The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/fs/inotify.c

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    1 /*
    2  * fs/inotify.c - inode-based file event notifications
    3  *
    4  * Authors:
    5  *      John McCutchan  <ttb@tentacle.dhs.org>
    6  *      Robert Love     <rml@novell.com>
    7  *
    8  * Kernel API added by: Amy Griffis <amy.griffis@hp.com>
    9  *
   10  * Copyright (C) 2005 John McCutchan
   11  * Copyright 2006 Hewlett-Packard Development Company, L.P.
   12  *
   13  * This program is free software; you can redistribute it and/or modify it
   14  * under the terms of the GNU General Public License as published by the
   15  * Free Software Foundation; either version 2, or (at your option) any
   16  * later version.
   17  *
   18  * This program is distributed in the hope that it will be useful, but
   19  * WITHOUT ANY WARRANTY; without even the implied warranty of
   20  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   21  * General Public License for more details.
   22  */
   23 
   24 #include <linux/module.h>
   25 #include <linux/kernel.h>
   26 #include <linux/spinlock.h>
   27 #include <linux/idr.h>
   28 #include <linux/slab.h>
   29 #include <linux/fs.h>
   30 #include <linux/sched.h>
   31 #include <linux/init.h>
   32 #include <linux/list.h>
   33 #include <linux/writeback.h>
   34 #include <linux/inotify.h>
   35 
   36 static atomic_t inotify_cookie;
   37 
   38 /*
   39  * Lock ordering:
   40  *
   41  * dentry->d_lock (used to keep d_move() away from dentry->d_parent)
   42  * iprune_mutex (synchronize shrink_icache_memory())
   43  *      inode_lock (protects the super_block->s_inodes list)
   44  *      inode->inotify_mutex (protects inode->inotify_watches and watches->i_list)
   45  *              inotify_handle->mutex (protects inotify_handle and watches->h_list)
   46  *
   47  * The inode->inotify_mutex and inotify_handle->mutex and held during execution
   48  * of a caller's event handler.  Thus, the caller must not hold any locks
   49  * taken in their event handler while calling any of the published inotify
   50  * interfaces.
   51  */
   52 
   53 /*
   54  * Lifetimes of the three main data structures--inotify_handle, inode, and
   55  * inotify_watch--are managed by reference count.
   56  *
   57  * inotify_handle: Lifetime is from inotify_init() to inotify_destroy().
   58  * Additional references can bump the count via get_inotify_handle() and drop
   59  * the count via put_inotify_handle().
   60  *
   61  * inotify_watch: for inotify's purposes, lifetime is from inotify_add_watch()
   62  * to remove_watch_no_event().  Additional references can bump the count via
   63  * get_inotify_watch() and drop the count via put_inotify_watch().  The caller
   64  * is reponsible for the final put after receiving IN_IGNORED, or when using
   65  * IN_ONESHOT after receiving the first event.  Inotify does the final put if
   66  * inotify_destroy() is called.
   67  *
   68  * inode: Pinned so long as the inode is associated with a watch, from
   69  * inotify_add_watch() to the final put_inotify_watch().
   70  */
   71 
   72 /*
   73  * struct inotify_handle - represents an inotify instance
   74  *
   75  * This structure is protected by the mutex 'mutex'.
   76  */
   77 struct inotify_handle {
   78         struct idr              idr;            /* idr mapping wd -> watch */
   79         struct mutex            mutex;          /* protects this bad boy */
   80         struct list_head        watches;        /* list of watches */
   81         atomic_t                count;          /* reference count */
   82         u32                     last_wd;        /* the last wd allocated */
   83         const struct inotify_operations *in_ops; /* inotify caller operations */
   84 };
   85 
   86 static inline void get_inotify_handle(struct inotify_handle *ih)
   87 {
   88         atomic_inc(&ih->count);
   89 }
   90 
   91 static inline void put_inotify_handle(struct inotify_handle *ih)
   92 {
   93         if (atomic_dec_and_test(&ih->count)) {
   94                 idr_destroy(&ih->idr);
   95                 kfree(ih);
   96         }
   97 }
   98 
   99 /**
  100  * get_inotify_watch - grab a reference to an inotify_watch
  101  * @watch: watch to grab
  102  */
  103 void get_inotify_watch(struct inotify_watch *watch)
  104 {
  105         atomic_inc(&watch->count);
  106 }
  107 EXPORT_SYMBOL_GPL(get_inotify_watch);
  108 
  109 int pin_inotify_watch(struct inotify_watch *watch)
  110 {
  111         struct super_block *sb = watch->inode->i_sb;
  112         spin_lock(&sb_lock);
  113         if (sb->s_count >= S_BIAS) {
  114                 atomic_inc(&sb->s_active);
  115                 spin_unlock(&sb_lock);
  116                 atomic_inc(&watch->count);
  117                 return 1;
  118         }
  119         spin_unlock(&sb_lock);
  120         return 0;
  121 }
  122 
  123 /**
  124  * put_inotify_watch - decrements the ref count on a given watch.  cleans up
  125  * watch references if the count reaches zero.  inotify_watch is freed by
  126  * inotify callers via the destroy_watch() op.
