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TOMOYO Linux Cross Reference
Linux/fs/kernfs/dir.c

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  1 // SPDX-License-Identifier: GPL-2.0-only
  2 /*
  3  * fs/kernfs/dir.c - kernfs directory implementation
  4  *
  5  * Copyright (c) 2001-3 Patrick Mochel
  6  * Copyright (c) 2007 SUSE Linux Products GmbH
  7  * Copyright (c) 2007, 2013 Tejun Heo <tj@kernel.org>
  8  */
  9 
 10 #include <linux/sched.h>
 11 #include <linux/fs.h>
 12 #include <linux/namei.h>
 13 #include <linux/idr.h>
 14 #include <linux/slab.h>
 15 #include <linux/security.h>
 16 #include <linux/hash.h>
 17 
 18 #include "kernfs-internal.h"
 19 
 20 DEFINE_MUTEX(kernfs_mutex);
 21 static DEFINE_SPINLOCK(kernfs_rename_lock);     /* kn->parent and ->name */
 22 static char kernfs_pr_cont_buf[PATH_MAX];       /* protected by rename_lock */
 23 static DEFINE_SPINLOCK(kernfs_idr_lock);        /* root->ino_idr */
 24 
 25 #define rb_to_kn(X) rb_entry((X), struct kernfs_node, rb)
 26 
 27 static bool kernfs_active(struct kernfs_node *kn)
 28 {
 29         lockdep_assert_held(&kernfs_mutex);
 30         return atomic_read(&kn->active) >= 0;
 31 }
 32 
 33 static bool kernfs_lockdep(struct kernfs_node *kn)
 34 {
 35 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 36         return kn->flags & KERNFS_LOCKDEP;
 37 #else
 38         return false;
 39 #endif
 40 }
 41 
 42 static int kernfs_name_locked(struct kernfs_node *kn, char *buf, size_t buflen)
 43 {
 44         if (!kn)
 45                 return strlcpy(buf, "(null)", buflen);
 46 
 47         return strlcpy(buf, kn->parent ? kn->name : "/", buflen);
 48 }
 49 
 50 /* kernfs_node_depth - compute depth from @from to @to */
 51 static size_t kernfs_depth(struct kernfs_node *from, struct kernfs_node *to)
 52 {
 53         size_t depth = 0;
 54 
 55         while (to->parent && to != from) {
 56                 depth++;
 57                 to = to->parent;
 58         }
 59         return depth;
 60 }
 61 
 62 static struct kernfs_node *kernfs_common_ancestor(struct kernfs_node *a,
 63                                                   struct kernfs_node *b)
 64 {
 65         size_t da, db;
 66         struct kernfs_root *ra = kernfs_root(a), *rb = kernfs_root(b);
 67 
 68         if (ra != rb)
 69                 return NULL;
 70 
 71         da = kernfs_depth(ra->kn, a);
 72         db = kernfs_depth(rb->kn, b);
 73 
 74         while (da > db) {
 75                 a = a->parent;
 76                 da--;
 77         }
 78         while (db > da) {
 79                 b = b->parent;
 80                 db--;
 81         }
 82 
 83         /* worst case b and a will be the same at root */
 84         while (b != a) {
 85                 b = b->parent;
 86                 a = a->parent;
 87         }
 88 
 89         return a;
 90 }
 91 
 92 /**
 93  * kernfs_path_from_node_locked - find a pseudo-absolute path to @kn_to,
 94  * where kn_from is treated as root of the path.
 95  * @kn_from: kernfs node which should be treated as root for the path
 96  * @kn_to: kernfs node to which path is needed
 97  * @buf: buffer to copy the path into
 98  * @buflen: size of @buf
 99  *
100  * We need to handle couple of scenarios here:
101  * [1] when @kn_from is an ancestor of @kn_to at some level
102  * kn_from: /n1/n2/n3
103  * kn_to:   /n1/n2/n3/n4/n5
104  * result:  /n4/n5
105  *
106  * [2] when @kn_from is on a different hierarchy and we need to find common
107  * ancestor between @kn_from and @kn_to.
108  * kn_from: /n1/n2/n3/n4
109  * kn_to:   /n1/n2/n5
110  * result:  /../../n5
111  * OR
112  * kn_from: /n1/n2/n3/n4/n5   [depth=5]
113  * kn_to:   /n1/n2/n3         [depth=3]
114  * result:  /../..
115  *
116  * [3] when @kn_to is NULL result will be "(null)"
117  *
118  * Returns the length of the full path.  If the full length is equal to or
119  * greater than @buflen, @buf contains the truncated path with the trailing
120  * '\0'.  On error, -errno is returned.
121  */
122 static int kernfs_path_from_node_locked(struct kernfs_node *kn_to,
123                                         struct kernfs_node *kn_from,
124                                         char *buf, size_t buflen)
125 {
126         struct kernfs_node *kn, *common;
127         const char parent_str[] = "/..";
128         size_t depth_from, depth_to, len = 0;
129         int i, j;
130 
131         if (!kn_to)
132                 return strlcpy(buf, "(null)", buflen);
133 
134         if (!kn_from)
135                 kn_from = kernfs_root(kn_to)->kn;
136 
137         if (kn_from == kn_to)
138                 return strlcpy(buf, "/", buflen);
139 
140         common = kernfs_common_ancestor(kn_from, kn_to);
141         if (WARN_ON(!common))
142                 return -EINVAL;
143 
144         depth_to = kernfs_depth(common, kn_to);
145         depth_from = kernfs_depth(common, kn_from);
146 
147         if (buf)
148                 buf[0] = '\0';
149 
150         for (i = 0; i < depth_from; i++)
151                 len += strlcpy(buf + len, parent_str,
152                                len < buflen ? buflen - len : 0);
153 
154         /* Calculate how many bytes we need for the rest */
155         for (i = depth_to - 1; i >= 0; i--) {
156                 for (kn = kn_to, j = 0; j < i; j++)
157                         kn = kn->parent;
158                 len += strlcpy(buf + len, "/",
159                                len < buflen ? buflen - len : 0);
160                 len += strlcpy(buf + len, kn->name,
161                                len < buflen ? buflen - len : 0);
162         }
163 
164         return len;
165 }
166 
167 /**
168  * kernfs_name - obtain the name of a given node
169  * @kn: kernfs_node of interest
170  * @buf: buffer to copy @kn's name into
171  * @buflen: size of @buf
172  *
173  * Copies the name of @kn into @buf of @buflen bytes.  The behavior is
174  * similar to strlcpy().  It returns the length of @kn's name and if @buf
175  * isn't long enough, it's filled upto @buflen-1 and nul terminated.
176  *
177  * Fills buffer with "(null)" if @kn is NULL.
178  *
179  * This function can be called from any context.
180  */
181 int kernfs_name(struct kernfs_node *kn, char *buf, size_t buflen)
182 {
183         unsigned long flags;
184         int ret;
185 
186         spin_lock_irqsave(&kernfs_rename_lock, flags);
187         ret = kernfs_name_locked(kn, buf, buflen);
188         spin_unlock_irqrestore(&kernfs_rename_lock, flags);
189         return ret;
190 }
191 
192 /**
193  * kernfs_path_from_node - build path of node @to relative to @from.
194  * @from: parent kernfs_node relative to which we need to build the path
195  * @to: kernfs_node of interest
196  * @buf: buffer to copy @to's path into
197  * @buflen: size of @buf
198  *
199  * Builds @to's path relative to @from in @buf. @from and @to must
200  * be on the same kernfs-root. If @from is not parent of @to, then a relative
201  * path (which includes '..'s) as needed to reach from @from to @to is
202  * returned.
203  *
204  * Returns the length of the full path.  If the full length is equal to or
205  * greater than @buflen, @buf contains the truncated path with the trailing
206  * '\0'.  On error, -errno is returned.
