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Re: [Qemu-block] [PATCH v19 00/25] qcow2: persistent dirty bitmaps

From: Vladimir Sementsov-Ogievskiy
Subject: Re: [Qemu-block] [PATCH v19 00/25] qcow2: persistent dirty bitmaps
Date: Wed, 31 May 2017 19:08:21 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.1.1

09 should be reworked as discussed in v18 thread, so wait for v20, I hope I'll make it in two days.

30.05.2017 11:16, Vladimir Sementsov-Ogievskiy wrote:
Hi all!

There is a new update of qcow2-bitmap series - v19.

git: https://src.openvz.org/scm/~vsementsov/qemu.git (tag qcow2-bitmap-v19)


rebased on master

05: move 'sign-off' over 'reviewed-by's
08: error_report -> error_setg in qcow2_truncate (because of rebase)
09: return EPERM in bdrv_aligned_pwritev and bdrv_co_pdiscard if there
     are readonly bitmaps. EPERM is chosen because it is already used for
     readonly image in bdrv_co_pdiscard.
     Also handle readonly bitmap in block_dirty_bitmap_clear_prepare and
     Max's r-b is not added
10: fix grammar in comment
     add Max's r-b
12, 13, 15, 21: add Max's r-b
24: fix grammar in comment
25: fix grammar and wording in comment
     also, I see contextual changes in inactiavate mechanism. Hope, they do not
     affect these series.


rebased on master (sorry for v17)

08: contextual: qcow2_do_open is changed instead of qcow2_open
     rename s/need_update_header/update_header/ in qcow2_do_open, to not do it 
in 10
     save r-b's by Max and John
09: new patch
10: load_bitmap_data: do not clear bitmap parameter - it should be already 
     (it actually created before single load_bitmap_data() call)
     if some bitmaps are loaded, but we can't write the image (it is readonly
     or inactive), so we can't mark bitmaps "in use" in the image, mark
     corresponding BdrvDirtyBitmap read-only.
     change error_setg to error_setg_errno for "Can't update bitmap directory"
     no needs to rename s/need_update_header/update_header/ here, as it done in 
13: function bdrv_has_persistent_bitmaps becomes 
     to handle readonly field.
14: declaration moved to the bottom of .h, save r-b's
15: firstly check bdrv_has_changed_persistent_bitmaps and only then fail on 
!can_write, and then QSIMPLEQ_INIT(&drop_tables)
     skip readonly bitmaps in saving loop
18: remove '#optional', 2.9 -> 2.10, save r-b's
19: remove '#optional', 2.9 -> 2.10, save r-b's
20: 2.9 -> 2.10, save r-b's
21: add check of read-only image open, drop r-b's
24: add comment to qapi/block-core.json, that block-dirty-bitmap-add removes 
     from storage. r-b's by Max and John saved

08: add r-b's by Max and John
09: clear unknown autoclear features from BDRVQcow2State before calling
     qcow2_load_autoloading_dirty_bitmaps(), and also do not extra update
     header if it is updated by qcow2_load_autoloading_dirty_bitmaps().
11: new patch, splitted out from 16
12: rewrite commit message
14: changing bdrv_close moved to separate new patch 11
     s/1/1ULL/ ; s/%u/%llu/ for two errors
16: s/No/Not/
     add Max's r-b
24: new patch


mostly by Kevin's comments:
07: just moved here, as preparation for merging refcounts to 08
08: move "qcow2-bitmap: refcounts" staff to this patch, to not break qcow2-img 
     drop r-b's
     move necessary supporting static functions to this patch too (to not break 
     fprintf -> error_report
     other small changes with error messages and comments
     code style
     for qcow2-bitmap.c:
       'include "exec/log.h"' was dropped
       s/1/(1U << 0) for BME_FLAG_IN_USE
       add BME_TABLE_ENTRY_FLAG_ALL_ONES to replace magic 1
       don't check 'cluster_size <= 0' in check_table_entry
old "[PATCH v15 08/25] block: introduce auto-loading bitmaps" was dropped
09: was "[PATCH v15 09/25] qcow2: add .bdrv_load_autoloading_dirty_bitmaps"
     drop r-b's
     some staff was moved to 08
     update_header_sync - error on bdrv_flush fail
     rename disk_sectors_in_bitmap_cluster to sectors_covered_by_bitmap_cluster
      and adjust comment.
      so, variable for storing this function result: s/dsc/sbc/
     also, as Qcow2BitmapTable already introduced in 08,
        s/table_offset/table.offset/ and s/table_size/table.size, etc..
     update_ext_header_and_dir_in_place: add comments, add additional
       update_header_sync, to reduce indeterminacy in case of error.
     call qcow2_load_autoloading_dirty_bitmaps directly from qcow2_open
     no .bdrv_load_autoloading_dirty_bitmaps
11: drop bdrv_store_persistent_dirty_bitmaps at all.
     drop r-b's
13: rename patch, rewrite commit msg
     drop r-b's
     move bdrv_release_named_dirty_bitmaps in bdrv_close() after 
     Qcow2BitmapTable is already introduced, so no
       s/table_offset/table.offset/ and s/table_size/table.size, etc.. here
     old 25 with check_constraints_on_bitmap() improvements merged here (Eric)
     like in 09, s/dsc/sbc/ and 
     no .bdrv_store_persistent_dirty_bitmaps
     call qcow2_store_persistent_dirty_bitmaps directly from qcow2_inactivate
15: corresponding part of 25 merged here. Add John's r-b, as 25 was also 
reviewed by John.
16: add John's r-b

