sysfs: add sysfs_dirent->s_parent

Add sysfs_dirent->s_parent.  With this patch, each sd points to and
holds a reference to its parent.  This allows walking sysfs tree
without referencing sd->s_dentry which can go away anytime if the user
doesn't control when it's deleted.

sd->s_parent is initialized and parent is referenced in
sysfs_attach_dirent().  Reference to parent is released when the sd is
released, so as long as reference to a sd is held, s_parent can be
followed.

dentry walk in sysfs_readdir() is convereted to s_parent walk.

This will be used to reimplement symlink such that it uses only
sysfs_dirent tree.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 1 insertions, 0 deletions

diff --git a/fs/sysfs/mount.c b/fs/sysfs/mount.c
index 00ab9125d398..31c1fc67f604 100644
--- a/fs/sysfs/mount.c
+++ b/fs/sysfs/mount.c
@@ -28,6 +28,7 @@ static const struct super_operations sysfs_ops = {
 };
 
 static struct sysfs_dirent sysfs_root = {
+        .s_count        = ATOMIC_INIT(1),
         .s_sibling      = LIST_HEAD_INIT(sysfs_root.s_sibling),
         .s_children     = LIST_HEAD_INIT(sysfs_root.s_children),
         .s_element      = NULL,