sysfs, kernfs: introduce kernfs_remove[_by_name[_ns]]()

[deliverable/linux.git] / fs / sysfs / dir.c

/*
 * 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 <teheo@suse.de>
 *
 * 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_symlink_target_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);

/**
 *      sysfs_name_hash
 *      @name: Null terminated string to hash
 *      @ns:   Namespace tag to hash
 *
 *      Returns 31 bit hash of ns + name (so it fits in an off_t )
 */
static unsigned int sysfs_name_hash(const char *name, const void *ns)
{
        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 char *name,
                              const void *ns, 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_name, left->s_ns,
                                  right);
}

/**
 *      sysfs_link_sibling - link sysfs_dirent into sibling rbtree
 *      @sd: sysfs_dirent of interest
 *
 *      Link @sd into its sibling rbtree which starts from
 *      sd->s_parent->s_dir.children.
 *
 *      Locking:
 *      mutex_lock(sysfs_mutex)
 *
 *      RETURNS:
 *      0 on susccess -EEXIST on failure.
 */
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;
}

/**
 *      sysfs_unlink_sibling - unlink sysfs_dirent from sibling rbtree
 *      @sd: sysfs_dirent of interest
 *
 *      Unlink @sd from its sibling rbtree which starts from
 *      sd->s_parent->s_dir.children.
 *
 *      Locking:
 *      mutex_lock(sysfs_mutex)
 */
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);
}

/**
 *      sysfs_get_active - get an active reference to sysfs_dirent
 *      @sd: sysfs_dirent to get an active reference to
 *
 *      Get an active reference of @sd.  This function is noop if @sd
 *      is NULL.
 *
 *      RETURNS:
 *      Pointer to @sd on success, NULL on failure.
 */
struct sysfs_dirent *sysfs_get_active(struct sysfs_dirent *sd)
{
        if (unlikely(!sd))
                return NULL;

        if (!atomic_inc_unless_negative(&sd->s_active))
                return NULL;

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

/**
 *      sysfs_put_active - put an active reference to sysfs_dirent
 *      @sd: sysfs_dirent to put an active reference to
 *
 *      Put an active reference to @sd.  This function is noop if @sd
 *      is NULL.
 */
void sysfs_put_active(struct sysfs_dirent *sd)
{
        int v;

        if (unlikely(!sd))
                return;

        if (likely(!sysfs_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);
}

/**
 *      sysfs_deactivate - deactivate sysfs_dirent
 *      @sd: sysfs_dirent to deactivate
 *
 *      Deny new active references and drain existing ones.
 */
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;

        WARN(!(sd->s_flags & SYSFS_FLAG_REMOVED),
                "sysfs: free using entry: %s/%s\n",
                parent_sd ? parent_sd->s_name : "", sd->s_name);

        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;

        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 */
        if (sd->s_parent && (sd->s_parent->s_flags & SYSFS_FLAG_NS) &&
            sysfs_info(dentry->d_sb)->ns != 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.
         */
        mutex_unlock(&sysfs_mutex);

        /* 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 (check_submounts_and_drop(dentry) != 0)
                goto out_valid;

        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 | SYSFS_FLAG_REMOVED;

        return sd;

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

/**
 *      sysfs_addrm_start - prepare for sysfs_dirent add/remove
 *      @acxt: pointer to sysfs_addrm_cxt to be used
 *
 *      This function is called when the caller is about to add or remove
 *      sysfs_dirent.  This function acquires sysfs_mutex.  @acxt is used
 *      to keep and pass context to other addrm functions.
 *
 *      LOCKING:
 *      Kernel thread context (may sleep).  sysfs_mutex is locked on
 *      return.
 */
void sysfs_addrm_start(struct sysfs_addrm_cxt *acxt)
        __acquires(sysfs_mutex)
{
        memset(acxt, 0, sizeof(*acxt));

        mutex_lock(&sysfs_mutex);
}

/**
 *      __sysfs_add_one - add sysfs_dirent to parent without warning
 *      @acxt: addrm context to use
 *      @sd: sysfs_dirent to be added
 *      @parent_sd: the parent sysfs_dirent to add @sd to
 *
 *      Get @parent_sd and set @sd->s_parent to it and increment nlink of
 *      the parent inode if @sd is a directory and link into the children
 *      list of the parent.
 *
 *      This function should be called between calls to
 *      sysfs_addrm_start() and sysfs_addrm_finish() and should be
 *      passed the same @acxt as passed to sysfs_addrm_start().
 *
 *      LOCKING:
 *      Determined by sysfs_addrm_start().
 *
 *      RETURNS:
 *      0 on success, -EEXIST if entry with the given name already
 *      exists.
 */
int __sysfs_add_one(struct sysfs_addrm_cxt *acxt, struct sysfs_dirent *sd,
                    struct sysfs_dirent *parent_sd)
{
        bool has_ns = parent_sd->s_flags & SYSFS_FLAG_NS;
        struct sysfs_inode_attrs *ps_iattr;
        int ret;

