dir.c

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/*
 * fs/sysfs/dir.c - sysfs core and dir operation implementation
 *
 * Copyright (c) 2001-3 Patrick Mochel
 * Copyright (c) 2007 SUSE Linux Products GmbH
 * Copyright (c) 2007 Tejun Heo <[email protected]>
 *
 * This file is released under the GPLv2.
 *
 * Please see Documentation/filesystems/sysfs.txt for more information.
 */

#undef DEBUG

#include <linux/fs.h>
#include <linux/mount.h>
#include <linux/module.h>
#include <linux/kobject.h>
#include <linux/namei.h>
#include <linux/idr.h>
#include <linux/completion.h>
#include <linux/mutex.h>
#include <linux/slab.h>
#include <linux/security.h>
#include <linux/hash.h>
#include "sysfs.h"

DEFINE_MUTEX(sysfs_mutex);
DEFINE_SPINLOCK(sysfs_assoc_lock);

#define to_sysfs_dirent(X) rb_entry((X), struct sysfs_dirent, s_rb);

static DEFINE_SPINLOCK(sysfs_ino_lock);
static DEFINE_IDA(sysfs_ino_ida);

static unsigned int sysfs_name_hash(const void *ns, const char *name)
{
    unsigned long hash = init_name_hash();
    unsigned int len = strlen(name);
    while (len--)
        hash = partial_name_hash(*name++, hash);
    hash = ( end_name_hash(hash) ^ hash_ptr( (void *)ns, 31 ) );
    hash &= 0x7fffffffU;
    /* Reserve hash numbers 0, 1 and INT_MAX for magic directory entries */
    if (hash < 1)
        hash += 2;
    if (hash >= INT_MAX)
        hash = INT_MAX - 1;
    return hash;
}

static int sysfs_name_compare(unsigned int hash, const void *ns,
    const char *name, const struct sysfs_dirent *sd)
{
    if (hash != sd->s_hash)
        return hash - sd->s_hash;
    if (ns != sd->s_ns)
        return ns - sd->s_ns;
    return strcmp(name, sd->s_name);
}

static int sysfs_sd_compare(const struct sysfs_dirent *left,
                const struct sysfs_dirent *right)
{
    return sysfs_name_compare(left->s_hash, left->s_ns, left->s_name,
                  right);
}

static int sysfs_link_sibling(struct sysfs_dirent *sd)
{
    struct rb_node **node = &sd->s_parent->s_dir.children.rb_node;
    struct rb_node *parent = NULL;

    if (sysfs_type(sd) == SYSFS_DIR)
        sd->s_parent->s_dir.subdirs++;

    while (*node) {
        struct sysfs_dirent *pos;
        int result;

        pos = to_sysfs_dirent(*node);
        parent = *node;
        result = sysfs_sd_compare(sd, pos);
        if (result < 0)
            node = &pos->s_rb.rb_left;
        else if (result > 0)
            node = &pos->s_rb.rb_right;
        else
            return -EEXIST;
    }
    /* add new node and rebalance the tree */
    rb_link_node(&sd->s_rb, parent, node);
    rb_insert_color(&sd->s_rb, &sd->s_parent->s_dir.children);
    return 0;
}

static void sysfs_unlink_sibling(struct sysfs_dirent *sd)
{
    if (sysfs_type(sd) == SYSFS_DIR)
        sd->s_parent->s_dir.subdirs--;

    rb_erase(&sd->s_rb, &sd->s_parent->s_dir.children);
}

#ifdef CONFIG_DEBUG_LOCK_ALLOC

/* Test for attributes that want to ignore lockdep for read-locking */
static bool ignore_lockdep(struct sysfs_dirent *sd)
{
    return sysfs_type(sd) == SYSFS_KOBJ_ATTR &&
            sd->s_attr.attr->ignore_lockdep;
}

