sysfs: make attr namespace interface less convoluted

sysfs ns (namespace) implementation became more convoluted than
necessary while trying to hide ns information from visible interface.
The relatively recent attr ns support is a good example.

* attr ns tag is determined by sysfs_ops->namespace() callback while
  dir tag is determined by kobj_type->namespace().  The placement is
  arbitrary.

* Instead of performing operations with explicit ns tag, the namespace
  callback is routed through sysfs_attr_ns(), sysfs_ops->namespace(),
  class_attr_namespace(), class_attr->namespace().  It's not simpler
  in any sense.  The only thing this convolution does is traversing
  the whole stack backwards.

The namespace callbacks are unncessary because the operations involved
are inherently synchronous.  The information can be provided in in
straight-forward top-down direction and reversing that direction is
unnecessary and against basic design principles.

This backward interface is unnecessarily convoluted and hinders
properly separating out sysfs from driver model / kobject for proper
layering.  This patch updates attr ns support such that

* sysfs_ops->namespace() and class_attr->namespace() are dropped.

* sysfs_{create|remove}_file_ns(), which take explicit @ns param, are
  added and sysfs_{create|remove}_file() are now simple wrappers
  around the ns aware functions.

* ns handling is dropped from sysfs_chmod_file().  Nobody uses it at
  this point.  sysfs_chmod_file_ns() can be added later if necessary.

* Explicit @ns is propagated through class_{create|remove}_file_ns()
  and netdev_class_{create|remove}_file_ns().

* driver/net/bonding which is currently the only user of attr
  namespace is updated to use netdev_class_{create|remove}_file_ns()
  with @bh->net as the ns tag instead of using the namespace callback.

This patch should be an equivalent conversion without any functional
difference.  It makes the code easier to follow, reduces lines of code
a bit and helps proper separation and layering.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Kay Sievers <kay@vrfy.org>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 18 insertions, 6 deletions

diff --git a/include/linux/device.h b/include/linux/device.h
index 2a9d6ed59579..ce690ea34547 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -427,8 +427,6 @@ struct class_attribute {
 			char *buf);
 	ssize_t (*store)(struct class *class, struct class_attribute *attr,
 			const char *buf, size_t count);
-	const void *(*namespace)(struct class *class,
-				 const struct class_attribute *attr);
 };
 
 #define CLASS_ATTR(_name, _mode, _show, _store) \
@@ -438,10 +436,24 @@ struct class_attribute {
 #define CLASS_ATTR_RO(_name) \
 	struct class_attribute class_attr_##_name = __ATTR_RO(_name)
 
-extern int __must_check class_create_file(struct class *class,
-					  const struct class_attribute *attr);
-extern void class_remove_file(struct class *class,
-			      const struct class_attribute *attr);
+extern int __must_check class_create_file_ns(struct class *class,
+					     const struct class_attribute *attr,
+					     const void *ns);
+extern void class_remove_file_ns(struct class *class,
+				 const struct class_attribute *attr,
+				 const void *ns);
+
+static inline int __must_check class_create_file(struct class *class,
+					const struct class_attribute *attr)
+{
+	return class_create_file_ns(class, attr, NULL);
+}
+
+static inline void class_remove_file(struct class *class,
+				     const struct class_attribute *attr)
+{
+	return class_remove_file_ns(class, attr, NULL);
+}
 
 /* Simple class attribute that is just a static string */
 struct class_attribute_string {