops;
1109         int ret;
1110 
1111         if (!scops || !scops->rmdir)
1112                 return -EPERM;
1113 
1114         if (!kernfs_get_active(kn))
1115                 return -ENODEV;
1116 
1117         ret = scops->rmdir(kn);
1118 
1119         kernfs_put_active(kn);
1120         return ret;
1121 }
1122 
1123 static int kernfs_iop_rename(struct inode *old_dir, struct dentry *old_dentry,
1124                              struct inode *new_dir, struct dentry *new_dentry,
1125                              unsigned int flags)
1126 {
1127         struct kernfs_node *kn = kernfs_dentry_node(old_dentry);
1128         struct kernfs_node *new_parent = new_dir->i_private;
1129         struct kernfs_syscall_ops *scops = kernfs_root(kn)->syscall_ops;
1130         int ret;
1131 
1132         if (flags)
1133                 return -EINVAL;
1134 
1135         if (!scops || !scops->rename)
1136                 return -EPERM;
1137 
1138         if (!kernfs_get_active(kn))
1139                 return -ENODEV;
1140 
1141         if (!kernfs_get_active(new_parent)) {
1142                 kernfs_put_active(kn);
1143                 return -ENODEV;
1144         }
1145 
1146         ret = scops->rename(kn, new_parent, new_dentry->d_name.name);
1147 
1148         kernfs_put_active(new_parent);
1149         kernfs_put_active(kn);
1150         return ret;
1151 }
1152 
1153 const struct inode_operations kernfs_dir_iops = {
1154         .lookup         = kernfs_iop_lookup,
1155         .permission     = kernfs_iop_permission,
1156         .setattr        = kernfs_iop_setattr,
1157         .getattr        = kernfs_iop_getattr,
1158         .listxattr      = kernfs_iop_listxattr,
1159 
1160         .mkdir          = kernfs_iop_mkdir,
1161         .rmdir          = kernfs_iop_rmdir,
1162         .rename         = kernfs_iop_rename,
1163 };
1164 
1165 static struct kernfs_node *kernfs_leftmost_descendant(struct kernfs_node *pos)
1166 {
1167         struct kernfs_node *last;
1168 
1169         while (true) {
1170                 struct rb_node *rbn;
1171 
1172                 last = pos;
1173 
1174                 if (kernfs_type(pos) != KERNFS_DIR)
1175                         break;
1176 
1177                 rbn = rb_first(&pos->dir.children);
1178                 if (!rbn)
1179                         break;
1180 
1181                 pos = rb_to_kn(rbn);
1182         }
1183 
1184         return last;
1185 }
1186 
1187 /**
1188  * kernfs_next_descendant_post - find the next descendant for post-order walk
1189  * @pos: the current position (%NULL to initiate traversal)
1190  * @root: kernfs_node whose descendants to walk
1191  *
1192  * Find the next descendant to visit for post-order traversal of @root's
1193  * descendants.  @root is included in the iteration and the last node to be
1194  * visited.
1195  */
1196 static struct kernfs_node *kernfs_next_descendant_post(struct kernfs_node *pos,
1197                                                        struct kernfs_node *root)
1198 {
1199         struct rb_node *rbn;
1200 
1201         lockdep_assert_held(&kernfs_mutex);
1202 
1203         /* if first iteration, visit leftmost descendant which may be root */
1204         if (!pos)
1205                 return kernfs_leftmost_descendant(root);
1206 
1207         /* if we visited @root, we're done */
1208         if (pos == root)
1209                 return NULL;
1210 
1211         /* if there's an unvisited sibling, visit its leftmost descendant */
1212         rbn = rb_next(&pos->rb);
1213         if (rbn)
1214                 return kernfs_leftmost_descendant(rb_to_kn(rbn));
1215 
1216         /* no sibling left, visit parent */
1217         return pos->parent;
1218 }
1219 
1220 /**
1221  * kernfs_activate - activate a node which started deactivated
1222  * @kn: kernfs_node whose subtree is to be activated
1223  *
1224  * If the root has KERNFS_ROOT_CREATE_DEACTIVATED set, a newly created node
1225  * needs to be explicitly activated.  A node which hasn't been activated
1226  * isn't visible to userland and deactivation is skipped during its
1227  * removal.  This is useful to construct atomic init sequences where
1228  * creation of multiple nodes should either succeed or fail atomically.
1229  *
1230  * The caller is responsible for ensuring that this function is not called
1231  * after kernfs_remove*() is invoked on @kn.
