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

Block layer patches

# gpg: Signature made Wed 30 Mar 2016 11:57:54 BST using RSA key ID C88F2FD6
# gpg: Good signature from "Kevin Wolf <kwolf@redhat.com>"

* remotes/kevin/tags/for-upstream: (48 commits)
  iotests: Test qemu-img convert -S 0 behavior
  block/null-{co,aio}: Implement get_block_status()
  block/null-{co,aio}: Allow reading zeroes
  qemu-img: Fix preallocation with -S 0 for convert
  block: Remove bdrv_(set_)enable_write_cache()
  block: Remove BDRV_O_CACHE_WB
  block: Remove bdrv_parse_cache_flags()
  qemu-io: Use bdrv_parse_cache_mode() in reopen_f()
  block: Use bdrv_parse_cache_mode() in drive_init()
  raw: Support BDRV_REQ_FUA
  nbd: Support BDRV_REQ_FUA
  iscsi: Support BDRV_REQ_FUA
  block: Introduce bdrv_co_writev_flags()
  block/qapi: Use blk_enable_write_cache()
  block: Move enable_write_cache to BB level
  block: Handle flush error in bdrv_pwrite_sync()
  block: Always set writeback mode in blk_new_open()
  block: blockdev_init(): Call blk_set_enable_write_cache() explicitly
  xen_disk: Call blk_set_enable_write_cache() explicitly
  qemu-img: Call blk_set_enable_write_cache() explicitly
  ...

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