#else

static inline bool ignore_lockdep(struct sysfs_dirent *sd)
{
    return true;
}

#endif

struct sysfs_dirent *sysfs_get_active(struct sysfs_dirent *sd)
{
    if (unlikely(!sd))
        return NULL;

    while (1) {
        int v, t;

        v = atomic_read(&sd->s_active);
        if (unlikely(v < 0))
            return NULL;

        t = atomic_cmpxchg(&sd->s_active, v, v + 1);
        if (likely(t == v))
            break;
        if (t < 0)
            return NULL;

        cpu_relax();
    }

    if (likely(!ignore_lockdep(sd)))
        rwsem_acquire_read(&sd->dep_map, 0, 1, _RET_IP_);
    return sd;
}

void sysfs_put_active(struct sysfs_dirent *sd)
{
    int v;

    if (unlikely(!sd))
        return;

    if (likely(!ignore_lockdep(sd)))
        rwsem_release(&sd->dep_map, 1, _RET_IP_);
    v = atomic_dec_return(&sd->s_active);
    if (likely(v != SD_DEACTIVATED_BIAS))
        return;

    /* atomic_dec_return() is a mb(), we'll always see the updated
     * sd->u.completion.
     */
    complete(sd->u.completion);
}

static void sysfs_deactivate(struct sysfs_dirent *sd)
{
    DECLARE_COMPLETION_ONSTACK(wait);
    int v;

    BUG_ON(!(sd->s_flags & SYSFS_FLAG_REMOVED));

    if (!(sysfs_type(sd) & SYSFS_ACTIVE_REF))
        return;

    sd->u.completion = (void *)&wait;

    rwsem_acquire(&sd->dep_map, 0, 0, _RET_IP_);
    /* atomic_add_return() is a mb(), put_active() will always see
     * the updated sd->u.completion.
     */
    v = atomic_add_return(SD_DEACTIVATED_BIAS, &sd->s_active);

    if (v != SD_DEACTIVATED_BIAS) {
        lock_contended(&sd->dep_map, _RET_IP_);
        wait_for_completion(&wait);
    }

    lock_acquired(&sd->dep_map, _RET_IP_);
    rwsem_release(&sd->dep_map, 1, _RET_IP_);
}

static int sysfs_alloc_ino(unsigned int *pino)
{
    int ino, rc;

 retry:
    spin_lock(&sysfs_ino_lock);
    rc = ida_get_new_above(&sysfs_ino_ida, 2, &ino);
    spin_unlock(&sysfs_ino_lock);

    if (rc == -EAGAIN) {
        if (ida_pre_get(&sysfs_ino_ida, GFP_KERNEL))
            goto retry;
        rc = -ENOMEM;
    }

    *pino = ino;
    return rc;
}

static void sysfs_free_ino(unsigned int ino)
{
    spin_lock(&sysfs_ino_lock);
    ida_remove(&sysfs_ino_ida, ino);
    spin_unlock(&sysfs_ino_lock);
}

void release_sysfs_dirent(struct sysfs_dirent * sd)
{
    struct sysfs_dirent *parent_sd;

 repeat:
    /* Moving/renaming is always done while holding reference.
     * sd->s_parent won't change beneath us.
     */
    parent_sd = sd->s_parent;

    if (sysfs_type(sd) == SYSFS_KOBJ_LINK)
        sysfs_put(sd->s_symlink.target_sd);
    if (sysfs_type(sd) & SYSFS_COPY_NAME)
        kfree(sd->s_name);
    if (sd->s_iattr && sd->s_iattr->ia_secdata)
        security_release_secctx(sd->s_iattr->ia_secdata,
                    sd->s_iattr->ia_secdata_len);
    kfree(sd->s_iattr);
    sysfs_free_ino(sd->s_ino);
    kmem_cache_free(sysfs_dir_cachep, sd);

    sd = parent_sd;
    if (sd && atomic_dec_and_test(&sd->s_count))
        goto repeat;
}

static int sysfs_dentry_delete(const struct dentry *dentry)
{
    struct sysfs_dirent *sd = dentry->d_fsdata;
    return !(sd && !(sd->s_flags & SYSFS_FLAG_REMOVED));
}

static int sysfs_dentry_revalidate(struct dentry *dentry, unsigned int flags)
{
    struct sysfs_dirent *sd;
    int is_dir;
    int type;

    if (flags & LOOKUP_RCU)
        return -ECHILD;

    sd = dentry->d_fsdata;
    mutex_lock(&sysfs_mutex);

