dir.c

linux 内核源代码

 * This fakes mkdir(2) on a default_groups[] entry.  It
 * creates a dentry, attachs it, and then does fixup
 * on the sd->s_type.
 *
 * We could, perhaps, tweak our parent's ->mkdir for a minute and
 * try using vfs_mkdir.  Just a thought.
 */
static int create_default_group(struct config_group *parent_group,
				struct config_group *group)
{
	int ret;
	struct qstr name;
	struct configfs_dirent *sd;
	/* We trust the caller holds a reference to parent */
	struct dentry *child, *parent = parent_group->cg_item.ci_dentry;

	if (!group->cg_item.ci_name)
		group->cg_item.ci_name = group->cg_item.ci_namebuf;
	name.name = group->cg_item.ci_name;
	name.len = strlen(name.name);
	name.hash = full_name_hash(name.name, name.len);

	ret = -ENOMEM;
	child = d_alloc(parent, &name);
	if (child) {
		d_add(child, NULL);

		ret = configfs_attach_group(&parent_group->cg_item,
					    &group->cg_item, child);
		if (!ret) {
			sd = child->d_fsdata;
			sd->s_type |= CONFIGFS_USET_DEFAULT;
		} else {
			d_delete(child);
			dput(child);
		}
	}

	return ret;
}

static int populate_groups(struct config_group *group)
{
	struct config_group *new_group;
	struct dentry *dentry = group->cg_item.ci_dentry;
	int ret = 0;
	int i;

	if (group->default_groups) {
		/*
		 * FYI, we're faking mkdir here
		 * I'm not sure we need this semaphore, as we're called
		 * from our parent's mkdir.  That holds our parent's
		 * i_mutex, so afaik lookup cannot continue through our
		 * parent to find us, let alone mess with our tree.
		 * That said, taking our i_mutex is closer to mkdir
		 * emulation, and shouldn't hurt.
		 */
		mutex_lock(&dentry->d_inode->i_mutex);

		for (i = 0; group->default_groups[i]; i++) {
			new_group = group->default_groups[i];

			ret = create_default_group(group, new_group);
			if (ret)
				break;
		}

		mutex_unlock(&dentry->d_inode->i_mutex);
	}

	if (ret)
		detach_groups(group);

	return ret;
}

/*
 * All of link_obj/unlink_obj/link_group/unlink_group require that
 * subsys->su_mutex is held.
 */

static void unlink_obj(struct config_item *item)
{
	struct config_group *group;

	group = item->ci_group;
	if (group) {
		list_del_init(&item->ci_entry);

		item->ci_group = NULL;
		item->ci_parent = NULL;

		/* Drop the reference for ci_entry */
		config_item_put(item);

		/* Drop the reference for ci_parent */
		config_group_put(group);
	}
}

static void link_obj(struct config_item *parent_item, struct config_item *item)
{
	/*
	 * Parent seems redundant with group, but it makes certain
	 * traversals much nicer.
	 */
	item->ci_parent = parent_item;

	/*
	 * We hold a reference on the parent for the child's ci_parent
	 * link.
	 */
	item->ci_group = config_group_get(to_config_group(parent_item));
	list_add_tail(&item->ci_entry, &item->ci_group->cg_children);

	/*
	 * We hold a reference on the child for ci_entry on the parent's
	 * cg_children
	 */
	config_item_get(item);
}

static void unlink_group(struct config_group *group)
{
	int i;
	struct config_group *new_group;

	if (group->default_groups) {
		for (i = 0; group->default_groups[i]; i++) {
			new_group = group->default_groups[i];
			unlink_group(new_group);
		}
	}

	group->cg_subsys = NULL;
	unlink_obj(&group->cg_item);
}

static void link_group(struct config_group *parent_group, struct config_group *group)
{
	int i;
	struct config_group *new_group;
	struct configfs_subsystem *subsys = NULL; /* gcc is a turd */

	link_obj(&parent_group->cg_item, &group->cg_item);

	if (parent_group->cg_subsys)
		subsys = parent_group->cg_subsys;
	else if (configfs_is_root(&parent_group->cg_item))
		subsys = to_configfs_subsystem(group);
	else
		BUG();
	group->cg_subsys = subsys;

	if (group->default_groups) {
		for (i = 0; group->default_groups[i]; i++) {
			new_group = group->default_groups[i];
			link_group(group, new_group);
		}
	}
}

