[PATCH] configfs: User-driven configuration filesystem

Configfs, a file system for userspace-driven kernel object configuration.
The OCFS2 stack makes extensive use of this for propagation of cluster
configuration information into kernel.

Signed-off-by: Joel Becker <joel.becker@oracle.com>

1 files changed, 1102 insertions, 0 deletions

diff --git a/fs/configfs/dir.c b/fs/configfs/dir.c
new file mode 100644
index 000000000000..e48b539243a1
--- /dev/null
+++ b/fs/configfs/dir.c
@@ -0,0 +1,1102 @@
+/* -*- mode: c; c-basic-offset: 8; -*-
+ * vim: noexpandtab sw=8 ts=8 sts=0:
+ *
+ * dir.c - Operations for configfs directories.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public
+ * License along with this program; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 021110-1307, USA.
+ *
+ * Based on sysfs:
+ *      sysfs is Copyright (C) 2001, 2002, 2003 Patrick Mochel
+ *
+ * configfs Copyright (C) 2005 Oracle.  All rights reserved.
+ */
+
+#undef DEBUG
+
+#include <linux/fs.h>
+#include <linux/mount.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+
+#include <linux/configfs.h>
+#include "configfs_internal.h"
+
+DECLARE_RWSEM(configfs_rename_sem);
+
+static void configfs_d_iput(struct dentry * dentry,
+                            struct inode * inode)
+{
+        struct configfs_dirent * sd = dentry->d_fsdata;
+
+        if (sd) {
+                BUG_ON(sd->s_dentry != dentry);
+                sd->s_dentry = NULL;
+                configfs_put(sd);
+        }
+        iput(inode);
+}
+
+/*
+ * We _must_ delete our dentries on last dput, as the chain-to-parent
+ * behavior is required to clear the parents of default_groups.
+ */
+static int configfs_d_delete(struct dentry *dentry)
+{
+        return 1;
+}
+
+static struct dentry_operations configfs_dentry_ops = {
+        .d_iput         = configfs_d_iput,
+        /* simple_delete_dentry() isn't exported */
+        .d_delete       = configfs_d_delete,
+};
+
+/*
+ * Allocates a new configfs_dirent and links it to the parent configfs_dirent
+ */
+static struct configfs_dirent *configfs_new_dirent(struct configfs_dirent * parent_sd,
+                                                void * element)
+{
+        struct configfs_dirent * sd;
+
+        sd = kmalloc(sizeof(*sd), GFP_KERNEL);
+        if (!sd)
+                return NULL;
+
+        memset(sd, 0, sizeof(*sd));
+        atomic_set(&sd->s_count, 1);
+        INIT_LIST_HEAD(&sd->s_links);
+        INIT_LIST_HEAD(&sd->s_children);
+        list_add(&sd->s_sibling, &parent_sd->s_children);
+        sd->s_element = element;
+
+        return sd;
+}
+
+int configfs_make_dirent(struct configfs_dirent * parent_sd,
+                         struct dentry * dentry, void * element,
+                         umode_t mode, int type)
+{
+        struct configfs_dirent * sd;
+
+        sd = configfs_new_dirent(parent_sd, element);
+        if (!sd)
+                return -ENOMEM;
+
+        sd->s_mode = mode;
+        sd->s_type = type;
+        sd->s_dentry = dentry;
+        if (dentry) {
+                dentry->d_fsdata = configfs_get(sd);
+                dentry->d_op = &configfs_dentry_ops;
+        }
+
+        return 0;
+}
+
+static int init_dir(struct inode * inode)
+{
+        inode->i_op = &configfs_dir_inode_operations;
+        inode->i_fop = &configfs_dir_operations;
+
+        /* directory inodes start off with i_nlink == 2 (for "." entry) */
+        inode->i_nlink++;
+        return 0;
+}
+
+static int init_file(struct inode * inode)
+{
+        inode->i_size = PAGE_SIZE;
+        inode->i_fop = &configfs_file_operations;
+        return 0;
+}
+
+static int init_symlink(struct inode * inode)
+{
+        inode->i_op = &configfs_symlink_inode_operations;
+        return 0;
+}
+
+static int create_dir(struct config_item * k, struct dentry * p,
+                      struct dentry * d)
+{
+        int error;
+        umode_t mode = S_IFDIR| S_IRWXU | S_IRUGO | S_IXUGO;
+
+        error = configfs_create(d, mode, init_dir);
+        if (!error) {
+                error = configfs_make_dirent(p->d_fsdata, d, k, mode,
+                                           CONFIGFS_DIR);
+                if (!error) {
+                        p->d_inode->i_nlink++;
+                        (d)->d_op = &configfs_dentry_ops;
+                }
+        }
+        return error;
+}
+
+
+/**
+ *      configfs_create_dir - create a directory for an config_item.