    /* The sysfs dirent has been deleted */
    if (sd->s_flags & SYSFS_FLAG_REMOVED)
        goto out_bad;

    /* The sysfs dirent has been moved? */
    if (dentry->d_parent->d_fsdata != sd->s_parent)
        goto out_bad;

    /* The sysfs dirent has been renamed */
    if (strcmp(dentry->d_name.name, sd->s_name) != 0)
        goto out_bad;

    /* The sysfs dirent has been moved to a different namespace */
    type = KOBJ_NS_TYPE_NONE;
    if (sd->s_parent) {
        type = sysfs_ns_type(sd->s_parent);
        if (type != KOBJ_NS_TYPE_NONE &&
                sysfs_info(dentry->d_sb)->ns[type] != sd->s_ns)
            goto out_bad;
    }

    mutex_unlock(&sysfs_mutex);
out_valid:
    return 1;
out_bad:
    /* Remove the dentry from the dcache hashes.
     * If this is a deleted dentry we use d_drop instead of d_delete
     * so sysfs doesn't need to cope with negative dentries.
     *
     * If this is a dentry that has simply been renamed we
     * use d_drop to remove it from the dcache lookup on its
     * old parent.  If this dentry persists later when a lookup
     * is performed at its new name the dentry will be readded
     * to the dcache hashes.
     */
    is_dir = (sysfs_type(sd) == SYSFS_DIR);
    mutex_unlock(&sysfs_mutex);
    if (is_dir) {
        /* If we have submounts we must allow the vfs caches
         * to lie about the state of the filesystem to prevent
         * leaks and other nasty things.
         */
        if (have_submounts(dentry))
            goto out_valid;
        shrink_dcache_parent(dentry);
    }
    d_drop(dentry);
    return 0;
}

static void sysfs_dentry_release(struct dentry *dentry)
{
    sysfs_put(dentry->d_fsdata);
}

const struct dentry_operations sysfs_dentry_ops = {
    .d_revalidate   = sysfs_dentry_revalidate,
    .d_delete   = sysfs_dentry_delete,
    .d_release  = sysfs_dentry_release,
};

struct sysfs_dirent *sysfs_new_dirent(const char *name, umode_t mode, int type)
{
    char *dup_name = NULL;
    struct sysfs_dirent *sd;

    if (type & SYSFS_COPY_NAME) {
        name = dup_name = kstrdup(name, GFP_KERNEL);
        if (!name)
            return NULL;
    }

    sd = kmem_cache_zalloc(sysfs_dir_cachep, GFP_KERNEL);
    if (!sd)
        goto err_out1;

    if (sysfs_alloc_ino(&sd->s_ino))
        goto err_out2;

    atomic_set(&sd->s_count, 1);
    atomic_set(&sd->s_active, 0);

    sd->s_name = name;
    sd->s_mode = mode;
    sd->s_flags = type;

    return sd;

 err_out2:
    kmem_cache_free(sysfs_dir_cachep, sd);
 err_out1:
    kfree(dup_name);
    return NULL;
}

void sysfs_addrm_start(struct sysfs_addrm_cxt *acxt,
               struct sysfs_dirent *parent_sd)
{
    memset(acxt, 0, sizeof(*acxt));
    acxt->parent_sd = parent_sd;

    mutex_lock(&sysfs_mutex);
}

int __sysfs_add_one(struct sysfs_addrm_cxt *acxt, struct sysfs_dirent *sd)
{
    struct sysfs_inode_attrs *ps_iattr;
    int ret;

    if (!!sysfs_ns_type(acxt->parent_sd) != !!sd->s_ns) {
        WARN(1, KERN_WARNING "sysfs: ns %s in '%s' for '%s'\n",
            sysfs_ns_type(acxt->parent_sd)? "required": "invalid",
            acxt->parent_sd->s_name, sd->s_name);
        return -EINVAL;
    }

    sd->s_hash = sysfs_name_hash(sd->s_ns, sd->s_name);
    sd->s_parent = sysfs_get(acxt->parent_sd);

    ret = sysfs_link_sibling(sd);
    if (ret)
        return ret;

