The problem.  When implementing a network namespace I need to be able
to have multiple network devices with the same name.  Currently this
is a problem for /sys/class/net/*. 

What I want is a separate /sys/class/net directory in sysfs for each
network namespace, and I want to name each of them /sys/class/net.

I looked and the VFS actually allows that.  All that is needed is
for /sys/class/net to implement a follow link method to redirect
lookups to the real directory you want. 

Implementing a follow link method that is sensitive to the current
network namespace turns out to be 3 lines of code so it looks like a
clean approach.  Modifying sysfs so it doesn't get in my was is a bit
trickier. 

I am calling the concept of multiple directories all at the same path
in the filesystem shadow directories.  With the directory entry really
at that location the shadow master. 

The following patch modifies sysfs so it can handle a directory
structure slightly different from the kobject tree so I can implement
the shadow directories for handling /sys/class/net/.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
---
 fs/sysfs/dir.c          |  207 +++++++++++++++++++++++++++++++++++++++--------
 fs/sysfs/group.c        |    1 +
 fs/sysfs/inode.c        |   10 +++
 fs/sysfs/mount.c        |    2 +-
 fs/sysfs/sysfs.h        |    5 +
 include/linux/kobject.h |    4 +
 include/linux/sysfs.h   |   23 +++++-
 lib/kobject.c           |   42 +++++++++-
 8 files changed, 249 insertions(+), 45 deletions(-)

diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
index 511edef..dd23903 100644
--- a/fs/sysfs/dir.c
+++ b/fs/sysfs/dir.c
@@ -32,8 +32,7 @@ static struct dentry_operations sysfs_dentry_ops = {
 /*
  * Allocates a new sysfs_dirent and links it to the parent sysfs_dirent
  */
-static struct sysfs_dirent * sysfs_new_dirent(struct sysfs_dirent * parent_sd,
-						void * element)
+static struct sysfs_dirent * __sysfs_new_dirent(void * element)
 {
 	struct sysfs_dirent * sd;
 
@@ -45,12 +44,28 @@ static struct sysfs_dirent * sysfs_new_dirent(struct sysfs_dirent * parent_sd,
 	atomic_set(&sd->s_count, 1);
 	atomic_set(&sd->s_event, 1);
 	INIT_LIST_HEAD(&sd->s_children);
-	list_add(&sd->s_sibling, &parent_sd->s_children);
+	INIT_LIST_HEAD(&sd->s_sibling);
 	sd->s_element = element;
 
 	return sd;
 }
 
+static void __sysfs_list_dirent(struct sysfs_dirent *parent_sd,
+			      struct sysfs_dirent *sd)
+{
+	if (sd)
+		list_add(&sd->s_sibling, &parent_sd->s_children);
+}
+
+static struct sysfs_dirent * sysfs_new_dirent(struct sysfs_dirent *parent_sd,
+						void * element)
+{
+	struct sysfs_dirent *sd;
+	sd = __sysfs_new_dirent(element);
+	__sysfs_list_dirent(parent_sd, sd);
+	return sd;
+}
+
 /*
  *
  * Return -EEXIST if there is already a sysfs element with the same name for
@@ -77,14 +92,14 @@ int sysfs_dirent_exist(struct sysfs_dirent *parent_sd,
 }
 
 
-int sysfs_make_dirent(struct sysfs_dirent * parent_sd, struct dentry * dentry,
-			void * element, umode_t mode, int type)
+static struct sysfs_dirent *
+__sysfs_make_dirent(struct dentry *dentry, void *element, mode_t mode, int type)
 {
 	struct sysfs_dirent * sd;
 
-	sd = sysfs_new_dirent(parent_sd, element);
+	sd = __sysfs_new_dirent(element);
 	if (!sd)
-		return -ENOMEM;
+		goto out;
 
 	sd->s_mode = mode;
 	sd->s_type = type;
@@ -94,7 +109,19 @@ int sysfs_make_dirent(struct sysfs_dirent * parent_sd, struct dentry * dentry,
 		dentry->d_op = &sysfs_dentry_ops;
 	}
 
-	return 0;
+out:
+	return sd;
+}
+
+int sysfs_make_dirent(struct sysfs_dirent * parent_sd, struct dentry * dentry,
+			void * element, umode_t mode, int type)
+{
+	struct sysfs_dirent *sd;
+	
+	sd = __sysfs_make_dirent(dentry, element, mode, type);
+	__sysfs_list_dirent(parent_sd, sd);
+
+	return sd ? 0 : -ENOMEM;
 }
 
 static int init_dir(struct inode * inode)
@@ -165,11 +192,11 @@ int sysfs_create_subdir(struct kobject * k, const char * n, struct dentry ** d)
 
 /**
  *	sysfs_create_dir - create a directory for an object.
- *	@parent:	parent parent object.
  *	@kobj:		object we're creating directory for. 
+ *	@shadow_parent:	parent parent object.
  */
 