  127  * @watch: watch to release
  128  */
  129 void put_inotify_watch(struct inotify_watch *watch)
  130 {
  131         if (atomic_dec_and_test(&watch->count)) {
  132                 struct inotify_handle *ih = watch->ih;
  133 
  134                 iput(watch->inode);
  135                 ih->in_ops->destroy_watch(watch);
  136                 put_inotify_handle(ih);
  137         }
  138 }
  139 EXPORT_SYMBOL_GPL(put_inotify_watch);
  140 
  141 void unpin_inotify_watch(struct inotify_watch *watch)
  142 {
  143         struct super_block *sb = watch->inode->i_sb;
  144         put_inotify_watch(watch);
  145         deactivate_super(sb);
  146 }
  147 
  148 /*
  149  * inotify_handle_get_wd - returns the next WD for use by the given handle
  150  *
  151  * Callers must hold ih->mutex.  This function can sleep.
  152  */
  153 static int inotify_handle_get_wd(struct inotify_handle *ih,
  154                                  struct inotify_watch *watch)
  155 {
  156         int ret;
  157 
  158         do {
  159                 if (unlikely(!idr_pre_get(&ih->idr, GFP_KERNEL)))
  160                         return -ENOSPC;
  161                 ret = idr_get_new_above(&ih->idr, watch, ih->last_wd+1, &watch->wd);
  162         } while (ret == -EAGAIN);
  163 
  164         if (likely(!ret))
  165                 ih->last_wd = watch->wd;
  166 
  167         return ret;
  168 }
  169 
  170 /*
  171  * inotify_inode_watched - returns nonzero if there are watches on this inode
  172  * and zero otherwise.  We call this lockless, we do not care if we race.
  173  */
  174 static inline int inotify_inode_watched(struct inode *inode)
  175 {
  176         return !list_empty(&inode->inotify_watches);
  177 }
  178 
  179 /*
  180  * Get child dentry flag into synch with parent inode.
  181  * Flag should always be clear for negative dentrys.
  182  */
  183 static void set_dentry_child_flags(struct inode *inode, int watched)
  184 {
  185         struct dentry *alias;
  186 
  187         spin_lock(&dcache_lock);
  188         list_for_each_entry(alias, &inode->i_dentry, d_alias) {
  189                 struct dentry *child;
  190 
  191                 list_for_each_entry(child, &alias->d_subdirs, d_u.d_child) {
  192                         if (!child->d_inode)
  193                                 continue;
  194 
  195                         spin_lock(&child->d_lock);
  196                         if (watched)
  197                                 child->d_flags |= DCACHE_INOTIFY_PARENT_WATCHED;
  198                         else
  199                                 child->d_flags &=~DCACHE_INOTIFY_PARENT_WATCHED;
  200                         spin_unlock(&child->d_lock);
  201                 }
  202         }
  203         spin_unlock(&dcache_lock);
  204 }
  205 
  206 /*
  207  * inotify_find_handle - find the watch associated with the given inode and
  208  * handle
  209  *
  210  * Callers must hold inode->inotify_mutex.
  211  */
  212 static struct inotify_watch *inode_find_handle(struct inode *inode,
  213                                                struct inotify_handle *ih)
  214 {
  215         struct inotify_watch *watch;
  216 
  217         list_for_each_entry(watch, &inode->inotify_watches, i_list) {
  218                 if (watch->ih == ih)
  219                         return watch;
  220         }
  221 
  222         return NULL;
  223 }
  224 
  225 /*
  226  * remove_watch_no_event - remove watch without the IN_IGNORED event.
  227  *
  228  * Callers must hold both inode->inotify_mutex and ih->mutex.
