Merge tag 'for-linus-5.18-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/rw...

[people/ms/linux.git] / fs / configfs / dir.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * dir.c - Operations for configfs directories.
 *
 * 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/fsnotify.h>
#include <linux/mount.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/err.h>

#include <linux/configfs.h>
#include "configfs_internal.h"

/*
 * Protects mutations of configfs_dirent linkage together with proper i_mutex
 * Also protects mutations of symlinks linkage to target configfs_dirent
 * Mutators of configfs_dirent linkage must *both* have the proper inode locked
 * and configfs_dirent_lock locked, in that order.
 * This allows one to safely traverse configfs_dirent trees and symlinks without
 * having to lock inodes.
 *
 * Protects setting of CONFIGFS_USET_DROPPING: checking the flag
 * unlocked is not reliable unless in detach_groups() called from
 * rmdir()/unregister() and from configfs_attach_group()
 */
DEFINE_SPINLOCK(configfs_dirent_lock);

/*
 * All of link_obj/unlink_obj/link_group/unlink_group require that
 * subsys->su_mutex is held.
 * But parent configfs_subsystem is NULL when config_item is root.
 * Use this mutex when config_item is root.
 */
static DEFINE_MUTEX(configfs_subsystem_mutex);

static void configfs_d_iput(struct dentry * dentry,
                            struct inode * inode)
{
        struct configfs_dirent *sd = dentry->d_fsdata;

        if (sd) {
                /* Coordinate with configfs_readdir */
                spin_lock(&configfs_dirent_lock);
                /*
                 * Set sd->s_dentry to null only when this dentry is the one
                 * that is going to be killed.  Otherwise configfs_d_iput may
                 * run just after configfs_lookup and set sd->s_dentry to
                 * NULL even it's still in use.
                 */
                if (sd->s_dentry == dentry)
                        sd->s_dentry = NULL;

                spin_unlock(&configfs_dirent_lock);
                configfs_put(sd);
        }
        iput(inode);
}

const struct dentry_operations configfs_dentry_ops = {
        .d_iput         = configfs_d_iput,
        .d_delete       = always_delete_dentry,
};

#ifdef CONFIG_LOCKDEP

/*
 * Helpers to make lockdep happy with our recursive locking of default groups'
 * inodes (see configfs_attach_group() and configfs_detach_group()).
 * We put default groups i_mutexes in separate classes according to their depth
 * from the youngest non-default group ancestor.
 *
 * For a non-default group A having default groups A/B, A/C, and A/C/D, default
 * groups A/B and A/C will have their inode's mutex in class
 * default_group_class[0], and default group A/C/D will be in
 * default_group_class[1].
 *
 * The lock classes are declared and assigned in inode.c, according to the
 * s_depth value.
 * The s_depth value is initialized to -1, adjusted to >= 0 when attaching
 * default groups, and reset to -1 when all default groups are attached. During
 * attachment, if configfs_create() sees s_depth > 0, the lock class of the new
 * inode's mutex is set to default_group_class[s_depth - 1].
 */

static void configfs_init_dirent_depth(struct configfs_dirent *sd)
{
        sd->s_depth = -1;
}

static void configfs_set_dir_dirent_depth(struct configfs_dirent *parent_sd,
                                          struct configfs_dirent *sd)
{
        int parent_depth = parent_sd->s_depth;

        if (parent_depth >= 0)
                sd->s_depth = parent_depth + 1;
}

static void
configfs_adjust_dir_dirent_depth_before_populate(struct configfs_dirent *sd)
{
        /*
         * item's i_mutex class is already setup, so s_depth is now only
         * used to set new sub-directories s_depth, which is always done
         * with item's i_mutex locked.
         */
        /*
         *  sd->s_depth == -1 iff we are a non default group.
         *  else (we are a default group) sd->s_depth > 0 (see
         *  create_dir()).
         */
        if (sd->s_depth == -1)
                /*
                 * We are a non default group and we are going to create
                 * default groups.
                 */
                sd->s_depth = 0;
}

static void
configfs_adjust_dir_dirent_depth_after_populate(struct configfs_dirent *sd)
{
        /* We will not create default groups anymore. */
        sd->s_depth = -1;
}

#else /* CONFIG_LOCKDEP */

static void configfs_init_dirent_depth(struct configfs_dirent *sd)
{
}

static void configfs_set_dir_dirent_depth(struct configfs_dirent *parent_sd,
                                          struct configfs_dirent *sd)
{
}

static void
configfs_adjust_dir_dirent_depth_before_populate(struct configfs_dirent *sd)
{
}

static void
configfs_adjust_dir_dirent_depth_after_populate(struct configfs_dirent *sd)
{
}

#endif /* CONFIG_LOCKDEP */

static struct configfs_fragment *new_fragment(void)
{
        struct configfs_fragment *p;

        p = kmalloc(sizeof(struct configfs_fragment), GFP_KERNEL);
        if (p) {
                atomic_set(&p->frag_count, 1);
                init_rwsem(&p->frag_sem);
                p->frag_dead = false;
        }
        return p;
}

void put_fragment(struct configfs_fragment *frag)
{
        if (frag && atomic_dec_and_test(&frag->frag_count))
                kfree(frag);
}

struct configfs_fragment *get_fragment(struct configfs_fragment *frag)
{
        if (likely(frag))
                atomic_inc(&frag->frag_count);
        return frag;
}