1232  */
1233 void kernfs_activate(struct kernfs_node *kn)
1234 {
1235         struct kernfs_node *pos;
1236 
1237         mutex_lock(&kernfs_mutex);
1238 
1239         pos = NULL;
1240         while ((pos = kernfs_next_descendant_post(pos, kn))) {
1241                 if (!pos || (pos->flags & KERNFS_ACTIVATED))
1242                         continue;
1243 
1244                 WARN_ON_ONCE(pos->parent && RB_EMPTY_NODE(&pos->rb));
1245                 WARN_ON_ONCE(atomic_read(&pos->active) != KN_DEACTIVATED_BIAS);
1246 
1247                 atomic_sub(KN_DEACTIVATED_BIAS, &pos->active);
1248                 pos->flags |= KERNFS_ACTIVATED;
1249         }
1250 
1251         mutex_unlock(&kernfs_mutex);
1252 }
1253 
1254 static void __kernfs_remove(struct kernfs_node *kn)
1255 {
1256         struct kernfs_node *pos;
1257 
1258         lockdep_assert_held(&kernfs_mutex);
1259 
1260         /*
1261          * Short-circuit if non-root @kn has already finished removal.
1262          * This is for kernfs_remove_self() which plays with active ref
1263          * after removal.
1264          */
1265         if (!kn || (kn->parent && RB_EMPTY_NODE(&kn->rb)))
1266                 return;
1267 
1268         pr_debug("kernfs %s: removing\n", kn->name);
1269 
1270         /* prevent any new usage under @kn by deactivating all nodes */
1271         pos = NULL;
1272         while ((pos = kernfs_next_descendant_post(pos, kn)))
1273                 if (kernfs_active(pos))
1274                         atomic_add(KN_DEACTIVATED_BIAS, &pos->active);
1275 
1276         /* deactivate and unlink the subtree node-by-node */
1277         do {
1278                 pos = kernfs_leftmost_descendant(kn);
1279 
1280                 /*
1281                  * kernfs_drain() drops kernfs_mutex temporarily and @pos's
1282                  * base ref could have been put by someone else by the time
1283                  * the function returns.  Make sure it doesn't go away
1284                  * underneath us.
1285                  */
1286                 kernfs_get(pos);
1287 
1288                 /*
1289                  * Drain iff @kn was activated.  This avoids draining and
1290                  * its lockdep annotations for nodes which have never been
1291                  * activated and allows embedding kernfs_remove() in create
1292                  * error paths without worrying about draining.
1293                  */
1294                 if (kn->flags & KERNFS_ACTIVATED)
1295                         kernfs_drain(pos);
1296                 else
1297                         WARN_ON_ONCE(atomic_read(&kn->active) != KN_DEACTIVATED_BIAS);
1298 
1299                 /*
1300                  * kernfs_unlink_sibling() succeeds once per node.  Use it
1301                  * to decide who's responsible for cleanups.
1302                  */
1303                 if (!pos->parent || kernfs_unlink_sibling(pos)) {
1304                         struct kernfs_iattrs *ps_iattr =
1305                                 pos->parent ? pos->parent->iattr : NULL;
1306 
1307                         /* update timestamps on the parent */
1308                         if (ps_iattr) {
1309                                 ktime_get_real_ts(&ps_iattr->ia_iattr.ia_ctime);
1310                                 ps_iattr->ia_iattr.ia_mtime =
1311                                         ps_iattr->ia_iattr.ia_ctime;
1312                         }
1313 
1314                         kernfs_put(pos);
1315                 }
1316 
1317                 kernfs_put(pos);
1318         } while (pos != kn);
1319 }
1320 
1321 /**
1322  * kernfs_remove - remove a kernfs_node recursively
1323  * @kn: the kernfs_node to remove
1324  *
1325  * Remove @kn along with all its subdirectories and files.
1326  */
1327 void kernfs_remove(struct kernfs_node *kn)
1328 {
1329         mutex_lock(&kernfs_mutex);
1330         __kernfs_remove(kn);
1331         mutex_unlock(&kernfs_mutex);
1332 }
1333 
1334 /**
1335  * kernfs_break_active_protection - break out of active protection
1336  * @kn: the self kernfs_node
1337  *
1338  * The caller must be running off of a kernfs operation which is invoked
1339  * with an active reference - e.g. one of kernfs_ops.  Each invocation of
1340  * this function must also be matched with an invocation of
1341  * kernfs_unbreak_active_protection().
