sysfs: Add support for permanently empty directories to serve as mount points.

Add two functions sysfs_create_mount_point and
sysfs_remove_mount_point that hang a permanently empty directory off
of a kobject or remove a permanently emptpy directory hanging from a
kobject.  Export these new functions so modular filesystems can use
them.

Cc: stable@vger.kernel.org
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
index 0b45ff42f3741123a15f58d426e201a78d20b3d0..94374e43502599c466153858476bd42652a7ea1b 100644 (file)
--- a/fs/sysfs/dir.c
+++ b/fs/sysfs/dir.c
@@ -121,3 +121,37 @@ int sysfs_move_dir_ns(struct kobject *kobj, struct kobject *new_parent_kobj,
 
        return kernfs_rename_ns(kn, new_parent, kn->name, new_ns);
 }
+
+/**
+ * sysfs_create_mount_point - create an always empty directory
+ * @parent_kobj:  kobject that will contain this always empty directory
+ * @name: The name of the always empty directory to add
+ */
+int sysfs_create_mount_point(struct kobject *parent_kobj, const char *name)
+{
+       struct kernfs_node *kn, *parent = parent_kobj->sd;
+
+       kn = kernfs_create_empty_dir(parent, name);
+       if (IS_ERR(kn)) {
+               if (PTR_ERR(kn) == -EEXIST)
+                       sysfs_warn_dup(parent, name);
+               return PTR_ERR(kn);
+       }
+
+       return 0;
+}
+EXPORT_SYMBOL_GPL(sysfs_create_mount_point);
+
+/**
+ *     sysfs_remove_mount_point - remove an always empty directory.
+ *     @parent_kobj: kobject that will contain this always empty directory
+ *     @name: The name of the always empty directory to remove
+ *
+ */
+void sysfs_remove_mount_point(struct kobject *parent_kobj, const char *name)
+{
+       struct kernfs_node *parent = parent_kobj->sd;
+
+       kernfs_remove_by_name_ns(parent, name, NULL);
+}
+EXPORT_SYMBOL_GPL(sysfs_remove_mount_point);

diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h
index 99382c0df17eb3fc367e3b3eafd5dca3cb63975a..9f65758311a4efff6a325f0baeb33f86ec68e06f 100644 (file)
--- a/include/linux/sysfs.h
+++ b/include/linux/sysfs.h
@@ -210,6 +210,10 @@ int __must_check sysfs_rename_dir_ns(struct kobject *kobj, const char *new_name,
 int __must_check sysfs_move_dir_ns(struct kobject *kobj,
                                   struct kobject *new_parent_kobj,
                                   const void *new_ns);
+int __must_check sysfs_create_mount_point(struct kobject *parent_kobj,
+                                         const char *name);
+void sysfs_remove_mount_point(struct kobject *parent_kobj,
+                             const char *name);
 
 int __must_check sysfs_create_file_ns(struct kobject *kobj,
                                      const struct attribute *attr,
@@ -298,6 +302,17 @@ static inline int sysfs_move_dir_ns(struct kobject *kobj,
        return 0;
 }
 
+static inline int sysfs_create_mount_point(struct kobject *parent_kobj,
+                                          const char *name)
+{
+       return 0;
+}
+
+static inline void sysfs_remove_mount_point(struct kobject *parent_kobj,
+                                           const char *name)
+{
+}
+
 static inline int sysfs_create_file_ns(struct kobject *kobj,
                                       const struct attribute *attr,
                                       const void *ns)