Welcome to version 11. I hope you are enjoying our regular newsletter.
This patchset enables the in-memory part of the incremental backup
feature. A patchset by Vladimir Sementsov-Ogievskiy enables the
migration of in-memory dirty bitmaps, and a future patchset will
enable the storage and retrieval of dirty bitmaps to and from permanent
storage.
Enough changes have been made that most Reviewed-By lines from
previous iterations have been removed. (Sorry!)
This series was originally authored by Fam Zheng;
his cover letter is included below.
~John Snow
=================================================================
This is the in memory part of the incremental backup feature.
With the added commands, we can create a bitmap on a block
backend, from which point of time all the writes are tracked by
the bitmap, marking sectors as dirty. Later, we call drive-backup
and pass the bitmap to it, to do an incremental backup.
See the last patch which adds some tests for this use case.
Fam
=================================================================
For convenience, this patchset is available on github:
https://github.com/jnsnow/qemu/commits/dbm-backup
v11:
- Instead of copying BdrvDirtyBitmaps and keeping a pointer to the
object we were copied from, we instead "freeze" a bitmap in-place
without copying it. On success, we thaw and delete the bitmap.
On failure, we merge the bitmap with a "successor," which is an
anonymous bitmap attached as a child that records writes for us
for the duration of the backup operation.
This means that incremental backups can NEVER BE RETRIED in a
deterministic fashion. If an incremental backup fails on a set
of dirty sectors {x}, and a new set of dirty sectors {y} are
introduced during the backup, then any possible retry action
on an incremental backup can only operate on {x,y}. There is no
way to get an incremental backup "as it would have been."
So, the failure mode for incremental backup is to try again,
and the resulting image will simply be a differential from the
last successful dirty bitmap backup.
- Removed hbitmap_copy and bdrv_dirty_bitmap_copy.
- Added a small fixup patch:
- Update all granularity fields to be uint64_t.
- Update documentation around BdrvDirtyBitmap structure.
- Modified transactions to obey frozen attribute of BdrvDirtyBitmaps.
- Added frozen attribute to the info query.
v10 (Overview):
- I've included one of Vladimir's bitmap fixes as patch #1.
- QMP commands and transactions are now protected via
aio_context functions.
- QMP commands use "node-ref" as a parameter name now. Reasoning
is thus: Either a "device name" or a "node name" can be used to
reference a BDS, which is the key item we are actually acting
on with these bitmap commands. Thus, I refer to this unified
parameter as a "Node Reference," or "node-ref."
We could also argue for "backend-ref" or "device-ref" for the
reverse semantics: where we accept a unified parameter, but we
intend to resolve it to the BlockBackend instead of resolving
the parameter given to the BlockDriverState.
Or, we could use "reference" for both cases, and to match the
existing BlockdevRef command.
- All QMP commands added are now per-node via a unified parameter
name. Though backup only operates on "devices," you are free to
create bitmaps for any arbitrary node you wish. It is obviously
only useful for the root node, currently.
- Bitmap Sync modes (CONSUME, RESET) are removed. See below
(changelog, RFC questions) for more details.
- Code to recover the bitmap after a failure has been added,
but I have some major questions about drive_backup guarantees.
See RFC questions.
v10 (Detailed Changelog):
(1/13) New Patch:
- Included Vladimir Sementsov-Ogievskiy's patch that clarifies
the semantics of the bitmap primitives.
(3/13):
- Edited function names for consistency (Stefanha)
- Removed compile-time constants (Stefanha)
- Acquire aio_context for bitmap add/remove (Stefanha)
- Documented optional granularity for bitmap-add in
qmp-commands.hx file (Eric Blake)
- block_dirty_bitmap_lookup moved forward to this patch to allow
more re-use. (Stefanha)
- Fixed a problem where the block_dirty_bitmap_lookup didn't
always set an error if it returned NULL.
- Added an optional return BDS lookup parameter to
bdrv_dirty_bitmap_lookup.
- Renamed "device" to "node-ref" for block_dirty_bitmap_lookup,
adjusted calls to bdrv_lookup_bs() to reflect unified
parameter usage.
- qmp_block_dirty_bitmap_{add,remove} now reference arbitrary
node names via @node-ref.
(4/13):
- Default granularity and granularity getters are both
now uint64_t (Stefanha)
(5/13):
- Added documentation to warn about the necessity of updating
the hbitmap deep copy. (Stefanha)
(6/13)
- Renamed bdrv_reset_dirty_bitmap to bdrv_clear_dirty_bitmap
to be consistent with Vladimir's patches.
- Removed const qualifier for bdrv_copy_dirty_bitmap,
to accommodate patch 8.
(7/13) New Patch:
- Added an hbitmap_merge operation to join two bitmaps together.
(8/13) New Patch:
- Added bdrv_reclaim_dirty_bitmap() to allow us to "roll back" a
bitmap into the bitmap that it was spawned from. This will let
us maintain an accurate account of dirty sectors even after a
failure.
- This adds an "originator" pointer to the BdrvDirtyBitmap and
is why "const" was removed for copy.
(9/13):
- QMP semantics changes as outlined for Patch #3.