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

        if (sysfs_type(parent_sd) != SYSFS_DIR)
                return -EINVAL;

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

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

        /* Update timestamps on the parent */
        ps_iattr = 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;
        }

        /* Mark the entry added into directory tree */
        sd->s_flags &= ~SYSFS_FLAG_REMOVED;

        return 0;
}

/**
 *      sysfs_pathname - return full path to sysfs dirent
 *      @sd: sysfs_dirent whose path we want
 *      @path: caller allocated buffer of size PATH_MAX
 *
 *      Gives the name "/" to the sysfs_root entry; any path returned
 *      is relative to wherever sysfs is mounted.
 */
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;
}

void sysfs_warn_dup(struct sysfs_dirent *parent, const char *name)
{
        char *path;

        path = kzalloc(PATH_MAX, GFP_KERNEL);
        if (path) {
                sysfs_pathname(parent, path);
                strlcat(path, "/", PATH_MAX);
                strlcat(path, name, PATH_MAX);
        }

        WARN(1, KERN_WARNING "sysfs: cannot create duplicate filename '%s'\n",
             path ? path : name);

        kfree(path);
}

/**
 *      sysfs_add_one - add sysfs_dirent to parent
 *      @acxt: addrm context to use
 *      @sd: sysfs_dirent to be added
 *      @parent_sd: the parent sysfs_dirent to add @sd to
 *
 *      Get @parent_sd and set @sd->s_parent to it and increment nlink of
 *      the parent inode if @sd is a directory and link into the children
 *      list of the parent.
 *
 *      This function should be called between calls to
 *      sysfs_addrm_start() and sysfs_addrm_finish() and should be
 *      passed the same @acxt as passed to sysfs_addrm_start().
 *
 *      LOCKING:
 *      Determined by sysfs_addrm_start().
 *
 *      RETURNS:
 *      0 on success, -EEXIST if entry with the given name already
 *      exists.
 */
int sysfs_add_one(struct sysfs_addrm_cxt *acxt, struct sysfs_dirent *sd,
                  struct sysfs_dirent *parent_sd)
{
        int ret;

        ret = __sysfs_add_one(acxt, sd, parent_sd);

        if (ret == -EEXIST)
                sysfs_warn_dup(parent_sd, sd->s_name);
        return ret;
}

/**
 *      sysfs_remove_one - remove sysfs_dirent from parent
 *      @acxt: addrm context to use
 *      @sd: sysfs_dirent to be removed
 *
 *      Mark @sd removed and drop nlink of parent inode if @sd is a
 *      directory.  @sd is unlinked from the children list.
 *
 *      This function should be called between calls to
 *      sysfs_addrm_start() and sysfs_addrm_finish() and should be
 *      passed the same @acxt as passed to sysfs_addrm_start().
 *
 *      LOCKING:
 *      Determined by sysfs_addrm_start().
 */
static void sysfs_remove_one(struct sysfs_addrm_cxt *acxt,
                             struct sysfs_dirent *sd)
{
        struct sysfs_inode_attrs *ps_iattr;

        /*
         * Removal can be called multiple times on the same node.  Only the
         * first invocation is effective and puts the base ref.
         */
        if (sd->s_flags & SYSFS_FLAG_REMOVED)
                return;

        sysfs_unlink_sibling(sd);

        /* Update timestamps on the parent */
        ps_iattr = sd->s_parent->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;
}

/**
 *      sysfs_addrm_finish - finish up sysfs_dirent add/remove
 *      @acxt: addrm context to finish up
 *
 *      Finish up sysfs_dirent add/remove.  Resources acquired by
 *      sysfs_addrm_start() are released and removed sysfs_dirents are
 *      cleaned up.
 *
 *      LOCKING:
 *      sysfs_mutex is released.
 */
void sysfs_addrm_finish(struct sysfs_addrm_cxt *acxt)
        __releases(sysfs_mutex)
{
        /* 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);
                sysfs_unmap_bin_file(sd);
                sysfs_put(sd);
        }
}

/**
 *      sysfs_find_dirent - find sysfs_dirent with the given name
 *      @parent_sd: sysfs_dirent to search under
 *      @name: name to look for
 *      @ns: the namespace tag to use
 *
 *      Look for sysfs_dirent with name @name under @parent_sd.
 *
 *      LOCKING:
 *      mutex_lock(sysfs_mutex)
 *
 *      RETURNS:
 *      Pointer to sysfs_dirent if found, NULL if not.
 */
struct sysfs_dirent *sysfs_find_dirent(struct sysfs_dirent *parent_sd,
                                       const unsigned char *name,
                                       const void *ns)
{
        struct rb_node *node = parent_sd->s_dir.children.rb_node;
        bool has_ns = parent_sd->s_flags & SYSFS_FLAG_NS;
        unsigned int hash;