207  */
208 int kernfs_path_from_node(struct kernfs_node *to, struct kernfs_node *from,
209                           char *buf, size_t buflen)
210 {
211         unsigned long flags;
212         int ret;
213 
214         spin_lock_irqsave(&kernfs_rename_lock, flags);
215         ret = kernfs_path_from_node_locked(to, from, buf, buflen);
216         spin_unlock_irqrestore(&kernfs_rename_lock, flags);
217         return ret;
218 }
219 EXPORT_SYMBOL_GPL(kernfs_path_from_node);
220 
221 /**
222  * pr_cont_kernfs_name - pr_cont name of a kernfs_node
223  * @kn: kernfs_node of interest
224  *
225  * This function can be called from any context.
226  */
227 void pr_cont_kernfs_name(struct kernfs_node *kn)
228 {
229         unsigned long flags;
230 
231         spin_lock_irqsave(&kernfs_rename_lock, flags);
232 
233         kernfs_name_locked(kn, kernfs_pr_cont_buf, sizeof(kernfs_pr_cont_buf));
234         pr_cont("%s", kernfs_pr_cont_buf);
235 
236         spin_unlock_irqrestore(&kernfs_rename_lock, flags);
237 }
238 
239 /**
240  * pr_cont_kernfs_path - pr_cont path of a kernfs_node
241  * @kn: kernfs_node of interest
242  *
243  * This function can be called from any context.
244  */
245 void pr_cont_kernfs_path(struct kernfs_node *kn)
246 {
247         unsigned long flags;
248         int sz;
249 
250         spin_lock_irqsave(&kernfs_rename_lock, flags);
251 
252         sz = kernfs_path_from_node_locked(kn, NULL, kernfs_pr_cont_buf,
253                                           sizeof(kernfs_pr_cont_buf));
254         if (sz < 0) {
255                 pr_cont("(error)");
256                 goto out;
257         }
258 
259         if (sz >= sizeof(kernfs_pr_cont_buf)) {
260                 pr_cont("(name too long)");
261                 goto out;
262         }
263 
264         pr_cont("%s", kernfs_pr_cont_buf);
265 
266 out:
267         spin_unlock_irqrestore(&kernfs_rename_lock, flags);
268 }
269 
270 /**
271  * kernfs_get_parent - determine the parent node and pin it
272  * @kn: kernfs_node of interest
273  *
274  * Determines @kn's parent, pins and returns it.  This function can be
275  * called from any context.
276  */
277 struct kernfs_node *kernfs_get_parent(struct kernfs_node *kn)
278 {
279         struct kernfs_node *parent;
280         unsigned long flags;
281 
282         spin_lock_irqsave(&kernfs_rename_lock, flags);
283         parent = kn->parent;
284         kernfs_get(parent);
285         spin_unlock_irqrestore(&kernfs_rename_lock, flags);
286 
287         return parent;
288 }
289 
290 /**
291  *      kernfs_name_hash
292  *      @name: Null terminated string to hash
293  *      @ns:   Namespace tag to hash
294  *
295  *      Returns 31 bit hash of ns + name (so it fits in an off_t )
296  */
297 static unsigned int kernfs_name_hash(const char *name, const void *ns)
298 {
299         unsigned long hash = init_name_hash(ns);
300         unsigned int len = strlen(name);
301         while (len--)
302                 hash = partial_name_hash(*name++, hash);
303         hash = end_name_hash(hash);
304         hash &= 0x7fffffffU;
305         /* Reserve hash numbers 0, 1 and INT_MAX for magic directory entries */
306         if (hash < 2)
307                 hash += 2;
308         if (hash >= INT_MAX)
309                 hash = INT_MAX - 1;
310         return hash;
311 }
312 
313 static int kernfs_name_compare(unsigned int hash, const char *name,
314                                const void *ns, const struct kernfs_node *kn)
315 {
316         if (hash < kn->hash)
317                 return -1;
318         if (hash > kn->hash)
319                 return 1;
320         if (ns < kn->ns)
321                 return -1;
322         if (ns > kn->ns)
323                 return 1;
324         return strcmp(name, kn->name);
325 }
326 
327 static int kernfs_sd_compare(const struct kernfs_node *left,
328                              const struct kernfs_node *right)
329 {
330         return kernfs_name_compare(left->hash, left->name, left->ns, right);
331 }
332 
333 /**
334  *      kernfs_link_sibling - link kernfs_node into sibling rbtree
335  *      @kn: kernfs_node of interest
336  *
337  *      Link @kn into its sibling rbtree which starts from
338  *      @kn->parent->dir.children.
339  *
340  *      Locking:
341  *      mutex_lock(kernfs_mutex)
342  *
343  *      RETURNS:
344  *      0 on susccess -EEXIST on failure.
345  */
346 static int kernfs_link_sibling(struct kernfs_node *kn)
347 {
348         struct rb_node **node = &kn->parent->dir.children.rb_node;
349         struct rb_node *parent = NULL;
350 
351         while (*node) {
352                 struct kernfs_node *pos;
353                 int result;
354 
355                 pos = rb_to_kn(*node);
356                 parent = *node;
357                 result = kernfs_sd_compare(kn, pos);
358                 if (result < 0)
359                         node = &pos->rb.rb_left;
360                 else if (result > 0)
361                         node = &pos->rb.rb_right;
362                 else
363                         return -EEXIST;
364         }
365 
366         /* add new node and rebalance the tree */
367         rb_link_node(&kn->rb, parent, node);
368         rb_insert_color(&kn->rb, &kn->parent->dir.children);
369 
370         /* successfully added, account subdir number */
371         if (kernfs_type(kn) == KERNFS_DIR)
372                 kn->parent->dir.subdirs++;
373 
374         return 0;
375 }
376 
377 /**
378  *      kernfs_unlink_sibling - unlink kernfs_node from sibling rbtree
379  *      @kn: kernfs_node of interest
380  *
381  *      Try to unlink @kn from its sibling rbtree which starts from
382  *      kn->parent->dir.children.  Returns %true if @kn was actually
383  *      removed, %false if @kn wasn't on the rbtree.
384  *
385  *      Locking:
386  *      mutex_lock(kernfs_mutex)
387  */
388 static bool kernfs_unlink_sibling(struct kernfs_node *kn)
389 {
390         if (RB_EMPTY_NODE(&kn->rb))
391                 return false;
392 
393         if (kernfs_type(kn) == KERNFS_DIR)
394                 kn->parent->dir.subdirs--;
395 
396         rb_erase(&kn->rb, &kn->parent->dir.children);
397         RB_CLEAR_NODE(&kn->rb);
398         return true;
399 }
400 
401 /**
402  *      kernfs_get_active - get an active reference to kernfs_node
403  *      @kn: kernfs_node to get an active reference to
404  *
405  *      Get an active reference of @kn.  This function is noop if @kn
406  *      is NULL.
407  *
408  *      RETURNS:
409  *      Pointer to @kn on success, NULL on failure.
410  */
411 struct kernfs_node *kernfs_get_active(struct kernfs_node *kn)
412 {
413         if (unlikely(!kn))
414                 return NULL;
415 
416         if (!atomic_inc_unless_negative(&kn->active))
417                 return NULL;
418 
419         if (kernfs_lockdep(kn))
420                 rwsem_acquire_read(&kn->dep_map, 0, 1, _RET_IP_);
421         return kn;
422 }
423 
424 /**
425  *      kernfs_put_active - put an active reference to kernfs_node
426  *      @kn: kernfs_node to put an active reference to
427  *
428  *      Put an active reference to @kn.  This function is noop if @kn
429  *      is NULL.