/*
 * 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, int type,
                                                   struct configfs_fragment *frag)
{
        struct configfs_dirent * sd;

        sd = kmem_cache_zalloc(configfs_dir_cachep, GFP_KERNEL);
        if (!sd)
                return ERR_PTR(-ENOMEM);

        atomic_set(&sd->s_count, 1);
        INIT_LIST_HEAD(&sd->s_children);
        sd->s_element = element;
        sd->s_type = type;
        configfs_init_dirent_depth(sd);
        spin_lock(&configfs_dirent_lock);
        if (parent_sd->s_type & CONFIGFS_USET_DROPPING) {
                spin_unlock(&configfs_dirent_lock);
                kmem_cache_free(configfs_dir_cachep, sd);
                return ERR_PTR(-ENOENT);
        }
        sd->s_frag = get_fragment(frag);
        list_add(&sd->s_sibling, &parent_sd->s_children);
        spin_unlock(&configfs_dirent_lock);

        return sd;
}

/*
 *
 * Return -EEXIST if there is already a configfs element with the same
 * name for the same parent.
 *
 * called with parent inode's i_mutex held
 */
static int configfs_dirent_exists(struct configfs_dirent *parent_sd,
                                  const unsigned char *new)
{
        struct configfs_dirent * sd;

        list_for_each_entry(sd, &parent_sd->s_children, s_sibling) {
                if (sd->s_element) {
                        const unsigned char *existing = configfs_get_name(sd);
                        if (strcmp(existing, new))
                                continue;
                        else
                                return -EEXIST;
                }
        }

        return 0;
}


int configfs_make_dirent(struct configfs_dirent * parent_sd,
                         struct dentry * dentry, void * element,
                         umode_t mode, int type, struct configfs_fragment *frag)
{
        struct configfs_dirent * sd;

        sd = configfs_new_dirent(parent_sd, element, type, frag);
        if (IS_ERR(sd))
                return PTR_ERR(sd);

        sd->s_mode = mode;
        sd->s_dentry = dentry;
        if (dentry)
                dentry->d_fsdata = configfs_get(sd);

        return 0;
}

static void configfs_remove_dirent(struct dentry *dentry)
{
        struct configfs_dirent *sd = dentry->d_fsdata;

        if (!sd)
                return;
        spin_lock(&configfs_dirent_lock);
        list_del_init(&sd->s_sibling);
        spin_unlock(&configfs_dirent_lock);
        configfs_put(sd);
}

/**
 *      configfs_create_dir - create a directory for an config_item.
 *      @item:          config_itemwe're creating directory for.
 *      @dentry:        config_item's dentry.
 *      @frag:          config_item's fragment.
 *
 *      Note: user-created entries won't be allowed under this new directory
 *      until it is validated by configfs_dir_set_ready()
 */

static int configfs_create_dir(struct config_item *item, struct dentry *dentry,
                                struct configfs_fragment *frag)
{
        int error;
        umode_t mode = S_IFDIR| S_IRWXU | S_IRUGO | S_IXUGO;
        struct dentry *p = dentry->d_parent;
        struct inode *inode;

        BUG_ON(!item);

        error = configfs_dirent_exists(p->d_fsdata, dentry->d_name.name);
        if (unlikely(error))
                return error;

        error = configfs_make_dirent(p->d_fsdata, dentry, item, mode,
                                     CONFIGFS_DIR | CONFIGFS_USET_CREATING,
                                     frag);
        if (unlikely(error))
                return error;

        configfs_set_dir_dirent_depth(p->d_fsdata, dentry->d_fsdata);
        inode = configfs_create(dentry, mode);
        if (IS_ERR(inode))
                goto out_remove;

        inode->i_op = &configfs_dir_inode_operations;
        inode->i_fop = &configfs_dir_operations;
        /* directory inodes start off with i_nlink == 2 (for "." entry) */
        inc_nlink(inode);
        d_instantiate(dentry, inode);
        /* already hashed */
        dget(dentry);  /* pin directory dentries in core */
        inc_nlink(d_inode(p));
        item->ci_dentry = dentry;
        return 0;

out_remove:
        configfs_remove_dirent(dentry);
        return PTR_ERR(inode);
}

/*
 * Allow userspace to create new entries under a new directory created with
 * configfs_create_dir(), and under all of its chidlren directories recursively.
 * @sd          configfs_dirent of the new directory to validate
 *
 * Caller must hold configfs_dirent_lock.
 */
static void configfs_dir_set_ready(struct configfs_dirent *sd)
{
        struct configfs_dirent *child_sd;

        sd->s_type &= ~CONFIGFS_USET_CREATING;
        list_for_each_entry(child_sd, &sd->s_children, s_sibling)
                if (child_sd->s_type & CONFIGFS_USET_CREATING)
                        configfs_dir_set_ready(child_sd);
}

/*
 * Check that a directory does not belong to a directory hierarchy being
 * attached and not validated yet.
 * @sd          configfs_dirent of the directory to check
 *
 * @return      non-zero iff the directory was validated
 *
 * Note: takes configfs_dirent_lock, so the result may change from false to true
 * in two consecutive calls, but never from true to false.
 */
int configfs_dirent_is_ready(struct configfs_dirent *sd)
{
        int ret;

        spin_lock(&configfs_dirent_lock);
        ret = !(sd->s_type & CONFIGFS_USET_CREATING);
        spin_unlock(&configfs_dirent_lock);

        return ret;
}

int configfs_create_link(struct configfs_dirent *target, struct dentry *parent,
                struct dentry *dentry, char *body)
{
        int err = 0;
        umode_t mode = S_IFLNK | S_IRWXUGO;
        struct configfs_dirent *p = parent->d_fsdata;
        struct inode *inode;

        err = configfs_make_dirent(p, dentry, target, mode, CONFIGFS_ITEM_LINK,
                        p->s_frag);
        if (err)
                return err;

        inode = configfs_create(dentry, mode);
        if (IS_ERR(inode))
                goto out_remove;

        inode->i_link = body;
        inode->i_op = &configfs_symlink_inode_operations;
        d_instantiate(dentry, inode);
        dget(dentry);  /* pin link dentries in core */
        return 0;

out_remove:
        configfs_remove_dirent(dentry);
        return PTR_ERR(inode);
}

static void remove_dir(struct dentry * d)
{
        struct dentry * parent = dget(d->d_parent);

        configfs_remove_dirent(d);

        if (d_really_is_positive(d))
                simple_rmdir(d_inode(parent),d);

        pr_debug(" o %pd removing done (%d)\n", d, d_count(d));