  229  */
  230 static void remove_watch_no_event(struct inotify_watch *watch,
  231                                   struct inotify_handle *ih)
  232 {
  233         list_del(&watch->i_list);
  234         list_del(&watch->h_list);
  235 
  236         if (!inotify_inode_watched(watch->inode))
  237                 set_dentry_child_flags(watch->inode, 0);
  238 
  239         idr_remove(&ih->idr, watch->wd);
  240 }
  241 
  242 /**
  243  * inotify_remove_watch_locked - Remove a watch from both the handle and the
  244  * inode.  Sends the IN_IGNORED event signifying that the inode is no longer
  245  * watched.  May be invoked from a caller's event handler.
  246  * @ih: inotify handle associated with watch
  247  * @watch: watch to remove
  248  *
  249  * Callers must hold both inode->inotify_mutex and ih->mutex.
  250  */
  251 void inotify_remove_watch_locked(struct inotify_handle *ih,
  252                                  struct inotify_watch *watch)
  253 {
  254         remove_watch_no_event(watch, ih);
  255         ih->in_ops->handle_event(watch, watch->wd, IN_IGNORED, 0, NULL, NULL);
  256 }
  257 EXPORT_SYMBOL_GPL(inotify_remove_watch_locked);
  258 
  259 /* Kernel API for producing events */
  260 
  261 /*
  262  * inotify_d_instantiate - instantiate dcache entry for inode
  263  */
  264 void inotify_d_instantiate(struct dentry *entry, struct inode *inode)
  265 {
  266         struct dentry *parent;
  267 
  268         if (!inode)
  269                 return;
  270 
  271         spin_lock(&entry->d_lock);
  272         parent = entry->d_parent;
  273         if (parent->d_inode && inotify_inode_watched(parent->d_inode))
  274                 entry->d_flags |= DCACHE_INOTIFY_PARENT_WATCHED;
  275         spin_unlock(&entry->d_lock);
  276 }
  277 
  278 /*
  279  * inotify_d_move - dcache entry has been moved
  280  */
  281 void inotify_d_move(struct dentry *entry)
  282 {
  283         struct dentry *parent;
  284 
  285         parent = entry->d_parent;
  286         if (inotify_inode_watched(parent->d_inode))
  287                 entry->d_flags |= DCACHE_INOTIFY_PARENT_WATCHED;
  288         else
  289                 entry->d_flags &= ~DCACHE_INOTIFY_PARENT_WATCHED;
  290 }
  291 
  292 /**
  293  * inotify_inode_queue_event - queue an event to all watches on this inode
  294  * @inode: inode event is originating from
  295  * @mask: event mask describing this event
  296  * @cookie: cookie for synchronization, or zero
  297  * @name: filename, if any
  298  * @n_inode: inode associated with name
  299  */
  300 void inotify_inode_queue_event(struct inode *inode, u32 mask, u32 cookie,
  301                                const char *name, struct inode *n_inode)
  302 {
  303         struct inotify_watch *watch, *next;
  304 
  305         if (!inotify_inode_watched(inode))
  306                 return;
  307 
  308         mutex_lock(&inode->inotify_mutex);
  309         list_for_each_entry_safe(watch, next, &inode->inotify_watches, i_list) {
  310                 u32 watch_mask = watch->mask;
  311                 if (watch_mask & mask) {
  312                         struct inotify_handle *ih= watch->ih;
  313                         mutex_lock(&ih->mutex);
  314                         if (watch_mask & IN_ONESHOT)
  315                                 remove_watch_no_event(watch, ih);
  316                         ih->in_ops->handle_event(watch, watch->wd, mask, cookie,
  317                                                  name, n_inode);
  318                         mutex_unlock(&ih->mutex);
  319                 }
  320         }
  321         mutex_unlock(&inode->inotify_mutex);
  322 }
  323 EXPORT_SYMBOL_GPL(inotify_inode_queue_event);
  324 
  325 /**
  326  * inotify_dentry_parent_queue_event - queue an event to a dentry's parent
  327  * @dentry: the dentry in question, we queue against this dentry's parent
  328  * @mask: event mask describing this event
  329  * @cookie: cookie for synchronization, or zero
  330  * @name: filename, if any
  331  */
  332 void inotify_dentry_parent_queue_event(struct dentry *dentry, u32 mask,
  333                                        u32 cookie, const char *name)
  334 {
  335         struct dentry *parent;
  336         struct inode *inode;
  337 
  338         if (!(dentry->d_flags & DCACHE_INOTIFY_PARENT_WATCHED))
  339                 return;
  340 
  341         spin_lock(&dentry->d_lock);
  342         parent = dentry->d_parent;
  343         inode = parent->d_inode;
  344 
  345         if (inotify_inode_watched(inode)) {
  346                 dget(parent);
  347                 spin_unlock(&dentry->d_lock);
  348                 inotify_inode_queue_event(inode, mask, cookie, name,
  349                                           dentry->d_inode);
  350                 dput(parent);
  351         } else
  352                 spin_unlock(&dentry->d_lock);
  353 }
  354 EXPORT_SYMBOL_GPL(inotify_dentry_parent_queue_event);
  355 
  356 /**
  357  * inotify_get_cookie - return a unique cookie for use in synchronizing events.