430  */
431 void kernfs_put_active(struct kernfs_node *kn)
432 {
433         struct kernfs_root *root = kernfs_root(kn);
434         int v;
435 
436         if (unlikely(!kn))
437                 return;
438 
439         if (kernfs_lockdep(kn))
440                 rwsem_release(&kn->dep_map, 1, _RET_IP_);
441         v = atomic_dec_return(&kn->active);
442         if (likely(v != KN_DEACTIVATED_BIAS))
443                 return;
444 
445         wake_up_all(&root->deactivate_waitq);
446 }
447 
448 /**
449  * kernfs_drain - drain kernfs_node
450  * @kn: kernfs_node to drain
451  *
452  * Drain existing usages and nuke all existing mmaps of @kn.  Mutiple
453  * removers may invoke this function concurrently on @kn and all will
454  * return after draining is complete.
455  */
456 static void kernfs_drain(struct kernfs_node *kn)
457         __releases(&kernfs_mutex) __acquires(&kernfs_mutex)
458 {
459         struct kernfs_root *root = kernfs_root(kn);
460 
461         lockdep_assert_held(&kernfs_mutex);
462         WARN_ON_ONCE(kernfs_active(kn));
463 
464         mutex_unlock(&kernfs_mutex);
465 
466         if (kernfs_lockdep(kn)) {
467                 rwsem_acquire(&kn->dep_map, 0, 0, _RET_IP_);
468                 if (atomic_read(&kn->active) != KN_DEACTIVATED_BIAS)
469                         lock_contended(&kn->dep_map, _RET_IP_);
470         }
471 
472         /* but everyone should wait for draining */
473         wait_event(root->deactivate_waitq,
474                    atomic_read(&kn->active) == KN_DEACTIVATED_BIAS);
475 
476         if (kernfs_lockdep(kn)) {
477                 lock_acquired(&kn->dep_map, _RET_IP_);
478                 rwsem_release(&kn->dep_map, 1, _RET_IP_);
479         }
480 
481         kernfs_drain_open_files(kn);
482 
483         mutex_lock(&kernfs_mutex);
484 }
485 
486 /**
487  * kernfs_get - get a reference count on a kernfs_node
488  * @kn: the target kernfs_node
489  */
490 void kernfs_get(struct kernfs_node *kn)
491 {
492         if (kn) {
493                 WARN_ON(!atomic_read(&kn->count));
494                 atomic_inc(&kn->count);
495         }
496 }
497 EXPORT_SYMBOL_GPL(kernfs_get);
498 
499 /**
500  * kernfs_put - put a reference count on a kernfs_node
501  * @kn: the target kernfs_node
502  *
503  * Put a reference count of @kn and destroy it if it reached zero.
504  */
505 void kernfs_put(struct kernfs_node *kn)
506 {
507         struct kernfs_node *parent;
508         struct kernfs_root *root;
509 
510         /*
511          * kernfs_node is freed with ->count 0, kernfs_find_and_get_node_by_ino
512          * depends on this to filter reused stale node
513          */
514         if (!kn || !atomic_dec_and_test(&kn->count))
515                 return;
516         root = kernfs_root(kn);
517  repeat:
518         /*
519          * Moving/renaming is always done while holding reference.
520          * kn->parent won't change beneath us.
521          */
522         parent = kn->parent;
523 
524         WARN_ONCE(atomic_read(&kn->active) != KN_DEACTIVATED_BIAS,
525                   "kernfs_put: %s/%s: released with incorrect active_ref %d\n",
526                   parent ? parent->name : "", kn->name, atomic_read(&kn->active));
527 
528         if (kernfs_type(kn) == KERNFS_LINK)
529                 kernfs_put(kn->symlink.target_kn);
530 
531         kfree_const(kn->name);
532 
533         if (kn->iattr) {
534                 simple_xattrs_free(&kn->iattr->xattrs);
535                 kmem_cache_free(kernfs_iattrs_cache, kn->iattr);
536         }
537         spin_lock(&kernfs_idr_lock);
538         idr_remove(&root->ino_idr, kn->id.ino);
539         spin_unlock(&kernfs_idr_lock);
540         kmem_cache_free(kernfs_node_cache, kn);
541 
542         kn = parent;
543         if (kn) {
544                 if (atomic_dec_and_test(&kn->count))
545                         goto repeat;
546         } else {
547                 /* just released the root kn, free @root too */
548                 idr_destroy(&root->ino_idr);
549                 kfree(root);
550         }
551 }
552 EXPORT_SYMBOL_GPL(kernfs_put);
553 
554 static int kernfs_dop_revalidate(struct dentry *dentry, unsigned int flags)
555 {
556         struct kernfs_node *kn;
557 
558         if (flags & LOOKUP_RCU)
559                 return -ECHILD;
560 
561         /* Always perform fresh lookup for negatives */
562         if (d_really_is_negative(dentry))
563                 goto out_bad_unlocked;
564 
565         kn = kernfs_dentry_node(dentry);
566         mutex_lock(&kernfs_mutex);
567 
568         /* The kernfs node has been deactivated */
569         if (!kernfs_active(kn))
570                 goto out_bad;
571 
572         /* The kernfs node has been moved? */
573         if (kernfs_dentry_node(dentry->d_parent) != kn->parent)
574                 goto out_bad;
575 
576         /* The kernfs node has been renamed */
577         if (strcmp(dentry->d_name.name, kn->name) != 0)
578                 goto out_bad;
579 
580         /* The kernfs node has been moved to a different namespace */
581         if (kn->parent && kernfs_ns_enabled(kn->parent) &&
582             kernfs_info(dentry->d_sb)->ns != kn->ns)
583                 goto out_bad;
584 
585         mutex_unlock(&kernfs_mutex);
586         return 1;
587 out_bad:
588         mutex_unlock(&kernfs_mutex);
589 out_bad_unlocked:
590         return 0;
591 }
592 
593 const struct dentry_operations kernfs_dops = {
594         .d_revalidate   = kernfs_dop_revalidate,
595 };
596 
597 /**
598  * kernfs_node_from_dentry - determine kernfs_node associated with a dentry
599  * @dentry: the dentry in question
600  *
601  * Return the kernfs_node associated with @dentry.  If @dentry is not a
602  * kernfs one, %NULL is returned.
603  *
604  * While the returned kernfs_node will stay accessible as long as @dentry
605  * is accessible, the returned node can be in any state and the caller is
606  * fully responsible for determining what's accessible.
