FreeBSD/Linux Kernel Cross Reference
sys/fs/dcache.c

     /*
      * fs/dcache.c
      *
      * Complete reimplementation
      * (C) 1997 Thomas Schoebel-Theuer,
      * with heavy changes by Linus Torvalds
      */
     
     /*
     * Notes on the allocation strategy:
     *
     * The dcache is a master of the icache - whenever a dcache entry
     * exists, the inode will always exist. "iput()" is done either when
     * the dcache entry is deleted or garbage collected.
     */
    
    #include <linux/config.h>
    #include <linux/string.h>
    #include <linux/mm.h>
    #include <linux/fs.h>
    #include <linux/slab.h>
    #include <linux/init.h>
    #include <linux/smp_lock.h>
    #include <linux/cache.h>
    #include <linux/module.h>
    
    #include <asm/uaccess.h>
    
    #define DCACHE_PARANOIA 1
    /* #define DCACHE_DEBUG 1 */
    
    spinlock_t dcache_lock __cacheline_aligned_in_smp = SPIN_LOCK_UNLOCKED;
    
    /* Right now the dcache depends on the kernel lock */
    #define check_lock()    if (!kernel_locked()) BUG()
    
    static kmem_cache_t *dentry_cache; 
    
    /*
     * This is the single most critical data structure when it comes
     * to the dcache: the hashtable for lookups. Somebody should try
     * to make this good - I've just made it work.
     *
     * This hash-function tries to avoid losing too many bits of hash
     * information, yet avoid using a prime hash-size or similar.
     */
    #define D_HASHBITS     d_hash_shift
    #define D_HASHMASK     d_hash_mask
    
    static unsigned int d_hash_mask;
    static unsigned int d_hash_shift;
    static struct list_head *dentry_hashtable;
    static LIST_HEAD(dentry_unused);
    
    /* Statistics gathering. */
    struct dentry_stat_t dentry_stat = {0, 0, 45, 0,};
    
    /* no dcache_lock, please */
    static inline void d_free(struct dentry *dentry)
    {
            if (dentry->d_op && dentry->d_op->d_release)
                    dentry->d_op->d_release(dentry);
            if (dname_external(dentry)) 
                    kfree(dentry->d_name.name);
            kmem_cache_free(dentry_cache, dentry); 
            dentry_stat.nr_dentry--;
    }
    
    /*
     * Release the dentry's inode, using the filesystem
     * d_iput() operation if defined.
     * Called with dcache_lock held, drops it.
     */
    static inline void dentry_iput(struct dentry * dentry)
    {
            struct inode *inode = dentry->d_inode;
            if (inode) {
                    dentry->d_inode = NULL;
                    list_del_init(&dentry->d_alias);
                    spin_unlock(&dcache_lock);
                    if (dentry->d_op && dentry->d_op->d_iput)
                            dentry->d_op->d_iput(dentry, inode);
                    else
                            iput(inode);
            } else
                    spin_unlock(&dcache_lock);
    }
    
    /* 
     * This is dput
     *
     * This is complicated by the fact that we do not want to put
     * dentries that are no longer on any hash chain on the unused
     * list: we'd much rather just get rid of them immediately.
     *
     * However, that implies that we have to traverse the dentry
     * tree upwards to the parents which might _also_ now be
     * scheduled for deletion (it may have been only waiting for
     * its last child to go away).
    *
    * This tail recursion is done by hand as we don't want to depend
    * on the compiler to always get this right (gcc generally doesn't).
    * Real recursion would eat up our stack space.
    */
   
   /*
    * dput - release a dentry
    * @dentry: dentry to release 
    *
    * Release a dentry. This will drop the usage count and if appropriate
    * call the dentry unlink method as well as removing it from the queues and
    * releasing its resources. If the parent dentries were scheduled for release
    * they too may now get deleted.
    *
    * no dcache lock, please.
    */
   
   void dput(struct dentry *dentry)
   {
           if (!dentry)
                   return;
   
   repeat:
           if (!atomic_dec_and_lock(&dentry->d_count, &dcache_lock))
                   return;
   
           /* dput on a free dentry? */
           if (!list_empty(&dentry->d_lru))
                   BUG();
           /*
            * AV: ->d_delete() is _NOT_ allowed to block now.
            */
           if (dentry->d_op && dentry->d_op->d_delete) {
                   if (dentry->d_op->d_delete(dentry))
                           goto unhash_it;
           }
           /* Unreachable? Get rid of it */
           if (list_empty(&dentry->d_hash))
                   goto kill_it;
           list_add(&dentry->d_lru, &dentry_unused);
           dentry_stat.nr_unused++;
           spin_unlock(&dcache_lock);
           return;
   
   unhash_it:
           list_del_init(&dentry->d_hash);
   
   kill_it: {
                   struct dentry *parent;
                   list_del(&dentry->d_child);
                   /* drops the lock, at that point nobody can reach this dentry */
                   dentry_iput(dentry);
                   parent = dentry->d_parent;
                   d_free(dentry);
                   if (dentry == parent)
                           return;
                   dentry = parent;
                   goto repeat;
           }
   }
   