    /* Update timestamps on the parent */
    ps_iattr = acxt->parent_sd->s_iattr;
    if (ps_iattr) {
        struct iattr *ps_iattrs = &ps_iattr->ia_iattr;
        ps_iattrs->ia_ctime = ps_iattrs->ia_mtime = CURRENT_TIME;
    }

    return 0;
}

static char *sysfs_pathname(struct sysfs_dirent *sd, char *path)
{
    if (sd->s_parent) {
        sysfs_pathname(sd->s_parent, path);
        strlcat(path, "/", PATH_MAX);
    }
    strlcat(path, sd->s_name, PATH_MAX);
    return path;
}

int sysfs_add_one(struct sysfs_addrm_cxt *acxt, struct sysfs_dirent *sd)
{
    int ret;

    ret = __sysfs_add_one(acxt, sd);
    if (ret == -EEXIST) {
        char *path = kzalloc(PATH_MAX, GFP_KERNEL);
        WARN(1, KERN_WARNING
             "sysfs: cannot create duplicate filename '%s'\n",
             (path == NULL) ? sd->s_name
                    : (sysfs_pathname(acxt->parent_sd, path),
                       strlcat(path, "/", PATH_MAX),
                       strlcat(path, sd->s_name, PATH_MAX),
                       path));
        kfree(path);
    }

    return ret;
}

void sysfs_remove_one(struct sysfs_addrm_cxt *acxt, struct sysfs_dirent *sd)
{
    struct sysfs_inode_attrs *ps_iattr;

    BUG_ON(sd->s_flags & SYSFS_FLAG_REMOVED);

    sysfs_unlink_sibling(sd);

    /* Update timestamps on the parent */
    ps_iattr = acxt->parent_sd->s_iattr;
    if (ps_iattr) {
        struct iattr *ps_iattrs = &ps_iattr->ia_iattr;
        ps_iattrs->ia_ctime = ps_iattrs->ia_mtime = CURRENT_TIME;
    }

    sd->s_flags |= SYSFS_FLAG_REMOVED;
    sd->u.removed_list = acxt->removed;
    acxt->removed = sd;
}

void sysfs_addrm_finish(struct sysfs_addrm_cxt *acxt)
{
    /* release resources acquired by sysfs_addrm_start() */
    mutex_unlock(&sysfs_mutex);

    /* kill removed sysfs_dirents */
    while (acxt->removed) {
        struct sysfs_dirent *sd = acxt->removed;

        acxt->removed = sd->u.removed_list;

        sysfs_deactivate(sd);
        unmap_bin_file(sd);
        sysfs_put(sd);
    }
}

struct sysfs_dirent *sysfs_find_dirent(struct sysfs_dirent *parent_sd,
                       const void *ns,
                       const unsigned char *name)
{
    struct rb_node *node = parent_sd->s_dir.children.rb_node;
    unsigned int hash;

    if (!!sysfs_ns_type(parent_sd) != !!ns) {
        WARN(1, KERN_WARNING "sysfs: ns %s in '%s' for '%s'\n",
            sysfs_ns_type(parent_sd)? "required": "invalid",
            parent_sd->s_name, name);
        return NULL;
    }

    hash = sysfs_name_hash(ns, name);
    while (node) {
        struct sysfs_dirent *sd;
        int result;

        sd = to_sysfs_dirent(node);
        result = sysfs_name_compare(hash, ns, name, sd);
        if (result < 0)
            node = node->rb_left;
        else if (result > 0)
            node = node->rb_right;
        else
            return sd;
    }
    return NULL;
}

struct sysfs_dirent *sysfs_get_dirent(struct sysfs_dirent *parent_sd,
                      const void *ns,
                      const unsigned char *name)
{
    struct sysfs_dirent *sd;