+ *      @item:          config_itemwe're creating directory for.
+ *      @dentry:        config_item's dentry.
+ */
+
+static int configfs_create_dir(struct config_item * item, struct dentry *dentry)
+{
+        struct dentry * parent;
+        int error = 0;
+
+        BUG_ON(!item);
+
+        if (item->ci_parent)
+                parent = item->ci_parent->ci_dentry;
+        else if (configfs_mount && configfs_mount->mnt_sb)
+                parent = configfs_mount->mnt_sb->s_root;
+        else
+                return -EFAULT;
+
+        error = create_dir(item,parent,dentry);
+        if (!error)
+                item->ci_dentry = dentry;
+        return error;
+}
+
+int configfs_create_link(struct configfs_symlink *sl,
+                         struct dentry *parent,
+                         struct dentry *dentry)
+{
+        int err = 0;
+        umode_t mode = S_IFLNK | S_IRWXUGO;
+
+        err = configfs_create(dentry, mode, init_symlink);
+        if (!err) {
+                err = configfs_make_dirent(parent->d_fsdata, dentry, sl,
+                                         mode, CONFIGFS_ITEM_LINK);
+                if (!err)
+                        dentry->d_op = &configfs_dentry_ops;
+        }
+        return err;
+}
+
+static void remove_dir(struct dentry * d)
+{
+        struct dentry * parent = dget(d->d_parent);
+        struct configfs_dirent * sd;
+
+        sd = d->d_fsdata;
+        list_del_init(&sd->s_sibling);
+        configfs_put(sd);
+        if (d->d_inode)
+                simple_rmdir(parent->d_inode,d);
+
+        pr_debug(" o %s removing done (%d)\n",d->d_name.name,
+                 atomic_read(&d->d_count));
+
+        dput(parent);
+}
+
+/**
+ * configfs_remove_dir - remove an config_item's directory.
+ * @item:       config_item we're removing.
+ *
+ * The only thing special about this is that we remove any files in
+ * the directory before we remove the directory, and we've inlined
+ * what used to be configfs_rmdir() below, instead of calling separately.
+ */
+
+static void configfs_remove_dir(struct config_item * item)
+{
+        struct dentry * dentry = dget(item->ci_dentry);
+
+        if (!dentry)
+                return;
+
+        remove_dir(dentry);
+        /**
+         * Drop reference from dget() on entrance.
+         */
+        dput(dentry);
+}
+
+
+/* attaches attribute's configfs_dirent to the dentry corresponding to the
+ * attribute file
+ */
+static int configfs_attach_attr(struct configfs_dirent * sd, struct dentry * dentry)
+{
+        struct configfs_attribute * attr = sd->s_element;
+        int error;
+
+        error = configfs_create(dentry, (attr->ca_mode & S_IALLUGO) | S_IFREG, init_file);
+        if (error)
+                return error;
+
+        dentry->d_op = &configfs_dentry_ops;
+        dentry->d_fsdata = configfs_get(sd);
+        sd->s_dentry = dentry;
+        d_rehash(dentry);
+
+        return 0;
+}
+
+static struct dentry * configfs_lookup(struct inode *dir,
+                                       struct dentry *dentry,
+                                       struct nameidata *nd)
+{
+        struct configfs_dirent * parent_sd = dentry->d_parent->d_fsdata;
+        struct configfs_dirent * sd;
+        int found = 0;
+        int err = 0;
+
+        list_for_each_entry(sd, &parent_sd->s_children, s_sibling) {
+                if (sd->s_type & CONFIGFS_NOT_PINNED) {
+                        const unsigned char * name = configfs_get_name(sd);
+
+                        if (strcmp(name, dentry->d_name.name))
+                                continue;
+
+                        found = 1;
+                        err = configfs_attach_attr(sd, dentry);
+                        break;
+                }
+        }
+
+        if (!found) {
+                /*
+                 * If it doesn't exist and it isn't a NOT_PINNED item,
+                 * it must be negative.