  358  */
  359 u32 inotify_get_cookie(void)
  360 {
  361         return atomic_inc_return(&inotify_cookie);
  362 }
  363 EXPORT_SYMBOL_GPL(inotify_get_cookie);
  364 
  365 /**
  366  * inotify_unmount_inodes - an sb is unmounting.  handle any watched inodes.
  367  * @list: list of inodes being unmounted (sb->s_inodes)
  368  *
  369  * Called with inode_lock held, protecting the unmounting super block's list
  370  * of inodes, and with iprune_mutex held, keeping shrink_icache_memory() at bay.
  371  * We temporarily drop inode_lock, however, and CAN block.
  372  */
  373 void inotify_unmount_inodes(struct list_head *list)
  374 {
  375         struct inode *inode, *next_i, *need_iput = NULL;
  376 
  377         list_for_each_entry_safe(inode, next_i, list, i_sb_list) {
  378                 struct inotify_watch *watch, *next_w;
  379                 struct inode *need_iput_tmp;
  380                 struct list_head *watches;
  381 
  382                 /*
  383                  * If i_count is zero, the inode cannot have any watches and
  384                  * doing an __iget/iput with MS_ACTIVE clear would actually
  385                  * evict all inodes with zero i_count from icache which is
  386                  * unnecessarily violent and may in fact be illegal to do.
  387                  */
  388                 if (!atomic_read(&inode->i_count))
  389                         continue;
  390 
  391                 /*
  392                  * We cannot __iget() an inode in state I_CLEAR, I_FREEING, or
  393                  * I_WILL_FREE which is fine because by that point the inode
  394                  * cannot have any associated watches.
  395                  */
  396                 if (inode->i_state & (I_CLEAR | I_FREEING | I_WILL_FREE))
  397                         continue;
  398 
  399                 need_iput_tmp = need_iput;
  400                 need_iput = NULL;
  401                 /* In case inotify_remove_watch_locked() drops a reference. */
  402                 if (inode != need_iput_tmp)
  403                         __iget(inode);
  404                 else
  405                         need_iput_tmp = NULL;
  406                 /* In case the dropping of a reference would nuke next_i. */
  407                 if ((&next_i->i_sb_list != list) &&
  408                                 atomic_read(&next_i->i_count) &&
  409                                 !(next_i->i_state & (I_CLEAR | I_FREEING |
  410                                         I_WILL_FREE))) {
  411                         __iget(next_i);
  412                         need_iput = next_i;
  413                 }
  414 
  415                 /*
  416                  * We can safely drop inode_lock here because we hold
  417                  * references on both inode and next_i.  Also no new inodes
  418                  * will be added since the umount has begun.  Finally,
  419                  * iprune_mutex keeps shrink_icache_memory() away.
  420                  */
  421                 spin_unlock(&inode_lock);
  422 
  423                 if (need_iput_tmp)
  424                         iput(need_iput_tmp);
  425 
  426                 /* for each watch, send IN_UNMOUNT and then remove it */
  427                 mutex_lock(&inode->inotify_mutex);
  428                 watches = &inode->inotify_watches;
  429                 list_for_each_entry_safe(watch, next_w, watches, i_list) {
  430                         struct inotify_handle *ih= watch->ih;
  431                         get_inotify_watch(watch);
  432                         mutex_lock(&ih->mutex);
  433                         ih->in_ops->handle_event(watch, watch->wd, IN_UNMOUNT, 0,
  434                                                  NULL, NULL);
  435                         inotify_remove_watch_locked(ih, watch);
  436                         mutex_unlock(&ih->mutex);
  437                         put_inotify_watch(watch);
  438                 }
  439                 mutex_unlock(&inode->inotify_mutex);
  440                 iput(inode);            
  441 
  442                 spin_lock(&inode_lock);
  443         }
  444 }
  445 EXPORT_SYMBOL_GPL(inotify_unmount_inodes);
  446 
  447 /**
  448  * inotify_inode_is_dead - an inode has been deleted, cleanup any watches
  449  * @inode: inode that is about to be removed
