- add ->unlocked_ioctl method and a do_ioctl wrapper in ioctl.c so all
  places calling ->ioctl get it.  THis provides us a patch to migrate away
  from holding bkl across ioctl implementations.

- add ->compat_ioctl method and call it in compat_sys_ioctl before doing
  the hash lookup for registered handlers.

- streamline compat_sys_ioctl and move the complex error reporting into a
  function of its own

From: "Michael S. Tsirkin" <mst@mellanox.co.il>

Handle generic ioctl commands by falling back on static conversion
functions in fs/compat_ioctl.c on -ENOIOCTLCMD code.

From: "Michael S. Tsirkin" <mst@mellanox.co.il>

With new unlocked_ioctl and ioctl_compat, ioctls can now be as fast as
read/write.  So lets use fget_light/fput_light there, to get some speedup
in common case on SMP.
Signed-off-by: Michael s. Tsirkin <mst@mellanox.co.il>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>