1342  *
1343  * This function releases the active reference of @kn the caller is
1344  * holding.  Once this function is called, @kn may be removed at any point
1345  * and the caller is solely responsible for ensuring that the objects it
1346  * dereferences are accessible.
1347  */
1348 void kernfs_break_active_protection(struct kernfs_node *kn)
1349 {
1350         /*
1351          * Take out ourself out of the active ref dependency chain.  If
1352          * we're called without an active ref, lockdep will complain.
1353          */
1354         kernfs_put_active(kn);
1355 }
1356 
1357 /**
1358  * kernfs_unbreak_active_protection - undo kernfs_break_active_protection()
1359  * @kn: the self kernfs_node
1360  *
1361  * If kernfs_break_active_protection() was called, this function must be
1362  * invoked before finishing the kernfs operation.  Note that while this
1363  * function restores the active reference, it doesn't and can't actually
1364  * restore the active protection - @kn may already or be in the process of
1365  * being removed.  Once kernfs_break_active_protection() is invoked, that
1366  * protection is irreversibly gone for the kernfs operation instance.
1367  *
1368  * While this function may be called at any point after
1369  * kernfs_break_active_protection() is invoked, its most useful location
1370  * would be right before the enclosing kernfs operation returns.
1371  */
1372 void kernfs_unbreak_active_protection(struct kernfs_node *kn)
1373 {
1374         /*
1375          * @kn->active could be in any state; however, the increment we do
1376          * here will be undone as soon as the enclosing kernfs operation
1377          * finishes and this temporary bump can't break anything.  If @kn
1378          * is alive, nothing changes.  If @kn is being deactivated, the
1379          * soon-to-follow put will either finish deactivation or restore
1380          * deactivated state.  If @kn is already removed, the temporary
1381          * bump is guaranteed to be gone before @kn is released.
1382          */
1383         atomic_inc(&kn->active);
1384         if (kernfs_lockdep(kn))
1385                 rwsem_acquire(&kn->dep_map, 0, 1, _RET_IP_);
1386 }
1387 
1388 /**
1389  * kernfs_remove_self - remove a kernfs_node from its own method
1390  * @kn: the self kernfs_node to remove
1391  *
1392  * The caller must be running off of a kernfs operation which is invoked
1393  * with an active reference - e.g. one of kernfs_ops.  This can be used to
1394  * implement a file operation which deletes itself.
1395  *
1396  * For example, the "delete" file for a sysfs device directory can be
1397  * implemented by invoking kernfs_remove_self() on the "delete" file
1398  * itself.  This function breaks the circular dependency of trying to
1399  * deactivate self while holding an active ref itself.  It isn't necessary
1400  * to modify the usual removal path to use kernfs_remove_self().  The
1401  * "delete" implementation can simply invoke kernfs_remove_self() on self
1402  * before proceeding with the usual removal path.  kernfs will ignore later
1403  * kernfs_remove() on self.
1404  *
1405  * kernfs_remove_self() can be called multiple times concurrently on the
1406  * same kernfs_node.  Only the first one actually performs removal and
1407  * returns %true.  All others will wait until the kernfs operation which
1408  * won self-removal finishes and return %false.  Note that the losers wait
1409  * for the completion of not only the winning kernfs_remove_self() but also
1410  * the whole kernfs_ops which won the arbitration.  This can be used to
1411  * guarantee, for example, all concurrent writes to a "delete" file to
1412  * finish only after the whole operation is complete.
1413  */
1414 bool kernfs_remove_self(struct kernfs_node *kn)
1415 {
1416         bool ret;
1417 
1418         mutex_lock(&kernfs_mutex);
1419         kernfs_break_active_protection(kn);
1420 
1421         /*
1422          * SUICIDAL is used to arbitrate among competing invocations.  Only
1423          * the first one will actually perform removal.  When the removal
1424          * is complete, SUICIDED is set and the active ref is restored
1425          * while holding kernfs_mutex.  The ones which lost arbitration
1426          * waits for SUICDED && drained which can happen only after the
1427          * enclosing kernfs operation which executed the winning instance
1428          * of kernfs_remove_self() finished.