   /**
    * d_invalidate - invalidate a dentry
    * @dentry: dentry to invalidate
    *
    * Try to invalidate the dentry if it turns out to be
    * possible. If there are other dentries that can be
    * reached through this one we can't delete it and we
    * return -EBUSY. On success we return 0.
    *
    * no dcache lock.
    */
    
   int d_invalidate(struct dentry * dentry)
   {
           /*
            * If it's already been dropped, return OK.
            */
           spin_lock(&dcache_lock);
           if (list_empty(&dentry->d_hash)) {
                   spin_unlock(&dcache_lock);
                   return 0;
           }
           /*
            * Check whether to do a partial shrink_dcache
            * to get rid of unused child entries.
            */
           if (!list_empty(&dentry->d_subdirs)) {
                   spin_unlock(&dcache_lock);
                   shrink_dcache_parent(dentry);
                   spin_lock(&dcache_lock);
           }
   
           /*
            * Somebody else still using it?
            *
            * If it's a directory, we can't drop it
            * for fear of somebody re-populating it
            * with children (even though dropping it
            * would make it unreachable from the root,
            * we might still populate it if it was a
            * working directory or similar).
            */
           if (atomic_read(&dentry->d_count) > 1) {
                   if (dentry->d_inode && S_ISDIR(dentry->d_inode->i_mode)) {
                           spin_unlock(&dcache_lock);
                           return -EBUSY;
                   }
           }
   
           list_del_init(&dentry->d_hash);
           spin_unlock(&dcache_lock);
           return 0;
   }
   
   /* This should be called _only_ with dcache_lock held */
   
   static inline struct dentry * __dget_locked(struct dentry *dentry)
   {
           atomic_inc(&dentry->d_count);
           if (atomic_read(&dentry->d_count) == 1) {
                   dentry_stat.nr_unused--;
                   list_del_init(&dentry->d_lru);
           }
           return dentry;
   }
   
   struct dentry * dget_locked(struct dentry *dentry)
   {
           return __dget_locked(dentry);
   }
   
   /**
    * d_find_alias - grab a hashed alias of inode
    * @inode: inode in question
    *
    * If inode has a hashed alias - acquire the reference to alias and
    * return it. Otherwise return NULL. Notice that if inode is a directory
    * there can be only one alias and it can be unhashed only if it has
    * no children.
    */
   
   struct dentry * d_find_alias(struct inode *inode)
   {
           struct list_head *head, *next, *tmp;
           struct dentry *alias;
   
           spin_lock(&dcache_lock);
           head = &inode->i_dentry;
           next = inode->i_dentry.next;
           while (next != head) {
                   tmp = next;
                   next = tmp->next;
                   alias = list_entry(tmp, struct dentry, d_alias);
                   if (!list_empty(&alias->d_hash)) {
                           __dget_locked(alias);
                           spin_unlock(&dcache_lock);
                           return alias;
                   }
           }
           spin_unlock(&dcache_lock);
           return NULL;
   }
   
   /*
    *      Try to kill dentries associated with this inode.
    * WARNING: you must own a reference to inode.
    */
   void d_prune_aliases(struct inode *inode)
   {
           struct list_head *tmp, *head = &inode->i_dentry;
   restart:
           spin_lock(&dcache_lock);
           tmp = head;
           while ((tmp = tmp->next) != head) {
                   struct dentry *dentry = list_entry(tmp, struct dentry, d_alias);
                   if (!atomic_read(&dentry->d_count)) {
                           __dget_locked(dentry);
                           spin_unlock(&dcache_lock);
                           d_drop(dentry);
                           dput(dentry);
                           goto restart;
                   }
           }
           spin_unlock(&dcache_lock);
   }
   
   /*
    * Throw away a dentry - free the inode, dput the parent.
    * This requires that the LRU list has already been
    * removed.
    * Called with dcache_lock, drops it and then regains.
    */
   static inline void prune_one_dentry(struct dentry * dentry)
   {
           struct dentry * parent;
   
           list_del_init(&dentry->d_hash);
           list_del(&dentry->d_child);
           dentry_iput(dentry);
           parent = dentry->d_parent;
           d_free(dentry);
           if (parent != dentry)
                   dput(parent);
           spin_lock(&dcache_lock);
   }
   
   /**
    * prune_dcache - shrink the dcache
    * @count: number of entries to try and free
    *
    * Shrink the dcache. This is done when we need
    * more memory, or simply when we need to unmount
    * something (at which point we need to unuse
    * all dentries).
    *
    * This function may fail to free any resources if
    * all the dentries are in use.
    */
    
   void prune_dcache(int count)
   {
           spin_lock(&dcache_lock);
           for (;;) {
                   struct dentry *dentry;
                   struct list_head *tmp;
   
                   tmp = dentry_unused.prev;
   
                   if (tmp == &dentry_unused)
                           break;
                   list_del_init(tmp);
                   dentry = list_entry(tmp, struct dentry, d_lru);
   