607  */
608 struct kernfs_node *kernfs_node_from_dentry(struct dentry *dentry)
609 {
610         if (dentry->d_sb->s_op == &kernfs_sops &&
611             !d_really_is_negative(dentry))
612                 return kernfs_dentry_node(dentry);
613         return NULL;
614 }
615 
616 static struct kernfs_node *__kernfs_new_node(struct kernfs_root *root,
617                                              struct kernfs_node *parent,
618                                              const char *name, umode_t mode,
619                                              kuid_t uid, kgid_t gid,
620                                              unsigned flags)
621 {
622         struct kernfs_node *kn;
623         u32 gen;
624         int cursor;
625         int ret;
626 
627         name = kstrdup_const(name, GFP_KERNEL);
628         if (!name)
629                 return NULL;
630 
631         kn = kmem_cache_zalloc(kernfs_node_cache, GFP_KERNEL);
632         if (!kn)
633                 goto err_out1;
634 
635         idr_preload(GFP_KERNEL);
636         spin_lock(&kernfs_idr_lock);
637         cursor = idr_get_cursor(&root->ino_idr);
638         ret = idr_alloc_cyclic(&root->ino_idr, kn, 1, 0, GFP_ATOMIC);
639         if (ret >= 0 && ret < cursor)
640                 root->next_generation++;
641         gen = root->next_generation;
642         spin_unlock(&kernfs_idr_lock);
643         idr_preload_end();
644         if (ret < 0)
645                 goto err_out2;
646         kn->id.ino = ret;
647         kn->id.generation = gen;
648 
649         /*
650          * set ino first. This RELEASE is paired with atomic_inc_not_zero in
651          * kernfs_find_and_get_node_by_ino
652          */
653         atomic_set_release(&kn->count, 1);
654         atomic_set(&kn->active, KN_DEACTIVATED_BIAS);
655         RB_CLEAR_NODE(&kn->rb);
656 
657         kn->name = name;
658         kn->mode = mode;
659         kn->flags = flags;
660 
661         if (!uid_eq(uid, GLOBAL_ROOT_UID) || !gid_eq(gid, GLOBAL_ROOT_GID)) {
662                 struct iattr iattr = {
663                         .ia_valid = ATTR_UID | ATTR_GID,
664                         .ia_uid = uid,
665                         .ia_gid = gid,
666                 };
667 
668                 ret = __kernfs_setattr(kn, &iattr);
669                 if (ret < 0)
670                         goto err_out3;
671         }
672 
673         if (parent) {
674                 ret = security_kernfs_init_security(parent, kn);
675                 if (ret)
676                         goto err_out3;
677         }
678 
679         return kn;
680 
681  err_out3:
682         idr_remove(&root->ino_idr, kn->id.ino);
683  err_out2:
684         kmem_cache_free(kernfs_node_cache, kn);
685  err_out1:
686         kfree_const(name);
687         return NULL;
688 }
689 
690 struct kernfs_node *kernfs_new_node(struct kernfs_node *parent,
691                                     const char *name, umode_t mode,
692                                     kuid_t uid, kgid_t gid,
693                                     unsigned flags)
694 {
695         struct kernfs_node *kn;
696 
697         kn = __kernfs_new_node(kernfs_root(parent), parent,
698                                name, mode, uid, gid, flags);
699         if (kn) {
700                 kernfs_get(parent);
701                 kn->parent = parent;
702         }
703         return kn;
704 }
705 
706 /*
707  * kernfs_find_and_get_node_by_ino - get kernfs_node from inode number
708  * @root: the kernfs root
709  * @ino: inode number
710  *
711  * RETURNS:
712  * NULL on failure. Return a kernfs node with reference counter incremented
713  */
714 struct kernfs_node *kernfs_find_and_get_node_by_ino(struct kernfs_root *root,
715                                                     unsigned int ino)
716 {
717         struct kernfs_node *kn;
718 
719         rcu_read_lock();
720         kn = idr_find(&root->ino_idr, ino);
721         if (!kn)
722                 goto out;
723 
724         /*
725          * Since kernfs_node is freed in RCU, it's possible an old node for ino
726          * is freed, but reused before RCU grace period. But a freed node (see
727          * kernfs_put) or an incompletedly initialized node (see
728          * __kernfs_new_node) should have 'count' 0. We can use this fact to
729          * filter out such node.
730          */
731         if (!atomic_inc_not_zero(&kn->count)) {
732                 kn = NULL;
733                 goto out;
734         }
735 
736         /*
737          * The node could be a new node or a reused node. If it's a new node,
738          * we are ok. If it's reused because of RCU (because of
739          * SLAB_TYPESAFE_BY_RCU), the __kernfs_new_node always sets its 'ino'
740          * before 'count'. So if 'count' is uptodate, 'ino' should be uptodate,
741          * hence we can use 'ino' to filter stale node.
742          */
743         if (kn->id.ino != ino)
744                 goto out;
745         rcu_read_unlock();
746 
747         return kn;
748 out:
749         rcu_read_unlock();
750         kernfs_put(kn);
751         return NULL;
752 }
753 
754 /**
755  *      kernfs_add_one - add kernfs_node to parent without warning
756  *      @kn: kernfs_node to be added
757  *
758  *      The caller must already have initialized @kn->parent.  This
759  *      function increments nlink of the parent's inode if @kn is a
760  *      directory and link into the children list of the parent.
761  *
762  *      RETURNS:
763  *      0 on success, -EEXIST if entry with the given name already
764  *      exists.
765  */
766 int kernfs_add_one(struct kernfs_node *kn)
767 {
768         struct kernfs_node *parent = kn->parent;
769         struct kernfs_iattrs *ps_iattr;
770         bool has_ns;
771         int ret;
772 
773         mutex_lock(&kernfs_mutex);
774 
775         ret = -EINVAL;
776         has_ns = kernfs_ns_enabled(parent);
777         if (WARN(has_ns != (bool)kn->ns, KERN_WARNING "kernfs: ns %s in '%s' for '%s'\n",
778                  has_ns ? "required" : "invalid", parent->name, kn->name))
779                 goto out_unlock;
780 
781         if (kernfs_type(parent) != KERNFS_DIR)
782                 goto out_unlock;
783 
784         ret = -ENOENT;
785         if (parent->flags & KERNFS_EMPTY_DIR)
786                 goto out_unlock;
787 
788         if ((parent->flags & KERNFS_ACTIVATED) && !kernfs_active(parent))
789                 goto out_unlock;
790 
791         kn->hash = kernfs_name_hash(kn->name, kn->ns);
792 
793         ret = kernfs_link_sibling(kn);
794         if (ret)
795                 goto out_unlock;
796 
797         /* Update timestamps on the parent */
798         ps_iattr = parent->iattr;
799         if (ps_iattr) {
800                 ktime_get_real_ts64(&ps_iattr->ia_ctime);
801                 ps_iattr->ia_mtime = ps_iattr->ia_ctime;
802         }
803 
804         mutex_unlock(&kernfs_mutex);
805 
806         /*
807          * Activate the new node unless CREATE_DEACTIVATED is requested.
808          * If not activated here, the kernfs user is responsible for
809          * activating the node with kernfs_activate().  A node which hasn't
810          * been activated is not visible to userland and its removal won't
811          * trigger deactivation.
812          */
813         if (!(kernfs_root(kn)->flags & KERNFS_ROOT_CREATE_DEACTIVATED))
814                 kernfs_activate(kn);
815         return 0;
816 
817 out_unlock:
818         mutex_unlock(&kernfs_mutex);
819         return ret;
820 }
821 
822 /**
823  * kernfs_find_ns - find kernfs_node with the given name
824  * @parent: kernfs_node to search under
825  * @name: name to look for
826  * @ns: the namespace tag to use
827  *
828  * Look for kernfs_node with name @name under @parent.  Returns pointer to
829  * the found kernfs_node on success, %NULL on failure.
830  */
831 static struct kernfs_node *kernfs_find_ns(struct kernfs_node *parent,
832                                           const unsigned char *name,
833                                           const void *ns)
834 {
835         struct rb_node *node = parent->dir.children.rb_node;
836         bool has_ns = kernfs_ns_enabled(parent);
837         unsigned int hash;
838 
839         lockdep_assert_held(&kernfs_mutex);
840 
841         if (has_ns != (bool)ns) {
842                 WARN(1, KERN_WARNING "kernfs: ns %s in '%s' for '%s'\n",
843                      has_ns ? "required" : "invalid", parent->name, name);
844                 return NULL;
845         }
846 
847         hash = kernfs_name_hash(name, ns);
848         while (node) {
849                 struct kernfs_node *kn;
850                 int result;
851 
852                 kn = rb_to_kn(node);
853                 result = kernfs_name_compare(hash, name, ns, kn);
854                 if (result < 0)
855                         node = node->rb_left;
856                 else if (result > 0)
857                         node = node->rb_right;
858                 else
859                         return kn;
860         }
861         return NULL;
862 }
863 
864 static struct kernfs_node *kernfs_walk_ns(struct kernfs_node *parent,
865                                           const unsigned char *path,
866                                           const void *ns)
867 {
868         size_t len;
869         char *p, *name;
870 
871         lockdep_assert_held(&kernfs_mutex);
872 
873         /* grab kernfs_rename_lock to piggy back on kernfs_pr_cont_buf */
874         spin_lock_irq(&kernfs_rename_lock);
875 
876         len = strlcpy(kernfs_pr_cont_buf, path, sizeof(kernfs_pr_cont_buf));
877 
878         if (len >= sizeof(kernfs_pr_cont_buf)) {
879                 spin_unlock_irq(&kernfs_rename_lock);
880                 return NULL;
881         }
882 
883         p = kernfs_pr_cont_buf;
884 
885         while ((name = strsep(&p, "/")) && parent) {
886                 if (*name == '\0')
887                         continue;
888                 parent = kernfs_find_ns(parent, name, ns);
889         }
890 
891         spin_unlock_irq(&kernfs_rename_lock);
892 
893         return parent;
894 }
895 
896 /**
897  * kernfs_find_and_get_ns - find and get kernfs_node with the given name
898  * @parent: kernfs_node to search under
899  * @name: name to look for
900  * @ns: the namespace tag to use
901  *
902  * Look for kernfs_node with name @name under @parent and get a reference
903  * if found.  This function may sleep and returns pointer to the found
904  * kernfs_node on success, %NULL on failure.
