sysfs, kernfs: move dir core code to fs/kernfs/dir.c

Move core dir code to fs/kernfs/dir.c.  fs/sysfs/dir.c now only
contains sysfs_warn_dup() and sysfs wrappers around kernfs interfaces.
The respective declarations in fs/sysfs/sysfs.h are moved to
fs/kernfs/kernfs-internal.h.

This is pure relocation.

v2: sysfs_symlink_target_lock was mistakenly relocated to kernfs.  It
    should remain with sysfs.  Fixed.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

2 files changed, 1005 insertions, 0 deletions

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index 1061602ce81a..a4ca4de3cb21 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -7,3 +7,991 @@
  *
  * This file is released under the GPLv2.
  */
+
+#include <linux/fs.h>
+#include <linux/namei.h>
+#include <linux/idr.h>
+#include <linux/slab.h>
+#include <linux/security.h>
+#include <linux/hash.h>
+
+#include "kernfs-internal.h"
+
+DEFINE_MUTEX(sysfs_mutex);
+
+#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 (sd->s_flags & SYSFS_FLAG_LOCKDEP)
+                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 (sd->s_flags & SYSFS_FLAG_LOCKDEP)
+                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);
+}
+
+/**
+ * kernfs_get - get a reference count on a sysfs_dirent
+ * @sd: the target sysfs_dirent
+ */
+void kernfs_get(struct sysfs_dirent *sd)
+{
+        if (sd) {
+                WARN_ON(!atomic_read(&sd->s_count));
+                atomic_inc(&sd->s_count);
+        }
+}
+EXPORT_SYMBOL_GPL(kernfs_get);
+
+/**
+ * kernfs_put - put a reference count on a sysfs_dirent
+ * @sd: the target sysfs_dirent
+ *
+ * Put a reference count of @sd and destroy it if it reached zero.
+ */
+void kernfs_put(struct sysfs_dirent *sd)
+{
+        struct sysfs_dirent *parent_sd;
+
+        if (!sd || !atomic_dec_and_test(&sd->s_count))
+                return;
+ 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)
+                kernfs_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;
+}
+EXPORT_SYMBOL_GPL(kernfs_put);
+
+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)
+{
+        kernfs_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 = parent_sd;
+        kernfs_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_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);
+                kernfs_put(sd);
+        }
+}
+
+/**
+ * kernfs_find_ns - find sysfs_dirent with the given name
+ * @parent: 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.  Returns pointer to
+ * the found sysfs_dirent on success, %NULL on failure.
+ */
+static struct sysfs_dirent *kernfs_find_ns(struct sysfs_dirent *parent,
+                                           const unsigned char *name,
+                                           const void *ns)
+{
+        struct rb_node *node = parent->s_dir.children.rb_node;
+        bool has_ns = parent->s_flags & SYSFS_FLAG_NS;
+        unsigned int hash;
+
+        lockdep_assert_held(&sysfs_mutex);
+
+        if (has_ns != (bool)ns) {
+                WARN(1, KERN_WARNING "sysfs: ns %s in '%s' for '%s'\n",
+                     has_ns ? "required" : "invalid",
+                     parent->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;
+}
+
+/**
+ * kernfs_find_and_get_ns - find and get sysfs_dirent with the given name
+ * @parent: 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 and get a reference
+ * if found.  This function may sleep and returns pointer to the found
+ * sysfs_dirent on success, %NULL on failure.
+ */
+struct sysfs_dirent *kernfs_find_and_get_ns(struct sysfs_dirent *parent,
+                                            const char *name, const void *ns)
+{
+        struct sysfs_dirent *sd;
+
+        mutex_lock(&sysfs_mutex);
+        sd = kernfs_find_ns(parent, name, ns);
+        kernfs_get(sd);
+        mutex_unlock(&sysfs_mutex);
+
+        return sd;
+}
+EXPORT_SYMBOL_GPL(kernfs_find_and_get_ns);
+
+/**
+ * kernfs_create_dir_ns - create a directory