                   /* If the dentry was recently referenced, don't free it. */
                   if (dentry->d_vfs_flags & DCACHE_REFERENCED) {
                           dentry->d_vfs_flags &= ~DCACHE_REFERENCED;
                           list_add(&dentry->d_lru, &dentry_unused);
                           continue;
                   }
                   dentry_stat.nr_unused--;
   
                   /* Unused dentry with a count? */
                   if (atomic_read(&dentry->d_count))
                           BUG();
   
                   prune_one_dentry(dentry);
                   if (!--count)
                           break;
           }
           spin_unlock(&dcache_lock);
   }
   
   /*
    * Shrink the dcache for the specified super block.
    * This allows us to unmount a device without disturbing
    * the dcache for the other devices.
    *
    * This implementation makes just two traversals of the
    * unused list.  On the first pass we move the selected
    * dentries to the most recent end, and on the second
    * pass we free them.  The second pass must restart after
    * each dput(), but since the target dentries are all at
    * the end, it's really just a single traversal.
    */
   
   /**
    * shrink_dcache_sb - shrink dcache for a superblock
    * @sb: superblock
    *
    * Shrink the dcache for the specified super block. This
    * is used to free the dcache before unmounting a file
    * system
    */
   
   void shrink_dcache_sb(struct super_block * sb)
   {
           struct list_head *tmp, *next;
           struct dentry *dentry;
   
           /*
            * Pass one ... move the dentries for the specified
            * superblock to the most recent end of the unused list.
            */
           spin_lock(&dcache_lock);
           next = dentry_unused.next;
           while (next != &dentry_unused) {
                   tmp = next;
                   next = tmp->next;
                   dentry = list_entry(tmp, struct dentry, d_lru);
                   if (dentry->d_sb != sb)
                           continue;
                   list_del(tmp);
                   list_add(tmp, &dentry_unused);
           }
   
           /*
            * Pass two ... free the dentries for this superblock.
            */
   repeat:
           next = dentry_unused.next;
           while (next != &dentry_unused) {
                   tmp = next;
                   next = tmp->next;
                   dentry = list_entry(tmp, struct dentry, d_lru);
                   if (dentry->d_sb != sb)
                           continue;
                   if (atomic_read(&dentry->d_count))
                           continue;
                   dentry_stat.nr_unused--;
                   list_del_init(tmp);
                   prune_one_dentry(dentry);
                   goto repeat;
           }
           spin_unlock(&dcache_lock);
   }
   
   /*
    * Search for at least 1 mount point in the dentry's subdirs.
    * We descend to the next level whenever the d_subdirs
    * list is non-empty and continue searching.
    */
    
   /**
    * have_submounts - check for mounts over a dentry
    * @parent: dentry to check.
    *
    * Return true if the parent or its subdirectories contain
    * a mount point
    */
    
   int have_submounts(struct dentry *parent)
   {
           struct dentry *this_parent = parent;
           struct list_head *next;
   
           spin_lock(&dcache_lock);
           if (d_mountpoint(parent))
                   goto positive;
   repeat:
           next = this_parent->d_subdirs.next;
   resume:
           while (next != &this_parent->d_subdirs) {
                   struct list_head *tmp = next;
                   struct dentry *dentry = list_entry(tmp, struct dentry, d_child);
                   next = tmp->next;
                   /* Have we found a mount point ? */
                   if (d_mountpoint(dentry))
                           goto positive;
                   if (!list_empty(&dentry->d_subdirs)) {
                           this_parent = dentry;
                           goto repeat;
                   }
           }
           /*
            * All done at this level ... ascend and resume the search.
            */
           if (this_parent != parent) {
                   next = this_parent->d_child.next; 
                   this_parent = this_parent->d_parent;
                   goto resume;
           }
           spin_unlock(&dcache_lock);
           return 0; /* No mount points found in tree */
   positive:
           spin_unlock(&dcache_lock);
           return 1;
   }
   
   /*
    * Search the dentry child list for the specified parent,
    * and move any unused dentries to the end of the unused
    * list for prune_dcache(). We descend to the next level
    * whenever the d_subdirs list is non-empty and continue
    * searching.
    */
   static int select_parent(struct dentry * parent)
   {
           struct dentry *this_parent = parent;
           struct list_head *next;
           int found = 0;
   
           spin_lock(&dcache_lock);
   repeat:
           next = this_parent->d_subdirs.next;
   resume:
           while (next != &this_parent->d_subdirs) {
                   struct list_head *tmp = next;
                   struct dentry *dentry = list_entry(tmp, struct dentry, d_child);
                   next = tmp->next;
                   if (!atomic_read(&dentry->d_count)) {
                           list_del(&dentry->d_lru);
                           list_add(&dentry->d_lru, dentry_unused.prev);
                           found++;
                   }
                   /*
                    * Descend a level if the d_subdirs list is non-empty.
                    */
                   if (!list_empty(&dentry->d_subdirs)) {
                           this_parent = dentry;
   #ifdef DCACHE_DEBUG
   printk(KERN_DEBUG "select_parent: descending to %s/%s, found=%d\n",
   dentry->d_parent->d_name.name, dentry->d_name.name, found);
   #endif
                           goto repeat;
                   }
           }
           /*
            * All done at this level ... ascend and resume the search.
            */
           if (this_parent != parent) {
                   next = this_parent->d_child.next; 
                   this_parent = this_parent->d_parent;
   #ifdef DCACHE_DEBUG
   printk(KERN_DEBUG "select_parent: ascending to %s/%s, found=%d\n",
   this_parent->d_parent->d_name.name, this_parent->d_name.name, found);
   #endif
                   goto resume;
           }
           spin_unlock(&dcache_lock);
           return found;
   }
   
