While shadow directories appear to be a good idea, the current scheme
of controlling their creation and destruction outside of sysfs appears
to be a locking and maintenance nightmare in the face of sysfs directories
dynamically coming and going.  Which can now occur for directories containing
network devices when CONFIG_SYSFS_DEPRECATED is not set.

This patch removes everything from the initial shadow directory support
that allowed the shadow directory creation to be controlled at a higher
level.  So except for a few bits of sysfs_rename_dir everything from
commit b592fcfe7f06c15ec11774b5be7ce0de3aa86e73 is now gone.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
---
I have sanitized my changes to sysfs_rename_dir since last time I posted
this patch.

 fs/sysfs/dir.c          |  155 ++--------------------------------------------
 fs/sysfs/group.c        |    1 -
 fs/sysfs/inode.c        |   10 ---
 fs/sysfs/mount.c        |    2 +-
 fs/sysfs/sysfs.h        |    6 --
 include/linux/kobject.h |    5 --
 include/linux/sysfs.h   |   27 +-------
 lib/kobject.c           |   44 ++------------
 8 files changed, 18 insertions(+), 232 deletions(-)

diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
index 048e605..40b9efe 100644
--- a/fs/sysfs/dir.c
+++ b/fs/sysfs/dir.c
@@ -569,9 +569,6 @@ static void sysfs_drop_dentry(struct sysfs_dirent *sd)
 	spin_unlock(&dcache_lock);
 	spin_unlock(&sysfs_assoc_lock);
 
-	/* dentries for shadowed inodes are pinned, unpin */
-	if (dentry && sysfs_is_shadowed_inode(dentry->d_inode))
-		dput(dentry);
 	dput(dentry);
 
 	/* adjust nlink and update timestamp */
@@ -723,19 +720,15 @@ int sysfs_create_subdir(struct kobject *kobj, const char *name,
 /**
  *	sysfs_create_dir - create a directory for an object.
  *	@kobj:		object we're creating directory for. 
- *	@shadow_parent:	parent object.
  */
-int sysfs_create_dir(struct kobject *kobj,
-		     struct sysfs_dirent *shadow_parent_sd)
+int sysfs_create_dir(struct kobject * kobj)
 {
 	struct sysfs_dirent *parent_sd, *sd;
 	int error = 0;
 
 	BUG_ON(!kobj);
 
-	if (shadow_parent_sd)
-		parent_sd = shadow_parent_sd;
-	else if (kobj->parent)
+	if (kobj->parent)
 		parent_sd = kobj->parent->sd;
 	else if (sysfs_mount && sysfs_mount->mnt_sb)
 		parent_sd = sysfs_mount->mnt_sb->s_root->d_fsdata;
@@ -887,8 +880,7 @@ void sysfs_remove_dir(struct kobject * kobj)
 	__sysfs_remove_dir(sd);
 }
 
-int sysfs_rename_dir(struct kobject *kobj, struct sysfs_dirent *new_parent_sd,
-		     const char *new_name)
+int sysfs_rename_dir(struct kobject *kobj, const char *new_name)
 {
 	struct sysfs_dirent *sd = kobj->sd;
 	struct dentry *new_parent = NULL;
@@ -903,11 +895,7 @@ int sysfs_rename_dir(struct kobject *kobj, struct sysfs_dirent *new_parent_sd,
 		goto out_dput;
 	}
 
-	new_parent = sysfs_get_dentry(new_parent_sd);
-	if (IS_ERR(new_parent)) {
-		error = PTR_ERR(new_parent);
-		goto out_dput;
-	}
+	new_parent = dget(old_dentry->d_parent);
 
 	/* lock new_parent and get dentry for new name */
 	mutex_lock(&new_parent->d_inode->i_mutex);
@@ -918,14 +906,8 @@ int sysfs_rename_dir(struct kobject *kobj, struct sysfs_dirent *new_parent_sd,
 		goto out_unlock;
 	}
 
-	/* By allowing two different directories with the same
-	 * d_parent we allow this routine to move between different
-	 * shadows of the same directory
-	 */
 	error = -EINVAL;
-	if (old_dentry->d_parent->d_inode != new_parent->d_inode ||
-	    new_dentry->d_parent->d_inode != new_parent->d_inode ||
-	    old_dentry == new_dentry)
+	if (old_dentry == new_dentry)
 		goto out_unlock;
 
 	error = -EEXIST;
@@ -942,23 +924,15 @@ int sysfs_rename_dir(struct kobject *kobj, struct sysfs_dirent *new_parent_sd,
 	if (error)
 		goto out_drop;
 
