2 files changed, 99 insertions, 0 deletions

diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
index c6f3b697064c..987211296106 100644
--- a/fs/sysfs/dir.c
+++ b/fs/sysfs/dir.c
@@ -63,6 +63,104 @@ void sysfs_unlink_sibling(struct sysfs_dirent *sd)
 }
 
 /**
+ *      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 climbs sysfs_dirent tree till it
+ *      reaches a sysfs_dirent with valid dentry attached and descends
+ *      down from there looking up dentry for each step.
+ *
+ *      LOCKING:
+ *      Kernel thread context (may sleep)
+ *
+ *      RETURNS:
+ *      Pointer to found dentry on success, ERR_PTR() value on error.
+ */
+struct dentry *sysfs_get_dentry(struct sysfs_dirent *sd)
+{
+        struct sysfs_dirent *cur;
+        struct dentry *parent_dentry, *dentry;
+        int i, depth;
+
+        /* Find the first parent which has valid s_dentry and get the
+         * dentry.
+         */
+        mutex_lock(&sysfs_mutex);
+ restart0:
+        spin_lock(&sysfs_assoc_lock);
+ restart1:
+        spin_lock(&dcache_lock);
+
+        dentry = NULL;
+        depth = 0;
+        cur = sd;
+        while (!cur->s_dentry || !cur->s_dentry->d_inode) {
+                if (cur->s_flags & SYSFS_FLAG_REMOVED) {
+                        dentry = ERR_PTR(-ENOENT);
+                        depth = 0;
+                        break;
+                }
+                cur = cur->s_parent;
+                depth++;
+        }
+        if (!IS_ERR(dentry))
+                dentry = dget_locked(cur->s_dentry);
+
+        spin_unlock(&dcache_lock);
+        spin_unlock(&sysfs_assoc_lock);
+
+        /* from the found dentry, look up depth times */
+        while (depth--) {
+                /* find and get depth'th ancestor */
+                for (cur = sd, i = 0; cur && i < depth; i++)
+                        cur = cur->s_parent;
+
+                /* This can happen if tree structure was modified due
+                 * to move/rename.  Restart.
+                 */
+                if (i != depth) {
+                        dput(dentry);
+                        goto restart0;
+                }
+
+                sysfs_get(cur);
+
+                mutex_unlock(&sysfs_mutex);
+
+                /* look it up */
+                parent_dentry = dentry;
+                dentry = lookup_one_len_kern(cur->s_name, parent_dentry,
+                                             strlen(cur->s_name));
+                dput(parent_dentry);
+
+                if (IS_ERR(dentry)) {
+                        sysfs_put(cur);
+                        return dentry;
+                }
+
+                mutex_lock(&sysfs_mutex);
+                spin_lock(&sysfs_assoc_lock);
+
+                /* This, again, can happen if tree structure has
+                 * changed and we looked up the wrong thing.  Restart.
+                 */
+                if (cur->s_dentry != dentry) {
+                        dput(dentry);
+                        sysfs_put(cur);
+                        goto restart1;
+                }
+
+                spin_unlock(&sysfs_assoc_lock);
+
+                sysfs_put(cur);
+        }
+
+        mutex_unlock(&sysfs_mutex);
+        return dentry;
+}
+
+/**
  *      sysfs_get_active - get an active reference to sysfs_dirent
  *      @sd: sysfs_dirent to get an active reference to
  *
diff --git a/fs/sysfs/sysfs.h b/fs/sysfs/sysfs.h
index 92fe1e51a29b..72530dc666fd 100644
--- a/fs/sysfs/sysfs.h
+++ b/fs/sysfs/sysfs.h
@@ -54,6 +54,7 @@ struct sysfs_addrm_cxt {
 extern struct vfsmount * sysfs_mount;
 extern struct kmem_cache *sysfs_dir_cachep;
 
+extern struct dentry *sysfs_get_dentry(struct sysfs_dirent *sd);
 extern void sysfs_link_sibling(struct sysfs_dirent *sd);
 extern void sysfs_unlink_sibling(struct sysfs_dirent *sd);
 extern struct sysfs_dirent *sysfs_get_active(struct sysfs_dirent *sd);