driverfs: Add struct attribute

driverfs can only handle passing struct device to read/write functions. In order to free it of this limitation,
we need a common data structure for driverfs to pass around. 

The only thing that driverfs really needs are the name and mode of the file, which are now located in struct
attribute.

struct device_attribute gets a struct attribute member, which holds the name and mode. With the DEVICE_ATTR 
macro, users of the structure require no modification.

device_create_file is modified to take a struct attribute parameter

a to_dev_attr() macro is introduced to convert between a struct attribute to a struct device_attribute

drivers/base/fs.c

@@ -30,7 +30,7 @@ int device_create_file(struct device * dev, struct device_attribute * entry)
 
 	if (dev) {
 		get_device(dev);
-		error = driverfs_create_file(entry,&dev->dir);
+		error = driverfs_create_file(&entry->attr,&dev->dir);
 		put_device(dev);
 	}
 	return error;
@@ -46,7 +46,7 @@ void device_remove_file(struct device * dev, struct device_attribute * attr)
 {
 	if (dev) {
 		get_device(dev);
-		driverfs_remove_file(&dev->dir,attr->name);
+		driverfs_remove_file(&dev->dir,attr->attr.name);
 		put_device(dev);
 	}
 }

fs/driverfs/inode.c

@@ -282,7 +282,7 @@ driverfs_read_file(struct file *file, char *buf, size_t count, loff_t *ppos)
 	struct device * dev;
 
 	dir = file->f_dentry->d_parent->d_fsdata;
-	entry = (struct device_attribute *)file->f_dentry->d_fsdata;
+	entry = to_dev_attr(file->f_dentry->d_fsdata);
 	if (!entry) {
 		DBG("%s: file entry is NULL\n",__FUNCTION__);
 		return -ENOENT;
@@ -349,7 +349,7 @@ driverfs_write_file(struct file *file, const char *buf, size_t count, loff_t *pp
 
 	dir = file->f_dentry->d_parent->d_fsdata;
 
-	entry = (struct device_attribute *)file->f_dentry->d_fsdata;
+	entry = to_dev_attr(file->f_dentry->d_fsdata);
 	if (!entry) {
 		DBG("%s: file entry is NULL\n",__FUNCTION__);
 		return -ENOENT;
@@ -618,7 +618,7 @@ driverfs_create_dir(struct driver_dir_entry * entry,
  * @parent:	directory to create it in
  */
 int
-driverfs_create_file(struct device_attribute * entry,
+driverfs_create_file(struct attribute * entry,
 		     struct driver_dir_entry * parent)
 {
 	struct dentry * dentry;

include/linux/driverfs_fs.h

@@ -32,23 +32,28 @@ struct driver_dir_entry {
 	mode_t			mode;
 };
 
+struct attribute {
+	char			* name;
+	mode_t			mode;
+};
+
 struct device;
 
 struct device_attribute {
-	char			* name;
-	mode_t			mode;
+	struct attribute	attr;
 	ssize_t (*show)(struct device * dev, char * buf, size_t count, loff_t off);
 	ssize_t (*store)(struct device * dev, const char * buf, size_t count, loff_t off);
 };
 
 #define DEVICE_ATTR(_name,_str,_mode,_show,_store)	\
 struct device_attribute dev_attr_##_name = { 		\
-	.name	= _str,		\
-	.mode	= _mode,	\
+	.attr = {.name	= _str,	.mode	= _mode },	\
 	.show	= _show,				\
 	.store	= _store,				\
 };
 
+#define to_dev_attr(_attr) container_of(_attr,struct device_attribute,attr)
+
 extern int
 driverfs_create_dir(struct driver_dir_entry *, struct driver_dir_entry *);
 
@@ -56,7 +61,7 @@ extern void
 driverfs_remove_dir(struct driver_dir_entry * entry);
 
 extern int
-driverfs_create_file(struct device_attribute * entry,
+driverfs_create_file(struct attribute * attr,
 		     struct driver_dir_entry * parent);
 
 extern int