+                 */
+                return simple_lookup(dir, dentry, nd);
+        }
+
+        return ERR_PTR(err);
+}
+
+/*
+ * Only subdirectories count here.  Files (CONFIGFS_NOT_PINNED) are
+ * attributes and are removed by rmdir().  We recurse, taking i_sem
+ * on all children that are candidates for default detach.  If the
+ * result is clean, then configfs_detach_group() will handle dropping
+ * i_sem.  If there is an error, the caller will clean up the i_sem
+ * holders via configfs_detach_rollback().
+ */
+static int configfs_detach_prep(struct dentry *dentry)
+{
+        struct configfs_dirent *parent_sd = dentry->d_fsdata;
+        struct configfs_dirent *sd;
+        int ret;
+
+        ret = -EBUSY;
+        if (!list_empty(&parent_sd->s_links))
+                goto out;
+
+        ret = 0;
+        list_for_each_entry(sd, &parent_sd->s_children, s_sibling) {
+                if (sd->s_type & CONFIGFS_NOT_PINNED)
+                        continue;
+                if (sd->s_type & CONFIGFS_USET_DEFAULT) {
+                        down(&sd->s_dentry->d_inode->i_sem);
+                        /* Mark that we've taken i_sem */
+                        sd->s_type |= CONFIGFS_USET_DROPPING;
+
+                        ret = configfs_detach_prep(sd->s_dentry);
+                        if (!ret)
+                                continue;
+                } else
+                        ret = -ENOTEMPTY;
+
+                break;
+        }
+
+out:
+        return ret;
+}
+
+/*
+ * Walk the tree, dropping i_sem wherever CONFIGFS_USET_DROPPING is
+ * set.
+ */
+static void configfs_detach_rollback(struct dentry *dentry)
+{
+        struct configfs_dirent *parent_sd = dentry->d_fsdata;
+        struct configfs_dirent *sd;
+
+        list_for_each_entry(sd, &parent_sd->s_children, s_sibling) {
+                if (sd->s_type & CONFIGFS_USET_DEFAULT) {
+                        configfs_detach_rollback(sd->s_dentry);
+
+                        if (sd->s_type & CONFIGFS_USET_DROPPING) {
+                                sd->s_type &= ~CONFIGFS_USET_DROPPING;
+                                up(&sd->s_dentry->d_inode->i_sem);
+                        }
+                }
+        }
+}
+
+static void detach_attrs(struct config_item * item)
+{
+        struct dentry * dentry = dget(item->ci_dentry);
+        struct configfs_dirent * parent_sd;
+        struct configfs_dirent * sd, * tmp;
+
+        if (!dentry)
+                return;
+
+        pr_debug("configfs %s: dropping attrs for  dir\n",
+                 dentry->d_name.name);
+
+        parent_sd = dentry->d_fsdata;
+        list_for_each_entry_safe(sd, tmp, &parent_sd->s_children, s_sibling) {
+                if (!sd->s_element || !(sd->s_type & CONFIGFS_NOT_PINNED))
+                        continue;
+                list_del_init(&sd->s_sibling);
+                configfs_drop_dentry(sd, dentry);
+                configfs_put(sd);
+        }
+
+        /**
+         * Drop reference from dget() on entrance.