+	mutex_lock(&sysfs_mutex);
 	dup_name = sd->s_name;
 	sd->s_name = new_name;
+	mutex_unlock(&sysfs_mutex);
 
 	/* move under the new parent */
 	d_add(new_dentry, NULL);
 	d_move(sd->s_dentry, new_dentry);
 
-	mutex_lock(&sysfs_mutex);
-
-	sysfs_unlink_sibling(sd);
-	sysfs_get(new_parent_sd);
-	sysfs_put(sd->s_parent);
-	sd->s_parent = new_parent_sd;
-	sysfs_link_sibling(sd);
-
-	mutex_unlock(&sysfs_mutex);
-
 	error = 0;
 	goto out_unlock;
 
@@ -1189,121 +1163,6 @@ static loff_t sysfs_dir_lseek(struct file * file, loff_t offset, int origin)
 	return offset;
 }
 
-
-/**
- *	sysfs_make_shadowed_dir - Setup so a directory can be shadowed
- *	@kobj:	object we're creating shadow of.
- */
-
-int sysfs_make_shadowed_dir(struct kobject *kobj,
-	void * (*follow_link)(struct dentry *, struct nameidata *))
-{
-	struct dentry *dentry;
-	struct inode *inode;
-	struct inode_operations *i_op;
-
-	/* get dentry for @kobj->sd, dentry of a shadowed dir is pinned */
-	dentry = sysfs_get_dentry(kobj->sd);
-	if (IS_ERR(dentry))
-		return PTR_ERR(dentry);
-
-	inode = dentry->d_inode;
-	if (inode->i_op != &sysfs_dir_inode_operations) {
-		dput(dentry);
-		return -EINVAL;
-	}
-
-	i_op = kmalloc(sizeof(*i_op), GFP_KERNEL);
-	if (!i_op)
-		return -ENOMEM;
-
-	memcpy(i_op, &sysfs_dir_inode_operations, sizeof(*i_op));
-	i_op->follow_link = follow_link;
-
-	/* Locking of inode->i_op?
-	 * Since setting i_op is a single word write and they
-	 * are atomic we should be ok here.
-	 */
-	inode->i_op = i_op;
-	return 0;
-}
-
-/**
- *	sysfs_create_shadow_dir - create a shadow directory for an object.
- *	@kobj:	object we're creating directory for.
- *
- *	sysfs_make_shadowed_dir must already have been called on this
- *	directory.
- */
-
-struct sysfs_dirent *sysfs_create_shadow_dir(struct kobject *kobj)
-{
-	struct sysfs_dirent *parent_sd = kobj->sd->s_parent;
-	struct dentry *dir, *parent, *shadow;
-	struct inode *inode;
-	struct sysfs_dirent *sd;
-	struct sysfs_addrm_cxt acxt;
-
-	dir = sysfs_get_dentry(kobj->sd);
-	if (IS_ERR(dir)) {
-		sd = (void *)dir;
-		goto out;
-	}
-	parent = dir->d_parent;
-
-	inode = dir->d_inode;
-	sd = ERR_PTR(-EINVAL);
-	if (!sysfs_is_shadowed_inode(inode))
-		goto out_dput;
-
-	shadow = d_alloc(parent, &dir->d_name);
-	if (!shadow)
-		goto nomem;
-
-	sd = sysfs_new_dirent("_SHADOW_", inode->i_mode, SYSFS_DIR);
-	if (!sd)
-		goto nomem;
-	sd->s_elem.dir.kobj = kobj;
-
-	sysfs_addrm_start(&acxt, parent_sd);
-
-	/* add but don't link into children list */
-	sysfs_add_one(&acxt, sd);
-
-	/* attach and instantiate dentry */
-	sysfs_attach_dentry(sd, shadow);
-	d_instantiate(shadow, igrab(inode));
-	inc_nlink(inode);	/* tj: synchronization? */
-
-	sysfs_addrm_finish(&acxt);
-
-	dget(shadow);		/* Extra count - pin the dentry in core */
-
-	goto out_dput;
-
- nomem:
-	dput(shadow);
-	sd = ERR_PTR(-ENOMEM);
- out_dput:
-	dput(dir);
- out:
-	return sd;
-}
-
-/**
- *	sysfs_remove_shadow_dir - remove an object's directory.
- *	@shadow_sd: sysfs_dirent of shadow directory
- *
- *	The only thing special about this is that we remove any files in
- *	the directory before we remove the directory, and we've inlined
- *	what used to be sysfs_rmdir() below, instead of calling separately.
- */
-
-void sysfs_remove_shadow_dir(struct sysfs_dirent *shadow_sd)
-{
-	__sysfs_remove_dir(shadow_sd);
-}
-
 const struct file_operations sysfs_dir_operations = {
 	.open		= sysfs_dir_open,
 	.release	= sysfs_dir_close,
diff --git a/fs/sysfs/group.c b/fs/sysfs/group.c
index f318b73..4606f7c 100644
--- a/fs/sysfs/group.c
+++ b/fs/sysfs/group.c
@@ -13,7 +13,6 @@
 #include <linux/dcache.h>
 #include <linux/namei.h>
 #include <linux/err.h>
-#include <linux/fs.h>
 #include <asm/semaphore.h>
 #include "sysfs.h"
 