        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.
 *
 * Caller holds the mutex of the item's inode
 */

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);
}

static struct dentry * configfs_lookup(struct inode *dir,
                                       struct dentry *dentry,
                                       unsigned int flags)
{
        struct configfs_dirent * parent_sd = dentry->d_parent->d_fsdata;
        struct configfs_dirent * sd;
        struct inode *inode = NULL;

        if (dentry->d_name.len > NAME_MAX)
                return ERR_PTR(-ENAMETOOLONG);

        /*
         * Fake invisibility if dir belongs to a group/default groups hierarchy
         * being attached
         *
         * This forbids userspace to read/write attributes of items which may
         * not complete their initialization, since the dentries of the
         * attributes won't be instantiated.
         */
        if (!configfs_dirent_is_ready(parent_sd))
                return ERR_PTR(-ENOENT);

        spin_lock(&configfs_dirent_lock);
        list_for_each_entry(sd, &parent_sd->s_children, s_sibling) {
                if ((sd->s_type & CONFIGFS_NOT_PINNED) &&
                    !strcmp(configfs_get_name(sd), dentry->d_name.name)) {
                        struct configfs_attribute *attr = sd->s_element;
                        umode_t mode = (attr->ca_mode & S_IALLUGO) | S_IFREG;

                        dentry->d_fsdata = configfs_get(sd);
                        sd->s_dentry = dentry;
                        spin_unlock(&configfs_dirent_lock);

                        inode = configfs_create(dentry, mode);
                        if (IS_ERR(inode)) {
                                configfs_put(sd);
                                return ERR_CAST(inode);
                        }
                        if (sd->s_type & CONFIGFS_ITEM_BIN_ATTR) {
                                inode->i_size = 0;
                                inode->i_fop = &configfs_bin_file_operations;
                        } else {
                                inode->i_size = PAGE_SIZE;
                                inode->i_fop = &configfs_file_operations;
                        }
                        goto done;
                }
        }
        spin_unlock(&configfs_dirent_lock);
done:
        d_add(dentry, inode);
        return NULL;
}

/*
 * Only subdirectories count here.  Files (CONFIGFS_NOT_PINNED) are
 * attributes and are removed by rmdir().  We recurse, setting
 * CONFIGFS_USET_DROPPING on all children that are candidates for
 * default detach.
 * If there is an error, the caller will reset the flags via
 * configfs_detach_rollback().
 */
static int configfs_detach_prep(struct dentry *dentry, struct dentry **wait)
{
        struct configfs_dirent *parent_sd = dentry->d_fsdata;
        struct configfs_dirent *sd;
        int ret;

        /* Mark that we're trying to drop the group */
        parent_sd->s_type |= CONFIGFS_USET_DROPPING;

        ret = -EBUSY;
        if (parent_sd->s_links)
                goto out;

        ret = 0;
        list_for_each_entry(sd, &parent_sd->s_children, s_sibling) {
                if (!sd->s_element ||
                    (sd->s_type & CONFIGFS_NOT_PINNED))
                        continue;
                if (sd->s_type & CONFIGFS_USET_DEFAULT) {
                        /* Abort if racing with mkdir() */
                        if (sd->s_type & CONFIGFS_USET_IN_MKDIR) {
                                if (wait)
                                        *wait= dget(sd->s_dentry);
                                return -EAGAIN;
                        }

                        /*
                         * Yup, recursive.  If there's a problem, blame
                         * deep nesting of default_groups
                         */
                        ret = configfs_detach_prep(sd->s_dentry, wait);
                        if (!ret)
                                continue;
                } else
                        ret = -ENOTEMPTY;

                break;
        }

out:
        return ret;
}

/*
 * Walk the tree, resetting CONFIGFS_USET_DROPPING wherever it was
 * set.
 */
static void configfs_detach_rollback(struct dentry *dentry)
{
        struct configfs_dirent *parent_sd = dentry->d_fsdata;
        struct configfs_dirent *sd;

        parent_sd->s_type &= ~CONFIGFS_USET_DROPPING;

        list_for_each_entry(sd, &parent_sd->s_children, s_sibling)
                if (sd->s_type & CONFIGFS_USET_DEFAULT)
                        configfs_detach_rollback(sd->s_dentry);
}

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;
                spin_lock(&configfs_dirent_lock);
                list_del_init(&sd->s_sibling);
                spin_unlock(&configfs_dirent_lock);
                configfs_drop_dentry(sd, dentry);
                configfs_put(sd);
        }

        /**
         * Drop reference from dget() on entrance.
         */
        dput(dentry);
}

static int populate_attrs(struct config_item *item)
{
        const struct config_item_type *t = item->ci_type;
        struct configfs_attribute *attr;
        struct configfs_bin_attribute *bin_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 (t->ct_bin_attrs) {
                for (i = 0; (bin_attr = t->ct_bin_attrs[i]) != NULL; i++) {
                        error = configfs_create_bin_file(item, bin_attr);
                        if (error)
                                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,
                                 struct configfs_fragment *frag);
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;

                inode_lock(d_inode(child));

                configfs_detach_group(sd->s_element);
                d_inode(child)->i_flags |= S_DEAD;
                dont_mount(child);

                inode_unlock(d_inode(child));