+         */
+        dput(dentry);
+}
+
+static int populate_attrs(struct config_item *item)
+{
+        struct config_item_type *t = item->ci_type;
+        struct configfs_attribute *attr;
+        int error = 0;
+        int i;
+
+        if (!t)
+                return -EINVAL;
+        if (t->ct_attrs) {
+                for (i = 0; (attr = t->ct_attrs[i]) != NULL; i++) {
+                        if ((error = configfs_create_file(item, attr)))
+                                break;
+                }
+        }
+
+        if (error)
+                detach_attrs(item);
+
+        return error;
+}
+
+static int configfs_attach_group(struct config_item *parent_item,
+                                 struct config_item *item,
+                                 struct dentry *dentry);
+static void configfs_detach_group(struct config_item *item);
+
+static void detach_groups(struct config_group *group)
+{
+        struct dentry * dentry = dget(group->cg_item.ci_dentry);
+        struct dentry *child;
+        struct configfs_dirent *parent_sd;
+        struct configfs_dirent *sd, *tmp;
+
+        if (!dentry)
+                return;
+
+        parent_sd = dentry->d_fsdata;
+        list_for_each_entry_safe(sd, tmp, &parent_sd->s_children, s_sibling) {
+                if (!sd->s_element ||
+                    !(sd->s_type & CONFIGFS_USET_DEFAULT))
+                        continue;
+
+                child = sd->s_dentry;
+
+                configfs_detach_group(sd->s_element);
+                child->d_inode->i_flags |= S_DEAD;
+
+                /*
+                 * From rmdir/unregister, a configfs_detach_prep() pass
+                 * has taken our i_sem for us.  Drop it.
+                 * From mkdir/register cleanup, there is no sem held.
+                 */
+                if (sd->s_type & CONFIGFS_USET_DROPPING)
+                        up(&child->d_inode->i_sem);
+
+                d_delete(child);
+                dput(child);
+        }
+
+        /**
+         * Drop reference from dget() on entrance.
+         */
+        dput(dentry);
+}
+
+/*
+ * 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 && 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_sem, so afaik lookup cannot continue through our
+                 * parent to find us, let alone mess with our tree.
+                 * That said, taking our i_sem is closer to mkdir
+                 * emulation, and shouldn't hurt. */
+                down(&dentry->d_inode->i_sem);
+
+                for (i = 0; group->default_groups[i]; i++) {
+                        new_group = group->default_groups[i];
+
+                        ret = create_default_group(group, new_group);
+                        if (ret)
+                                break;
+                }
+
+                up(&dentry->d_inode->i_sem);
+        }
+
+        if (ret)
+                detach_groups(group);
+
+        return ret;
+}
+
+/*
+ * All of link_obj/unlink_obj/link_group/unlink_group require that
+ * subsys->su_sem 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;
+                config_item_put(item);
+
+                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;
+        item->ci_group = config_group_get(to_config_group(parent_item));
+        list_add_tail(&item->ci_entry, &item->ci_group->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);
+}
+
+/*
+ * 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 (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);
+}
+
+
+static int configfs_mkdir(struct inode *dir, struct dentry *dentry, int mode)
+{
+        int ret;
+        struct config_group *group;
+        struct config_item *item;
+        struct config_item *parent_item;
+        struct configfs_subsystem *subsys;
+        struct configfs_dirent *sd;
+        struct config_item_type *type;
+        struct module *owner;
+        char *name;
+
+        if (dentry->d_parent == configfs_sb->s_root)
+                return -EPERM;
+
+        sd = dentry->d_parent->d_fsdata;
+        if (!(sd->s_type & CONFIGFS_USET_DIR))
+                return -EPERM;
+
+        parent_item = configfs_get_config_item(dentry->d_parent);
+        type = parent_item->ci_type;
+        subsys = to_config_group(parent_item)->cg_subsys;
+        BUG_ON(!subsys);
+
+        if (!type || !type->ct_group_ops ||
+            (!type->ct_group_ops->make_group &&
+             !type->ct_group_ops->make_item)) {
