+/**
+ * sysfs_link_sibling - link sysfs_dirent into sibling list
+ * @sd: sysfs_dirent of interest
+ *
+ * Link @sd into its sibling list which starts from
+ * sd->s_parent->s_dir.children.
+ *
+ * Locking:
+ * mutex_lock(sysfs_mutex)
+ */
+static void sysfs_link_sibling(struct sysfs_dirent *sd)
+{
+ struct sysfs_dirent *parent_sd = sd->s_parent;
+ struct sysfs_dirent **pos;
+
+ BUG_ON(sd->s_sibling);
+
+ /* Store directory entries in order by ino. This allows
+ * readdir to properly restart without having to add a
+ * cursor into the s_dir.children list.
+ */
+ for (pos = &parent_sd->s_dir.children; *pos; pos = &(*pos)->s_sibling) {
+ if (sd->s_ino < (*pos)->s_ino)
+ break;
+ }
+ sd->s_sibling = *pos;
+ *pos = sd;
+}
+
+/**
+ * sysfs_unlink_sibling - unlink sysfs_dirent from sibling list
+ * @sd: sysfs_dirent of interest
+ *
+ * Unlink @sd from its sibling list which starts from
+ * sd->s_parent->s_dir.children.
+ *
+ * Locking:
+ * mutex_lock(sysfs_mutex)
+ */
+static void sysfs_unlink_sibling(struct sysfs_dirent *sd)
+{
+ struct sysfs_dirent **pos;
+
+ for (pos = &sd->s_parent->s_dir.children; *pos;
+ pos = &(*pos)->s_sibling) {
+ if (*pos == sd) {
+ *pos = sd->s_sibling;
+ sd->s_sibling = NULL;
+ break;
+ }
+ }
+}
+
+/**
+ * sysfs_get_dentry - get dentry for the given sysfs_dirent
+ * @sd: sysfs_dirent of interest
+ *
+ * Get dentry for @sd. Dentry is looked up if currently not
+ * present. This function descends from the root looking up
+ * dentry for each step.
+ *
+ * LOCKING:
+ * mutex_lock(sysfs_rename_mutex)
+ *
+ * RETURNS:
+ * Pointer to found dentry on success, ERR_PTR() value on error.
+ */
+struct dentry *sysfs_get_dentry(struct sysfs_dirent *sd)
+{
+ struct dentry *dentry = dget(sysfs_sb->s_root);
+
+ while (dentry->d_fsdata != sd) {
+ struct sysfs_dirent *cur;
+ struct dentry *parent;
+
+ /* find the first ancestor which hasn't been looked up */
+ cur = sd;
+ while (cur->s_parent != dentry->d_fsdata)
+ cur = cur->s_parent;
+
+ /* look it up */
+ parent = dentry;
+ mutex_lock(&parent->d_inode->i_mutex);
+ dentry = lookup_one_noperm(cur->s_name, parent);
+ mutex_unlock(&parent->d_inode->i_mutex);
+ dput(parent);
+
+ if (IS_ERR(dentry))
+ break;
+ }
+ return dentry;
+}
+
+/**
+ * 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.
+ */
+static 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))
+ return sd;
+ if (t < 0)
+ return NULL;
+
+ cpu_relax();
+ }
+}
+
+/**
+ * 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.
+ */
+static void sysfs_put_active(struct sysfs_dirent *sd)
+{
+ struct completion *cmpl;
+ int v;
+
+ if (unlikely(!sd))
+ return;
+
+ 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->s_sibling.
+ */
+ cmpl = (void *)sd->s_sibling;
+ complete(cmpl);
+}
+
+/**
+ * sysfs_get_active_two - get active references to sysfs_dirent and parent
+ * @sd: sysfs_dirent of interest
+ *
+ * Get active reference to @sd and its parent. Parent's active
+ * reference is grabbed first. This function is noop if @sd is
+ * NULL.
+ *
+ * RETURNS:
+ * Pointer to @sd on success, NULL on failure.
+ */
+struct sysfs_dirent *sysfs_get_active_two(struct sysfs_dirent *sd)
+{
+ if (sd) {
+ if (sd->s_parent && unlikely(!sysfs_get_active(sd->s_parent)))
+ return NULL;
+ if (unlikely(!sysfs_get_active(sd))) {
+ sysfs_put_active(sd->s_parent);
+ return NULL;
+ }
+ }
+ return sd;
+}
+
+/**
+ * sysfs_put_active_two - put active references to sysfs_dirent and parent
+ * @sd: sysfs_dirent of interest
+ *
+ * Put active references to @sd and its parent. This function is
+ * noop if @sd is NULL.
+ */
+void sysfs_put_active_two(struct sysfs_dirent *sd)
+{
+ if (sd) {
+ sysfs_put_active(sd);
+ sysfs_put_active(sd->s_parent);
+ }
+}
+
+/**
+ * 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_sibling || !(sd->s_flags & SYSFS_FLAG_REMOVED));
+ sd->s_sibling = (void *)&wait;
+
+ /* atomic_add_return() is a mb(), put_active() will always see
+ * the updated sd->s_sibling.
+ */
+ v = atomic_add_return(SD_DEACTIVATED_BIAS, &sd->s_active);
+
+ if (v != SD_DEACTIVATED_BIAS)
+ wait_for_completion(&wait);
+
+ sd->s_sibling = NULL;
+}
+