                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,
                                struct configfs_fragment *frag)
{
        int ret;
        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;

        ret = -ENOMEM;
        child = d_alloc_name(parent, group->cg_item.ci_name);
        if (child) {
                d_add(child, NULL);

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

        return ret;
}

static int populate_groups(struct config_group *group,
                           struct configfs_fragment *frag)
{
        struct config_group *new_group;
        int ret = 0;

        list_for_each_entry(new_group, &group->default_groups, group_entry) {
                ret = create_default_group(group, new_group, frag);
                if (ret) {
                        detach_groups(group);
                        break;
                }
        }

        return ret;
}

void configfs_remove_default_groups(struct config_group *group)
{
        struct config_group *g, *n;

        list_for_each_entry_safe(g, n, &group->default_groups, group_entry) {
                list_del(&g->group_entry);
                config_item_put(&g->cg_item);
        }
}
EXPORT_SYMBOL(configfs_remove_default_groups);

/*
 * 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)
{
        struct config_group *new_group;

        list_for_each_entry(new_group, &group->default_groups, group_entry)
                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)
{
        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;

        list_for_each_entry(new_group, &group->default_groups, group_entry)
                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,
                                struct configfs_fragment *frag)
{
        int ret;

        ret = configfs_create_dir(item, dentry, frag);
        if (!ret) {
                ret = populate_attrs(item);
                if (ret) {
                        /*
                         * We are going to remove an inode and its dentry but
                         * the VFS may already have hit and used them. Thus,
                         * we must lock them as rmdir() would.
                         */
                        inode_lock(d_inode(dentry));
                        configfs_remove_dir(item);
                        d_inode(dentry)->i_flags |= S_DEAD;
                        dont_mount(dentry);
                        inode_unlock(d_inode(dentry));
                        d_delete(dentry);
                }
        }

        return ret;
}

/* Caller holds the mutex of the item's inode */
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,
                                 struct configfs_fragment *frag)
{
        int ret;
        struct configfs_dirent *sd;

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

                /*
                 * FYI, we're faking mkdir in populate_groups()
                 * We must lock the group's inode to avoid races with the VFS
                 * which can already hit the inode and try to add/remove entries
                 * under it.
                 *
                 * We must also lock the inode to remove it safely in case of
                 * error, as rmdir() would.
                 */
                inode_lock_nested(d_inode(dentry), I_MUTEX_CHILD);
                configfs_adjust_dir_dirent_depth_before_populate(sd);
                ret = populate_groups(to_config_group(item), frag);
                if (ret) {
                        configfs_detach_item(item);
                        d_inode(dentry)->i_flags |= S_DEAD;
                        dont_mount(dentry);
                }
                configfs_adjust_dir_dirent_depth_after_populate(sd);
                inode_unlock(d_inode(dentry));
                if (ret)
                        d_delete(dentry);
        }

        return ret;
}

/* Caller holds the mutex of the group's inode */
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)
{
        const 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)
{
        const 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)
{
        pr_info("%*s\"%s\":\n", level, " ", configfs_get_name(sd));

#define type_print(_type) if (sd->s_type & _type) pr_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 dependent 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 configfs_dirent_lock.
 * 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 configfs_dirent_lock helps
 * locking 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 deliberately ignore items tagged as dropping since they are virtually
 * dead, as well as items in the middle of attachment since they virtually
 * do not exist yet. This completes the locking out of racing mkdir() and
 * rmdir().
 * Note: subdirectories in the middle of attachment start with s_type =
 * CONFIGFS_DIR|CONFIGFS_USET_CREATING set by create_dir().  When
 * CONFIGFS_USET_CREATING is set, we ignore the item.  The actual set of
 * s_type is in configfs_new_dirent(), which has configfs_dirent_lock.
 *
 * If the target is not found, -ENOENT is bubbled up.
 *
 * This adds a requirement that all config_items be unique!
 *
 * This is recursive.  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;
        int ret = 0;

        BUG_ON(!origin || !origin->d_fsdata);
        sd = origin->d_fsdata;

        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) &&
                    !(child_sd->s_type & CONFIGFS_USET_DROPPING) &&
                    !(child_sd->s_type & CONFIGFS_USET_CREATING)) {
                        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 */
        ret = -ENOENT;

out:
        return ret;
}

static int configfs_do_depend_item(struct dentry *subsys_dentry,
                                   struct config_item *target)
{
        struct configfs_dirent *p;
        int ret;

        spin_lock(&configfs_dirent_lock);
        /* Scan the tree, return 0 if found */
        ret = configfs_depend_prep(subsys_dentry, target);
        if (ret)
                goto out_unlock_dirent_lock;

        /*
         * We are sure that the item is not about to be removed by rmdir(), and
         * not in the middle of attachment by mkdir().
         */
        p = target->ci_dentry->d_fsdata;
        p->s_dependent_count += 1;

out_unlock_dirent_lock:
        spin_unlock(&configfs_dirent_lock);

        return ret;
}

static inline struct configfs_dirent *
configfs_find_subsys_dentry(struct configfs_dirent *root_sd,
                            struct config_item *subsys_item)
{
        struct configfs_dirent *p;
        struct configfs_dirent *ret = NULL;

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

        return ret;
}


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

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

        /*
         * 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().
         */
        inode_lock(d_inode(root));

        subsys_sd = configfs_find_subsys_dentry(root->d_fsdata, s_item);
        if (!subsys_sd) {
                ret = -ENOENT;
                goto out_unlock_fs;
        }