+ * @parent: parent in which to create a new directory
+ * @name: name of the new directory
+ * @priv: opaque data associated with the new directory
+ * @ns: optional namespace tag of the directory
+ *
+ * Returns the created node on success, ERR_PTR() value on failure.
+ */
+struct sysfs_dirent *kernfs_create_dir_ns(struct sysfs_dirent *parent,
+                                          const char *name, void *priv,
+                                          const void *ns)
+{
+        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 ERR_PTR(-ENOMEM);
+
+        sd->s_ns = ns;
+        sd->priv = priv;
+
+        /* link in */
+        sysfs_addrm_start(&acxt);
+        rc = sysfs_add_one(&acxt, sd, parent);
+        sysfs_addrm_finish(&acxt);
+
+        if (!rc)
+                return sd;
+
+        kernfs_put(sd);
+        return ERR_PTR(rc);
+}
+
+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 = kernfs_find_ns(parent_sd, dentry->d_name.name, ns);
+
+        /* no such entry */
+        if (!sd) {
+                ret = ERR_PTR(-ENOENT);
+                goto out_unlock;
+        }
+        kernfs_get(sd);
+        dentry->d_fsdata = 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 = kernfs_find_ns(dir_sd, name, ns);
+        if (sd)
+                __kernfs_remove(&acxt, sd);
+
+        sysfs_addrm_finish(&acxt);
+
+        if (sd)
+                return 0;
+        else
+                return -ENOENT;
+}
+
+/**
+ * kernfs_rename_ns - move and rename a kernfs_node
+ * @sd: target node
+ * @new_parent: new parent to put @sd under
+ * @new_name: new name
+ * @new_ns: new namespace tag
+ */
+int kernfs_rename_ns(struct sysfs_dirent *sd, struct sysfs_dirent *new_parent,
+                     const char *new_name, const void *new_ns)
+{
+        int error;
+
+        mutex_lock(&sysfs_mutex);
+
+        error = 0;
+        if ((sd->s_parent == new_parent) && (sd->s_ns == new_ns) &&
+            (strcmp(sd->s_name, new_name) == 0))
+                goto out;       /* nothing to rename */
+
+        error = -EEXIST;
+        if (kernfs_find_ns(new_parent, 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);
+        kernfs_get(new_parent);
+        kernfs_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;
+        sysfs_link_sibling(sd);
+
+        error = 0;
+ out:
+        mutex_unlock(&sysfs_mutex);
+        return error;
+}
+
+/**
+ * kernfs_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 kernfs_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)
+{
+        kernfs_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;
+                kernfs_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 = pos;
+                kernfs_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,
+};
diff --git a/fs/kernfs/kernfs-internal.h b/fs/kernfs/kernfs-internal.h
index 933ac8d5d07a..31f0dbe1881b 100644
--- a/fs/kernfs/kernfs-internal.h
+++ b/fs/kernfs/kernfs-internal.h
@@ -14,6 +14,7 @@
 #include <linux/lockdep.h>
 #include <linux/fs.h>
 #include <linux/rbtree.h>
+#include <linux/mutex.h>
 
 #include <linux/kernfs.h>
 
@@ -125,4 +126,20 @@ int sysfs_setxattr(struct dentry *dentry, const char *name, const void *value,
                    size_t size, int flags);
 int sysfs_inode_init(void);
 
+/*
+ * dir.c
+ */
+extern struct mutex sysfs_mutex;
+extern const struct dentry_operations sysfs_dentry_ops;
+extern const struct file_operations sysfs_dir_operations;
+extern const struct inode_operations sysfs_dir_inode_operations;
+
+struct sysfs_dirent *sysfs_get_active(struct sysfs_dirent *sd);
+void sysfs_put_active(struct sysfs_dirent *sd);
+void sysfs_addrm_start(struct sysfs_addrm_cxt *acxt);
+int sysfs_add_one(struct sysfs_addrm_cxt *acxt, struct sysfs_dirent *sd,
+                  struct sysfs_dirent *parent_sd);
+void sysfs_addrm_finish(struct sysfs_addrm_cxt *acxt);
+struct sysfs_dirent *sysfs_new_dirent(const char *name, umode_t mode, int type);
+
 #endif  /* __KERNFS_INTERNAL_H */