- Enable/Disable now protected by aio_context (Stefanha)
(10/13):
- Add coroutine_fn annotation to block backup helper. (Stefanha)
- Removed sync_bitmap_gran from BackupBlockJob, just use the
getter on the BdrvDirtyBitmap instead. (Stefanha)
- bdrv_dirty_iter_set was renamed to bdrv_set_dirty_iter.
- Calls to bdrv_reset_dirty_bitmap are modified to
bdrv_clear_dirty_bitmap to reflect the rename in patch #6.
- Bitmap usage modes (RESET vs. CONSUME) has been deleted, for
the reason of targeting a simpler core usage first before
targeting optimizations. CONSUME is particularly problematic
in the case of errors; so this mode is omitted for now.
- Adjusted error message to use MirrorSyncMode enum, not
(incorrectly) the BitmapSyncMode enum.
- In the event of a failure, the sync_bitmap is now merged back
into the original bitmap so that we do not lose any dirty
bitmap information needlessly.
(11/13):
- Changed block_dirty_bitmap_add_abort to use
qmp_block_dirty_bitmap_remove:
- Old code used bdrv_lookup_bs to acquire bitmap and bs
anyway, and ignored the failure case.
- New code relies on the same information, and with a NULL
errp pointer we will similarly ignore the failure case.
prepare() should have properly vetted this information
before this point anyway.
This new code is also now protected via aio_context through
the use of the QMP commands.
- More code re-use of block_dirty_bitmap_lookup to get both the
bs and bitmap pointers.
- aio_context protection and cleanup in new abort methods.
(13/13):
- Modified test for new parameter names.
v9:
- Edited commit message, for English embetterment (02/10)
- Rebased on top of stefanha/block-next (06,08/10)
- Adjusted error message and line length (07/10)
v8:
- Changed int64_t return for bdrv_dbm_calc_def_granularity to
uint64_t (2/10)
- Updated commit message (2/10)
- Removed redundant check for null in device parameter (2/10)
- Removed comment cruft. (2/10)
- Removed redundant local_err propagation (several)
- Updated commit message (3/10)
- Fix HBitmap copy loop index (4/10)
- Remove redundant ternary (5/10)
- Shift up the block_dirty_bitmap_lookup function (6/10)
- Error messages cleanup (7/10)
- Add an assertion to explain the re-use of .prepare() for two
transactions.
(8/10)
- Removed BDS argument from bitmap enable/disable helper; it was
unused. (8/10)
v7: (highlights)
- First version being authored by jsnow
- Addressed most list feedback from V6, many small changes.
All feedback was either addressed on-list (as a wontfix) or patched.
- Replaced all error_set with error_setg
- Replaced all bdrv_find with bdrv_lookup_bs()
- Adjusted the max granularity to share a common function with
backup/mirror that attempts to "guess" a reasonable default.
It clamps between [4K,64K] currently.
- The BdrvDirtyBitmap object now counts granularity exclusively in
bytes to match its interface.
It leaves the sector granularity concerns to HBitmap.
- Reworked the backup loop to utilize the hbitmap iterator.
There are some extra concerns to handle arrhythmic cases where the
granularity of the bitmap does not match the backup cluster size.
This iteration works best when it does match, but it's not a
deal-breaker if it doesn't -- it just gets less efficient.
- Reworked the transactional functions so that abort() wouldn't "undo"
a redundant command. They now have been split into a prepare and a
commit function (with state) and do not provide an abort command.
- Added a block_dirty_bitmap_lookup(device, name, errp) function to
shorten a few of the commands added in this series, particularly
qmp_enable, qmp_disable, and the transaction preparations.
v6: Re-send of v5.
v5: Rebase to master.
v4: Last version tailored by Fam Zheng.
==
Fam Zheng (7):
qapi: Add optional field "name" to block dirty bitmap
qmp: Add block-dirty-bitmap-add and block-dirty-bitmap-remove
block: Introduce bdrv_dirty_bitmap_granularity()
qmp: Add block-dirty-bitmap-enable and block-dirty-bitmap-disable
qapi: Add transaction support to block-dirty-bitmap-{add, enable,
disable}
qmp: Add dirty bitmap status fields in query-block
qemu-iotests: Add tests for drive-backup sync=dirty-bitmap
John Snow (5):
block: Add bdrv_clear_dirty_bitmap
hbitmap: add hbitmap_merge
block: Add bitmap successors
qmp: Add support of "dirty-bitmap" sync mode for drive-backup
block: BdrvDirtyBitmap miscellaneous fixup
Vladimir Sementsov-Ogievskiy (1):
block: fix spoiling all dirty bitmaps by mirror and migration
block.c | 254
+++++++++++++++++++++++++++++++++++++--
block/backup.c | 120 +++++++++++++++----
block/mirror.c | 27 ++---
blockdev.c | 273
+++++++++++++++++++++++++++++++++++++++++-
hmp.c | 3 +-
include/block/block.h | 31 ++++-
include/block/block_int.h | 2 +
include/qemu/hbitmap.h | 11 ++
migration/block.c | 7 +-
qapi-schema.json | 5 +-
qapi/block-core.json | 103 +++++++++++++++-
qmp-commands.hx | 68 ++++++++++-
tests/qemu-iotests/056 | 33 ++++-
tests/qemu-iotests/056.out | 4 +-
tests/qemu-iotests/iotests.py | 8 ++
util/hbitmap.c | 28 +++++
16 files changed, 910 insertions(+), 67 deletions(-)