        /* Ok, now we can trust subsys/s_item */
        ret = configfs_do_depend_item(subsys_sd->s_dentry, target);

out_unlock_fs:
        inode_unlock(d_inode(root));

        /*
         * 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 the client driver is
 * pinned, thus the subsystem is pinned, and therefore configfs is pinned.
 */
void configfs_undepend_item(struct config_item *target)
{
        struct configfs_dirent *sd;

        /*
         * Since we can trust everything is pinned, we just need
         * configfs_dirent_lock.
         */
        spin_lock(&configfs_dirent_lock);

        sd = target->ci_dentry->d_fsdata;
        BUG_ON(sd->s_dependent_count < 1);

        sd->s_dependent_count -= 1;

        /*
         * After this unlock, we cannot trust the item to stay alive!
         * DO NOT REFERENCE item after this unlock.
         */
        spin_unlock(&configfs_dirent_lock);
}
EXPORT_SYMBOL(configfs_undepend_item);

/*
 * caller_subsys is a caller's subsystem not target's. This is used to
 * determine if we should lock root and check subsys or not. When we are
 * in the same subsystem as our target there is no need to do locking as
 * we know that subsys is valid and is not unregistered during this function
 * as we are called from callback of one of his children and VFS holds a lock
 * on some inode. Otherwise we have to lock our root to  ensure that target's
 * subsystem it is not unregistered during this function.
 */
int configfs_depend_item_unlocked(struct configfs_subsystem *caller_subsys,
                                  struct config_item *target)
{
        struct configfs_subsystem *target_subsys;
        struct config_group *root, *parent;
        struct configfs_dirent *subsys_sd;
        int ret = -ENOENT;

        /* Disallow this function for configfs root */
        if (configfs_is_root(target))
                return -EINVAL;

        parent = target->ci_group;
        /*
         * This may happen when someone is trying to depend root
         * directory of some subsystem
         */
        if (configfs_is_root(&parent->cg_item)) {
                target_subsys = to_configfs_subsystem(to_config_group(target));
                root = parent;
        } else {
                target_subsys = parent->cg_subsys;
                /* Find a cofnigfs root as we may need it for locking */
                for (root = parent; !configfs_is_root(&root->cg_item);
                     root = root->cg_item.ci_group)
                        ;
        }

        if (target_subsys != caller_subsys) {
                /*
                 * We are in other configfs subsystem, so we have to do
                 * additional locking to prevent other subsystem from being
                 * unregistered
                 */
                inode_lock(d_inode(root->cg_item.ci_dentry));

                /*
                 * As we are trying to depend item from other subsystem
                 * we have to check if this subsystem is still registered
                 */
                subsys_sd = configfs_find_subsys_dentry(
                                root->cg_item.ci_dentry->d_fsdata,
                                &target_subsys->su_group.cg_item);
                if (!subsys_sd)
                        goto out_root_unlock;
        } else {
                subsys_sd = target_subsys->su_group.cg_item.ci_dentry->d_fsdata;
        }

        /* Now we can execute core of depend item */
        ret = configfs_do_depend_item(subsys_sd->s_dentry, target);

        if (target_subsys != caller_subsys)
out_root_unlock:
                /*
                 * We were called from subsystem other than our target so we
                 * took some locks so now it's time to release them
                 */
                inode_unlock(d_inode(root->cg_item.ci_dentry));

        return ret;
}
EXPORT_SYMBOL(configfs_depend_item_unlocked);

static int configfs_mkdir(struct user_namespace *mnt_userns, struct inode *dir,
                          struct dentry *dentry, umode_t mode)
{
        int ret = 0;
        int module_got = 0;
        struct config_group *group = NULL;
        struct config_item *item = NULL;
        struct config_item *parent_item;
        struct configfs_subsystem *subsys;
        struct configfs_dirent *sd;
        const struct config_item_type *type;
        struct module *subsys_owner = NULL, *new_item_owner = NULL;
        struct configfs_fragment *frag;
        char *name;

        sd = dentry->d_parent->d_fsdata;

        /*
         * Fake invisibility if dir belongs to a group/default groups hierarchy
         * being attached
         */
        if (!configfs_dirent_is_ready(sd)) {
                ret = -ENOENT;
                goto out;
        }

        if (!(sd->s_type & CONFIGFS_USET_DIR)) {
                ret = -EPERM;
                goto out;
        }

        frag = new_fragment();
        if (!frag) {
                ret = -ENOMEM;
                goto out;
        }

        /* Get a working ref for the duration of this function */
        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)) {
                ret = -EPERM;  /* Lack-of-mkdir returns -EPERM */
                goto out_put;
        }

        /*
         * The subsystem may belong to a different module than the item
         * being created.  We don't want to safely pin the new item but
         * fail to pin the subsystem it sits under.
         */
        if (!subsys->su_group.cg_item.ci_type) {
                ret = -EINVAL;
                goto out_put;
        }
        subsys_owner = subsys->su_group.cg_item.ci_type->ct_owner;
        if (!try_module_get(subsys_owner)) {
                ret = -EINVAL;
                goto out_put;
        }

        name = kmalloc(dentry->d_name.len + 1, GFP_KERNEL);
        if (!name) {
                ret = -ENOMEM;
                goto out_subsys_put;
        }

        snprintf(name, dentry->d_name.len + 1, "%s", dentry->d_name.name);

        mutex_lock(&subsys->su_mutex);
        if (type->ct_group_ops->make_group) {
                group = type->ct_group_ops->make_group(to_config_group(parent_item), name);
                if (!group)
                        group = ERR_PTR(-ENOMEM);
                if (!IS_ERR(group)) {
                        link_group(to_config_group(parent_item), group);
                        item = &group->cg_item;
                } else
                        ret = PTR_ERR(group);
        } else {
                item = type->ct_group_ops->make_item(to_config_group(parent_item), name);
                if (!item)
                        item = ERR_PTR(-ENOMEM);
                if (!IS_ERR(item))
                        link_obj(parent_item, item);
                else
                        ret = PTR_ERR(item);
        }
        mutex_unlock(&subsys->su_mutex);

        kfree(name);
        if (ret) {
                /*
                 * If ret != 0, then link_obj() was never called.
                 * There are no extra references to clean up.
                 */
                goto out_subsys_put;
        }