1429          */
1430         if (!(kn->flags & KERNFS_SUICIDAL)) {
1431                 kn->flags |= KERNFS_SUICIDAL;
1432                 __kernfs_remove(kn);
1433                 kn->flags |= KERNFS_SUICIDED;
1434                 ret = true;
1435         } else {
1436                 wait_queue_head_t *waitq = &kernfs_root(kn)->deactivate_waitq;
1437                 DEFINE_WAIT(wait);
1438 
1439                 while (true) {
1440                         prepare_to_wait(waitq, &wait, TASK_UNINTERRUPTIBLE);
1441 
1442                         if ((kn->flags & KERNFS_SUICIDED) &&
1443                             atomic_read(&kn->active) == KN_DEACTIVATED_BIAS)
1444                                 break;
1445 
1446                         mutex_unlock(&kernfs_mutex);
1447                         schedule();
1448                         mutex_lock(&kernfs_mutex);
1449                 }
1450                 finish_wait(waitq, &wait);
1451                 WARN_ON_ONCE(!RB_EMPTY_NODE(&kn->rb));
1452                 ret = false;
1453         }
1454 
1455         /*
1456          * This must be done while holding kernfs_mutex; otherwise, waiting
1457          * for SUICIDED && deactivated could finish prematurely.
1458          */
1459         kernfs_unbreak_active_protection(kn);
1460 
1461         mutex_unlock(&kernfs_mutex);
1462         return ret;
1463 }
1464 
1465 /**
1466  * kernfs_remove_by_name_ns - find a kernfs_node by name and remove it
1467  * @parent: parent of the target
1468  * @name: name of the kernfs_node to remove
1469  * @ns: namespace tag of the kernfs_node to remove
1470  *
1471  * Look for the kernfs_node with @name and @ns under @parent and remove it.
1472  * Returns 0 on success, -ENOENT if such entry doesn't exist.
1473  */
1474 int kernfs_remove_by_name_ns(struct kernfs_node *parent, const char *name,
1475                              const void *ns)
1476 {
1477         struct kernfs_node *kn;
1478 
1479         if (!parent) {
1480                 WARN(1, KERN_WARNING "kernfs: can not remove '%s', no directory\n",
1481                         name);
1482                 return -ENOENT;
1483         }
1484 
1485         mutex_lock(&kernfs_mutex);
1486 
1487         kn = kernfs_find_ns(parent, name, ns);
1488         if (kn)
1489                 __kernfs_remove(kn);
1490 
1491         mutex_unlock(&kernfs_mutex);
1492 
1493         if (kn)
1494                 return 0;
1495         else
1496                 return -ENOENT;
1497 }
1498 
1499 /**
1500  * kernfs_rename_ns - move and rename a kernfs_node
1501  * @kn: target node
1502  * @new_parent: new parent to put @sd under
1503  * @new_name: new name
1504  * @new_ns: new namespace tag
1505  */
1506 int kernfs_rename_ns(struct kernfs_node *kn, struct kernfs_node *new_parent,
1507                      const char *new_name, const void *new_ns)
1508 {
1509         struct kernfs_node *old_parent;
1510         const char *old_name = NULL;
1511         int error;
1512 
1513         /* can't move or rename root */
1514         if (!kn->parent)
1515                 return -EINVAL;
1516 
1517         mutex_lock(&kernfs_mutex);
1518 
1519         error = -ENOENT;
1520         if (!kernfs_active(kn) || !kernfs_active(new_parent) ||
1521             (new_parent->flags & KERNFS_EMPTY_DIR))
1522                 goto out;
1523 
1524         error = 0;
1525         if ((kn->parent == new_parent) && (kn->ns == new_ns) &&
1526             (strcmp(kn->name, new_name) == 0))
1527                 goto out;       /* nothing to rename */
1528 
1529         error = -EEXIST;
1530         if (kernfs_find_ns(new_parent, new_name, new_ns))
1531                 goto out;
1532 
1533         /* rename kernfs_node */
1534         if (strcmp(kn->name, new_name) != 0) {
1535                 error = -ENOMEM;
1536                 new_name = kstrdup_const(new_name, GFP_KERNEL);
1537                 if (!new_name)
1538                         goto out;
1539         } else {
1540                 new_name = NULL;
1541         }
1542 
1543         /*
1544          * Move to the appropriate place in the appropriate directories rbtree.
