Merge remote-tracking branch 'remotes/cody/tags/block-pull-request' into staging

# gpg: Signature made Wed 29 Jun 2016 04:09:26 BST
# gpg:                using RSA key 0xBDBE7B27C0DE3057
# gpg: Good signature from "Jeffrey Cody <jcody@redhat.com>"
# gpg:                 aka "Jeffrey Cody <jeff@codyprime.org>"
# gpg:                 aka "Jeffrey Cody <codyprime@gmail.com>"
# Primary key fingerprint: 9957 4B4D 3474 90E7 9D98  D624 BDBE 7B27 C0DE 3057

* remotes/cody/tags/block-pull-request:
  mirror: fix misleading comments
  blockjob: assert(cb) when create job
  iotests: add small-granularity mirror test
  mirror: limit niov to IOV_MAX elements, again
  mirror: clarify mirror_do_read return code
  block/gluster: add support for selecting debug logging level
  mirror: fix trace_mirror_yield_in_flight usage in mirror_iteration()
  block/nfs: add support for libnfs pagecache
  block/nfs: refuse readahead if cache.direct is on
  block/gluster: add support for SEEK_DATA/SEEK_HOLE

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