-int sysfs_create_dir(struct kobject * kobj)
+int sysfs_create_dir(struct kobject * kobj, struct dentry *shadow_parent)
 {
 	struct dentry * dentry = NULL;
 	struct dentry * parent;
@@ -177,7 +204,9 @@ int sysfs_create_dir(struct kobject * kobj)
 
 	BUG_ON(!kobj);
 
-	if (kobj->parent)
+	if (shadow_parent)
+		parent = shadow_parent;
+	else if (kobj->parent)
 		parent = kobj->parent->dentry;
 	else if (sysfs_mount && sysfs_mount->mnt_sb)
 		parent = sysfs_mount->mnt_sb->s_root;
@@ -298,21 +327,12 @@ void sysfs_remove_subdir(struct dentry * d)
 }
 
 
-/**
- *	sysfs_remove_dir - remove an object's directory.
- *	@kobj:	object. 
- *
- *	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_dir(struct kobject * kobj)
+static void __sysfs_remove_dir(struct dentry *dentry)
 {
-	struct dentry * dentry = dget(kobj->dentry);
 	struct sysfs_dirent * parent_sd;
 	struct sysfs_dirent * sd, * tmp;
 
+	dget(dentry);
 	if (!dentry)
 		return;
 
@@ -333,32 +353,60 @@ void sysfs_remove_dir(struct kobject * kobj)
 	 * Drop reference from dget() on entrance.
 	 */
 	dput(dentry);
+}
+
+/**
+ *	sysfs_remove_dir - remove an object's directory.
+ *	@kobj:	object. 
+ *
+ *	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_dir(struct kobject * kobj)
+{
+	__sysfs_remove_dir(kobj->dentry);
 	kobj->dentry = NULL;
 }
 
-int sysfs_rename_dir(struct kobject * kobj, const char *new_name)
+int sysfs_rename_dir(struct kobject * kobj, struct dentry *new_parent,
+		     const char *new_name)
 {
 	int error = 0;
-	struct dentry * new_dentry, * parent;
-
-	if (!strcmp(kobject_name(kobj), new_name))
-		return -EINVAL;
+	struct dentry * new_dentry;
 
-	if (!kobj->parent)
-		return -EINVAL;
+	if (!new_parent)
+		return -EFAULT;
 
 	down_write(&sysfs_rename_sem);
-	parent = kobj->parent->dentry;
-
-	mutex_lock(&parent->d_inode->i_mutex);
+	mutex_lock(&new_parent->d_inode->i_mutex);
 
-	new_dentry = lookup_one_len(new_name, parent, strlen(new_name));
+	new_dentry = lookup_one_len(new_name, new_parent, strlen(new_name));
 	if (!IS_ERR(new_dentry)) {
-  		if (!new_dentry->d_inode) {
+		/* By allowing two different directories with the
+		 * same d_parent we allow this routine to move
+		 * between different shadows of the same directory
+		 */
+		if (kobj->dentry->d_parent->d_inode != new_parent->d_inode)
+			return -EINVAL;
+		else if (new_dentry->d_parent->d_inode != new_parent->d_inode)
+			error = -EINVAL;
+		else if (new_dentry == kobj->dentry)
+			error = -EINVAL;
+		else if (!new_dentry->d_inode) {
 			error = kobject_set_name(kobj, "%s", new_name);
 			if (!error) {
+				struct sysfs_dirent *sd, *parent_sd;
+
 				d_add(new_dentry, NULL);
 				d_move(kobj->dentry, new_dentry);
+
+				sd = kobj->dentry->d_fsdata;
+				parent_sd = new_parent->d_fsdata;
+
+				list_del_init(&sd->s_sibling);
+				list_add(&sd->s_sibling, &parent_sd->s_children);
 			}
 			else
 				d_drop(new_dentry);
@@ -366,7 +414,7 @@ int sysfs_rename_dir(struct kobject * kobj, const char *new_name)
 			error = -EEXIST;
 		dput(new_dentry);
 	}
-	mutex_unlock(&parent->d_inode->i_mutex);
+	mutex_unlock(&new_parent->d_inode->i_mutex);
 	up_write(&sysfs_rename_sem);
 
 	return error;
@@ -547,6 +595,95 @@ 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 inode *inode;
+	struct inode_operations *i_op;
+
+	inode = kobj->dentry->d_inode;
+	if (inode->i_op != &sysfs_dir_inode_operations)
+		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 dentry *sysfs_create_shadow_dir(struct kobject *kobj)
+{
+	struct sysfs_dirent *sd;
+	struct dentry *parent, *dir, *shadow;
+	struct inode *inode;
+
+	dir = kobj->dentry;
+	inode = dir->d_inode;
+	parent = dir->d_parent;
+	shadow = ERR_PTR(-EINVAL);
+	if (!sysfs_is_shadowed_inode(inode))
+		goto out;
+
+	shadow = d_alloc(parent, &dir->d_name);
+	if (!shadow)
+		goto nomem;
+
+	sd = __sysfs_make_dirent(shadow, kobj, inode->i_mode, SYSFS_DIR);
+	if (!sd)
+		goto nomem;
+
+	d_instantiate(shadow, igrab(inode));
+	inc_nlink(inode);
+	inc_nlink(parent->d_inode);
+	shadow->d_op = &sysfs_dentry_ops;
+
+	dget(shadow);		/* Extra count - pin the dentry in core */
+
+out:
+	return shadow;
+nomem:
+	dput(shadow);
+	shadow = ERR_PTR(-ENOMEM);
+	goto out;
+}
+
+/**
+ *	sysfs_remove_shadow_dir - remove an object's directory.
+ *	@shadow: dentry of shadow directory
+ *
+ *	The only thing special about this is that we remove any files in 
+ *	the direct