1545          */
1546         kernfs_unlink_sibling(kn);
1547         kernfs_get(new_parent);
1548 
1549         /* rename_lock protects ->parent and ->name accessors */
1550         spin_lock_irq(&kernfs_rename_lock);
1551 
1552         old_parent = kn->parent;
1553         kn->parent = new_parent;
1554 
1555         kn->ns = new_ns;
1556         if (new_name) {
1557                 old_name = kn->name;
1558                 kn->name = new_name;
1559         }
1560 
1561         spin_unlock_irq(&kernfs_rename_lock);
1562 
1563         kn->hash = kernfs_name_hash(kn->name, kn->ns);
1564         kernfs_link_sibling(kn);
1565 
1566         kernfs_put(old_parent);
1567         kfree_const(old_name);
1568 
1569         error = 0;
1570  out:
1571         mutex_unlock(&kernfs_mutex);
1572         return error;
1573 }
1574 
1575 /* Relationship between s_mode and the DT_xxx types */
1576 static inline unsigned char dt_type(struct kernfs_node *kn)
1577 {
1578         return (kn->mode >> 12) & 15;
1579 }
1580 
1581 static int kernfs_dir_fop_release(struct inode *inode, struct file *filp)
1582 {
1583         kernfs_put(filp->private_data);
1584         return 0;
1585 }
1586 
1587 static struct kernfs_node *kernfs_dir_pos(const void *ns,
1588         struct kernfs_node *parent, loff_t hash, struct kernfs_node *pos)
1589 {
1590         if (pos) {
1591                 int valid = kernfs_active(pos) &&
1592                         pos->parent == parent && hash == pos->hash;
1593                 kernfs_put(pos);
1594                 if (!valid)
1595                         pos = NULL;
1596         }
1597         if (!pos && (hash > 1) && (hash < INT_MAX)) {
1598                 struct rb_node *node = parent->dir.children.rb_node;
1599                 while (node) {
1600                         pos = rb_to_kn(node);
1601 
1602                         if (hash < pos->hash)
1603                                 node = node->rb_left;
1604                         else if (hash > pos->hash)
1605                                 node = node->rb_right;
1606                         else
1607                                 break;
1608                 }
1609         }
1610         /* Skip over entries which are dying/dead or in the wrong namespace */
1611         while (pos && (!kernfs_active(pos) || pos->ns != ns)) {
1612                 struct rb_node *node = rb_next(&pos->rb);
1613                 if (!node)
1614                         pos = NULL;
1615                 else
1616                         pos = rb_to_kn(node);
1617         }
1618         return pos;
1619 }
1620 
1621 static struct kernfs_node *kernfs_dir_next_pos(const void *ns,
1622         struct kernfs_node *parent, ino_t ino, struct kernfs_node *pos)
1623 {
1624         pos = kernfs_dir_pos(ns, parent, ino, pos);
1625         if (pos) {
1626                 do {
1627                         struct rb_node *node = rb_next(&pos->rb);
1628                         if (!node)
1629                                 pos = NULL;
1630                         else
1631                                 pos = rb_to_kn(node);
1632                 } while (pos && (!kernfs_active(pos) || pos->ns != ns));
1633         }
1634         return pos;
1635 }
1636 
1637 static int kernfs_fop_readdir(struct file *file, struct dir_context *ctx)
1638 {
1639         struct dentry *dentry = file->f_path.dentry;
1640         struct kernfs_node *parent = kernfs_dentry_node(dentry);
1641         struct kernfs_node *pos = file->private_data;
1642         const void *ns = NULL;
1643 
1644         if (!dir_emit_dots(file, ctx))
1645                 return 0;
1646         mutex_lock(&kernfs_mutex);
1647 
1648         if (kernfs_ns_enabled(parent))
1649                 ns = kernfs_info(dentry->d_sb)->ns;
1650 
1651         for (pos = kernfs_dir_pos(ns, parent, ctx->pos, pos);
1652              pos;
1653              pos = kernfs_dir_next_pos(ns, parent, ctx->pos, pos)) {
1654                 const char *name = pos->name;
1655                 unsigned int type = dt_type(pos);
1656                 int len = strlen(name);
1657                 ino_t ino = pos->id.ino;
1658 
1659                 ctx->pos = pos->hash;
1660                 file->private_data = pos;
1661                 kernfs_get(pos);
1662 
1663                 mutex_unlock(&kernfs_mutex);
1664                 if (!dir_emit(ctx, name, len, ino, type))
1665                         return 0;
1666                 mutex_lock(&kernfs_mutex);
1667         }
1668         mutex_unlock(&kernfs_mutex);
1669         file->private_data = NULL;
1670         ctx->pos = INT_MAX;
1671         return 0;
1672 }
1673 
1674 const struct file_operations kernfs_dir_fops = {
1675         .read           = generic_read_dir,
1676         .iterate_shared = kernfs_fop_readdir,
1677         .release        = kernfs_dir_fop_release,
1678         .llseek         = generic_file_llseek,
1679 };
1680 

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