The compression filter driver is introduced as suggested by Max.
A sample usage of the filter can be found in the test #214.
Now, multiple clusters can be written compressed.
It is useful for the backup job.

v10:
  01: The option 'compress' moved up in the QAPI BlockdevDriver list
      to fit its alphabetic order (noticed by Eric).
  02: bdrv_filter_default_perms assigned to .bdrv_child_perm in the
      compression filter driver interface (suggested by Max, noticed
      by Vladimir).

  Discussed in the email thread with the message ID:
  <1574779398-88772-1-git-send-email-andrey.shinkevich@virtuozzo.com>

Andrey Shinkevich (3):
  block: introduce compress filter driver
  qcow2: Allow writing compressed data of multiple clusters
  tests/qemu-iotests: add case to write compressed data of multiple
    clusters

 block/Makefile.objs        |   1 +
 block/filter-compress.c    | 166 +++++++++++++++++++++++++++++++++++++++++++++
 block/qcow2.c              | 102 ++++++++++++++++++++--------
 qapi/block-core.json       |  10 +--
 tests/qemu-iotests/214     |  43 ++++++++++++
 tests/qemu-iotests/214.out |  14 ++++
 6 files changed, 305 insertions(+), 31 deletions(-)
 create mode 100644 block/filter-compress.c

-- 
1.8.3.1