  450  */
  451 void inotify_inode_is_dead(struct inode *inode)
  452 {
  453         struct inotify_watch *watch, *next;
  454 
  455         mutex_lock(&inode->inotify_mutex);
  456         list_for_each_entry_safe(watch, next, &inode->inotify_watches, i_list) {
  457                 struct inotify_handle *ih = watch->ih;
  458                 mutex_lock(&ih->mutex);
  459                 inotify_remove_watch_locked(ih, watch);
  460                 mutex_unlock(&ih->mutex);
  461         }
  462         mutex_unlock(&inode->inotify_mutex);
  463 }
  464 EXPORT_SYMBOL_GPL(inotify_inode_is_dead);
  465 
  466 /* Kernel Consumer API */
  467 
  468 /**
  469  * inotify_init - allocate and initialize an inotify instance
  470  * @ops: caller's inotify operations
  471  */
  472 struct inotify_handle *inotify_init(const struct inotify_operations *ops)
  473 {
  474         struct inotify_handle *ih;
  475 
  476         ih = kmalloc(sizeof(struct inotify_handle), GFP_KERNEL);
  477         if (unlikely(!ih))
  478                 return ERR_PTR(-ENOMEM);
  479 
  480         idr_init(&ih->idr);
  481         INIT_LIST_HEAD(&ih->watches);
  482         mutex_init(&ih->mutex);
  483         ih->last_wd = 0;
  484         ih->in_ops = ops;
  485         atomic_set(&ih->count, 0);
  486         get_inotify_handle(ih);
  487 
  488         return ih;
  489 }
  490 EXPORT_SYMBOL_GPL(inotify_init);
  491 
  492 /**
  493  * inotify_init_watch - initialize an inotify watch
  494  * @watch: watch to initialize
  495  */
  496 void inotify_init_watch(struct inotify_watch *watch)
  497 {
  498         INIT_LIST_HEAD(&watch->h_list);
  499         INIT_LIST_HEAD(&watch->i_list);
  500         atomic_set(&watch->count, 0);
  501         get_inotify_watch(watch); /* initial get */
  502 }
  503 EXPORT_SYMBOL_GPL(inotify_init_watch);
  504 
  505 /*
  506  * Watch removals suck violently.  To kick the watch out we need (in this
  507  * order) inode->inotify_mutex and ih->mutex.  That's fine if we have
  508  * a hold on inode; however, for all other cases we need to make damn sure
  509  * we don't race with umount.  We can *NOT* just grab a reference to a
  510  * watch - inotify_unmount_inodes() will happily sail past it and we'll end
  511  * with reference to inode potentially outliving its superblock.  Ideally
  512  * we just want to grab an active reference to superblock if we can; that
  513  * will make sure we won't go into inotify_umount_inodes() until we are
  514  * done.  Cleanup is just deactivate_super().  However, that leaves a messy
  515  * case - what if we *are* racing with umount() and active references to
  516  * superblock can't be acquired anymore?  We can bump ->s_count, grab
  517  * ->s_umount, which will almost certainly wait until the superblock is shut
  518  * down and the watch in question is pining for fjords.  That's fine, but
  519  * there is a problem - we might have hit the window between ->s_active
  520  * getting to 0 / ->s_count - below S_BIAS (i.e. the moment when superblock
  521  * is past the point of no return and is heading for shutdown) and the
  522  * moment when deactivate_super() acquires ->s_umount.  We could just do
  523  * drop_super() yield() and retry, but that's rather antisocial and this
  524  * stuff is luser-triggerable.  OTOH, having grabbed ->s_umount and having
  525  * found that we'd got there first (i.e. that ->s_root is non-NULL) we know
  526  * that we won't race with inotify_umount_inodes().  So we could grab a
  527  * reference to watch and do the rest as above, just with drop_super() instead
  528  * of deactivate_super(), right?  Wrong.  We had to drop ih->mutex before we
  529  * could grab ->s_umount.  So the watch could've been gone already.
  530  *
  531  * That still can be dealt with - we need to save watch->wd, do idr_find()
  532  * and compare its result with our pointer.  If they match, we either have
  533  * the damn thing still alive or we'd lost not one but two races at once,
  534  * the watch had been killed and a new one got created with the same ->wd
  535  * at the same address.  That couldn't have happened in inotify_destroy(),
  536  * but inotify_rm_wd() could run into that.  Still, "new one got created"
  537  * is not a problem - we have every right to kill it or leave it alone,
  538  * whatever's more convenient.