   /**
    * shrink_dcache_parent - prune dcache
    * @parent: parent of entries to prune
    *
    * Prune the dcache to remove unused children of the parent dentry.
    */
    
   void shrink_dcache_parent(struct dentry * parent)
   {
           int found;
   
           while ((found = select_parent(parent)) != 0)
                   prune_dcache(found);
   }
   
   /*
    * This is called from kswapd when we think we need some
    * more memory, but aren't really sure how much. So we
    * carefully try to free a _bit_ of our dcache, but not
    * too much.
    *
    * Priority:
    *   0 - very urgent: shrink everything
    *  ...
    *   6 - base-level: try to shrink a bit.
    */
   int shrink_dcache_memory(int priority, unsigned int gfp_mask)
   {
           int count = 0;
   
           /*
            * Nasty deadlock avoidance.
            *
            * ext2_new_block->getblk->GFP->shrink_dcache_memory->prune_dcache->
            * prune_one_dentry->dput->dentry_iput->iput->inode->i_sb->s_op->
            * put_inode->ext2_discard_prealloc->ext2_free_blocks->lock_super->
            * DEADLOCK.
            *
            * We should make sure we don't hold the superblock lock over
            * block allocations, but for now:
            */
           if (!(gfp_mask & __GFP_FS))
                   return 0;
   
           count = dentry_stat.nr_unused / priority;
   
           prune_dcache(count);
           return kmem_cache_shrink(dentry_cache);
   }
   
   #define NAME_ALLOC_LEN(len)     ((len+16) & ~15)
   
   /**
    * d_alloc      -       allocate a dcache entry
    * @parent: parent of entry to allocate
    * @name: qstr of the name
    *
    * Allocates a dentry. It returns %NULL if there is insufficient memory
    * available. On a success the dentry is returned. The name passed in is
    * copied and the copy passed in may be reused after this call.
    */
    
   struct dentry * d_alloc(struct dentry * parent, const struct qstr *name)
   {
           char * str;
           struct dentry *dentry;
   
           dentry = kmem_cache_alloc(dentry_cache, GFP_KERNEL); 
           if (!dentry)
                   return NULL;
   
           if (name->len > DNAME_INLINE_LEN-1) {
                   str = kmalloc(NAME_ALLOC_LEN(name->len), GFP_KERNEL);
                   if (!str) {
                           kmem_cache_free(dentry_cache, dentry); 
                           return NULL;
                   }
           } else
                   str = dentry->d_iname; 
   
           memcpy(str, name->name, name->len);
           str[name->len] = 0;
   
           atomic_set(&dentry->d_count, 1);
           dentry->d_vfs_flags = 0;
           dentry->d_flags = 0;
           dentry->d_inode = NULL;
           dentry->d_parent = NULL;
           dentry->d_sb = NULL;
           dentry->d_name.name = str;
           dentry->d_name.len = name->len;
           dentry->d_name.hash = name->hash;
           dentry->d_op = NULL;
           dentry->d_fsdata = NULL;
           dentry->d_mounted = 0;
           INIT_LIST_HEAD(&dentry->d_hash);
           INIT_LIST_HEAD(&dentry->d_lru);
           INIT_LIST_HEAD(&dentry->d_subdirs);
           INIT_LIST_HEAD(&dentry->d_alias);
           if (parent) {
                   dentry->d_parent = dget(parent);
                   dentry->d_sb = parent->d_sb;
                   spin_lock(&dcache_lock);
                   list_add(&dentry->d_child, &parent->d_subdirs);
                   spin_unlock(&dcache_lock);
           } else
                   INIT_LIST_HEAD(&dentry->d_child);
   
           dentry_stat.nr_dentry++;
           return dentry;
   }
   
   /**
    * d_instantiate - fill in inode information for a dentry
    * @entry: dentry to complete
    * @inode: inode to attach to this dentry
    *
    * Fill in inode information in the entry.
    *
    * This turns negative dentries into productive full members
    * of society.
    *
    * NOTE! This assumes that the inode count has been incremented
    * (or otherwise set) by the caller to indicate that it is now
    * in use by the dcache.
    */
    
   void d_instantiate(struct dentry *entry, struct inode * inode)
   {
           if (!list_empty(&entry->d_alias)) BUG();
           spin_lock(&dcache_lock);
           if (inode)
                   list_add(&entry->d_alias, &inode->i_dentry);
           entry->d_inode = inode;
           spin_unlock(&dcache_lock);
   }
   
