Merge branch 'stable/for-jens-3.4' into linux-next

* stable/for-jens-3.4:
  xen/blkback: Fix warning error.
  xen/blkback: Make optional features be really optional.
  xen/blkback: Squash the discard support for 'file' and 'phy' type.
  xen-blkfront: make blkif_io_lock spinlock per-device
  xen/blkfront: don't put bdev right after getting it
  xen-blkfront: use bitmap_set() and bitmap_clear()
  xen/blkback: Enable blkback on HVM guests
  xen/blkback: use grant-table.c hypercall wrappers