  539  *
  540  * So we can use idr_find(...) == watch && watch->inode->i_sb == sb as
  541  * "grab it and kill it" check.  If it's been our original watch, we are
  542  * fine, if it's a newcomer - nevermind, just pretend that we'd won the
  543  * race and kill the fscker anyway; we are safe since we know that its
  544  * superblock won't be going away.
  545  *
  546  * And yes, this is far beyond mere "not very pretty"; so's the entire
  547  * concept of inotify to start with.
  548  */
  549 
  550 /**
  551  * pin_to_kill - pin the watch down for removal
  552  * @ih: inotify handle
  553  * @watch: watch to kill
  554  *
  555  * Called with ih->mutex held, drops it.  Possible return values:
  556  * 0 - nothing to do, it has died
  557  * 1 - remove it, drop the reference and deactivate_super()
  558  * 2 - remove it, drop the reference and drop_super(); we tried hard to avoid
  559  * that variant, since it involved a lot of PITA, but that's the best that
  560  * could've been done.
  561  */
  562 static int pin_to_kill(struct inotify_handle *ih, struct inotify_watch *watch)
  563 {
  564         struct super_block *sb = watch->inode->i_sb;
  565         s32 wd = watch->wd;
  566 
  567         spin_lock(&sb_lock);
  568         if (sb->s_count >= S_BIAS) {
  569                 atomic_inc(&sb->s_active);
  570                 spin_unlock(&sb_lock);
  571                 get_inotify_watch(watch);
  572                 mutex_unlock(&ih->mutex);
  573                 return 1;       /* the best outcome */
  574         }
  575         sb->s_count++;
  576         spin_unlock(&sb_lock);
  577         mutex_unlock(&ih->mutex); /* can't grab ->s_umount under it */
  578         down_read(&sb->s_umount);
  579         if (likely(!sb->s_root)) {
  580                 /* fs is already shut down; the watch is dead */
  581                 drop_super(sb);
  582                 return 0;
  583         }
  584         /* raced with the final deactivate_super() */
  585         mutex_lock(&ih->mutex);
  586         if (idr_find(&ih->idr, wd) != watch || watch->inode->i_sb != sb) {
  587                 /* the watch is dead */
  588                 mutex_unlock(&ih->mutex);
  589                 drop_super(sb);
  590                 return 0;
  591         }
  592         /* still alive or freed and reused with the same sb and wd; kill */
  593         get_inotify_watch(watch);
  594         mutex_unlock(&ih->mutex);
  595         return 2;
  596 }
  597 
  598 static void unpin_and_kill(struct inotify_watch *watch, int how)
  599 {
  600         struct super_block *sb = watch->inode->i_sb;
  601         put_inotify_watch(watch);
  602         switch (how) {
  603         case 1:
  604                 deactivate_super(sb);
  605                 break;
  606         case 2:
  607                 drop_super(sb);
  608         }
  609 }
  610 
  611 /**
  612  * inotify_destroy - clean up and destroy an inotify instance
  613  * @ih: inotify handle
  614  */
  615 void inotify_destroy(struct inotify_handle *ih)
  616 {
  617         /*
  618          * Destroy all of the watches for this handle. Unfortunately, not very
  619          * pretty.  We cannot do a simple iteration over the list, because we
  620          * do not know the inode until we iterate to the watch.  But we need to
  621          * hold inode->inotify_mutex before ih->mutex.  The following works.
  622          *
  623          * AV: it had to become even uglier to start working ;-/
  624          */
  625         while (1) {
  626                 struct inotify_watch *watch;
  627                 struct list_head *watches;
  628                 struct super_block *sb;
  629                 struct inode *inode;
  630                 int how;
  631 
  632                 mutex_lock(&ih->mutex);
  633                 watches = &ih->watches;
  634                 if (list_empty(watches)) {
  635                         mutex_unlock(&ih->mutex);
  636                         break;
  637                 }
  638                 watch = list_first_entry(watches, struct inotify_watch, h_list);
  639                 sb = watch->inode->i_sb;
  640                 how = pin_to_kill(ih, watch);
  641                 if (!how)
  642                         continue;
  643 
  644                 inode = watch->inode;
  645                 mutex_lock(&inode->inotify_mutex);
  646                 mutex_lock(&ih->mutex);
  647 
  648                 /* make sure we didn't race with another list removal */
  649                 if (likely(idr_find(&ih->idr, watch->wd))) {
  650                         remove_watch_no_event(watch, ih);
  651                         put_inotify_watch(watch);
  652                 }
  653 
  654                 mutex_unlock(&ih->mutex);
  655                 mutex_unlock(&inode->inotify_mutex);
  656                 unpin_and_kill(watch, how);
  657         }
  658 
  659         /* free this handle: the put matching the get in inotify_init() */
  660         put_inotify_handle(ih);
  661 }
  662 EXPORT_SYMBOL_GPL(inotify_destroy);
  663 
  664 /**
  665  * inotify_find_watch - find an existing watch for an (ih,inode) pair
  666  * @ih: inotify handle
  667  * @inode: inode to watch
  668  * @watchp: pointer to existing inotify_watch
  669  *
  670  * Caller must pin given inode (via nameidata).