905  */
906 struct kernfs_node *kernfs_find_and_get_ns(struct kernfs_node *parent,
907                                            const char *name, const void *ns)
908 {
909         struct kernfs_node *kn;
910 
911         mutex_lock(&kernfs_mutex);
912         kn = kernfs_find_ns(parent, name, ns);
913         kernfs_get(kn);
914         mutex_unlock(&kernfs_mutex);
915 
916         return kn;
917 }
918 EXPORT_SYMBOL_GPL(kernfs_find_and_get_ns);
919 
920 /**
921  * kernfs_walk_and_get_ns - find and get kernfs_node with the given path
922  * @parent: kernfs_node to search under
923  * @path: path to look for
924  * @ns: the namespace tag to use
925  *
926  * Look for kernfs_node with path @path under @parent and get a reference
927  * if found.  This function may sleep and returns pointer to the found
928  * kernfs_node on success, %NULL on failure.
929  */
930 struct kernfs_node *kernfs_walk_and_get_ns(struct kernfs_node *parent,
931                                            const char *path, const void *ns)
932 {
933         struct kernfs_node *kn;
934 
935         mutex_lock(&kernfs_mutex);
936         kn = kernfs_walk_ns(parent, path, ns);
937         kernfs_get(kn);
938         mutex_unlock(&kernfs_mutex);
939 
940         return kn;
941 }
942 
943 /**
944  * kernfs_create_root - create a new kernfs hierarchy
945  * @scops: optional syscall operations for the hierarchy
946  * @flags: KERNFS_ROOT_* flags
947  * @priv: opaque data associated with the new directory
948  *
949  * Returns the root of the new hierarchy on success, ERR_PTR() value on
950  * failure.
951  */
952 struct kernfs_root *kernfs_create_root(struct kernfs_syscall_ops *scops,
953                                        unsigned int flags, void *priv)
954 {
955         struct kernfs_root *root;
956         struct kernfs_node *kn;
957 
958         root = kzalloc(sizeof(*root), GFP_KERNEL);
959         if (!root)
960                 return ERR_PTR(-ENOMEM);
961 
962         idr_init(&root->ino_idr);
963         INIT_LIST_HEAD(&root->supers);
964         root->next_generation = 1;
965 
966         kn = __kernfs_new_node(root, NULL, "", S_IFDIR | S_IRUGO | S_IXUGO,
967                                GLOBAL_ROOT_UID, GLOBAL_ROOT_GID,
968                                KERNFS_DIR);
969         if (!kn) {
970                 idr_destroy(&root->ino_idr);
971                 kfree(root);
972                 return ERR_PTR(-ENOMEM);
973         }
974 
975         kn->priv = priv;
976         kn->dir.root = root;
977 
978         root->syscall_ops = scops;
979         root->flags = flags;
980         root->kn = kn;
981         init_waitqueue_head(&root->deactivate_waitq);
982 
983         if (!(root->flags & KERNFS_ROOT_CREATE_DEACTIVATED))
984                 kernfs_activate(kn);
985 
986         return root;
987 }
988 
989 /**
990  * kernfs_destroy_root - destroy a kernfs hierarchy
991  * @root: root of the hierarchy to destroy
992  *
993  * Destroy the hierarchy anchored at @root by removing all existing
994  * directories and destroying @root.
995  */
996 void kernfs_destroy_root(struct kernfs_root *root)
997 {
998         kernfs_remove(root->kn);        /* will also free @root */
999 }
1000 
1001 /**
1002  * kernfs_create_dir_ns - create a directory
1003  * @parent: parent in which to create a new directory
1004  * @name: name of the new directory
1005  * @mode: mode of the new directory
1006  * @uid: uid of the new directory
1007  * @gid: gid of the new directory
1008  * @priv: opaque data associated with the new directory
1009  * @ns: optional namespace tag of the directory
1010  *
1011  * Returns the created node on success, ERR_PTR() value on failure.
1012  */
1013 struct kernfs_node *kernfs_create_dir_ns(struct kernfs_node *parent,
1014                                          const char *name, umode_t mode,
1015                                          kuid_t uid, kgid_t gid,
1016                                          void *priv, const void *ns)
1017 {
1018         struct kernfs_node *kn;
1019         int rc;
1020 
1021         /* allocate */
1022         kn = kernfs_new_node(parent, name, mode | S_IFDIR,
1023                              uid, gid, KERNFS_DIR);
1024         if (!kn)
1025                 return ERR_PTR(-ENOMEM);
1026 
1027         kn->dir.root = parent->dir.root;
1028         kn->ns = ns;
1029         kn->priv = priv;
1030 
1031         /* link in */
1032         rc = kernfs_add_one(kn);
1033         if (!rc)
1034                 return kn;
1035 
1036         kernfs_put(kn);
1037         return ERR_PTR(rc);
1038 }
1039 
1040 /**
1041  * kernfs_create_empty_dir - create an always empty directory
1042  * @parent: parent in which to create a new directory
1043  * @name: name of the new directory
1044  *
1045  * Returns the created node on success, ERR_PTR() value on failure.