   /**
    * d_alloc_root - allocate root dentry
    * @root_inode: inode to allocate the root for
    *
    * Allocate a root ("/") dentry for the inode given. The inode is
    * instantiated and returned. %NULL is returned if there is insufficient
    * memory or the inode passed is %NULL.
    */
    
   struct dentry * d_alloc_root(struct inode * root_inode)
   {
           struct dentry *res = NULL;
   
           if (root_inode) {
                   res = d_alloc(NULL, &(const struct qstr) { "/", 1, 0 });
                   if (res) {
                           res->d_sb = root_inode->i_sb;
                           res->d_parent = res;
                           d_instantiate(res, root_inode);
                   }
           }
           return res;
   }
   
   static inline struct list_head * d_hash(struct dentry * parent, unsigned long hash)
   {
           hash += (unsigned long) parent / L1_CACHE_BYTES;
           hash = hash ^ (hash >> D_HASHBITS);
           return dentry_hashtable + (hash & D_HASHMASK);
   }
   
   /**
    * d_lookup - search for a dentry
    * @parent: parent dentry
    * @name: qstr of name we wish to find
    *
    * Searches the children of the parent dentry for the name in question. If
    * the dentry is found its reference count is incremented and the dentry
    * is returned. The caller must use d_put to free the entry when it has
    * finished using it. %NULL is returned on failure.
    */
    
   struct dentry * d_lookup(struct dentry * parent, struct qstr * name)
   {
           unsigned int len = name->len;
           unsigned int hash = name->hash;
           const unsigned char *str = name->name;
           struct list_head *head = d_hash(parent,hash);
           struct list_head *tmp;
   
           spin_lock(&dcache_lock);
           tmp = head->next;
           for (;;) {
                   struct dentry * dentry = list_entry(tmp, struct dentry, d_hash);
                   if (tmp == head)
                           break;
                   tmp = tmp->next;
                   if (dentry->d_name.hash != hash)
                           continue;
                   if (dentry->d_parent != parent)
                           continue;
                   if (parent->d_op && parent->d_op->d_compare) {
                           if (parent->d_op->d_compare(parent, &dentry->d_name, name))
                                   continue;
                   } else {
                           if (dentry->d_name.len != len)
                                   continue;
                           if (memcmp(dentry->d_name.name, str, len))
                                   continue;
                   }
                   __dget_locked(dentry);
                   dentry->d_vfs_flags |= DCACHE_REFERENCED;
                   spin_unlock(&dcache_lock);
                   return dentry;
           }
           spin_unlock(&dcache_lock);
           return NULL;
   }
   
   /**
    * d_validate - verify dentry provided from insecure source
    * @dentry: The dentry alleged to be valid child of @dparent
    * @dparent: The parent dentry (known to be valid)
    * @hash: Hash of the dentry
    * @len: Length of the name
    *
    * An insecure source has sent us a dentry, here we verify it and dget() it.
    * This is used by ncpfs in its readdir implementation.
    * Zero is returned in the dentry is invalid.
    */
    
   int d_validate(struct dentry *dentry, struct dentry *dparent)
   {
           unsigned long dent_addr = (unsigned long) dentry;
           unsigned long min_addr = PAGE_OFFSET;
           unsigned long align_mask = 0x0F;
           struct list_head *base, *lhp;
   
           if (dent_addr < min_addr)
                   goto out;
           if (dent_addr > (unsigned long)high_memory - sizeof(struct dentry))
                   goto out;
           if (dent_addr & align_mask)
                   goto out;
           if ((!kern_addr_valid(dent_addr)) || (!kern_addr_valid(dent_addr -1 +
                                                   sizeof(struct dentry))))
                   goto out;
   
           if (dentry->d_parent != dparent)
                   goto out;
   
           spin_lock(&dcache_lock);
           lhp = base = d_hash(dparent, dentry->d_name.hash);
           while ((lhp = lhp->next) != base) {
                   if (dentry == list_entry(lhp, struct dentry, d_hash)) {
                           __dget_locked(dentry);
                           spin_unlock(&dcache_lock);
                           return 1;
                   }
           }
           spin_unlock(&dcache_lock);
   out:
           return 0;
   }
   
   /*
    * When a file is deleted, we have two options:
    * - turn this dentry into a negative dentry
    * - unhash this dentry and free it.
    *
    * Usually, we want to just turn this into
    * a negative dentry, but if anybody else is
    * currently using the dentry or the inode
    * we can't do that and we fall back on removing
    * it from the hash queues and waiting for
    * it to be deleted later when it has no users
    */
    
   /**
    * d_delete - delete a dentry
    * @dentry: The dentry to delete
    *
    * Turn the dentry into a negative dentry if possible, otherwise
    * remove it from the hash queues so it can be deleted later
    */
    
   void d_delete(struct dentry * dentry)
   {
           /*
            * Are we the only user?
            */
           spin_lock(&dcache_lock);
           if (atomic_read(&dentry->d_count) == 1) {
                   dentry_iput(dentry);
                   return;
           }
           spin_unlock(&dcache_lock);
   
           /*
            * If not, just drop the dentry and let dput
            * pick up the tab..
            */
           d_drop(dentry);
   }
   