  671  */
  672 s32 inotify_find_watch(struct inotify_handle *ih, struct inode *inode,
  673                        struct inotify_watch **watchp)
  674 {
  675         struct inotify_watch *old;
  676         int ret = -ENOENT;
  677 
  678         mutex_lock(&inode->inotify_mutex);
  679         mutex_lock(&ih->mutex);
  680 
  681         old = inode_find_handle(inode, ih);
  682         if (unlikely(old)) {
  683                 get_inotify_watch(old); /* caller must put watch */
  684                 *watchp = old;
  685                 ret = old->wd;
  686         }
  687 
  688         mutex_unlock(&ih->mutex);
  689         mutex_unlock(&inode->inotify_mutex);
  690 
  691         return ret;
  692 }
  693 EXPORT_SYMBOL_GPL(inotify_find_watch);
  694 
  695 /**
  696  * inotify_find_update_watch - find and update the mask of an existing watch
  697  * @ih: inotify handle
  698  * @inode: inode's watch to update
  699  * @mask: mask of events to watch
  700  *
  701  * Caller must pin given inode (via nameidata).
  702  */
  703 s32 inotify_find_update_watch(struct inotify_handle *ih, struct inode *inode,
  704                               u32 mask)
  705 {
  706         struct inotify_watch *old;
  707         int mask_add = 0;
  708         int ret;
  709 
  710         if (mask & IN_MASK_ADD)
  711                 mask_add = 1;
  712 
  713         /* don't allow invalid bits: we don't want flags set */
  714         mask &= IN_ALL_EVENTS | IN_ONESHOT;
  715         if (unlikely(!mask))
  716                 return -EINVAL;
  717 
  718         mutex_lock(&inode->inotify_mutex);
  719         mutex_lock(&ih->mutex);
  720 
  721         /*
  722          * Handle the case of re-adding a watch on an (inode,ih) pair that we
  723          * are already watching.  We just update the mask and return its wd.
  724          */
  725         old = inode_find_handle(inode, ih);
  726         if (unlikely(!old)) {
  727                 ret = -ENOENT;
  728                 goto out;
  729         }
  730 
  731         if (mask_add)
  732                 old->mask |= mask;
  733         else
  734                 old->mask = mask;
  735         ret = old->wd;
  736 out:
  737         mutex_unlock(&ih->mutex);
  738         mutex_unlock(&inode->inotify_mutex);
  739         return ret;
  740 }
  741 EXPORT_SYMBOL_GPL(inotify_find_update_watch);
  742 
  743 /**
  744  * inotify_add_watch - add a watch to an inotify instance
  745  * @ih: inotify handle
  746  * @watch: caller allocated watch structure
  747  * @inode: inode to watch
  748  * @mask: mask of events to watch
  749  *
  750  * Caller must pin given inode (via nameidata).
  751  * Caller must ensure it only calls inotify_add_watch() once per watch.
  752  * Calls inotify_handle_get_wd() so may sleep.
  753  */
  754 s32 inotify_add_watch(struct inotify_handle *ih, struct inotify_watch *watch,
  755                       struct inode *inode, u32 mask)
  756 {
  757         int ret = 0;
  758         int newly_watched;
  759 
  760         /* don't allow invalid bits: we don't want flags set */
  761         mask &= IN_ALL_EVENTS | IN_ONESHOT;
  762         if (unlikely(!mask))
  763                 return -EINVAL;
  764         watch->mask = mask;
  765 
  766         mutex_lock(&inode->inotify_mutex);
  767         mutex_lock(&ih->mutex);
  768 
  769         /* Initialize a new watch */
  770         ret = inotify_handle_get_wd(ih, watch);
  771         if (unlikely(ret))
  772                 goto out;
  773         ret = watch->wd;
  774 
  775         /* save a reference to handle and bump the count to make it official */
  776         get_inotify_handle(ih);
  777         watch->ih = ih;
  778 
  779         /*
  780          * Save a reference to the inode and bump the ref count to make it
  781          * official.  We hold a reference to nameidata, which makes this safe.
