Merge remote-tracking branch 'remotes/stefanha-gitlab/tags/block-pull-request' into...

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

Pull request

# gpg: Signature made Thu 08 Jul 2021 14:11:37 BST
# gpg:                using RSA key 8695A8BFD3F97CDAAC35775A9CA4ABB381AB73C8
# gpg: Good signature from "Stefan Hajnoczi <stefanha@redhat.com>" [full]
# gpg:                 aka "Stefan Hajnoczi <stefanha@gmail.com>" [full]
# Primary key fingerprint: 8695 A8BF D3F9 7CDA AC35  775A 9CA4 ABB3 81AB 73C8

* remotes/stefanha-gitlab/tags/block-pull-request:
  block/io: Merge discard request alignments
  block: Add backend_defaults property
  block/file-posix: Optimize for macOS
  util/async: print leaked BH name when AioContext finalizes
  util/async: add a human-readable name to BHs for debugging

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