1046  */
1047 struct kernfs_node *kernfs_create_empty_dir(struct kernfs_node *parent,
1048                                             const char *name)
1049 {
1050         struct kernfs_node *kn;
1051         int rc;
1052 
1053         /* allocate */
1054         kn = kernfs_new_node(parent, name, S_IRUGO|S_IXUGO|S_IFDIR,
1055                              GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, KERNFS_DIR);
1056         if (!kn)
1057                 return ERR_PTR(-ENOMEM);
1058 
1059         kn->flags |= KERNFS_EMPTY_DIR;
1060         kn->dir.root = parent->dir.root;
1061         kn->ns = NULL;
1062         kn->priv = NULL;
1063 
1064         /* link in */
1065         rc = kernfs_add_one(kn);
1066         if (!rc)
1067                 return kn;
1068 
1069         kernfs_put(kn);
1070         return ERR_PTR(rc);
1071 }
1072 
1073 static struct dentry *kernfs_iop_lookup(struct inode *dir,
1074                                         struct dentry *dentry,
1075                                         unsigned int flags)
1076 {
1077         struct dentry *ret;
1078         struct kernfs_node *parent = dir->i_private;
1079         struct kernfs_node *kn;
1080         struct inode *inode;
1081         const void *ns = NULL;
1082 
1083         mutex_lock(&kernfs_mutex);
1084 
1085         if (kernfs_ns_enabled(parent))
1086                 ns = kernfs_info(dir->i_sb)->ns;
1087 
1088         kn = kernfs_find_ns(parent, dentry->d_name.name, ns);
1089 
1090         /* no such entry */
1091         if (!kn || !kernfs_active(kn)) {
1092                 ret = NULL;
1093                 goto out_unlock;
1094         }
1095 
1096         /* attach dentry and inode */
1097         inode = kernfs_get_inode(dir->i_sb, kn);
1098         if (!inode) {
1099                 ret = ERR_PTR(-ENOMEM);
1100                 goto out_unlock;
1101         }
1102 
1103         /* instantiate and hash dentry */
1104         ret = d_splice_alias(inode, dentry);
1105  out_unlock:
1106         mutex_unlock(&kernfs_mutex);
1107         return ret;
1108 }
1109 
1110 static int kernfs_iop_mkdir(struct inode *dir, struct dentry *dentry,
1111                             umode_t mode)
1112 {
1113         struct kernfs_node *parent = dir->i_private;
1114         struct kernfs_syscall_ops *scops = kernfs_root(parent)->syscall_ops;
1115         int ret;
1116 
1117         if (!scops || !scops->mkdir)
1118                 return -EPERM;
1119 
1120         if (!kernfs_get_active(parent))
1121                 return -ENODEV;
1122 
1123         ret = scops->mkdir(parent, dentry->d_name.name, mode);
1124 
1125         kernfs_put_active(parent);
1126         return ret;
1127 }
1128 
1129 static int kernfs_iop_rmdir(struct inode *dir, struct dentry *dentry)
1130 {
1131         struct kernfs_node *kn  = kernfs_dentry_node(dentry);
1132         struct kernfs_syscall_ops *scops = kernfs_root(kn)->syscall_ops;
1133         int ret;
1134 
1135         if (!scops || !scops->rmdir)
1136                 return -EPERM;
1137 
1138         if (!kernfs_get_active(kn))
1139                 return -ENODEV;
1140 
1141         ret = scops->rmdir(kn);
1142 
1143         kernfs_put_active(kn);
1144         return ret;
1145 }
1146 
1147 static int kernfs_iop_rename(struct inode *old_dir, struct dentry *old_dentry,
1148                              struct inode *new_dir, struct dentry *new_dentry,
1149                              unsigned int flags)
1150 {
1151         struct kernfs_node *kn = kernfs_dentry_node(old_dentry);
1152         struct kernfs_node *new_parent = new_dir->i_private;
1153         struct kernfs_syscall_ops *scops = kernfs_root(kn)->syscall_ops;
1154         int ret;
1155 
1156         if (flags)
1157                 return -EINVAL;
1158 
1159         if (!scops || !scops->rename)
1160                 return -EPERM;
1161 
1162         if (!kernfs_get_active(kn))
1163                 return -ENODEV;
1164 
1165         if (!kernfs_get_active(new_parent)) {
1166                 kernfs_put_active(kn);
1167                 return -ENODEV;
1168         }
1169 
1170         ret = scops->rename(kn, new_parent, new_dentry->d_name.name);
1171 
1172         kernfs_put_active(new_parent);
1173         kernfs_put_active(kn);
1174         return ret;
1175 }
1176 
1177 const struct inode_operations kernfs_dir_iops = {
1178         .lookup         = kernfs_iop_lookup,
1179         .permission     = kernfs_iop_permission,
1180         .setattr        = kernfs_iop_setattr,
1181         .getattr        = kernfs_iop_getattr,
1182         .listxattr      = kernfs_iop_listxattr,
1183 
1184         .mkdir          = kernfs_iop_mkdir,
1185         .rmdir          = kernfs_iop_rmdir,
1186         .rename         = kernfs_iop_rename,
1187 };
1188 
1189 static struct kernfs_node *kernfs_leftmost_descendant(struct kernfs_node *pos)
1190 {
1191         struct kernfs_node *last;
1192 
1193         while (true) {
1194                 struct rb_node *rbn;
1195 
1196                 last = pos;
1197 
1198                 if (kernfs_type(pos) != KERNFS_DIR)
1199                         break;
1200 
1201                 rbn = rb_first(&pos->dir.children);
1202                 if (!rbn)
1203                         break;
1204 
1205                 pos = rb_to_kn(rbn);
1206         }
1207 
1208         return last;
1209 }
1210 
1211 /**
1212  * kernfs_next_descendant_post - find the next descendant for post-order walk
1213  * @pos: the current position (%NULL to initiate traversal)
1214  * @root: kernfs_node whose descendants to walk
1215  *
1216  * Find the next descendant to visit for post-order traversal of @root's
1217  * descendants.  @root is included in the iteration and the last node to be
1218  * visited.
1219  */
1220 static struct kernfs_node *kernfs_next_descendant_post(struct kernfs_node *pos,
1221                                                        struct kernfs_node *root)
1222 {
1223         struct rb_node *rbn;
1224 
1225         lockdep_assert_held(&kernfs_mutex);
1226 
1227         /* if first iteration, visit leftmost descendant which may be root */
1228         if (!pos)
1229                 return kernfs_leftmost_descendant(root);
1230 
1231         /* if we visited @root, we're done */
1232         if (pos == root)
1233                 return NULL;
1234 
1235         /* if there's an unvisited sibling, visit its leftmost descendant */
1236         rbn = rb_next(&pos->rb);
1237         if (rbn)
1238                 return kernfs_leftmost_descendant(rb_to_kn(rbn));
1239 
1240         /* no sibling left, visit parent */
1241         return pos->parent;
1242 }
1243 
1244 /**
1245  * kernfs_activate - activate a node which started deactivated
1246  * @kn: kernfs_node whose subtree is to be activated
1247  *
1248  * If the root has KERNFS_ROOT_CREATE_DEACTIVATED set, a newly created node
1249  * needs to be explicitly activated.  A node which hasn't been activated
1250  * isn't visible to userland and deactivation is skipped during its
1251  * removal.  This is useful to construct atomic init sequences where
1252  * creation of multiple nodes should either succeed or fail atomically.
1253  *
1254  * The caller is responsible for ensuring that this function is not called
1255  * after kernfs_remove*() is invoked on @kn.
1256  */
1257 void kernfs_activate(struct kernfs_node *kn)
1258 {
1259         struct kernfs_node *pos;
1260 
1261         mutex_lock(&kernfs_mutex);
1262 
1263         pos = NULL;
1264         while ((pos = kernfs_next_descendant_post(pos, kn))) {
1265                 if (!pos || (pos->flags & KERNFS_ACTIVATED))
1266                         continue;
1267 
1268                 WARN_ON_ONCE(pos->parent && RB_EMPTY_NODE(&pos->rb));
1269                 WARN_ON_ONCE(atomic_read(&pos->active) != KN_DEACTIVATED_BIAS);
1270 
1271                 atomic_sub(KN_DEACTIVATED_BIAS, &pos->active);
1272                 pos->flags |= KERNFS_ACTIVATED;
1273         }
1274 
1275         mutex_unlock(&kernfs_mutex);
1276 }
1277 
1278 static void __kernfs_remove(struct kernfs_node *kn)
1279 {
1280         struct kernfs_node *pos;
1281 
1282         lockdep_assert_held(&kernfs_mutex);
1283 
1284         /*
1285          * Short-circuit if non-root @kn has already finished removal.
1286          * This is for kernfs_remove_self() which plays with active ref
1287          * after removal.
1288          */
1289         if (!kn || (kn->parent && RB_EMPTY_NODE(&kn->rb)))
1290                 return;
1291 
1292         pr_debug("kernfs %s: removing\n", kn->name);
1293 
1294         /* prevent any new usage under @kn by deactivating all nodes */
1295         pos = NULL;
1296         while ((pos = kernfs_next_descendant_post(pos, kn)))
1297                 if (kernfs_active(pos))
1298                         atomic_add(KN_DEACTIVATED_BIAS, &pos->active);
1299 
1300         /* deactivate and unlink the subtree node-by-node */
1301         do {
1302                 pos = kernfs_leftmost_descendant(kn);
1303 
1304                 /*
1305                  * kernfs_drain() drops kernfs_mutex temporarily and @pos's
1306                  * base ref could have been put by someone else by the time
1307                  * the function returns.  Make sure it doesn't go away
1308                  * underneath us.