+                config_item_put(parent_item);
+                return -EPERM;  /* What lack-of-mkdir returns */
+        }
+
+        name = kmalloc(dentry->d_name.len + 1, GFP_KERNEL);
+        if (!name) {
+                config_item_put(parent_item);
+                return -ENOMEM;
+        }
+        snprintf(name, dentry->d_name.len + 1, "%s", dentry->d_name.name);
+
+        down(&subsys->su_sem);
+        group = NULL;
+        item = NULL;
+        if (type->ct_group_ops->make_group) {
+                group = type->ct_group_ops->make_group(to_config_group(parent_item), name);
+                if (group) {
+                        link_group(to_config_group(parent_item), group);
+                        item = &group->cg_item;
+                }
+        } else {
+                item = type->ct_group_ops->make_item(to_config_group(parent_item), name);
+                if (item)
+                        link_obj(parent_item, item);
+        }
+        up(&subsys->su_sem);
+
+        kfree(name);
+        if (!item) {
+                config_item_put(parent_item);
+                return -ENOMEM;
+        }
+
+        ret = -EINVAL;
+        type = item->ci_type;
+        if (type) {
+                owner = type->ct_owner;
+                if (try_module_get(owner)) {
+                        if (group) {
+                                ret = configfs_attach_group(parent_item,
+                                                            item,
+                                                            dentry);
+                        } else {
+                                ret = configfs_attach_item(parent_item,
+                                                           item,
+                                                           dentry);
+                        }
+
+                        if (ret) {
+                                down(&subsys->su_sem);
+                                if (group)
+                                        unlink_group(group);
+                                else
+                                        unlink_obj(item);
+                                client_drop_item(parent_item, item);
+                                up(&subsys->su_sem);
+
+                                config_item_put(parent_item);
+                                module_put(owner);
+                        }
+                }
+        }
+
+        return ret;
+}
+
+static int configfs_rmdir(struct inode *dir, struct dentry *dentry)
+{
+        struct config_item *parent_item;
+        struct config_item *item;
+        struct configfs_subsystem *subsys;
+        struct configfs_dirent *sd;
+        struct module *owner = NULL;
+        int ret;
+
+        if (dentry->d_parent == configfs_sb->s_root)
+                return -EPERM;
+
+        sd = dentry->d_fsdata;
+        if (sd->s_type & CONFIGFS_USET_DEFAULT)
+                return -EPERM;
+
+        parent_item = configfs_get_config_item(dentry->d_parent);
+        subsys = to_config_group(parent_item)->cg_subsys;
+        BUG_ON(!subsys);
+
+        if (!parent_item->ci_type) {
+                config_item_put(parent_item);
+                return -EINVAL;
+        }
+
+        ret = configfs_detach_prep(dentry);
+        if (ret) {
+                configfs_detach_rollback(dentry);
+                config_item_put(parent_item);
+                return ret;
+        }
+
+        item = configfs_get_config_item(dentry);
+
+        /* Drop reference from above, item already holds one. */
+        config_item_put(parent_item);
+
+        if (item->ci_type)
+                owner = item->ci_type->ct_owner;
+
+        if (sd->s_type & CONFIGFS_USET_DIR) {
+                configfs_detach_group(item);
+
+                down(&subsys->su_sem);
+                unlink_group(to_config_group(item));
+        } else {
+                configfs_detach_item(item);
+
+                down(&subsys->su_sem);
+                unlink_obj(item);
+        }
+
+        client_drop_item(parent_item, item);
+        up(&subsys->su_sem);
+
+        /* Drop our reference from above */
+        config_item_put(item);
+
+        module_put(owner);
+
+        return 0;
+}
+
+struct inode_operations configfs_dir_inode_operations = {
+        .mkdir          = configfs_mkdir,
+        .rmdir          = configfs_rmdir,
+        .symlink        = configfs_symlink,
+        .unlink         = configfs_unlink,