/*
 * The goal is that configfs_attach_item() (and
 * configfs_attach_group()) can be called from either the VFS or this
 * module.  That is, they assume that the items have been created,
 * the dentry allocated, and the dcache is all ready to go.
 *
 * If they fail, they must clean up after themselves as if they
 * had never been called.  The caller (VFS or local function) will
 * handle cleaning up the dcache bits.
 *
 * configfs_detach_group() and configfs_detach_item() behave similarly on
 * the way out.  They assume that the proper semaphores are held, they
 * clean up the configfs items, and they expect their callers will
 * handle the dcache bits.
 */
static int configfs_attach_item(struct config_item *parent_item,
				struct config_item *item,
				struct dentry *dentry)
{
	int ret;

	ret = configfs_create_dir(item, dentry);
	if (!ret) {
		ret = populate_attrs(item);
		if (ret) {
			configfs_remove_dir(item);
			d_delete(dentry);
		}
	}

	return ret;
}

static void configfs_detach_item(struct config_item *item)
{
	detach_attrs(item);
	configfs_remove_dir(item);
}

static int configfs_attach_group(struct config_item *parent_item,
				 struct config_item *item,
				 struct dentry *dentry)
{
	int ret;
	struct configfs_dirent *sd;

	ret = configfs_attach_item(parent_item, item, dentry);
	if (!ret) {
		sd = dentry->d_fsdata;
		sd->s_type |= CONFIGFS_USET_DIR;

		ret = populate_groups(to_config_group(item));
		if (ret) {
			configfs_detach_item(item);
			d_delete(dentry);
		}
	}

	return ret;
}

static void configfs_detach_group(struct config_item *item)
{
	detach_groups(to_config_group(item));
	configfs_detach_item(item);
}

/*
 * After the item has been detached from the filesystem view, we are
 * ready to tear it out of the hierarchy.  Notify the client before
 * we do that so they can perform any cleanup that requires
 * navigating the hierarchy.  A client does not need to provide this
 * callback.  The subsystem semaphore MUST be held by the caller, and
 * references must be valid for both items.  It also assumes the
 * caller has validated ci_type.
 */
static void client_disconnect_notify(struct config_item *parent_item,
				     struct config_item *item)
{
	struct config_item_type *type;

	type = parent_item->ci_type;
	BUG_ON(!type);

	if (type->ct_group_ops && type->ct_group_ops->disconnect_notify)
		type->ct_group_ops->disconnect_notify(to_config_group(parent_item),
						      item);
}

/*
 * Drop the initial reference from make_item()/make_group()
 * This function assumes that reference is held on item
 * and that item holds a valid reference to the parent.  Also, it
 * assumes the caller has validated ci_type.
 */
static void client_drop_item(struct config_item *parent_item,
			     struct config_item *item)
{
	struct config_item_type *type;

	type = parent_item->ci_type;
	BUG_ON(!type);

	/*
	 * If ->drop_item() exists, it is responsible for the
	 * config_item_put().
	 */
	if (type->ct_group_ops && type->ct_group_ops->drop_item)
		type->ct_group_ops->drop_item(to_config_group(parent_item),
					      item);
	else
		config_item_put(item);
}

#ifdef DEBUG
static void configfs_dump_one(struct configfs_dirent *sd, int level)
{
	printk(KERN_INFO "%*s\"%s\":\n", level, " ", configfs_get_name(sd));

#define type_print(_type) if (sd->s_type & _type) printk(KERN_INFO "%*s %s\n", level, " ", #_type);
	type_print(CONFIGFS_ROOT);
	type_print(CONFIGFS_DIR);
	type_print(CONFIGFS_ITEM_ATTR);
	type_print(CONFIGFS_ITEM_LINK);
	type_print(CONFIGFS_USET_DIR);
	type_print(CONFIGFS_USET_DEFAULT);
	type_print(CONFIGFS_USET_DROPPING);
#undef type_print
}

static int configfs_dump(struct configfs_dirent *sd, int level)
{
	struct configfs_dirent *child_sd;
	int ret = 0;

	configfs_dump_one(sd, level);

	if (!(sd->s_type & (CONFIGFS_DIR|CONFIGFS_ROOT)))
		return 0;

	list_for_each_entry(child_sd, &sd->s_children, s_sibling) {
		ret = configfs_dump(child_sd, level + 2);
		if (ret)
			break;
	}

	return ret;
}
#endif


/*
 * configfs_depend_item() and configfs_undepend_item()
 *
 * WARNING: Do not call these from a configfs callback!
 *
 * This describes these functions and their helpers.
 *
 * Allow another kernel system to depend on a config_item.  If this
 * happens, the item cannot go away until the dependant can live without
 * it.  The idea is to give client modules as simple an interface as
 * possible.  When a system asks them to depend on an item, they just
 * call configfs_depend_item().  If the item is live and the client
 * driver is in good shape, we'll happily do the work for them.
 *
 * Why is the locking complex?  Because configfs uses the VFS to handle
 * all locking, but this function is called outside the normal
 * VFS->configfs path.  So it must take VFS locks to prevent the
 * VFS->configfs stuff (configfs_mkdir(), configfs_rmdir(), etc).  This is
 * why you can't call these functions underneath configfs callbacks.
 *
 * Note, btw, that this can be called at *any* time, even when a configfs
 * subsystem isn't registered, or when configfs is loading or unloading.
 * Just like configfs_register_subsystem().  So we take the same
 * precautions.  We pin the filesystem.  We lock each i_mutex _in_order_
 * on our way down the tree.  If we can find the target item in the
 * configfs tree, it must be part of the subsystem tree as well, so we
 * do not need the subsystem semaphore.  Holding the i_mutex chain locks
 * out mkdir() and rmdir(), who might be racing us.
 */