    mutex_lock(&sysfs_mutex);
    sd = sysfs_find_dirent(parent_sd, ns, name);
    sysfs_get(sd);
    mutex_unlock(&sysfs_mutex);

    return sd;
}
EXPORT_SYMBOL_GPL(sysfs_get_dirent);

static int create_dir(struct kobject *kobj, struct sysfs_dirent *parent_sd,
    enum kobj_ns_type type, const void *ns, const char *name,
    struct sysfs_dirent **p_sd)
{
    umode_t mode = S_IFDIR| S_IRWXU | S_IRUGO | S_IXUGO;
    struct sysfs_addrm_cxt acxt;
    struct sysfs_dirent *sd;
    int rc;

    /* allocate */
    sd = sysfs_new_dirent(name, mode, SYSFS_DIR);
    if (!sd)
        return -ENOMEM;

    sd->s_flags |= (type << SYSFS_NS_TYPE_SHIFT);
    sd->s_ns = ns;
    sd->s_dir.kobj = kobj;

    /* link in */
    sysfs_addrm_start(&acxt, parent_sd);
    rc = sysfs_add_one(&acxt, sd);
    sysfs_addrm_finish(&acxt);

    if (rc == 0)
        *p_sd = sd;
    else
        sysfs_put(sd);

    return rc;
}

int sysfs_create_subdir(struct kobject *kobj, const char *name,
            struct sysfs_dirent **p_sd)
{
    return create_dir(kobj, kobj->sd,
              KOBJ_NS_TYPE_NONE, NULL, name, p_sd);
}

static enum kobj_ns_type sysfs_read_ns_type(struct kobject *kobj)
{
    const struct kobj_ns_type_operations *ops;
    enum kobj_ns_type type;

    ops = kobj_child_ns_ops(kobj);
    if (!ops)
        return KOBJ_NS_TYPE_NONE;

    type = ops->type;
    BUG_ON(type <= KOBJ_NS_TYPE_NONE);
    BUG_ON(type >= KOBJ_NS_TYPES);
    BUG_ON(!kobj_ns_type_registered(type));

    return type;
}

int sysfs_create_dir(struct kobject * kobj)
{
    enum kobj_ns_type type;
    struct sysfs_dirent *parent_sd, *sd;
    const void *ns = NULL;
    int error = 0;

    BUG_ON(!kobj);

    if (kobj->parent)
        parent_sd = kobj->parent->sd;
    else
        parent_sd = &sysfs_root;

    if (!parent_sd)
        return -ENOENT;

    if (sysfs_ns_type(parent_sd))
        ns = kobj->ktype->namespace(kobj);
    type = sysfs_read_ns_type(kobj);

    error = create_dir(kobj, parent_sd, type, ns, kobject_name(kobj), &sd);
    if (!error)
        kobj->sd = sd;
    return error;
}

static struct dentry * sysfs_lookup(struct inode *dir, struct dentry *dentry,
                unsigned int flags)
{
    struct dentry *ret = NULL;
    struct dentry *parent = dentry->d_parent;
    struct sysfs_dirent *parent_sd = parent->d_fsdata;
    struct sysfs_dirent *sd;
    struct inode *inode;
    enum kobj_ns_type type;
    const void *ns;

    mutex_lock(&sysfs_mutex);

    type = sysfs_ns_type(parent_sd);
    ns = sysfs_info(dir->i_sb)->ns[type];

    sd = sysfs_find_dirent(parent_sd, ns, dentry->d_name.name);

    /* no such entry */
    if (!sd) {
        ret = ERR_PTR(-ENOENT);
        goto out_unlock;
    }
    dentry->d_fsdata = sysfs_get(sd);

    /* attach dentry and inode */
    inode = sysfs_get_inode(dir->i_sb, sd);
    if (!inode) {
        ret = ERR_PTR(-ENOMEM);
        goto out_unlock;
    }