+        .lookup         = configfs_lookup,
+};
+
+#if 0
+int configfs_rename_dir(struct config_item * item, const char *new_name)
+{
+        int error = 0;
+        struct dentry * new_dentry, * parent;
+
+        if (!strcmp(config_item_name(item), new_name))
+                return -EINVAL;
+
+        if (!item->parent)
+                return -EINVAL;
+
+        down_write(&configfs_rename_sem);
+        parent = item->parent->dentry;
+
+        down(&parent->d_inode->i_sem);
+
+        new_dentry = lookup_one_len(new_name, parent, strlen(new_name));
+        if (!IS_ERR(new_dentry)) {
+                if (!new_dentry->d_inode) {
+                        error = config_item_set_name(item, "%s", new_name);
+                        if (!error) {
+                                d_add(new_dentry, NULL);
+                                d_move(item->dentry, new_dentry);
+                        }
+                        else
+                                d_delete(new_dentry);
+                } else
+                        error = -EEXIST;
+                dput(new_dentry);
+        }
+        up(&parent->d_inode->i_sem);
+        up_write(&configfs_rename_sem);
+
+        return error;
+}
+#endif
+
+static int configfs_dir_open(struct inode *inode, struct file *file)
+{
+        struct dentry * dentry = file->f_dentry;
+        struct configfs_dirent * parent_sd = dentry->d_fsdata;
+
+        down(&dentry->d_inode->i_sem);
+        file->private_data = configfs_new_dirent(parent_sd, NULL);
+        up(&dentry->d_inode->i_sem);
+
+        return file->private_data ? 0 : -ENOMEM;
+
+}
+
+static int configfs_dir_close(struct inode *inode, struct file *file)
+{
+        struct dentry * dentry = file->f_dentry;
+        struct configfs_dirent * cursor = file->private_data;
+
+        down(&dentry->d_inode->i_sem);
+        list_del_init(&cursor->s_sibling);
+        up(&dentry->d_inode->i_sem);
+
+        release_configfs_dirent(cursor);
+
+        return 0;
+}
+
+/* Relationship between s_mode and the DT_xxx types */
+static inline unsigned char dt_type(struct configfs_dirent *sd)
+{
+        return (sd->s_mode >> 12) & 15;
+}
+
+static int configfs_readdir(struct file * filp, void * dirent, filldir_t filldir)
+{
+        struct dentry *dentry = filp->f_dentry;
+        struct configfs_dirent * parent_sd = dentry->d_fsdata;
+        struct configfs_dirent *cursor = filp->private_data;
+        struct list_head *p, *q = &cursor->s_sibling;
+        ino_t ino;
+        int i = filp->f_pos;
+
+        switch (i) {
+                case 0:
+                        ino = dentry->d_inode->i_ino;
+                        if (filldir(dirent, ".", 1, i, ino, DT_DIR) < 0)
+                                break;
+                        filp->f_pos++;
+                        i++;
+                        /* fallthrough */
+                case 1:
+                        ino = parent_ino(dentry);
+                        if (filldir(dirent, "..", 2, i, ino, DT_DIR) < 0)
+                                break;
+                        filp->f_pos++;
+                        i++;
+                        /* fallthrough */
+                default:
+                        if (filp->f_pos == 2) {
+                                list_del(q);
+                                list_add(q, &parent_sd->s_children);
+                        }
+                        for (p=q->next; p!= &parent_sd->s_children; p=p->next) {
+                                struct configfs_dirent *next;
+                                const char * name;
+                                int len;
+
+                                next = list_entry(p, struct configfs_dirent,
+                                                   s_sibling);
+                                if (!next->s_element)
+                                        continue;
+
+                                name = configfs_get_name(next);
+                                len = strlen(name);
+                                if (next->s_dentry)
+                                        ino = next->s_dentry->d_inode->i_ino;
+                                else
+                                        ino = iunique(configfs_sb, 2);
+
+                                if (filldir(dirent, name, len, filp->f_pos, ino,
+                                                 dt_type(next)) < 0)
+                                        return 0;
+
+                                list_del(q);