diff --git a/fs/sysfs/inode.c b/fs/sysfs/inode.c
index 10d1b52..9671164 100644
--- a/fs/sysfs/inode.c
+++ b/fs/sysfs/inode.c
@@ -34,16 +34,6 @@ static const struct inode_operations sysfs_inode_operations ={
 	.setattr	= sysfs_setattr,
 };
 
-void sysfs_delete_inode(struct inode *inode)
-{
-	/* Free the shadowed directory inode operations */
-	if (sysfs_is_shadowed_inode(inode)) {
-		kfree(inode->i_op);
-		inode->i_op = NULL;
-	}
-	return generic_delete_inode(inode);
-}
-
 int sysfs_setattr(struct dentry * dentry, struct iattr * iattr)
 {
 	struct inode * inode = dentry->d_inode;
diff --git a/fs/sysfs/mount.c b/fs/sysfs/mount.c
index fbc7b65..0c016e1 100644
--- a/fs/sysfs/mount.c
+++ b/fs/sysfs/mount.c
@@ -21,7 +21,7 @@ struct kmem_cache *sysfs_dir_cachep;
 
 static const struct super_operations sysfs_ops = {
 	.statfs		= simple_statfs,
-	.drop_inode	= sysfs_delete_inode,
+	.drop_inode	= generic_delete_inode,
 };
 
 struct sysfs_dirent sysfs_root = {
diff --git a/fs/sysfs/sysfs.h b/fs/sysfs/sysfs.h
index 6b8c8d7..b55e510 100644
--- a/fs/sysfs/sysfs.h
+++ b/fs/sysfs/sysfs.h
@@ -70,7 +70,6 @@ extern void sysfs_remove_one(struct sysfs_addrm_cxt *acxt,
 			     struct sysfs_dirent *sd);
 extern int sysfs_addrm_finish(struct sysfs_addrm_cxt *acxt);
 
-extern void sysfs_delete_inode(struct inode *inode);
 extern struct inode * sysfs_get_inode(struct sysfs_dirent *sd);
 extern void sysfs_instantiate(struct dentry *dentry, struct inode *inode);
 
@@ -121,8 +120,3 @@ static inline void sysfs_put(struct sysfs_dirent * sd)
 	if (sd && atomic_dec_and_test(&sd->s_count))
 		release_sysfs_dirent(sd);
 }
-
-static inline int sysfs_is_shadowed_inode(struct inode *inode)
-{
-	return S_ISDIR(inode->i_mode) && inode->i_op->follow_link;
-}
diff --git a/include/linux/kobject.h b/include/linux/kobject.h
index aa2fe22..7108a3e 100644
--- a/include/linux/kobject.h
+++ b/include/linux/kobject.h
@@ -80,14 +80,9 @@ extern void kobject_init(struct kobject *);
 extern void kobject_cleanup(struct kobject *);
 
 extern int __must_check kobject_add(struct kobject *);
-extern int __must_check kobject_shadow_add(struct kobject *kobj,
-					   struct sysfs_dirent *shadow_parent);
 extern void kobject_del(struct kobject *);
 
 extern int __must_check ko