    /* instantiate and hash dentry */
    ret = d_materialise_unique(dentry, inode);
 out_unlock:
    mutex_unlock(&sysfs_mutex);
    return ret;
}

const struct inode_operations sysfs_dir_inode_operations = {
    .lookup     = sysfs_lookup,
    .permission = sysfs_permission,
    .setattr    = sysfs_setattr,
    .getattr    = sysfs_getattr,
    .setxattr   = sysfs_setxattr,
};

static void remove_dir(struct sysfs_dirent *sd)
{
    struct sysfs_addrm_cxt acxt;

    sysfs_addrm_start(&acxt, sd->s_parent);
    sysfs_remove_one(&acxt, sd);
    sysfs_addrm_finish(&acxt);
}

void sysfs_remove_subdir(struct sysfs_dirent *sd)
{
    remove_dir(sd);
}


static void __sysfs_remove_dir(struct sysfs_dirent *dir_sd)
{
    struct sysfs_addrm_cxt acxt;
    struct rb_node *pos;

    if (!dir_sd)
        return;

    pr_debug("sysfs %s: removing dir\n", dir_sd->s_name);
    sysfs_addrm_start(&acxt, dir_sd);
    pos = rb_first(&dir_sd->s_dir.children);
    while (pos) {
        struct sysfs_dirent *sd = to_sysfs_dirent(pos);
        pos = rb_next(pos);
        if (sysfs_type(sd) != SYSFS_DIR)
            sysfs_remove_one(&acxt, sd);
    }
    sysfs_addrm_finish(&acxt);

    remove_dir(dir_sd);
}

void sysfs_remove_dir(struct kobject * kobj)
{
    struct sysfs_dirent *sd = kobj->sd;

    spin_lock(&sysfs_assoc_lock);
    kobj->sd = NULL;
    spin_unlock(&sysfs_assoc_lock);

    __sysfs_remove_dir(sd);
}

int sysfs_rename(struct sysfs_dirent *sd,
    struct sysfs_dirent *new_parent_sd, const void *new_ns,
    const char *new_name)
{
    int error;

    mutex_lock(&sysfs_mutex);

    error = 0;
    if ((sd->s_parent == new_parent_sd) && (sd->s_ns == new_ns) &&
        (strcmp(sd->s_name, new_name) == 0))
        goto out;   /* nothing to rename */

    error = -EEXIST;
    if (sysfs_find_dirent(new_parent_sd, new_ns, new_name))
        goto out;

    /* rename sysfs_dirent */
    if (strcmp(sd->s_name, new_name) != 0) {
        error = -ENOMEM;
        new_name = kstrdup(new_name, GFP_KERNEL);
        if (!new_name)
            goto out;

        kfree(sd->s_name);
        sd->s_name = new_name;
    }

    /* Move to the appropriate place in the appropriate directories rbtree. */
    sysfs_unlink_sibling(sd);
    sysfs_get(new_parent_sd);
    sysfs_put(sd->s_parent);
    sd->s_ns = new_ns;
    sd->s_hash = sysfs_name_hash(sd->s_ns, sd->s_name);
    sd->s_parent = new_parent_sd;
    sysfs_link_sibling(sd);

    error = 0;
 out:
    mutex_unlock(&sysfs_mutex);
    return error;
}

int sysfs_rename_dir(struct kobject *kobj, const char *new_name)
{
    struct sysfs_dirent *parent_sd = kobj->sd->s_parent;
    const void *new_ns = NULL;

    if (sysfs_ns_type(parent_sd))
        new_ns = kobj->ktype->namespace(kobj);

    return sysfs_rename(kobj->sd, parent_sd, new_ns, new_name);
}

int sysfs_move_dir(struct kobject *kobj, struct kobject *new_parent_kobj)
{
    struct sysfs_dirent *sd = kobj->sd;
    struct sysfs_dirent *new_parent_sd;
    const void *new_ns = NULL;