+                                list_add(q, p);
+                                p = q;
+                                filp->f_pos++;
+                        }
+        }
+        return 0;
+}
+
+static loff_t configfs_dir_lseek(struct file * file, loff_t offset, int origin)
+{
+        struct dentry * dentry = file->f_dentry;
+
+        down(&dentry->d_inode->i_sem);
+        switch (origin) {
+                case 1:
+                        offset += file->f_pos;
+                case 0:
+                        if (offset >= 0)
+                                break;
+                default:
+                        up(&file->f_dentry->d_inode->i_sem);
+                        return -EINVAL;
+        }
+        if (offset != file->f_pos) {
+                file->f_pos = offset;
+                if (file->f_pos >= 2) {
+                        struct configfs_dirent *sd = dentry->d_fsdata;
+                        struct configfs_dirent *cursor = file->private_data;
+                        struct list_head *p;
+                        loff_t n = file->f_pos - 2;
+
+                        list_del(&cursor->s_sibling);
+                        p = sd->s_children.next;
+                        while (n && p != &sd->s_children) {
+                                struct configfs_dirent *next;
+                                next = list_entry(p, struct configfs_dirent,
+                                                   s_sibling);
+                                if (next->s_element)
+                                        n--;
+                                p = p->next;
+                        }
+                        list_add_tail(&cursor->s_sibling, p);
+                }
+        }
+        up(&dentry->d_inode->i_sem);
+        return offset;
+}
+
+struct file_operations configfs_dir_operations = {
+        .open           = configfs_dir_open,
+        .release        = configfs_dir_close,
+        .llseek         = configfs_dir_lseek,
+        .read           = generic_read_dir,
+        .readdir        = configfs_readdir,
+};
+
+int configfs_register_subsystem(struct configfs_subsystem *subsys)
+{
+        int err;
+        struct config_group *group = &subsys->su_group;
+        struct qstr name;
+        struct dentry *dentry;
+        struct configfs_dirent *sd;
+
+        err = configfs_pin_fs();
+        if (err)
+                return err;
+
+        if (!group->cg_item.ci_name)
+                group->cg_item.ci_name = group->cg_item.ci_namebuf;
+
+        sd = configfs_sb->s_root->d_fsdata;
+        link_group(to_config_group(sd->s_element), group);
+
+        down(&configfs_sb->s_root->d_inode->i_sem);
+
+        name.name = group->cg_item.ci_name;
+        name.len = strlen(name.name);
+        name.hash = full_name_hash(name.name, name.len);
+
+        err = -ENOMEM;
+        dentry = d_alloc(configfs_sb->s_root, &name);
+        if (!dentry)
+                goto out_release;
+
+        d_add(dentry, NULL);
+
+        err = configfs_attach_group(sd->s_element, &group->cg_item,
+                                    dentry);
+        if (!err)
+                dentry = NULL;
+        else
+                d_delete(dentry);
+
+        up(&configfs_sb->s_root->d_inode->i_sem);
+
+        if (dentry) {
+            dput(dentry);
+out_release:
+            unlink_group(group);
+            configfs_release_fs();
+        }
+
+        return err;
+}
+
+void configfs_unregister_subsystem(struct configfs_subsystem *subsys)
+{
+        struct config_group *group = &subsys->su_group;
+        struct dentry *dentry = group->cg_item.ci_dentry;
+
+        if (dentry->d_parent != configfs_sb->s_root) {
+                printk(KERN_ERR "configfs: Tried to unregister non-subsystem!\n");
+                return;
+        }
+
+        down(&configfs_sb->s_root->d_inode->i_sem);
+        down(&dentry->d_inode->i_sem);
+        if (configfs_detach_prep(dentry)) {
+                printk(KERN_ERR "configfs: Tried to unregister non-empty subsystem!\n");
+        }
+        configfs_detach_group(&group->cg_item);
+        dentry->d_inode->i_flags |= S_DEAD;
+        up(&dentry->d_inode->i_sem);
+
+        d_delete(dentry);
+
+        up(&configfs_sb->s_root->d_inode->i_sem);
+
+        dput(dentry);
+
+        unlink_group(group);
+        configfs_release_fs();
+}
+
+EXPORT_SYMBOL(configfs_register_subsystem);
+EXPORT_SYMBOL(configfs_unregister_subsystem);