13,14: add John's r-b
15: qcow2_can_store_new_dirty_bitmap:
       - check max dirty bitmaps and bitmap directory overhead
       - switch to error_prepend
     rm Max's r-b
     not add John's r-b
17-24: add John's r-b
25: changed because 15 changed,
     not add John's r-b


07: use '|=' to update need_update_header
     add John's r-b
     add Max's r-b
09: remove unused bitmap_table_to_cpu()
     left Max's r-b, hope it's ok
     add John's r-b
10: remove extra new line
     add John's r-b
11: add John's r-b
12: add John's r-b
13: small fixes by John's review:
        - remove weird g_free of NULL pointer from
            if (tb == NULL) {
                return -EINVAL;
        - remove extra comment "/* errp is already set */"
        - s/"Too large bitmap directory"/"Bitmap directory is too large"/
     left Max's r-b, hope you don't mind
22: add Max's r-b
23: add Max's r-b
24: add Max's r-b
25: new patch to improve error message on check_constraints_on_bitmap fail
v13: Just a fix for style checker.
13: line over 80
14: line over 80
22: s/if () \n{/if () {/

07: do not update header in qcow2_read_extensions, instead do it in the
     end of qcow2_open, where it is updated also to clear unknown
     autoclear features.
     Wrong bdrv_is_root_node used instead of bdrv_is_read_only is fixed
08: add Max's r-b
09: contextual: s/raw_bsd/raw-format/
     qcow2-bitmap.c: copyright s/2016/2017/
     fix compilation: move update_header_sync() to this patch
     add Max's r-b
13: update_header_sync() is moved to 09
     add Max's r-b
15: add Max's r-b
16: As qmp-commands.txt is removed from master, remove it here too.
     Sentence "For now only Qcow2 disks support persistent bitmaps.
      Default is false." moved to qapi/block-core.json.
     Hope that is OK, Max's r-b is not dropped.
17: qmp-commands.txt deleted, r-b is not dropped too.
18: s/is failed/has failed/, add Max's r-b
19: copyright: s/2016/2017/
21: drop "res->corruptions > 0 => ret = -EINVAL", add Max's r-b
22: actually, patch is replaced with a new one, however some parts are the same.
     instead of changing bdrv_release_dirty_bitmap behaviour, create new
23: improve comment, about not-exists is not an error
24: new patch

Old 24 (qcow2-bitmap: cache bitmap list in BDRVQcow2State) will be sent
separately, to be applied after these series.

Also: about bdrv_dirty_bitmap_set_persistance: I've decided not change its 
for now and just call bdrv_remove_persistent_dirty_bitmap from
qmp_block_dirty_bitmap_remove. Reasons:
1. Do not change reviewed part.
2. I'm not sure, that this complication of BdrvDirtyBitmap.persistent semantics
    is good (current semantics are just: .persistent means that bitmap should be
    saved on disk close). .persistent actually is not very related to "is there
    stored version of the bitmap in the image".
3. It may be done later.
4. It is not actually needed for now, as the only usage is dropping bitmap in
    bdrv_remove_persistent_dirty_bitmap. May be in future it will be needed,
    when we will have qmp interfaces for finer control of persistent dirty 


Fix automatic build test fail.

18: wording - "ASCII representation of SHA256 ..."
24: fix redeclaration error. (This is still RFC, may be not needed patch,
     see description in v10 below).