        /*
         * link_obj() has been called (via link_group() for groups).
         * From here on out, errors must clean that up.
         */

        type = item->ci_type;
        if (!type) {
                ret = -EINVAL;
                goto out_unlink;
        }

        new_item_owner = type->ct_owner;
        if (!try_module_get(new_item_owner)) {
                ret = -EINVAL;
                goto out_unlink;
        }

        /*
         * I hate doing it this way, but if there is
         * an error,  module_put() probably should
         * happen after any cleanup.
         */
        module_got = 1;

        /*
         * Make racing rmdir() fail if it did not tag parent with
         * CONFIGFS_USET_DROPPING
         * Note: if CONFIGFS_USET_DROPPING is already set, attach_group() will
         * fail and let rmdir() terminate correctly
         */
        spin_lock(&configfs_dirent_lock);
        /* This will make configfs_detach_prep() fail */
        sd->s_type |= CONFIGFS_USET_IN_MKDIR;
        spin_unlock(&configfs_dirent_lock);

        if (group)
                ret = configfs_attach_group(parent_item, item, dentry, frag);
        else
                ret = configfs_attach_item(parent_item, item, dentry, frag);

        spin_lock(&configfs_dirent_lock);
        sd->s_type &= ~CONFIGFS_USET_IN_MKDIR;
        if (!ret)
                configfs_dir_set_ready(dentry->d_fsdata);
        spin_unlock(&configfs_dirent_lock);

out_unlink:
        if (ret) {
                /* Tear down everything we built up */
                mutex_lock(&subsys->su_mutex);

                client_disconnect_notify(parent_item, item);
                if (group)
                        unlink_group(group);
                else
                        unlink_obj(item);
                client_drop_item(parent_item, item);

                mutex_unlock(&subsys->su_mutex);

                if (module_got)
                        module_put(new_item_owner);
        }

out_subsys_put:
        if (ret)
                module_put(subsys_owner);

out_put:
        /*
         * link_obj()/link_group() took a reference from child->parent,
         * so the parent is safely pinned.  We can drop our working
         * reference.
         */
        config_item_put(parent_item);
        put_fragment(frag);

out:
        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 configfs_fragment *frag;
        struct module *subsys_owner = NULL, *dead_item_owner = NULL;
        int ret;

        sd = dentry->d_fsdata;
        if (sd->s_type & CONFIGFS_USET_DEFAULT)
                return -EPERM;

        /* Get a working ref until we have the child */
        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;
        }

        /* configfs_mkdir() shouldn't have allowed this */
        BUG_ON(!subsys->su_group.cg_item.ci_type);
        subsys_owner = subsys->su_group.cg_item.ci_type->ct_owner;

        /*
         * Ensure that no racing symlink() will make detach_prep() fail while
         * the new link is temporarily attached
         */
        do {
                struct dentry *wait;

                mutex_lock(&configfs_symlink_mutex);
                spin_lock(&configfs_dirent_lock);
                /*
                 * Here's where we check for dependents.  We're protected by
                 * configfs_dirent_lock.
                 * If no dependent, atomically tag the item as dropping.
                 */
                ret = sd->s_dependent_count ? -EBUSY : 0;
                if (!ret) {
                        ret = configfs_detach_prep(dentry, &wait);
                        if (ret)
                                configfs_detach_rollback(dentry);
                }
                spin_unlock(&configfs_dirent_lock);
                mutex_unlock(&configfs_symlink_mutex);

                if (ret) {
                        if (ret != -EAGAIN) {
                                config_item_put(parent_item);
                                return ret;
                        }

                        /* Wait until the racing operation terminates */
                        inode_lock(d_inode(wait));
                        inode_unlock(d_inode(wait));
                        dput(wait);
                }
        } while (ret == -EAGAIN);

        frag = sd->s_frag;
        if (down_write_killable(&frag->frag_sem)) {
                spin_lock(&configfs_dirent_lock);
                configfs_detach_rollback(dentry);
                spin_unlock(&configfs_dirent_lock);
                config_item_put(parent_item);
                return -EINTR;
        }
        frag->frag_dead = true;
        up_write(&frag->frag_sem);

        /* Get a working ref for the duration of this function */
        item = configfs_get_config_item(dentry);

        /* Drop reference from above, item already holds one. */
        config_item_put(parent_item);

        if (item->ci_type)
                dead_item_owner = item->ci_type->ct_owner;

        if (sd->s_type & CONFIGFS_USET_DIR) {
                configfs_detach_group(item);

                mutex_lock(&subsys->su_mutex);
                client_disconnect_notify(parent_item, item);
                unlink_group(to_config_group(item));
        } else {
                configfs_detach_item(item);

                mutex_lock(&subsys->su_mutex);
                client_disconnect_notify(parent_item, item);
                unlink_obj(item);
        }

        client_drop_item(parent_item, item);
        mutex_unlock(&subsys->su_mutex);