/*
 * configfs_depend_prep()
 *
 * Only subdirectories count here.  Files (CONFIGFS_NOT_PINNED) are
 * attributes.  This is similar but not the same to configfs_detach_prep().
 * Note that configfs_detach_prep() expects the parent to be locked when it
 * is called, but we lock the parent *inside* configfs_depend_prep().  We
 * do that so we can unlock it if we find nothing.
 *
 * Here we do a depth-first search of the dentry hierarchy looking for
 * our object.  We take i_mutex on each step of the way down.  IT IS
 * ESSENTIAL THAT i_mutex LOCKING IS ORDERED.  If we come back up a branch,
 * we'll drop the i_mutex.
 *
 * If the target is not found, -ENOENT is bubbled up and we have released
 * all locks.  If the target was found, the locks will be cleared by
 * configfs_depend_rollback().
 *
 * This adds a requirement that all config_items be unique!
 *
 * This is recursive because the locking traversal is tricky.  There isn't
 * much on the stack, though, so folks that need this function - be careful
 * about your stack!  Patches will be accepted to make it iterative.
 */
static int configfs_depend_prep(struct dentry *origin,
				struct config_item *target)
{
	struct configfs_dirent *child_sd, *sd = origin->d_fsdata;
	int ret = 0;

	BUG_ON(!origin || !sd);

	/* Lock this guy on the way down */
	mutex_lock(&sd->s_dentry->d_inode->i_mutex);
	if (sd->s_element == target)  /* Boo-yah */
		goto out;

	list_for_each_entry(child_sd, &sd->s_children, s_sibling) {
		if (child_sd->s_type & CONFIGFS_DIR) {
			ret = configfs_depend_prep(child_sd->s_dentry,
						   target);
			if (!ret)
				goto out;  /* Child path boo-yah */
		}
	}

	/* We looped all our children and didn't find target */
	mutex_unlock(&sd->s_dentry->d_inode->i_mutex);
	ret = -ENOENT;

out:
	return ret;
}

/*
 * This is ONLY called if configfs_depend_prep() did its job.  So we can
 * trust the entire path from item back up to origin.
 *
 * We walk backwards from item, unlocking each i_mutex.  We finish by
 * unlocking origin.
 */
static void configfs_depend_rollback(struct dentry *origin,
				     struct config_item *item)
{
	struct dentry *dentry = item->ci_dentry;

	while (dentry != origin) {
		mutex_unlock(&dentry->d_inode->i_mutex);
		dentry = dentry->d_parent;
	}

	mutex_unlock(&origin->d_inode->i_mutex);
}

int configfs_depend_item(struct configfs_subsystem *subsys,
			 struct config_item *target)
{
	int ret;
	struct configfs_dirent *p, *root_sd, *subsys_sd = NULL;
	struct config_item *s_item = &subsys->su_group.cg_item;

	/*
	 * Pin the configfs filesystem.  This means we can safely access
	 * the root of the configfs filesystem.
	 */
	ret = configfs_pin_fs();
	if (ret)
		return ret;

	/*
	 * Next, lock the root directory.  We're going to check that the
	 * subsystem is really registered, and so we need to lock out
	 * configfs_[un]register_subsystem().
	 */
	mutex_lock(&configfs_sb->s_root->d_inode->i_mutex);

	root_sd = configfs_sb->s_root->d_fsdata;

	list_for_each_entry(p, &root_sd->s_children, s_sibling) {
		if (p->s_type & CONFIGFS_DIR) {
			if (p->s_element == s_item) {
				subsys_sd = p;
				break;
			}
		}
	}

	if (!subsys_sd) {
		ret = -ENOENT;
		goto out_unlock_fs;
	}

	/* Ok, now we can trust subsys/s_item */

	/* Scan the tree, locking i_mutex recursively, return 0 if found */
	ret = configfs_depend_prep(subsys_sd->s_dentry, target);
	if (ret)
		goto out_unlock_fs;

	/* We hold all i_mutexes from the subsystem down to the target */
	p = target->ci_dentry->d_fsdata;
	p->s_dependent_count += 1;

	configfs_depend_rollback(subsys_sd->s_dentry, target);

out_unlock_fs:
	mutex_unlock(&configfs_sb->s_root->d_inode->i_mutex);

	/*
	 * If we succeeded, the fs is pinned via other methods.  If not,
	 * we're done with it anyway.  So release_fs() is always right.
	 */
	configfs_release_fs();

	return ret;
}
EXPORT_SYMBOL(configfs_depend_item);

/*
 * Release the dependent linkage.  This is much simpler than
 * configfs_depend_item() because we know that that the client driver is
 * pinned, thus the subsystem is pinned, and therefore configfs is pinned.
 */
void configfs_undepend_item(struct configfs_subsystem *subsys,
			    struct config_item *target)
{