   /**
    * d_rehash     - add an entry back to the hash
    * @entry: dentry to add to the hash
    *
    * Adds a dentry to the hash according to its name.
    */
    
   void d_rehash(struct dentry * entry)
   {
           struct list_head *list = d_hash(entry->d_parent, entry->d_name.hash);
           if (!list_empty(&entry->d_hash)) BUG();
           spin_lock(&dcache_lock);
           list_add(&entry->d_hash, list);
           spin_unlock(&dcache_lock);
   }
   
   #define do_switch(x,y) do { \
           __typeof__ (x) __tmp = x; \
           x = y; y = __tmp; } while (0)
   
   /*
    * When switching names, the actual string doesn't strictly have to
    * be preserved in the target - because we're dropping the target
    * anyway. As such, we can just do a simple memcpy() to copy over
    * the new name before we switch.
    *
    * Note that we have to be a lot more careful about getting the hash
    * switched - we have to switch the hash value properly even if it
    * then no longer matches the actual (corrupted) string of the target.
    * The hash value has to match the hash queue that the dentry is on..
    */
   static inline void switch_names(struct dentry * dentry, struct dentry * target)
   {
           const unsigned char *old_name, *new_name;
   
           check_lock();
           memcpy(dentry->d_iname, target->d_iname, DNAME_INLINE_LEN); 
           old_name = target->d_name.name;
           new_name = dentry->d_name.name;
           if (old_name == target->d_iname)
                   old_name = dentry->d_iname;
           if (new_name == dentry->d_iname)
                   new_name = target->d_iname;
           target->d_name.name = new_name;
           dentry->d_name.name = old_name;
   }
   
   /*
    * We cannibalize "target" when moving dentry on top of it,
    * because it's going to be thrown away anyway. We could be more
    * polite about it, though.
    *
    * This forceful removal will result in ugly /proc output if
    * somebody holds a file open that got deleted due to a rename.
    * We could be nicer about the deleted file, and let it show
    * up under the name it got deleted rather than the name that
    * deleted it.
    *
    * Careful with the hash switch. The hash switch depends on
    * the fact that any list-entry can be a head of the list.
    * Think about it.
    */
    
   /**
    * d_move - move a dentry
    * @dentry: entry to move
    * @target: new dentry
    *
    * Update the dcache to reflect the move of a file name. Negative
    * dcache entries should not be moved in this way.
    */
     
   void d_move(struct dentry * dentry, struct dentry * target)
   {
           check_lock();
   
           if (!dentry->d_inode)
                   printk(KERN_WARNING "VFS: moving negative dcache entry\n");
   
           spin_lock(&dcache_lock);
           /* Move the dentry to the target hash queue */
           list_del(&dentry->d_hash);
           list_add(&dentry->d_hash, &target->d_hash);
   
           /* Unhash the target: dput() will then get rid of it */
           list_del_init(&target->d_hash);
   
           list_del(&dentry->d_child);
           list_del(&target->d_child);
   
           /* Switch the parents and the names.. */
           switch_names(dentry, target);
           do_switch(dentry->d_parent, target->d_parent);
           do_switch(dentry->d_name.len, target->d_name.len);
           do_switch(dentry->d_name.hash, target->d_name.hash);
   
           /* And add them back to the (new) parent lists */
           list_add(&target->d_child, &target->d_parent->d_subdirs);
           list_add(&dentry->d_child, &dentry->d_parent->d_subdirs);
           spin_unlock(&dcache_lock);
   }
   
   /**
    * d_path - return the path of a dentry
    * @dentry: dentry to report
    * @vfsmnt: vfsmnt to which the dentry belongs
    * @root: root dentry
    * @rootmnt: vfsmnt to which the root dentry belongs
    * @buffer: buffer to return value in
    * @buflen: buffer length
    *
    * Convert a dentry into an ASCII path name. If the entry has been deleted
    * the string " (deleted)" is appended. Note that this is ambiguous. Returns
    * the buffer.
    *
    * "buflen" should be %PAGE_SIZE or more. Caller holds the dcache_lock.
    */
   char * __d_path(struct dentry *dentry, struct vfsmount *vfsmnt,
                   struct dentry *root, struct vfsmount *rootmnt,
                   char *buffer, int buflen)
   {
           char * end = buffer+buflen;
           char * retval;
           int namelen;
   
           *--end = '\0';
           buflen--;
           if (!IS_ROOT(dentry) && list_empty(&dentry->d_hash)) {
                   buflen -= 10;
                   end -= 10;
                   memcpy(end, " (deleted)", 10);
           }
   