Modify the device class code so that normal manipulations work
in the presence of shadow directories.  Some of the shadow directory
support still needs to be implemented in the implementation of the
class but these modifications are sufficient to make that simple.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
---
 drivers/base/class.c   |   34 ++++++++++++++++++++++++++++++++--
 include/linux/device.h |    4 ++++
 2 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/drivers/base/class.c b/drivers/base/class.c
index 8bf2ca2..f72ddc0 100644
--- a/drivers/base/class.c
+++ b/drivers/base/class.c
@@ -136,6 +136,18 @@ static void remove_class_attrs(struct class * cls)
 	}
 }
 
+static int class_setup_shadow(struct class *cls)
+{
+	if (!cls->class_device_dparent && !cls->class_follow_link)
+		return 0;
+
+	if (!cls->class_device_dparent || !cls->class_device_dparent)
+		return -EINVAL;
+
+	return sysfs_make_shadowed_dir(&cls->subsys.kset.kobj,
+					cls->class_follow_link);
+}
+
 int class_register(struct class * cls)
 {
 	int error;
@@ -154,6 +166,11 @@ int class_register(struct class * cls)
 
 	error = subsystem_register(&cls->subsys);
 	if (!error) {
+		error = class_setup_shadow(cls);
+		if (error)
+			subsystem_unregister(&cls->subsys);
+	}
+	if (!error) {
 		error = add_class_attrs(class_get(cls));
 		class_put(cls);
 	}
@@ -582,6 +599,7 @@ int class_device_add(struct class_device *class_dev)
 	struct class *parent_class = NULL;
 	struct class_device *parent_class_dev = NULL;
 	struct class_interface *class_intf;
+	struct dentry *dparent;
 	int error = -EINVAL;
 
 	class_dev = class_device_get(class_dev);
@@ -610,7 +628,11 @@ int class_device_add(struct class_device *class_dev)
 	else
 		class_dev->kobj.parent = &parent_class->subsys.kset.kobj;
 
-	error = kobject_add(&class_dev->kobj);
+	if (parent_class->class_device_dparent)
+		dparent = parent_class->class_device_dparent(class_dev);
+	else
+		dparent = parent_class->subsys.kset.kobj.dentry;
+	error = kobject_shadow_add(&class_dev->kobj, dparent);
 	if (error)
 		goto out2;
 
@@ -841,11 +863,15 @@ int class_device_rename(struct class_device *class_dev, char *new_name)
 {
 	int error = 0;
 	char *old_class_name = NULL, *new_class_name = NULL;
+	struct class *class;
+	struct dentry *new_parent;
 
 	class_dev = class_device_get(class_dev);
 	if (!class_dev)
 		return -EINVAL;
 
+	class = class_dev->class;
+
 	pr_debug("CLASS: renaming '%s' to '%s'\n", class_dev->class_id,
 		 new_name);
 
@@ -857,7 +883,11 @@ int class_device_rename(struct class_device *class_dev, char *new_name)
 
 	strlcpy(class_dev->class_id, new_name, KOBJ_NAME_LEN);
 
-	error = kobject_rename(&class_dev->kobj, new_name);
+	if (class->class_device_dparent)
+		new_parent = class->class_device_dparent(class_dev);
+	else
+		new_parent = class->subsys.kset.kobj.dentry;
+	error = kobject_shadow_rename(&class_dev->kobj, new_parent, new_name);
 
 #ifdef CONFIG_SYSFS_DEPRECATED
 	if (class_dev->dev) {
diff --git a/include/linux/device.h b/include/linux/device.h
index f44247f..162e840 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -33,6 +33,7 @@ struct device;
 struct device_driver;
 struct class;
 struct class_device;
+struct nameidata;
 
 struct bus_type {
 	const char		* name;
@@ -197,6 +198,9 @@ struct class {
 
 	int	(*suspend)(struct device *, pm_message_t state);
 	int	(*resume)(struct device *);
+
+	struct dentry *(*class_device_dparent)(struct class_device *);
+	void *(*class_follow_link)(struct dentry *dentry, struct nameidata *nd);
 };
 
 extern int __must_check class_register(struct class *);
-- 
1.4.4.1.g278f

_______________________________________________
Containers mailing list
Containers@lists.osdl.org
https://lists.osdl.org/mailman/listinfo/containers