  782          */
  783         watch->inode = igrab(inode);
  784 
  785         /* Add the watch to the handle's and the inode's list */
  786         newly_watched = !inotify_inode_watched(inode);
  787         list_add(&watch->h_list, &ih->watches);
  788         list_add(&watch->i_list, &inode->inotify_watches);
  789         /*
  790          * Set child flags _after_ adding the watch, so there is no race
  791          * windows where newly instantiated children could miss their parent's
  792          * watched flag.
  793          */
  794         if (newly_watched)
  795                 set_dentry_child_flags(inode, 1);
  796 
  797 out:
  798         mutex_unlock(&ih->mutex);
  799         mutex_unlock(&inode->inotify_mutex);
  800         return ret;
  801 }
  802 EXPORT_SYMBOL_GPL(inotify_add_watch);
  803 
  804 /**
  805  * inotify_clone_watch - put the watch next to existing one
  806  * @old: already installed watch
  807  * @new: new watch
  808  *
  809  * Caller must hold the inotify_mutex of inode we are dealing with;
  810  * it is expected to remove the old watch before unlocking the inode.
  811  */
  812 s32 inotify_clone_watch(struct inotify_watch *old, struct inotify_watch *new)
  813 {
  814         struct inotify_handle *ih = old->ih;
  815         int ret = 0;
  816 
  817         new->mask = old->mask;
  818         new->ih = ih;
  819 
  820         mutex_lock(&ih->mutex);
  821 
  822         /* Initialize a new watch */
  823         ret = inotify_handle_get_wd(ih, new);
  824         if (unlikely(ret))
  825                 goto out;
  826         ret = new->wd;
  827 
  828         get_inotify_handle(ih);
  829 
  830         new->inode = igrab(old->inode);
  831 
  832         list_add(&new->h_list, &ih->watches);
  833         list_add(&new->i_list, &old->inode->inotify_watches);
  834 out:
  835         mutex_unlock(&ih->mutex);
  836         return ret;
  837 }
  838 
  839 void inotify_evict_watch(struct inotify_watch *watch)
  840 {
  841         get_inotify_watch(watch);
  842         mutex_lock(&watch->ih->mutex);
  843         inotify_remove_watch_locked(watch->ih, watch);
  844         mutex_unlock(&watch->ih->mutex);
  845 }
  846 
  847 /**
  848  * inotify_rm_wd - remove a watch from an inotify instance
  849  * @ih: inotify handle
  850  * @wd: watch descriptor to remove
  851  *
  852  * Can sleep.
  853  */
  854 int inotify_rm_wd(struct inotify_handle *ih, u32 wd)
  855 {
  856         struct inotify_watch *watch;
  857         struct super_block *sb;
  858         struct inode *inode;
  859         int how;
  860 
  861         mutex_lock(&ih->mutex);
  862         watch = idr_find(&ih->idr, wd);
  863         if (unlikely(!watch)) {
  864                 mutex_unlock(&ih->mutex);
  865                 return -EINVAL;
  866         }
  867         sb = watch->inode->i_sb;
  868         how = pin_to_kill(ih, watch);
  869         if (!how)
  870                 return 0;
  871 
  872         inode = watch->inode;
  873 
  874         mutex_lock(&inode->inotify_mutex);
  875         mutex_lock(&ih->mutex);
  876 
  877         /* make sure that we did not race */
  878         if (likely(idr_find(&ih->idr, wd) == watch))
  879                 inotify_remove_watch_locked(ih, watch);
  880 
  881         mutex_unlock(&ih->mutex);
  882         mutex_unlock(&inode->inotify_mutex);
  883         unpin_and_kill(watch, how);
  884 
  885         return 0;
  886 }
  887 EXPORT_SYMBOL_GPL(inotify_rm_wd);
  888 
  889 /**
  890  * inotify_rm_watch - remove a watch from an inotify instance
  891  * @ih: inotify handle
  892  * @watch: watch to remove
  893  *
  894  * Can sleep.
  895  */
  896 int inotify_rm_watch(struct inotify_handle *ih,
  897                      struct inotify_watch *watch)
  898 {
  899         return inotify_rm_wd(ih, watch->wd);
  900 }
  901 EXPORT_SYMBOL_GPL(inotify_rm_watch);
  902 
  903 /*
  904  * inotify_setup - core initialization function
  905  */
  906 static int __init inotify_setup(void)
  907 {
  908         atomic_set(&inotify_cookie, 0);
  909 
  910         return 0;
  911 }
  912 
  913 module_init(inotify_setup);

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