07: rm John's r-b
     not add Max's r-b
     fix subject s/dirty bitmaps/bitmaps
     improve WARNING message
     remove header ext if autoclear bit is unset, through qcow2_updata_header() 
- r-b blocking change
08: move bdrv_load_autoloading_dirty_bitmaps under asserts block (Max)
     fix typo in commit message
     move bdrv_load_autoloading_dirty_bitmaps after asserts
     John's r-b
09: rewrite check_dir_entry
     remove extra feature cluster_size=0 from check_table_entry
     which clears autoclear bit before trying to update bitmap directory
     bitmap_list_store - do not free old clusters if in_place=true
     changes in comments, fix indents
     add functions
       update_ext_header_and_dir_in_place (unset autoclear bit before trying to
                                           modify bitmap directory)
        (for usage in qcow2_load_autoloading_dirty_bitmaps)
11: add node name to error report
     Max's r-b
13: add type Qcow2BitmapTable
     move from bm.table_* to bm.table.*
     rewrite check_constraints_on_bitmap
     flush(bs->file) instead of flush(bs) in update_ext_header_and_dir
     assert(DIV_ROUND_UP(bm_size, dsc) == tb_size);
       and assert(write_size <= s->cluster_size); in store_bitmap_data
     fix: s/tb_size/tb_size * sizeof(tb[0]) in store_bitmap
     in qcow2_store_persistent_dirty_bitmaps:
       fail if !can_write
       fix counting of new_nb_bitmaps and new_dir_size
       free old clusters _after_ successful directory update (aggregate old 
         tables into drop_tables)
2 14: rename to can_store_new_dirty_bitmap
     Max's r-b
15: rename to can_store_new_dirty_bitmap
     rm extra !!
16: Max's r-b
     rename to can_store_new_dirty_bitmap
     Since s/2.8/2.9
17: Max's r-b
     Since s/2.8/2.9
18: hashing can fail in comment for qapi
     Since s/2.8/2.9
     remove dead comment
19: indentation
     Max's r-b
20: Max's r-b
21: fix error handling
     return 0 if nb_bitmaps == 0
new patches:
22-23: remove bitmap from file on bdrv_release_dirty_bitmap
24: experimental, RFC: cache bitmap list to bs, to not reload it from file.
     I'm not sure that is needed now, but if you want I can merge it to earlier


rebase on master!

01-04,06,07: John's r-b
03: rewording in comment ("The concurrent resetting ..."), John's r-b
07: reword error messages
     commit message: dirty bitmap -> bitmap
09: fix uninitialized ret in bitmap_list_store() (fix compilation warning)
18: fix compilation of tests/test-hbitmap

also, change constants names for qcow2: DIRTY_BITMAP -> BITMAP (as it is not
dirty bitmaps extension, but just bitmaps extension), QCOW -> QCOW2 (bitmaps
are only for qcow2)


Patches 01-06 are mostly unchanged, except for spelling and wording.
02 - add Eric's r-b
03,04 - add Max's r-b

07-09 is refactored "bitmap-read" part of the feature. Main changes:
- introduce bitmap list - normal list, which represents bitmap directory.
   Function bitmap_list_load loads bitmap directory, checks everything and
   creates normal list.
- introduce .bdrv_load_autoloading_dirty_bitmaps : instead of loading bitmaps
   in qcow2_open, lets load them only in bdrv_open, to avoid reloading in
- do not delete bitmaps after read, but mark them IN_USE

10 has contextual changes and rewording of comment. I've added Max's r-b, hope 
it's ok.

11: add error_report("Persistent bitmaps are lost") in case of failed bitmap 

12: add Max's r-b

13 is refactored "bitmap-store" part of the feature. see 07-09 description
- for now I just free old clusters and allocate new. This will be improved
   with a separate patch.

patch about "delete bitmaps on truncate" is removed. This case will be handled 
IN_USE, autoclear, check-constraints things are merged into other patches.

14-15 are mew patches, to early check possibility of creating persistent bitmap 
   specified name and granularity in specified BDS

16-17: spelling, rewording, indenting, tiny code simplifying, check can_store 
(by 14-15),
     s/if (autoload && !persistent)/if (has_autoload && !persistent)/,
     rebase (deleted qmp-commands.hx)

18: alternative to md5 in query-block:
   - separated qmp command -x-debug-block-dirty-bitmap-sha256
   - as adviced by Daniel P. Berrange in my parallel thread:
     - sha256 instead of md5
     - use qcrypto_hash_* instead of GChecksum
   - fix bug =) (size was wrong in hbitmap_md5)

19: s/3999/3fff/, use x-debug-block-dirty-bitmap-sha256

20: new patch to rename and publish inc_refcounts

21: some fixes and refactoring mostyly by Max's comments.

Max, Eric, great tanks for your review!
I hope, I've covered most of your comments by this update.