        /* Drop our reference from above */
        config_item_put(item);

        module_put(dead_item_owner);
        module_put(subsys_owner);

        return 0;
}

const struct inode_operations configfs_dir_inode_operations = {
        .mkdir          = configfs_mkdir,
        .rmdir          = configfs_rmdir,
        .symlink        = configfs_symlink,
        .unlink         = configfs_unlink,
        .lookup         = configfs_lookup,
        .setattr        = configfs_setattr,
};

const struct inode_operations configfs_root_inode_operations = {
        .lookup         = configfs_lookup,
        .setattr        = configfs_setattr,
};

static int configfs_dir_open(struct inode *inode, struct file *file)
{
        struct dentry * dentry = file->f_path.dentry;
        struct configfs_dirent * parent_sd = dentry->d_fsdata;
        int err;

        inode_lock(d_inode(dentry));
        /*
         * Fake invisibility if dir belongs to a group/default groups hierarchy
         * being attached
         */
        err = -ENOENT;
        if (configfs_dirent_is_ready(parent_sd)) {
                file->private_data = configfs_new_dirent(parent_sd, NULL, 0, NULL);
                if (IS_ERR(file->private_data))
                        err = PTR_ERR(file->private_data);
                else
                        err = 0;
        }
        inode_unlock(d_inode(dentry));

        return err;
}

static int configfs_dir_close(struct inode *inode, struct file *file)
{
        struct dentry * dentry = file->f_path.dentry;
        struct configfs_dirent * cursor = file->private_data;

        inode_lock(d_inode(dentry));
        spin_lock(&configfs_dirent_lock);
        list_del_init(&cursor->s_sibling);
        spin_unlock(&configfs_dirent_lock);
        inode_unlock(d_inode(dentry));

        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 *file, struct dir_context *ctx)
{
        struct dentry *dentry = file->f_path.dentry;
        struct super_block *sb = dentry->d_sb;
        struct configfs_dirent * parent_sd = dentry->d_fsdata;
        struct configfs_dirent *cursor = file->private_data;
        struct list_head *p, *q = &cursor->s_sibling;
        ino_t ino = 0;

        if (!dir_emit_dots(file, ctx))
                return 0;
        spin_lock(&configfs_dirent_lock);
        if (ctx->pos == 2)
                list_move(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;
                struct inode *inode = NULL;

                next = list_entry(p, struct configfs_dirent, s_sibling);
                if (!next->s_element)
                        continue;

                /*
                 * We'll have a dentry and an inode for
                 * PINNED items and for open attribute
                 * files.  We lock here to prevent a race
                 * with configfs_d_iput() clearing
                 * s_dentry before calling iput().
                 *
                 * Why do we go to the trouble?  If
                 * someone has an attribute file open,
                 * the inode number should match until
                 * they close it.  Beyond that, we don't
                 * care.
                 */
                dentry = next->s_dentry;
                if (dentry)
                        inode = d_inode(dentry);
                if (inode)
                        ino = inode->i_ino;
                spin_unlock(&configfs_dirent_lock);
                if (!inode)
                        ino = iunique(sb, 2);

                name = configfs_get_name(next);
                len = strlen(name);

                if (!dir_emit(ctx, name, len, ino, dt_type(next)))
                        return 0;

                spin_lock(&configfs_dirent_lock);
                list_move(q, p);
                p = q;
                ctx->pos++;
        }
        spin_unlock(&configfs_dirent_lock);
        return 0;
}

static loff_t configfs_dir_lseek(struct file *file, loff_t offset, int whence)
{
        struct dentry * dentry = file->f_path.dentry;

        switch (whence) {
                case 1:
                        offset += file->f_pos;
                        fallthrough;
                case 0:
                        if (offset >= 0)
                                break;
                        fallthrough;
                default:
                        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;

                        spin_lock(&configfs_dirent_lock);
                        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);
                        spin_unlock(&configfs_dirent_lock);
                }
        }
        return offset;
}

const struct file_operations configfs_dir_operations = {
        .open           = configfs_dir_open,
        .release        = configfs_dir_close,
        .llseek         = configfs_dir_lseek,
        .read           = generic_read_dir,
        .iterate_shared = configfs_readdir,
};

/**
 * configfs_register_group - creates a parent-child relation between two groups
 * @parent_group:       parent group
 * @group:              child group
 *
 * link groups, creates dentry for the child and attaches it to the
 * parent dentry.
 *
 * Return: 0 on success, negative errno code on error
 */
int configfs_register_group(struct config_group *parent_group,
                            struct config_group *group)
{
        struct configfs_subsystem *subsys = parent_group->cg_subsys;
        struct dentry *parent;
        struct configfs_fragment *frag;
        int ret;

        frag = new_fragment();
        if (!frag)
                return -ENOMEM;

        mutex_lock(&subsys->su_mutex);
        link_group(parent_group, group);
        mutex_unlock(&subsys->su_mutex);

        parent = parent_group->cg_item.ci_dentry;

        inode_lock_nested(d_inode(parent), I_MUTEX_PARENT);
        ret = create_default_group(parent_group, group, frag);
        if (ret)
                goto err_out;

        spin_lock(&configfs_dirent_lock);
        configfs_dir_set_ready(group->cg_item.ci_dentry->d_fsdata);
        spin_unlock(&configfs_dirent_lock);
        inode_unlock(d_inode(parent));
        put_fragment(frag);
        return 0;
err_out:
        inode_unlock(d_inode(parent));
        mutex_lock(&subsys->su_mutex);
        unlink_group(group);
        mutex_unlock(&subsys->su_mutex);
        put_fragment(frag);
        return ret;
}
EXPORT_SYMBOL(configfs_register_group);