           /* Get '/' right */
           retval = end-1;
           *retval = '/';
   
           for (;;) {
                   struct dentry * parent;
   
                   if (dentry == root && vfsmnt == rootmnt)
                           break;
                   if (dentry == vfsmnt->mnt_root || IS_ROOT(dentry)) {
                           /* Global root? */
                           if (vfsmnt->mnt_parent == vfsmnt)
                                   goto global_root;
                           dentry = vfsmnt->mnt_mountpoint;
                           vfsmnt = vfsmnt->mnt_parent;
                           continue;
                   }
                   parent = dentry->d_parent;
                   namelen = dentry->d_name.len;
                   buflen -= namelen + 1;
                   if (buflen < 0)
                           return ERR_PTR(-ENAMETOOLONG);
                   end -= namelen;
                   memcpy(end, dentry->d_name.name, namelen);
                   *--end = '/';
                   retval = end;
                   dentry = parent;
           }
   
           return retval;
   
   global_root:
           namelen = dentry->d_name.len;
           buflen -= namelen;
           if (buflen >= 0) {
                   retval -= namelen-1;    /* hit the slash */
                   memcpy(retval, dentry->d_name.name, namelen);
           } else
                   retval = ERR_PTR(-ENAMETOOLONG);
           return retval;
   }
  
  /*
   * NOTE! The user-level library version returns a
   * character pointer. The kernel system call just
   * returns the length of the buffer filled (which
   * includes the ending '\0' character), or a negative
   * error value. So libc would do something like
   *
   *      char *getcwd(char * buf, size_t size)
   *      {
   *              int retval;
   *
   *              retval = sys_getcwd(buf, size);
   *              if (retval >= 0)
   *                      return buf;
   *              errno = -retval;
   *              return NULL;
   *      }
   */
  asmlinkage long sys_getcwd(char *buf, unsigned long size)
  {
          int error;
          struct vfsmount *pwdmnt, *rootmnt;
          struct dentry *pwd, *root;
          char *page = (char *) __get_free_page(GFP_USER);
  
          if (!page)
                  return -ENOMEM;
  
          read_lock(&current->fs->lock);
          pwdmnt = mntget(current->fs->pwdmnt);
          pwd = dget(current->fs->pwd);
          rootmnt = mntget(current->fs->rootmnt);
          root = dget(current->fs->root);
          read_unlock(&current->fs->lock);
  
          error = -ENOENT;
          /* Has the current directory has been unlinked? */
          spin_lock(&dcache_lock);
          if (pwd->d_parent == pwd || !list_empty(&pwd->d_hash)) {
                  unsigned long len;
                  char * cwd;
  
                  cwd = __d_path(pwd, pwdmnt, root, rootmnt, page, PAGE_SIZE);
                  spin_unlock(&dcache_lock);
  
                  error = PTR_ERR(cwd);
                  if (IS_ERR(cwd))
                          goto out;
  
                  error = -ERANGE;
                  len = PAGE_SIZE + page - cwd;
                  if (len <= size) {
                          error = len;
                          if (copy_to_user(buf, cwd, len))
                                  error = -EFAULT;
                  }
          } else
                  spin_unlock(&dcache_lock);
  
  out:
          dput(pwd);
          mntput(pwdmnt);
          dput(root);
          mntput(rootmnt);
          free_page((unsigned long) page);
          return error;
  }
  
  /*
   * Test whether new_dentry is a subdirectory of old_dentry.
   *
   * Trivially implemented using the dcache structure
   */
  
  /**
   * is_subdir - is new dentry a subdirectory of old_dentry
   * @new_dentry: new dentry
   * @old_dentry: old dentry
   *
   * Returns 1 if new_dentry is a subdirectory of the parent (at any depth).
   * Returns 0 otherwise.
   */
    
  int is_subdir(struct dentry * new_dentry, struct dentry * old_dentry)
  {
          int result;
  
          result = 0;
          for (;;) {
                  if (new_dentry != old_dentry) {
                          struct dentry * parent = new_dentry->d_parent;
                          if (parent == new_dentry)
                                  break;
                          new_dentry = parent;
                          continue;
                  }
                  result = 1;
                  break;
          }
          return result;
  }
  
  void d_genocide(struct dentry *root)
  {
          struct dentry *this_parent = root;
          struct list_head *next;
  
          spin_lock(&dcache_lock);
  repeat:
          next = this_parent->d_subdirs.next;
  resume:
          while (next != &this_parent->d_subdirs) {
                  struct list_head *tmp = next;
                  struct dentry *dentry = list_entry(tmp, struct dentry, d_child);
                  next = tmp->next;
                  if (d_unhashed(dentry)||!dentry->d_inode)
                          continue;
                  if (!list_empty(&dentry->d_subdirs)) {
                          this_parent = dentry;
                          goto repeat;
                  }
                  atomic_dec(&dentry->d_count);
          }
          if (this_parent != root) {
                  next = this_parent->d_child.next; 
                  atomic_dec(&this_parent->d_count);
                  this_parent = this_parent->d_parent;
                  goto resume;
          }
          spin_unlock(&dcache_lock);
  }
  
  /**
   * find_inode_number - check for dentry with name
   * @dir: directory to check
   * @name: Name to find.
   *
   * Check whether a dentry already exists for the given name,
   * and return the inode number if it has an inode. Otherwise
   * 0 is returned.
   *
   * This routine is used to post-process directory listings for
   * filesystems using synthetic inode numbers, and is necessary
   * to keep getcwd() working.
   */
   
  ino_t find_inode_number(struct dentry *dir, struct qstr *name)
  {
          struct dentry * dentry;
          ino_t ino = 0;
  
