Merge remote-tracking branch 'remotes/kevin/tags/for-upstream' into staging

Block layer patches

# gpg: Signature made Wed 25 May 2016 18:32:40 BST using RSA key ID C88F2FD6
# gpg: Good signature from "Kevin Wolf <kwolf@redhat.com>"

* remotes/kevin/tags/for-upstream: (31 commits)
  blockjob: Remove BlockJob.bs
  commit: Use BlockBackend for I/O
  backup: Use BlockBackend for I/O
  backup: Remove bs parameter from backup_do_cow()
  backup: Pack Notifier within BackupBlockJob
  backup: Don't leak BackupBlockJob in error path
  mirror: Use BlockBackend for I/O
  mirror: Allow target that already has a BlockBackend
  stream: Use BlockBackend for I/O
  block: Make blk_co_preadv/pwritev() public
  block: Convert block job core to BlockBackend
  block: Default to enabled write cache in blk_new()
  block: Cancel jobs first in bdrv_close_all()
  block: keep a list of block jobs
  block: Rename blk_write_zeroes()
  dma-helpers: change BlockBackend to opaque value in DMAIOFunc
  dma-helpers: change interface to byte-based
  block: Propagate .drained_begin/end callbacks
  block: Fix reconfiguring graph with drained nodes
  block: Make bdrv_drain() use bdrv_drained_begin/end()
  ...

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>