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

Block layer patches:

- qemu-img convert -C is now required to enable copy offloading
- file-posix: Fix write_zeroes with unmap on block devices (would fall
  back to explicit writes on recent kernels)
- Fix query-blockstats interface for use with -blockdev
- Minor fixes and documentation updates

# gpg: Signature made Mon 30 Jul 2018 16:08:14 BST
# gpg:                using RSA key 7F09B272C88F2FD6
# gpg: Good signature from "Kevin Wolf <kwolf@redhat.com>"
# Primary key fingerprint: DC3D EB15 9A9A F95D 3D74  56FE 7F09 B272 C88F 2FD6

* remotes/kevin/tags/for-upstream:
  qemu-iotests: Test query-blockstats with -drive and -blockdev
  block/qapi: Include anonymous BBs in query-blockstats
  block/qapi: Add 'qdev' field to query-blockstats result
  file-posix: Fix write_zeroes with unmap on block devices
  block: Fix documentation for BDRV_REQ_MAY_UNMAP
  iotests: Add test for 'qemu-img convert -C' compatibility
  qemu-img: Add -C option for convert with copy offloading
  Revert "qemu-img: Document copy offloading implications with -S and -c"
  iotests: Don't lock /dev/null in 226
  docs: Describe using images in writing iotests
  file-posix: Handle EINTR in preallocation=full write
  qcow2: A grammar fix in conflicting cache sizing error message
  qcow: fix a reference leak

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