driver/base: implement subsys_virtual_register()

Kay tells me the most appropriate place to expose workqueues to
userland would be /sys/devices/virtual/workqueues/WQ_NAME which is
symlinked to /sys/bus/workqueue/devices/WQ_NAME and that we're lacking
a way to do that outside of driver core as virtual_device_parent()
isn't exported and there's no inteface to conveniently create a
virtual subsystem.

This patch implements subsys_virtual_register() by factoring out
subsys_register() from subsys_system_register() and using it with
virtual_device_parent() as the origin directory.  It's identical to
subsys_system_register() other than the origin directory but we aren't
gonna restrict the device names which should be used under it.

This will be used to expose workqueue attributes to userland.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Kay Sievers <kay.sievers@vrfy.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/linux/device.h b/include/linux/device.h
index 9d6464ea99c6..ee10d4e7be1a 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -302,6 +302,8 @@ void subsys_interface_unregister(struct subsys_interface *sif);
 
 int subsys_system_register(struct bus_type *subsys,
 			   const struct attribute_group **groups);
+int subsys_virtual_register(struct bus_type *subsys,
+			    const struct attribute_group **groups);
 
 /**
  * struct class - device classes