[Qemu-devel] [PATCH v3 00/18] bitmaps: introduce 'bitmap' sync mode

[John Snow]

This series adds a new "BITMAP" sync mode that is meant to replace the
existing "INCREMENTAL" sync mode.

This mode can have its behavior modified by issuing any of three bitmap sync
modes, passed as arguments to the job.

The three bitmap sync modes are:
- ON-SUCCESS: This is an alias for the old incremental mode. The bitmap is
              conditionally synchronized based on the return code of the job
              upon completion.
- NEVER: This is, effectively, the differential backup mode. It never clears
         the bitmap, as the name suggests.
- ALWAYS: Here is the new, exciting thing. The bitmap is always synchronized,
          even on failure. On success, this is identical to incremental, but
          on failure it clears only the bits that were copied successfully.
          This can be used to "resume" incremental backups from later points
          in times.

I wrote this series by accident on my way to implement incremental mode
for mirror, but this happened first -- the problem is that Mirror mode
uses its existing modes in a very particular way; and this was the best
way to add bitmap support into the mirror job properly.

Summary:
- 01-03: refactor blockdev-backup and drive-backup to share more interface code
- 04-05: add the new 'bitmap' sync mode with sync policy 'conditional',
         which is functionally identical to 'incremental' sync mode.
- 06:    add sync policy 'never' ("Differential" backups.)
- 07-11: rework some merging code to facilite patch 12;
- 12:    add sync policy 'always' ("Resumable" backups)
- 13-16: test infrastructure changes to support patch 16:
- 17:    new iotest!
- 18:    minor policy loosening as a QOL improvement

Future work:
 - Update bitmaps.rst to explain these. (WIP, it's hard, sorry!)
 - Add these modes to Mirror. (Done*, but needs tests.)
 - Allow the use of bitmaps and bitmap sync modes with non-BITMAP modes;
   This will allow for resumable/re-tryable full backups.

===
V3:
===

Key:
[----] : patches are identical
[####] : number of functional differences between upstream/downstream patch
[down] : patch is downstream-only
The flags [FC] indicate (F)unctional and (C)ontextual differences, respectively

001/18:[0006] [FC] 'qapi/block-core: Introduce BackupCommon'
002/18:[0032] [FC] 'drive-backup: create do_backup_common'
003/18:[0020] [FC] 'blockdev-backup: utilize do_backup_common'
004/18:[0006] [FC] 'qapi: add BitmapSyncMode enum'
005/18:[0019] [FC] 'block/backup: Add mirror sync mode 'bitmap''
006/18:[0010] [FC] 'block/backup: add 'never' policy to bitmap sync mode'
007/18:[----] [--] 'hbitmap: Fix merge when b is empty, and result is not an 
alias of a'
008/18:[----] [--] 'hbitmap: enable merging across granularities'
009/18:[0005] [FC] 'block/dirty-bitmap: add bdrv_dirty_bitmap_merge_internal'
010/18:[0003] [FC] 'block/dirty-bitmap: add bdrv_dirty_bitmap_get'
011/18:[0021] [FC] 'block/backup: upgrade copy_bitmap to BdrvDirtyBitmap'
012/18:[0020] [FC] 'block/backup: add 'always' bitmap sync policy'
013/18:[----] [--] 'iotests: add testing shim for script-style python tests'
014/18:[----] [--] 'iotests: teach run_job to cancel pending jobs'
015/18:[0005] [FC] 'iotests: teach FilePath to produce multiple paths'
016/18:[----] [--] 'iotests: Add virtio-scsi device helper'
017/18:[0038] [FC] 'iotests: add test 257 for bitmap-mode backups'
018/18:[----] [-C] 'block/backup: loosen restriction on readonly bitmaps'

001: Made suggested doc fixes.
     Changed 'since' to 4.2.
002: Added bds and aio_context to backup_common
     Removed accidental extraneous unref on target_bs
     Removed local_err propagation
003: Fallout from #002; hoist aio_context acquisition up into do_blockdev_backup
004: 'conditional' --> 'on-success'
005: Rediscover the lost stanza that ensures a bitmap mode was given
     Fallout from 2, 3, 4.
006: Block comment fix for patchew
     Fallout from #4
009: Fix assert() style issue. Why'd they let a macro be lowercase like that?
     Probably to make specifically my life difficult.
010: Fix style issue {
011: Fix long lines
     rename "bs" --> "target_bs" where appropriate
     Free copy_bitmap from the right node
012: Multiline comment changes for patchew
     Fallout from #4
015: Fix long line for patchew
     Reinstate that second newline that Max likes
017: Fallout from #4.

