[PATCH] USB: only make /sys/class/usb show up when there is something in it

Now /sys/class/usb is dynamically created when we have something to put
in it, and removed when all devices go away.

Just trying to cut down on the clutter in sysfs...

Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 54 insertions, 16 deletions

diff --git a/drivers/usb/core/file.c b/drivers/usb/core/file.c
index 70898716dd9a..f65b193cde3d 100644
--- a/drivers/usb/core/file.c
+++ b/drivers/usb/core/file.c
@@ -61,33 +61,66 @@ static struct file_operations usb_fops = {
         .open =         usb_open,
 };
 
-static struct class *usb_class;
+static struct usb_class {
+        struct kref kref;
+        struct class *class;
+} *usb_class;
 
-int usb_major_init(void)
+static int init_usb_class(void)
 {
-        int error;
+        int result = 0;
 
-        error = register_chrdev(USB_MAJOR, "usb", &usb_fops);
-        if (error) {
-                err("unable to get major %d for usb devices", USB_MAJOR);
-                goto out;
+        if (usb_class != NULL) {
+                kref_get(&usb_class->kref);
+                goto exit;
+        }
+
+        usb_class = kmalloc(sizeof(*usb_class), GFP_KERNEL);
+        if (!usb_class) {
+                result = -ENOMEM;
+                goto exit;
         }
 
-        usb_class = class_create(THIS_MODULE, "usb");
-        if (IS_ERR(usb_class)) {
-                error = PTR_ERR(usb_class);
+        kref_init(&usb_class->kref);
+        usb_class->class = class_create(THIS_MODULE, "usb");
+        if (IS_ERR(usb_class->class)) {
+                result = IS_ERR(usb_class->class);
                 err("class_create failed for usb devices");
-                unregister_chrdev(USB_MAJOR, "usb");
-                goto out;
+                kfree(usb_class);
+                usb_class = NULL;
         }
 
-out:
+exit:
+        return result;
+}
+
+static void release_usb_class(struct kref *kref)
+{
+        /* Ok, we cheat as we know we only have one usb_class */
+        class_destroy(usb_class->class);
+        kfree(usb_class);
+        usb_class = NULL;
+}
+
+static void destroy_usb_class(void)
+{
+        if (usb_class)
+                kref_put(&usb_class->kref, release_usb_class);
+}
+
+int usb_major_init(void)
+{
+        int error;
+
+        error = register_chrdev(USB_MAJOR, "usb", &usb_fops);
+        if (error)
+                err("unable to get major %d for usb devices", USB_MAJOR);
+
         return error;
 }
 
 void usb_major_cleanup(void)
 {
-        class_destroy(usb_class);
         unregister_chrdev(USB_MAJOR, "usb");
 }
 
@@ -149,6 +182,10 @@ int usb_register_dev(struct usb_interface *intf,
         if (retval)
                 goto exit;
 
+        retval = init_usb_class();
+        if (retval)
+                goto exit;
+
         intf->minor = minor;
 
         /* create a usb class device for this usb interface */
@@ -158,7 +195,7 @@ int usb_register_dev(struct usb_interface *intf,
                 ++temp;
         else
                 temp = name;
-        intf->usb_dev = device_create(usb_class, &intf->dev,
+        intf->usb_dev = device_create(usb_class->class, &intf->dev,
                                       MKDEV(USB_MAJOR, minor), "%s", temp);
         if (IS_ERR(intf->usb_dev)) {
                 spin_lock (&minor_lock);
@@ -205,9 +242,10 @@ void usb_deregister_dev(struct usb_interface *intf,
         spin_unlock (&minor_lock);
 
         snprintf(name, BUS_ID_SIZE, class_driver->name, intf->minor - minor_base);
-        device_destroy(usb_class, MKDEV(USB_MAJOR, intf->minor));
+        device_destroy(usb_class->class, MKDEV(USB_MAJOR, intf->minor));
         intf->usb_dev = NULL;
         intf->minor = -1;
+        destroy_usb_class();
 }
 EXPORT_SYMBOL(usb_deregister_dev);