v3: Rebase on master, small qapi docs improvements suggested by Markus

There several improvements to fleecing scheme:

1. support bitmap in copy-before-write filter

2. introduce fleecing block driver, which opens the door for a lot of
   image fleecing improvements.
   See "block: introduce fleecing block driver" commit message for
   details.

3. support "push backup with fleecing" scheme, when backup job is a
   client of common fleecing scheme. That helps when writes to final
   backup target are slow and we don't want guest writes hang waiting
   for copy-before-write operations to final target.

Vladimir Sementsov-Ogievskiy (19):
  block/block-copy: move copy_bitmap initialization to
    block_copy_state_new()
  block/dirty-bitmap: bdrv_merge_dirty_bitmap(): add return value
  block/block-copy: block_copy_state_new(): add bitmap parameter
  block/copy-before-write: add bitmap open parameter
  block/block-copy: add block_copy_reset()
  block: intoduce reqlist
  block/dirty-bitmap: introduce bdrv_dirty_bitmap_status()
  block/reqlist: add reqlist_wait_all()
  block: introduce FleecingState class
  block: introduce fleecing block driver
  block/copy-before-write: support fleecing block driver
  block/block-copy: add write-unchanged mode
  block/copy-before-write: use write-unchanged in fleecing mode
  iotests/image-fleecing: add test-case for fleecing format node
  iotests.py: add qemu_io_pipe_and_status()
  iotests/image-fleecing: add test case with bitmap
  block: blk_root(): return non-const pointer
  qapi: backup: add immutable-source parameter
  iotests/image-fleecing: test push backup with fleecing

 qapi/block-core.json                        |  58 ++++-
 block/fleecing.h                            | 151 +++++++++++
 include/block/block-copy.h                  |   4 +-
 include/block/block_int.h                   |   1 +
 include/block/dirty-bitmap.h                |   4 +-
 include/block/reqlist.h                     |  75 ++++++
 include/qemu/hbitmap.h                      |  11 +
 include/sysemu/block-backend.h              |   2 +-
 block/backup.c                              |  61 ++++-
 block/block-backend.c                       |   2 +-
 block/block-copy.c                          | 157 +++++-------
 block/copy-before-write.c                   |  70 +++++-
 block/dirty-bitmap.c                        |  15 +-
 block/fleecing-drv.c                        | 261 ++++++++++++++++++++
 block/fleecing.c                            | 182 ++++++++++++++
 block/monitor/bitmap-qmp-cmds.c             |   5 +-
 block/replication.c                         |   2 +-
 block/reqlist.c                             |  84 +++++++
 blockdev.c                                  |   1 +
 util/hbitmap.c                              |  36 +++
 MAINTAINERS                                 |   7 +-
 block/meson.build                           |   3 +
 tests/qemu-iotests/iotests.py               |   4 +
 tests/qemu-iotests/tests/image-fleecing     | 178 ++++++++++---
 tests/qemu-iotests/tests/image-fleecing.out | 223 ++++++++++++++++-
 25 files changed, 1441 insertions(+), 156 deletions(-)
 create mode 100644 block/fleecing.h
 create mode 100644 include/block/reqlist.h
 create mode 100644 block/fleecing-drv.c
 create mode 100644 block/fleecing.c
 create mode 100644 block/reqlist.c

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2.31.1