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

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

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

/**
 *      sysfs_get_dirent_ns - find and get sysfs_dirent with the given name
 *      @parent_sd: sysfs_dirent to search under
 *      @name: name to look for
 *      @ns: the namespace tag to use
 *
 *      Look for sysfs_dirent with name @name under @parent_sd and get
 *      it if found.
 *
 *      LOCKING:
 *      Kernel thread context (may sleep).  Grabs sysfs_mutex.
 *
 *      RETURNS:
 *      Pointer to sysfs_dirent if found, NULL if not.
 */
struct sysfs_dirent *sysfs_get_dirent_ns(struct sysfs_dirent *parent_sd,
                                         const unsigned char *name,
                                         const void *ns)
{
        struct sysfs_dirent *sd;

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

        return sd;
}
EXPORT_SYMBOL_GPL(sysfs_get_dirent_ns);

static int create_dir(struct kobject *kobj, struct sysfs_dirent *parent_sd,
                      const char *name, const void *ns,
                      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_ns = ns;
        sd->s_dir.kobj = kobj;

        /* link in */
        sysfs_addrm_start(&acxt);
        rc = sysfs_add_one(&acxt, sd, parent_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, name, NULL, p_sd);
}

/**
 * sysfs_create_dir_ns - create a directory for an object with a namespace tag
 * @kobj: object we're creating directory for
 * @ns: the namespace tag to use
 */
int sysfs_create_dir_ns(struct kobject *kobj, const void *ns)
{
        struct sysfs_dirent *parent_sd, *sd;
        int error = 0;

        BUG_ON(!kobj);

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

        if (!parent_sd)
                return -ENOENT;

        error = create_dir(kobj, parent_sd, kobject_name(kobj), ns, &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;
        const void *ns = NULL;

        mutex_lock(&sysfs_mutex);

        if (parent_sd->s_flags & SYSFS_FLAG_NS)
                ns = sysfs_info(dir->i_sb)->ns;

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

        /* 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 struct sysfs_dirent *sysfs_leftmost_descendant(struct sysfs_dirent *pos)
{
        struct sysfs_dirent *last;

        while (true) {
                struct rb_node *rbn;

                last = pos;

                if (sysfs_type(pos) != SYSFS_DIR)
                        break;

                rbn = rb_first(&pos->s_dir.children);
                if (!rbn)
                        break;

                pos = to_sysfs_dirent(rbn);
        }

        return last;
}

/**
 * sysfs_next_descendant_post - find the next descendant for post-order walk
 * @pos: the current position (%NULL to initiate traversal)
 * @root: sysfs_dirent whose descendants to walk
 *
 * Find the next descendant to visit for post-order traversal of @root's
 * descendants.  @root is included in the iteration and the last node to be
 * visited.
 */
static struct sysfs_dirent *sysfs_next_descendant_post(struct sysfs_dirent *pos,
                                                       struct sysfs_dirent *root)
{
        struct rb_node *rbn;

        lockdep_assert_held(&sysfs_mutex);

        /* if first iteration, visit leftmost descendant which may be root */
        if (!pos)
                return sysfs_leftmost_descendant(root);

        /* if we visited @root, we're done */
        if (pos == root)
                return NULL;

        /* if there's an unvisited sibling, visit its leftmost descendant */
        rbn = rb_next(&pos->s_rb);
        if (rbn)
                return sysfs_leftmost_descendant(to_sysfs_dirent(rbn));

        /* no sibling left, visit parent */
        return pos->s_parent;
}

static void __kernfs_remove(struct sysfs_addrm_cxt *acxt,
                            struct sysfs_dirent *sd)
{
        struct sysfs_dirent *pos, *next;

        if (!sd)
                return;

        pr_debug("sysfs %s: removing\n", sd->s_name);

        next = NULL;
        do {
                pos = next;
                next = sysfs_next_descendant_post(pos, sd);
                if (pos)
                        sysfs_remove_one(acxt, pos);
        } while (next);
}

/**
 * kernfs_remove - remove a sysfs_dirent recursively
 * @sd: the sysfs_dirent to remove
 *
 * Remove @sd along with all its subdirectories and files.
 */
void kernfs_remove(struct sysfs_dirent *sd)
{
        struct sysfs_addrm_cxt acxt;

        sysfs_addrm_start(&acxt);
        __kernfs_remove(&acxt, sd);
        sysfs_addrm_finish(&acxt);
}