    BUG_ON(!sd->s_parent);
    if (sysfs_ns_type(sd->s_parent))
        new_ns = kobj->ktype->namespace(kobj);
    new_parent_sd = new_parent_kobj && new_parent_kobj->sd ?
        new_parent_kobj->sd : &sysfs_root;

    return sysfs_rename(sd, new_parent_sd, new_ns, sd->s_name);
}

/* Relationship between s_mode and the DT_xxx types */
static inline unsigned char dt_type(struct sysfs_dirent *sd)
{
    return (sd->s_mode >> 12) & 15;
}

static int sysfs_dir_release(struct inode *inode, struct file *filp)
{
    sysfs_put(filp->private_data);
    return 0;
}

static struct sysfs_dirent *sysfs_dir_pos(const void *ns,
    struct sysfs_dirent *parent_sd, loff_t hash, struct sysfs_dirent *pos)
{
    if (pos) {
        int valid = !(pos->s_flags & SYSFS_FLAG_REMOVED) &&
            pos->s_parent == parent_sd &&
            hash == pos->s_hash;
        sysfs_put(pos);
        if (!valid)
            pos = NULL;
    }
    if (!pos && (hash > 1) && (hash < INT_MAX)) {
        struct rb_node *node = parent_sd->s_dir.children.rb_node;
        while (node) {
            pos = to_sysfs_dirent(node);

            if (hash < pos->s_hash)
                node = node->rb_left;
            else if (hash > pos->s_hash)
                node = node->rb_right;
            else
                break;
        }
    }
    /* Skip over entries in the wrong namespace */
    while (pos && pos->s_ns != ns) {
        struct rb_node *node = rb_next(&pos->s_rb);
        if (!node)
            pos = NULL;
        else
            pos = to_sysfs_dirent(node);
    }
    return pos;
}

static struct sysfs_dirent *sysfs_dir_next_pos(const void *ns,
    struct sysfs_dirent *parent_sd, ino_t ino, struct sysfs_dirent *pos)
{
    pos = sysfs_dir_pos(ns, parent_sd, ino, pos);
    if (pos) do {
        struct rb_node *node = rb_next(&pos->s_rb);
        if (!node)
            pos = NULL;
        else
            pos = to_sysfs_dirent(node);
    } while (pos && pos->s_ns != ns);
    return pos;
}

static int sysfs_readdir(struct file * filp, void * dirent, filldir_t filldir)
{
    struct dentry *dentry = filp->f_path.dentry;
    struct sysfs_dirent * parent_sd = dentry->d_fsdata;
    struct sysfs_dirent *pos = filp->private_data;
    enum kobj_ns_type type;
    const void *ns;
    ino_t ino;

    type = sysfs_ns_type(parent_sd);
    ns = sysfs_info(dentry->d_sb)->ns[type];

    if (filp->f_pos == 0) {
        ino = parent_sd->s_ino;
        if (filldir(dirent, ".", 1, filp->f_pos, ino, DT_DIR) == 0)
            filp->f_pos++;
    }
    if (filp->f_pos == 1) {
        if (parent_sd->s_parent)
            ino = parent_sd->s_parent->s_ino;
        else
            ino = parent_sd->s_ino;
        if (filldir(dirent, "..", 2, filp->f_pos, ino, DT_DIR) == 0)
            filp->f_pos++;
    }
    mutex_lock(&sysfs_mutex);
    for (pos = sysfs_dir_pos(ns, parent_sd, filp->f_pos, pos);
         pos;
         pos = sysfs_dir_next_pos(ns, parent_sd, filp->f_pos, pos)) {
        const char * name;
        unsigned int type;
        int len, ret;

        name = pos->s_name;
        len = strlen(name);
        ino = pos->s_ino;
        type = dt_type(pos);
        filp->f_pos = pos->s_hash;
        filp->private_data = sysfs_get(pos);

        mutex_unlock(&sysfs_mutex);
        ret = filldir(dirent, name, len, filp->f_pos, ino, type);
        mutex_lock(&sysfs_mutex);
        if (ret < 0)
            break;
    }
    mutex_unlock(&sysfs_mutex);
    if ((filp->f_pos > 1) && !pos) { /* EOF */
        filp->f_pos = INT_MAX;
        filp->private_data = NULL;
    }
    return 0;
}


const struct file_operations sysfs_dir_operations = {
    .read       = generic_read_dir,
    .readdir    = sysfs_readdir,
    .release    = sysfs_dir_release,
    .llseek     = generic_file_llseek,
};