dcache.c

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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);
	kmem_cache_shrink(dentry_cache);
	return 0;
}

#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;