/**
 * kernfs_remove_by_name_ns - find a sysfs_dirent by name and remove it
 * @dir_sd: parent of the target
 * @name: name of the sysfs_dirent to remove
 * @ns: namespace tag of the sysfs_dirent to remove
 *
 * Look for the sysfs_dirent with @name and @ns under @dir_sd and remove
 * it.  Returns 0 on success, -ENOENT if such entry doesn't exist.
 */
int kernfs_remove_by_name_ns(struct sysfs_dirent *dir_sd, const char *name,
                             const void *ns)
{
        struct sysfs_addrm_cxt acxt;
        struct sysfs_dirent *sd;

        if (!dir_sd) {
                WARN(1, KERN_WARNING "sysfs: can not remove '%s', no directory\n",
                        name);
                return -ENOENT;
        }

        sysfs_addrm_start(&acxt);

        sd = sysfs_find_dirent(dir_sd, name, ns);
        if (sd)
                __kernfs_remove(&acxt, sd);

        sysfs_addrm_finish(&acxt);

        if (sd)
                return 0;
        else
                return -ENOENT;
}

/**
 *      sysfs_remove_dir - remove an object's directory.
 *      @kobj:  object.
 *
 *      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 sysfs_rmdir() below, instead of calling separately.
 */
void sysfs_remove_dir(struct kobject *kobj)
{
        struct sysfs_dirent *sd = kobj->sd;

        /*
         * In general, kboject owner is responsible for ensuring removal
         * doesn't race with other operations and sysfs doesn't provide any
         * protection; however, when @kobj is used as a symlink target, the
         * symlinking entity usually doesn't own @kobj and thus has no
         * control over removal.  @kobj->sd may be removed anytime and
         * symlink code may end up dereferencing an already freed sd.
         *
         * sysfs_symlink_target_lock synchronizes @kobj->sd disassociation
         * against symlink operations so that symlink code can safely
         * dereference @kobj->sd.
         */
        spin_lock(&sysfs_symlink_target_lock);
        kobj->sd = NULL;
        spin_unlock(&sysfs_symlink_target_lock);

        if (sd) {
                WARN_ON_ONCE(sysfs_type(sd) != SYSFS_DIR);
                kernfs_remove(sd);
        }
}

int sysfs_rename(struct sysfs_dirent *sd, struct sysfs_dirent *new_parent_sd,
                 const char *new_name, const void *new_ns)
{
        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_name, new_ns))
                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_name, sd->s_ns);
        sd->s_parent = new_parent_sd;
        sysfs_link_sibling(sd);

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

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

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

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

        BUG_ON(!sd->s_parent);
        new_parent_sd = new_parent_kobj && new_parent_kobj->sd ?
                new_parent_kobj->sd : &sysfs_root;

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

/**
 * sysfs_enable_ns - enable namespace under a directory
 * @sd: directory of interest, should be empty
 *
 * This is to be called right after @sd is created to enable namespace
 * under it.  All children of @sd must have non-NULL namespace tags and
 * only the ones which match the super_block's tag will be visible.
 */
void sysfs_enable_ns(struct sysfs_dirent *sd)
{
        WARN_ON_ONCE(sysfs_type(sd) != SYSFS_DIR);
        WARN_ON_ONCE(!RB_EMPTY_ROOT(&sd->s_dir.children));
        sd->s_flags |= SYSFS_FLAG_NS;
}

/* 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 *file, struct dir_context *ctx)
{
        struct dentry *dentry = file->f_path.dentry;
        struct sysfs_dirent *parent_sd = dentry->d_fsdata;
        struct sysfs_dirent *pos = file->private_data;
        const void *ns = NULL;

        if (!dir_emit_dots(file, ctx))
                return 0;
        mutex_lock(&sysfs_mutex);

        if (parent_sd->s_flags & SYSFS_FLAG_NS)
                ns = sysfs_info(dentry->d_sb)->ns;

        for (pos = sysfs_dir_pos(ns, parent_sd, ctx->pos, pos);
             pos;
             pos = sysfs_dir_next_pos(ns, parent_sd, ctx->pos, pos)) {
                const char *name = pos->s_name;
                unsigned int type = dt_type(pos);
                int len = strlen(name);
                ino_t ino = pos->s_ino;
                ctx->pos = pos->s_hash;
                file->private_data = sysfs_get(pos);

                mutex_unlock(&sysfs_mutex);
                if (!dir_emit(ctx, name, len, ino, type))
                        return 0;
                mutex_lock(&sysfs_mutex);
        }
        mutex_unlock(&sysfs_mutex);
        file->private_data = NULL;
        ctx->pos = INT_MAX;
        return 0;
}

static loff_t sysfs_dir_llseek(struct file *file, loff_t offset, int whence)
{
        struct inode *inode = file_inode(file);
        loff_t ret;

        mutex_lock(&inode->i_mutex);
        ret = generic_file_llseek(file, offset, whence);
        mutex_unlock(&inode->i_mutex);

        return ret;
}

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