/**
 * configfs_unregister_group() - unregisters a child group from its parent
 * @group: parent group to be unregistered
 *
 * Undoes configfs_register_group()
 */
void configfs_unregister_group(struct config_group *group)
{
        struct configfs_subsystem *subsys = group->cg_subsys;
        struct dentry *dentry = group->cg_item.ci_dentry;
        struct dentry *parent = group->cg_item.ci_parent->ci_dentry;
        struct configfs_dirent *sd = dentry->d_fsdata;
        struct configfs_fragment *frag = sd->s_frag;

        down_write(&frag->frag_sem);
        frag->frag_dead = true;
        up_write(&frag->frag_sem);

        inode_lock_nested(d_inode(parent), I_MUTEX_PARENT);
        spin_lock(&configfs_dirent_lock);
        configfs_detach_prep(dentry, NULL);
        spin_unlock(&configfs_dirent_lock);

        configfs_detach_group(&group->cg_item);
        d_inode(dentry)->i_flags |= S_DEAD;
        dont_mount(dentry);
        d_drop(dentry);
        fsnotify_rmdir(d_inode(parent), dentry);
        inode_unlock(d_inode(parent));

        dput(dentry);

        mutex_lock(&subsys->su_mutex);
        unlink_group(group);
        mutex_unlock(&subsys->su_mutex);
}
EXPORT_SYMBOL(configfs_unregister_group);

/**
 * configfs_register_default_group() - allocates and registers a child group
 * @parent_group:       parent group
 * @name:               child group name
 * @item_type:          child item type description
 *
 * boilerplate to allocate and register a child group with its parent. We need
 * kzalloc'ed memory because child's default_group is initially empty.
 *
 * Return: allocated config group or ERR_PTR() on error
 */
struct config_group *
configfs_register_default_group(struct config_group *parent_group,
                                const char *name,
                                const struct config_item_type *item_type)
{
        int ret;
        struct config_group *group;

        group = kzalloc(sizeof(*group), GFP_KERNEL);
        if (!group)
                return ERR_PTR(-ENOMEM);
        config_group_init_type_name(group, name, item_type);

        ret = configfs_register_group(parent_group, group);
        if (ret) {
                kfree(group);
                return ERR_PTR(ret);
        }
        return group;
}
EXPORT_SYMBOL(configfs_register_default_group);

/**
 * configfs_unregister_default_group() - unregisters and frees a child group
 * @group:      the group to act on
 */
void configfs_unregister_default_group(struct config_group *group)
{
        configfs_unregister_group(group);
        kfree(group);
}
EXPORT_SYMBOL(configfs_unregister_default_group);

int configfs_register_subsystem(struct configfs_subsystem *subsys)
{
        int err;
        struct config_group *group = &subsys->su_group;
        struct dentry *dentry;
        struct dentry *root;
        struct configfs_dirent *sd;
        struct configfs_fragment *frag;

        frag = new_fragment();
        if (!frag)
                return -ENOMEM;

        root = configfs_pin_fs();
        if (IS_ERR(root)) {
                put_fragment(frag);
                return PTR_ERR(root);
        }

        if (!group->cg_item.ci_name)
                group->cg_item.ci_name = group->cg_item.ci_namebuf;

        sd = root->d_fsdata;
        mutex_lock(&configfs_subsystem_mutex);
        link_group(to_config_group(sd->s_element), group);
        mutex_unlock(&configfs_subsystem_mutex);

        inode_lock_nested(d_inode(root), I_MUTEX_PARENT);

        err = -ENOMEM;
        dentry = d_alloc_name(root, group->cg_item.ci_name);
        if (dentry) {
                d_add(dentry, NULL);

                err = configfs_attach_group(sd->s_element, &group->cg_item,
                                            dentry, frag);
                if (err) {
                        BUG_ON(d_inode(dentry));
                        d_drop(dentry);
                        dput(dentry);
                } else {
                        spin_lock(&configfs_dirent_lock);
                        configfs_dir_set_ready(dentry->d_fsdata);
                        spin_unlock(&configfs_dirent_lock);
                }
        }

        inode_unlock(d_inode(root));

        if (err) {
                mutex_lock(&configfs_subsystem_mutex);
                unlink_group(group);
                mutex_unlock(&configfs_subsystem_mutex);
                configfs_release_fs();
        }
        put_fragment(frag);

        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;
        struct dentry *root = dentry->d_sb->s_root;
        struct configfs_dirent *sd = dentry->d_fsdata;
        struct configfs_fragment *frag = sd->s_frag;

        if (dentry->d_parent != root) {
                pr_err("Tried to unregister non-subsystem!\n");
                return;
        }

        down_write(&frag->frag_sem);
        frag->frag_dead = true;
        up_write(&frag->frag_sem);

        inode_lock_nested(d_inode(root),
                          I_MUTEX_PARENT);
        inode_lock_nested(d_inode(dentry), I_MUTEX_CHILD);
        mutex_lock(&configfs_symlink_mutex);
        spin_lock(&configfs_dirent_lock);
        if (configfs_detach_prep(dentry, NULL)) {
                pr_err("Tried to unregister non-empty subsystem!\n");
        }
        spin_unlock(&configfs_dirent_lock);
        mutex_unlock(&configfs_symlink_mutex);
        configfs_detach_group(&group->cg_item);
        d_inode(dentry)->i_flags |= S_DEAD;
        dont_mount(dentry);
        inode_unlock(d_inode(dentry));

        d_drop(dentry);
        fsnotify_rmdir(d_inode(root), dentry);

        inode_unlock(d_inode(root));

        dput(dentry);

        mutex_lock(&configfs_subsystem_mutex);
        unlink_group(group);
        mutex_unlock(&configfs_subsystem_mutex);
        configfs_release_fs();
}

EXPORT_SYMBOL(configfs_register_subsystem);
EXPORT_SYMBOL(configfs_unregister_subsystem);