driverfs: Add ability to create and remove files for bus drivers

These behave identically to device attribute files, but with different types. 

We get struct bus_attribute, and a macro, BUS_ATTR for declaring attributes. It takes the same parameters
as DEVICE_ATTR, though the callbacks for bus attributes take a struct bus_type as the first parameter.

drivers/base/fs/bus.c

+#include <linux/module.h>
 #include <linux/device.h>
 #include <linux/init.h>
 #include <linux/stat.h>
 #include "fs.h"
 
-static struct driver_dir_entry bus_dir = {
-	name:	"bus",
-	mode:	(S_IFDIR| S_IRWXU | S_IRUGO | S_IXUGO),
+static struct driver_dir_entry bus_dir;
+
+#define to_bus_attr(_attr) container_of(_attr,struct bus_attribute,attr)
+
+#define to_bus(dir) container_of(dir,struct bus_type,dir)
+
+
+/* driverfs ops for device attribute files */
+
+static int
+bus_attr_open(struct driver_dir_entry * dir)
+{
+	struct bus_type * bus = to_bus(dir);
+	get_bus(bus);
+	return 0;
+}
+
+static int
+bus_attr_close(struct driver_dir_entry * dir)
+{
+	struct bus_type * bus = to_bus(dir);
+	put_bus(bus);
+	return 0;
+}
+
+static ssize_t
+bus_attr_show(struct driver_dir_entry * dir, struct attribute * attr,
+	      char * buf, size_t count, loff_t off)
+{
+	struct bus_attribute * bus_attr = to_bus_attr(attr);
+	struct bus_type * bus = to_bus(dir);
+	ssize_t ret = 0;
+
+	if (bus_attr->show)
+		ret = bus_attr->show(bus,buf,count,off);
+	return ret;
+}
+
+static ssize_t
+bus_attr_store(struct driver_dir_entry * dir, struct attribute * attr,
+	       const char * buf, size_t count, loff_t off)
+{
+	struct bus_attribute * bus_attr = to_bus_attr(attr);
+	struct bus_type * bus = to_bus(dir);
+	ssize_t ret = 0;
+
+	if (bus_attr->store)
+		ret = bus_attr->store(bus,buf,count,off);
+	return ret;
+}
+
+static struct driverfs_ops bus_attr_ops = {
+	open:	bus_attr_open,
+	close:	bus_attr_close,
+	show:	bus_attr_show,
+	store:	bus_attr_store,
 };
 
+int bus_create_file(struct bus_type * bus, struct bus_attribute * attr)
+{
+	int error;
+	if (get_bus(bus)) {
+		error = driverfs_create_file(&attr->attr,&bus->dir);
+		put_bus(bus);
+	} else
+		error = -EINVAL;
+	return error;
+}
+
+void bus_remove_file(struct bus_type * bus, struct bus_attribute * attr)
+{
+	if (get_bus(bus)) {
+		driverfs_remove_file(&bus->dir,attr->attr.name);
+		put_bus(bus);
+	}
+}
+
 int bus_make_dir(struct bus_type * bus)
 {
 	int error;
 	bus->dir.name = bus->name;
+	bus->dir.ops = &bus_attr_ops;
 
 	error = device_create_dir(&bus->dir,&bus_dir);
 	if (!error) {
@@ -32,6 +106,11 @@ void bus_remove_dir(struct bus_type * bus)
 	driverfs_remove_dir(&bus->dir);
 }
 
+static struct driver_dir_entry bus_dir = {
+	name:	"bus",
+	mode:	(S_IFDIR| S_IRWXU | S_IRUGO | S_IXUGO),
+};
+
 static int __init bus_init(void)
 {
 	/* make 'bus' driverfs directory */
@@ -40,3 +119,5 @@ static int __init bus_init(void)
 
 core_initcall(bus_init);
 
+EXPORT_SYMBOL(bus_create_file);
+EXPORT_SYMBOL(bus_remove_file);

include/linux/device.h

@@ -85,6 +85,24 @@ extern int bus_for_each_drv(struct bus_type * bus, void * data,
 			    int (*callback)(struct device_driver * drv, void * data));
 
 
+/* driverfs interface for exporting bus attributes */
+
+struct bus_attribute {
+	struct attribute	attr;
+	ssize_t (*show)(struct bus_type *, char * buf, size_t count, loff_t off);
+	ssize_t (*store)(struct bus_type *, const char * buf, size_t count, loff_t off);
+};
+
+#define BUS_ATTR(_name,_str,_mode,_show,_store)	\
+struct bus_attribute bus_attr_##_name = { 		\
+	.attr = {.name	= _str,	.mode	= _mode },	\
+	.show	= _show,				\
+	.store	= _store,				\
+};
+
+extern int bus_create_file(struct bus_type *, struct bus_attribute *);
+extern void bus_remove_file(struct bus_type *, struct bus_attribute *);
+
 struct device_driver {
 	char			* name;
 	struct bus_type		* bus;