          /*
           * Check for a fs-specific hash function. Note that we must
           * calculate the standard hash first, as the d_op->d_hash()
           * routine may choose to leave the hash value unchanged.
           */
          name->hash = full_name_hash(name->name, name->len);
          if (dir->d_op && dir->d_op->d_hash)
          {
                  if (dir->d_op->d_hash(dir, name) != 0)
                          goto out;
          }
  
          dentry = d_lookup(dir, name);
          if (dentry)
          {
                  if (dentry->d_inode)
                          ino = dentry->d_inode->i_ino;
                  dput(dentry);
          }
  out:
          return ino;
  }
  
  static void __init dcache_init(unsigned long mempages)
  {
          struct list_head *d;
          unsigned long order;
          unsigned int nr_hash;
          int i;
  
          /* 
           * A constructor could be added for stable state like the lists,
           * but it is probably not worth it because of the cache nature
           * of the dcache. 
           * If fragmentation is too bad then the SLAB_HWCACHE_ALIGN
           * flag could be removed here, to hint to the allocator that
           * it should not try to get multiple page regions.  
           */
          dentry_cache = kmem_cache_create("dentry_cache",
                                           sizeof(struct dentry),
                                           0,
                                           SLAB_HWCACHE_ALIGN,
                                           NULL, NULL);
          if (!dentry_cache)
                  panic("Cannot create dentry cache");
  
  #if PAGE_SHIFT < 13
          mempages >>= (13 - PAGE_SHIFT);
  #endif
          mempages *= sizeof(struct list_head);
          for (order = 0; ((1UL << order) << PAGE_SHIFT) < mempages; order++)
                  ;
  
          do {
                  unsigned long tmp;
  
                  nr_hash = (1UL << order) * PAGE_SIZE /
                          sizeof(struct list_head);
                  d_hash_mask = (nr_hash - 1);
  
                  tmp = nr_hash;
                  d_hash_shift = 0;
                  while ((tmp >>= 1UL) != 0UL)
                          d_hash_shift++;
  
                  dentry_hashtable = (struct list_head *)
                          __get_free_pages(GFP_ATOMIC, order);
          } while (dentry_hashtable == NULL && --order >= 0);
  
          printk(KERN_INFO "Dentry cache hash table entries: %d (order: %ld, %ld bytes)\n",
                          nr_hash, order, (PAGE_SIZE << order));
  
          if (!dentry_hashtable)
                  panic("Failed to allocate dcache hash table\n");
  
          d = dentry_hashtable;
          i = nr_hash;
          do {
                  INIT_LIST_HEAD(d);
                  d++;
                  i--;
          } while (i);
  }
  
  static void init_buffer_head(void * foo, kmem_cache_t * cachep, unsigned long flags)
  {
          if ((flags & (SLAB_CTOR_VERIFY|SLAB_CTOR_CONSTRUCTOR)) ==
              SLAB_CTOR_CONSTRUCTOR)
          {
                  struct buffer_head * bh = (struct buffer_head *) foo;
  
                  memset(bh, 0, sizeof(*bh));
                  init_waitqueue_head(&bh->b_wait);
          }
  }
  
  /* SLAB cache for __getname() consumers */
  kmem_cache_t *names_cachep;
  
  /* SLAB cache for file structures */
  kmem_cache_t *filp_cachep;
  
  /* SLAB cache for dquot structures */
  kmem_cache_t *dquot_cachep;
  
  /* SLAB cache for buffer_head structures */
  kmem_cache_t *bh_cachep;
  EXPORT_SYMBOL(bh_cachep);
  
  extern void bdev_cache_init(void);
  extern void cdev_cache_init(void);
  extern void iobuf_cache_init(void);
  
  void __init vfs_caches_init(unsigned long mempages)
  {
          bh_cachep = kmem_cache_create("buffer_head",
                          sizeof(struct buffer_head), 0,
                          SLAB_HWCACHE_ALIGN, init_buffer_head, NULL);
          if(!bh_cachep)
                  panic("Cannot create buffer head SLAB cache");
  
          names_cachep = kmem_cache_create("names_cache", 
                          PATH_MAX, 0, 
                          SLAB_HWCACHE_ALIGN, NULL, NULL);
          if (!names_cachep)
                  panic("Cannot create names SLAB cache");
  
          filp_cachep = kmem_cache_create("filp", 
                          sizeof(struct file), 0,
                          SLAB_HWCACHE_ALIGN, NULL, NULL);
          if(!filp_cachep)
                  panic("Cannot create filp SLAB cache");
  
  #if defined (CONFIG_QUOTA)
          dquot_cachep = kmem_cache_create("dquot", 
                          sizeof(struct dquot), sizeof(unsigned long) * 4,
                          SLAB_HWCACHE_ALIGN, NULL, NULL);
          if (!dquot_cachep)
                  panic("Cannot create dquot SLAB cache");
  #endif
  
          dcache_init(mempages);
          inode_init(mempages);
          files_init(mempages); 
          mnt_init(mempages);
          bdev_cache_init();
          cdev_cache_init();
          iobuf_cache_init();
  }

Cache object: ce1a35ce12fc1fbb94ac5b1e6d30d929