1309                  */
1310                 kernfs_get(pos);
1311 
1312                 /*
1313                  * Drain iff @kn was activated.  This avoids draining and
1314                  * its lockdep annotations for nodes which have never been
1315                  * activated and allows embedding kernfs_remove() in create
1316                  * error paths without worrying about draining.
1317                  */
1318                 if (kn->flags & KERNFS_ACTIVATED)
1319                         kernfs_drain(pos);
1320                 else
1321                         WARN_ON_ONCE(atomic_read(&kn->active) != KN_DEACTIVATED_BIAS);
1322 
1323                 /*
1324                  * kernfs_unlink_sibling() succeeds once per node.  Use it
1325                  * to decide who's responsible for cleanups.
1326                  */
1327                 if (!pos->parent || kernfs_unlink_sibling(pos)) {
1328                         struct kernfs_iattrs *ps_iattr =
1329                                 pos->parent ? pos->parent->iattr : NULL;
1330 
1331                         /* update timestamps on the parent */
1332                         if (ps_iattr) {
1333                                 ktime_get_real_ts64(&ps_iattr->ia_ctime);
1334                                 ps_iattr->ia_mtime = ps_iattr->ia_ctime;
1335                         }
1336 
1337                         kernfs_put(pos);
1338                 }
1339 
1340                 kernfs_put(pos);
1341         } while (pos != kn);
1342 }
1343 
1344 /**
1345  * kernfs_remove - remove a kernfs_node recursively
1346  * @kn: the kernfs_node to remove
1347  *
1348  * Remove @kn along with all its subdirectories and files.
1349  */
1350 void kernfs_remove(struct kernfs_node *kn)
1351 {
1352         mutex_lock(&kernfs_mutex);
1353         __kernfs_remove(kn);
1354         mutex_unlock(&kernfs_mutex);
1355 }
1356 
1357 /**
1358  * kernfs_break_active_protection - break out of active protection
1359  * @kn: the self kernfs_node
1360  *
1361  * The caller must be running off of a kernfs operation which is invoked
1362  * with an active reference - e.g. one of kernfs_ops.  Each invocation of
1363  * this function must also be matched with an invocation of
1364  * kernfs_unbreak_active_protection().
1365  *
1366  * This function releases the active reference of @kn the caller is
1367  * holding.  Once this function is called, @kn may be removed at any point
1368  * and the caller is solely responsible for ensuring that the objects it
1369  * dereferences are accessible.
1370  */
1371 void kernfs_break_active_protection(struct kernfs_node *kn)
1372 {
1373         /*
1374          * Take out ourself out of the active ref dependency chain.  If
1375          * we're called without an active ref, lockdep will complain.
1376          */
1377         kernfs_put_active(kn);
1378 }
1379 
1380 /**
1381  * kernfs_unbreak_active_protection - undo kernfs_break_active_protection()
1382  * @kn: the self kernfs_node
1383  *
1384  * If kernfs_break_active_protection() was called, this function must be
1385  * invoked before finishing the kernfs operation.  Note that while this
1386  * function restores the active reference, it doesn't and can't actually
1387  * restore the active protection - @kn may already or be in the process of
1388  * being removed.  Once kernfs_break_active_protection() is invoked, that
1389  * protection is irreversibly gone for the kernfs operation instance.
1390  *
1391  * While this function may be called at any point after
1392  * kernfs_break_active_protection() is invoked, its most useful location
1393  * would be right before the enclosing kernfs operation returns.
1394  */
1395 void kernfs_unbreak_active_protection(struct kernfs_node *kn)
1396 {
1397         /*
1398          * @kn->active could be in any state; however, the increment we do
1399          * here will be undone as soon as the enclosing kernfs operation
1400          * finishes and this temporary bump can't break anything.  If @kn
1401          * is alive, nothing changes.  If @kn is being deactivated, the
1402          * soon-to-follow put will either finish deactivation or restore
1403          * deactivated state.  If @kn is already removed, the temporary
1404          * bump is guaranteed to be gone before @kn is released.
1405          */
1406         atomic_inc(&kn->active);
1407         if (kernfs_lockdep(kn))
1408                 rwsem_acquire(&kn->dep_map, 0, 1, _RET_IP_);
1409 }
1410 
1411 /**
1412  * kernfs_remove_self - remove a kernfs_node from its own method
1413  * @kn: the self kernfs_node to remove
1414  *
1415  * The caller must be running off of a kernfs operation which is invoked
1416  * with an active reference - e.g. one of kernfs_ops.  This can be used to
1417  * implement a file operation which deletes itself.
1418  *
1419  * For example, the "delete" file for a sysfs device directory can be
1420  * implemented by invoking kernfs_remove_self() on the "delete" file
1421  * itself.  This function breaks the circular dependency of trying to
1422  * deactivate self while holding an active ref itself.  It isn't necessary
1423  * to modify the usual removal path to use kernfs_remove_self().  The
1424  * "delete" implementation can simply invoke kernfs_remove_self() on self
1425  * before proceeding with the usual removal path.  kernfs will ignore later
1426  * kernfs_remove() on self.
1427  *
1428  * kernfs_remove_self() can be called multiple times concurrently on the
1429  * same kernfs_node.  Only the first one actually performs removal and
1430  * returns %true.  All others will wait until the kernfs operation which
1431  * won self-removal finishes and return %false.  Note that the losers wait
1432  * for the completion of not only the winning kernfs_remove_self() but also
1433  * the whole kernfs_ops which won the arbitration.  This can be used to
1434  * guarantee, for example, all concurrent writes to a "delete" file to
1435  * finish only after the whole operation is complete.
1436  */
1437 bool kernfs_remove_self(struct kernfs_node *kn)
1438 {
1439         bool ret;
1440 
1441         mutex_lock(&kernfs_mutex);
1442         kernfs_break_active_protection(kn);
1443 
1444         /*
1445          * SUICIDAL is used to arbitrate among competing invocations.  Only
1446          * the first one will actually perform removal.  When the removal
1447          * is complete, SUICIDED is set and the active ref is restored
1448          * while holding kernfs_mutex.  The ones which lost arbitration
1449          * waits for SUICDED && drained which can happen only after the
1450          * enclosing kernfs operation which executed the winning instance
1451          * of kernfs_remove_self() finished.
1452          */
1453         if (!(kn->flags & KERNFS_SUICIDAL)) {
1454                 kn->flags |= KERNFS_SUICIDAL;
1455                 __kernfs_remove(kn);
1456                 kn->flags |= KERNFS_SUICIDED;
1457                 ret = true;
1458         } else {
1459                 wait_queue_head_t *waitq = &kernfs_root(kn)->deactivate_waitq;
1460                 DEFINE_WAIT(wait);
1461 
1462                 while (true) {
1463                         prepare_to_wait(waitq, &wait, TASK_UNINTERRUPTIBLE);
1464 
1465                         if ((kn->flags & KERNFS_SUICIDED) &&
1466                             atomic_read(&kn->active) == KN_DEACTIVATED_BIAS)
1467                                 break;
1468 
1469                         mutex_unlock(&kernfs_mutex);
1470                         schedule();
1471                         mutex_lock(&kernfs_mutex);
1472                 }
1473                 finish_wait(waitq, &wait);
1474                 WARN_ON_ONCE(!RB_EMPTY_NODE(&kn->rb));
1475                 ret = false;
1476         }
1477 
1478         /*
1479          * This must be done while holding kernfs_mutex; otherwise, waiting
1480          * for SUICIDED && deactivated could finish prematurely.