- handle reopening image RO->RW and incoming migration, set IN_USE for existing 
loaded bitmaps
   in these cases.
- reuse old, already allocated data clusters for bitmaps storing
- truncate bitmaps in the image on truncate


based on block-next (https://github.com/XanClic/qemu/commits/block-next)

- a lot of refactoring and reordering of patches.
- dead code removed (bdrv_dirty_bitmap_load, etc.)
- do not maintain extra data for now
- do not store dirty bitmap directory in memory
   (as we use it seldom, we can just reread if needed)

By Kevin's review:
01 - commit message changed: fix->improvement (as it was not a bug)
03 - r-b
04 - r-b
05 - add 21 patch to fix spec, also, removed all (I hope) mentions of
      "Bitmap Header", switch to one unified name for it - "Bitmap
      Directory Entry", to avoid misunderstanding with Qcow2 header.
      (also, add patch 22, to fix it in spec)
v6.06 - improve for_each_dir_entry loop, reorder patches, other small fixes
v6.07 ~> v7.09 - dead code removed, I've moved to one function
         .bdrv_store_persistent_bitmaps and have wrapper and callback in one
         patch (with also some other staff. If it not ok, I can split them)
v6.08 - about keeping bitmap directory instead of bitmap list: no I don't keep
         it at all.
v6.16 - old bdrv_ bitmap-storing related functions are removed. The new one is

based on block-next (https://github.com/XanClic/qemu/commits/block-next)

There are a lot of changes, reorderings and additions in comparement with v5.
One principal thing: now bitmaps are removed from image after loading instead
of marking them in_use. It is simpler and we do not need to store superfluous 
Also, we are no more interested in command line interface to dirty bitmaps.
So it is dropped.  If someone needs it I can add it later.

Vladimir Sementsov-Ogievskiy (25):
   specs/qcow2: fix bitmap granularity qemu-specific note
   specs/qcow2: do not use wording 'bitmap header'
   hbitmap: improve dirty iter
   tests: add hbitmap iter test
   block: fix bdrv_dirty_bitmap_granularity signature
   block/dirty-bitmap: add deserialize_ones func
   qcow2-refcount: rename inc_refcounts() and make it public
   qcow2: add bitmaps extension
   block/dirty-bitmap: add readonly field to BdrvDirtyBitmap
   qcow2: autoloading dirty bitmaps
   block/dirty-bitmap: add autoload field to BdrvDirtyBitmap
   block: bdrv_close: release bitmaps after drv->bdrv_close
   block: introduce persistent dirty bitmaps
   block/dirty-bitmap: add bdrv_dirty_bitmap_next()
   qcow2: add persistent dirty bitmaps support
   block: add bdrv_can_store_new_dirty_bitmap
   qcow2: add .bdrv_can_store_new_dirty_bitmap
   qmp: add persistent flag to block-dirty-bitmap-add
   qmp: add autoload parameter to block-dirty-bitmap-add
   qmp: add x-debug-block-dirty-bitmap-sha256
   iotests: test qcow2 persistent dirty bitmap
   block/dirty-bitmap: add bdrv_remove_persistent_dirty_bitmap
   qcow2: add .bdrv_remove_persistent_dirty_bitmap
   qmp: block-dirty-bitmap-remove: remove persistent
   block: release persistent bitmaps on inactivate

  block.c                      |   32 +-
  block/Makefile.objs          |    2 +-
  block/dirty-bitmap.c         |  137 ++++-
  block/io.c                   |    8 +
  block/qcow2-bitmap.c         | 1397 ++++++++++++++++++++++++++++++++++++++++++
  block/qcow2-refcount.c       |   59 +-
  block/qcow2.c                |  149 ++++-
  block/qcow2.h                |   41 ++
  blockdev.c                   |   77 ++-
  docs/specs/qcow2.txt         |    8 +-
  include/block/block.h        |    3 +
  include/block/block_int.h    |    8 +
  include/block/dirty-bitmap.h |   26 +-
  include/qemu/hbitmap.h       |   49 +-
  qapi/block-core.json         |   42 +-
  tests/Makefile.include       |    2 +-
  tests/qemu-iotests/165       |  105 ++++
  tests/qemu-iotests/165.out   |    5 +
  tests/qemu-iotests/group     |    1 +
  tests/test-hbitmap.c         |   19 +
  util/hbitmap.c               |   51 +-
  21 files changed, 2147 insertions(+), 74 deletions(-)
  create mode 100644 block/qcow2-bitmap.c
  create mode 100755 tests/qemu-iotests/165
  create mode 100644 tests/qemu-iotests/165.out

Best regards,

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