===
V2:
===

Changes:
004: Fixed typo
     Change @conditional docstring
005: Moved desugaring code into blockdev.c, facilitated by patches 1-3.
006: Change @never docstring slightly.
007: Merge will clear the target bitmap when both components bitmaps are empty,
     and the target bitmap is not an alias of either component bitmap.
008: Check orig_size (logical size) instead of size (actual size) to enable
         cross-granularity merging.
     Fix the sparse merge itself, based on the block/backup code.
     Clear the target bitmap before cross-granularity merge.
     Assert the size is itself equal when logical size and granularities are
         equal.
---: Dropped bdrv_dirty_bitmap_claim.
012: Rewrote the cleanup logic to hopefully be clearer.
     use merge intsead of dropped reclaim.
015: Changed docstring
     factored out filename pattern generation.
017: Fix mkpattern indent.
     Use integer division!!!
     Add parenthesis to boolean assignment
     Change test run ordering; update output to reflect this
     Use virtio-scsi-ccw when appropriate
     Update test output to reflect new test running order
018: Fallout from patches 1-3; restrictions only need loosened in one place
         instead of two.

Changes not made:
- Allowing 'cancel' to skip synchronization on cancel:
  Decided against it, opting for consistency. The user asked for a sync,
  and it's simpler logistically to execute on that desire.
  Use the new mode carefully, please!

John Snow (18):
  qapi/block-core: Introduce BackupCommon
  drive-backup: create do_backup_common
  blockdev-backup: utilize do_backup_common
  qapi: add BitmapSyncMode enum
  block/backup: Add mirror sync mode 'bitmap'
  block/backup: add 'never' policy to bitmap sync mode
  hbitmap: Fix merge when b is empty, and result is not an alias of a
  hbitmap: enable merging across granularities
  block/dirty-bitmap: add bdrv_dirty_bitmap_merge_internal
  block/dirty-bitmap: add bdrv_dirty_bitmap_get
  block/backup: upgrade copy_bitmap to BdrvDirtyBitmap
  block/backup: add 'always' bitmap sync policy
  iotests: add testing shim for script-style python tests
  iotests: teach run_job to cancel pending jobs
  iotests: teach FilePath to produce multiple paths
  iotests: Add virtio-scsi device helper
  iotests: add test 257 for bitmap-mode backups
  block/backup: loosen restriction on readonly bitmaps

 block/backup.c                |  135 +-
 block/dirty-bitmap.c          |   69 +-
 block/mirror.c                |    8 +-
 block/replication.c           |    2 +-
 blockdev.c                    |  208 ++--
 include/block/block_int.h     |    7 +-
 include/block/dirty-bitmap.h  |    4 +-
 migration/block.c             |    5 +-
 nbd/server.c                  |    2 +-
 qapi/block-core.json          |  138 +--
 tests/qemu-iotests/040        |    6 +-
 tests/qemu-iotests/093        |    6 +-
 tests/qemu-iotests/139        |    7 +-
 tests/qemu-iotests/238        |    5 +-
 tests/qemu-iotests/257        |  409 ++++++
 tests/qemu-iotests/257.out    | 2199 +++++++++++++++++++++++++++++++++
 tests/qemu-iotests/group      |    1 +
 tests/qemu-iotests/iotests.py |  100 +-
 util/hbitmap.c                |   49 +-
 19 files changed, 3048 insertions(+), 312 deletions(-)
 create mode 100755 tests/qemu-iotests/257
 create mode 100644 tests/qemu-iotests/257.out

-- 
2.21.0