1481          */
1482         kernfs_unbreak_active_protection(kn);
1483 
1484         mutex_unlock(&kernfs_mutex);
1485         return ret;
1486 }
1487 
1488 /**
1489  * kernfs_remove_by_name_ns - find a kernfs_node by name and remove it
1490  * @parent: parent of the target
1491  * @name: name of the kernfs_node to remove
1492  * @ns: namespace tag of the kernfs_node to remove
1493  *
1494  * Look for the kernfs_node with @name and @ns under @parent and remove it.
1495  * Returns 0 on success, -ENOENT if such entry doesn't exist.
1496  */
1497 int kernfs_remove_by_name_ns(struct kernfs_node *parent, const char *name,
1498                              const void *ns)
1499 {
1500         struct kernfs_node *kn;
1501 
1502         if (!parent) {
1503                 WARN(1, KERN_WARNING "kernfs: can not remove '%s', no directory\n",
1504                         name);
1505                 return -ENOENT;
1506         }
1507 
1508         mutex_lock(&kernfs_mutex);
1509 
1510         kn = kernfs_find_ns(parent, name, ns);
1511         if (kn)
1512                 __kernfs_remove(kn);
1513 
1514         mutex_unlock(&kernfs_mutex);
1515 
1516         if (kn)
1517                 return 0;
1518         else
1519                 return -ENOENT;
1520 }
1521 
1522 /**
1523  * kernfs_rename_ns - move and rename a kernfs_node
1524  * @kn: target node
1525  * @new_parent: new parent to put @sd under
1526  * @new_name: new name
1527  * @new_ns: new namespace tag
1528  */
1529 int kernfs_rename_ns(struct kernfs_node *kn, struct kernfs_node *new_parent,
1530                      const char *new_name, const void *new_ns)
1531 {
1532         struct kernfs_node *old_parent;
1533         const char *old_name = NULL;
1534         int error;
1535 
1536         /* can't move or rename root */
1537         if (!kn->parent)
1538                 return -EINVAL;
1539 
1540         mutex_lock(&kernfs_mutex);
1541 
1542         error = -ENOENT;
1543         if (!kernfs_active(kn) || !kernfs_active(new_parent) ||
1544             (new_parent->flags & KERNFS_EMPTY_DIR))
1545                 goto out;
1546 
1547         error = 0;
1548         if ((kn->parent == new_parent) && (kn->ns == new_ns) &&
1549             (strcmp(kn->name, new_name) == 0))
1550                 goto out;       /* nothing to rename */
1551 
1552         error = -EEXIST;
1553         if (kernfs_find_ns(new_parent, new_name, new_ns))
1554                 goto out;
1555 
1556         /* rename kernfs_node */
1557         if (strcmp(kn->name, new_name) != 0) {
1558                 error = -ENOMEM;
1559                 new_name = kstrdup_const(new_name, GFP_KERNEL);
1560                 if (!new_name)
1561                         goto out;
1562         } else {
1563                 new_name = NULL;
1564         }
1565 
1566         /*
1567          * Move to the appropriate place in the appropriate directories rbtree.
1568          */
1569         kernfs_unlink_sibling(kn);
1570         kernfs_get(new_parent);
1571 
1572         /* rename_lock protects ->parent and ->name accessors */
1573         spin_lock_irq(&kernfs_rename_lock);
1574 
1575         old_parent = kn->parent;
1576         kn->parent = new_parent;
1577 
1578         kn->ns = new_ns;
1579         if (new_name) {
1580                 old_name = kn->name;
1581                 kn->name = new_name;
1582         }
1583 
1584         spin_unlock_irq(&kernfs_rename_lock);
1585 
1586         kn->hash = kernfs_name_hash(kn->name, kn->ns);
1587         kernfs_link_sibling(kn);
1588 
1589         kernfs_put(old_parent);
1590         kfree_const(old_name);
1591 
1592         error = 0;
1593  out:
1594         mutex_unlock(&kernfs_mutex);
1595         return error;
1596 }
1597 
1598 /* Relationship between s_mode and the DT_xxx types */
1599 static inline unsigned char dt_type(struct kernfs_node *kn)
1600 {
1601         return (kn->mode >> 12) & 15;
1602 }
1603 
1604 static int kernfs_dir_fop_release(struct inode *inode, struct file *filp)
1605 {
1606         kernfs_put(filp->private_data);
1607         return 0;
1608 }
1609 
1610 static struct kernfs_node *kernfs_dir_pos(const void *ns,
1611         struct kernfs_node *parent, loff_t hash, struct kernfs_node *pos)
1612 {
1613         if (pos) {
1614                 int valid = kernfs_active(pos) &&
1615                         pos->parent == parent && hash == pos->hash;
1616                 kernfs_put(pos);
1617                 if (!valid)
1618                         pos = NULL;
1619         }
1620         if (!pos && (hash > 1) && (hash < INT_MAX)) {
1621                 struct rb_node *node = parent->dir.children.rb_node;
1622                 while (node) {
1623                         pos = rb_to_kn(node);
1624 
1625                         if (hash < pos->hash)
1626                                 node = node->rb_left;
1627                         else if (hash > pos->hash)
1628                                 node = node->rb_right;
1629                         else
1630                                 break;
1631                 }
1632         }
1633         /* Skip over entries which are dying/dead or in the wrong namespace */
1634         while (pos && (!kernfs_active(pos) || pos->ns != ns)) {
1635                 struct rb_node *node = rb_next(&pos->rb);
1636                 if (!node)
1637                         pos = NULL;
1638                 else
1639                         pos = rb_to_kn(node);
1640         }
1641         return pos;
1642 }
1643 
1644 static struct kernfs_node *kernfs_dir_next_pos(const void *ns,
1645         struct kernfs_node *parent, ino_t ino, struct kernfs_node *pos)
1646 {
1647         pos = kernfs_dir_pos(ns, parent, ino, pos);
1648         if (pos) {
1649                 do {
1650                         struct rb_node *node = rb_next(&pos->rb);
1651                         if (!node)
1652                                 pos = NULL;
1653                         else
1654                                 pos = rb_to_kn(node);
1655                 } while (pos && (!kernfs_active(pos) || pos->ns != ns));
1656         }
1657         return pos;
1658 }
1659 
1660 static int kernfs_fop_readdir(struct file *file, struct dir_context *ctx)
1661 {
1662         struct dentry *dentry = file->f_path.dentry;
1663         struct kernfs_node *parent = kernfs_dentry_node(dentry);
1664         struct kernfs_node *pos = file->private_data;
1665         const void *ns = NULL;
1666 
1667         if (!dir_emit_dots(file, ctx))
1668                 return 0;
1669         mutex_lock(&kernfs_mutex);
1670 
1671         if (kernfs_ns_enabled(parent))
1672                 ns = kernfs_info(dentry->d_sb)->ns;
1673 
1674         for (pos = kernfs_dir_pos(ns, parent, ctx->pos, pos);
1675              pos;
1676              pos = kernfs_dir_next_pos(ns, parent, ctx->pos, pos)) {
1677                 const char *name = pos->name;
1678                 unsigned int type = dt_type(pos);
1679                 int len = strlen(name);
1680                 ino_t ino = pos->id.ino;
1681 
1682                 ctx->pos = pos->hash;
1683                 file->private_data = pos;
1684                 kernfs_get(pos);
1685 
1686                 mutex_unlock(&kernfs_mutex);
1687                 if (!dir_emit(ctx, name, len, ino, type))
1688                         return 0;
1689                 mutex_lock(&kernfs_mutex);
1690         }
1691         mutex_unlock(&kernfs_mutex);
1692         file->private_data = NULL;
1693         ctx->pos = INT_MAX;
1694         return 0;
1695 }
1696 
1697 const struct file_operations kernfs_dir_fops = {
1698         .read           = generic_read_dir,
1699         .iterate_shared = kernfs_fop_readdir,
1700         .release        = kernfs_dir_fop_release,
1701         .llseek         = generic_file_llseek,
1702 };
1703 

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