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/drivers/base/base.h b/drivers/base/base.h
index 6ee17bb391a9..b8bdfe61daa6 100644
--- a/drivers/base/base.h
+++ b/drivers/base/base.h
@@ -101,6 +101,8 @@ static inline int hypervisor_init(void) { return 0; }
 extern int platform_bus_init(void);
 extern void cpu_dev_init(void);
 
+struct kobject *virtual_device_parent(struct device *dev);
+
 extern int bus_add_device(struct device *dev);
 extern void bus_probe_device(struct device *dev);
 extern void bus_remove_device(struct device *dev);