Re: [Qemu-devel] [PATCH v4 00/18] bitmaps: introduce 'bitmap' sync mode

[John Snow <jsnow@redhat.com>]

On 7/9/19 7:25 PM, John Snow wrote:
> 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.
> 
> ===
> V4:
> ===
> 
> [----] : 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:[----] [--] 'qapi/block-core: Introduce BackupCommon'
> 002/18:[----] [--] 'drive-backup: create do_backup_common'
> 003/18:[----] [--] 'blockdev-backup: utilize do_backup_common'
> 004/18:[----] [--] 'qapi: add BitmapSyncMode enum'
> 005/18:[----] [--] 'block/backup: Add mirror sync mode 'bitmap''
> 006/18:[----] [--] '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:[0004] [FC] 'block/dirty-bitmap: add bdrv_dirty_bitmap_merge_internal'
> 010/18:[----] [--] 'block/dirty-bitmap: add bdrv_dirty_bitmap_get'
> 011/18:[0008] [FC] 'block/backup: upgrade copy_bitmap to BdrvDirtyBitmap'
> 012/18:[----] [--] '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:[----] [--] 'iotests: teach FilePath to produce multiple paths'
> 016/18:[----] [--] 'iotests: Add virtio-scsi device helper'
> 017/18:[0063] [FC] 'iotests: add test 257 for bitmap-mode backups'
> 018/18:[----] [--] 'block/backup: loosen restriction on readonly bitmaps'
> 
> Changes:
> 009: Added assertions.
> 011: Moved copy bitmap to source node.
> 017: Rework get_bitmap to tolerate multiple anonymous bitmaps
>      Update test output to accommodate the same.
> 
> ===
> V3:
> ===
> 
> Changes:
> 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          |   73 +-
>  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        |  416 ++++++
>  tests/qemu-iotests/257.out    | 2247 +++++++++++++++++++++++++++++++++
>  tests/qemu-iotests/group      |    1 +
>  tests/qemu-iotests/iotests.py |  100 +-
>  util/hbitmap.c                |   49 +-
>  19 files changed, 3107 insertions(+), 312 deletions(-)
>  create mode 100755 tests/qemu-iotests/257
>  create mode 100644 tests/qemu-iotests/257.out
> 

Thanks, applied to my bitmaps tree:

https://github.com/jnsnow/qemu/commits/bitmaps
https://github.com/jnsnow/qemu.git

--js