This series implements an active and synchronous mirroring mode. Currently, the mirror block job is passive an asynchronous: Depending on your start conditions, some part of the source disk starts as "dirty". Then, the block job will (as a background operation) continuously copy dirty parts to the target disk until all of the source disk is clean. In the meantime, any write to the source disk dirties the affected area.
One effect of this operational mode is that the job may never converge: If the writes to the source happen faster than the block job copies data to the target, the job can never finish. When the active mode implemented in this series is enabled, every write request to the source will automatically trigger a synchronous write to the target right afterwards. Therefore, the source can never get dirty faster than data is copied to the target. Most importantly, once source and target are in sync (BLOCK_JOB_READY is emitted), they will not diverge (unless e.g. an I/O error occurs). Active mirroring also improves on a second issue of the passive mode: We do not have to read data from the source in order to write it to the target. When new data is written to the source in active mode, it is automatically mirrored to the target, which saves us the superfluous read from the source. Things to do on top of this series: - Allow switching between active and passive mode at runtime: Mainly hinges on the question of how to expose it to the user (ideally through a generic block-job-set-option command) - Implement an asynchronous active mode (launch both write operations to the source and the target at the same time, and do not wait for the target operation to finish) - Integrate the mirror BDS more tightly into the BDS graph: Both source and target should be BdrvChildren (and the source should not be the "backing" child). I'm working on this in a follow-up. - Improve the mirror job coroutine use: Currently more of a hack, a follow-up will make this nicer. - Add read-write-blocking mode: This series adds the write-blocking mode, where every write blocks until the data has been mirrored to the target. read-write-blocking would also mirror data on reads from the source, which saves some performance (because that data does not have to be read twice) at the cost of latency on mirroring read operations. (Will be in the same follow-up.) v2: - Dropped some work, moving it to a follow-up series (making source the file child, adding the read-write-blocking mode) - Patches 1 and 2: Dropped BdrvDeletedStatus, instead replacing it by bdrv_ref()/bdrv_unref() pairs (with some precautions so we don't get into an infinite recursion) - And added a test for this, patch 3 - Patch 4: Just rebase conflicts - Patch 5: Reworked the use of bytes_copied/now "bytes_handled", fixed the mirror_co_read() comment -- everything will be made nicer in a follow-up, I promise! - Patch 7: mirror_wait_for_free_in_flight_slot() may not wait put its own coroutine into a pseudo operation's waiting queue, or we may starve. (I noticed this when running the iotest added by this series under qcow v1, so the test is there!) - Patch 8: Drop the MirrorBlockJob.source field - Patch 10: Fixed the function description, and there was a rebase conflict (due to an additional user of hbitmap_iter_next()). - Patch 11: Block bitmaps use bytes instead of sectors now, so this patch gets a bit easier - Patch 12: Rebase conflict because of the change to patch 7 - Patch 14: - Dropped read-write-block mode (or rather, put it off to a follow-up) - Renamed "passive" -> "background" and "active-write" -> "write-blocking" - Some rebase conflicts - Reset dirty bitmap before the active write, re-set it on failure (instead of only clearing it on success); important to prevent double-writes (from background and active operations) - Use a bounce buffer for active operations - Patch 15: - Renamed "passive" -> "background" and "active-write" -> "write-blocking" - Aimed for 2.12 now... - Patch 16: Use BlockBackends and aio_write instead of an own write -B git-backport-diff to v1: 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 001/16:[0054] [FC] 'block: BDS deletion during bdrv_drain_recurse' 002/16:[down] 'block: BDS deletion in bdrv_do_drained_begin()' 003/16:[down] 'tests: Add bdrv-drain test for node deletion' 004/16:[0006] [FC] 'block/mirror: Pull out mirror_perform()' 005/16:[0050] [FC] 'block/mirror: Convert to coroutines' 006/16:[----] [-C] 'block/mirror: Use CoQueue to wait on in-flight ops' 007/16:[0021] [FC] 'block/mirror: Wait for in-flight op conflicts' 008/16:[0016] [FC] 'block/mirror: Use source as a BdrvChild' 009/16:[----] [--] 'block: Generalize should_update_child() rule' 010/16:[0005] [FC] 'hbitmap: Add @advance param to hbitmap_iter_next()' 011/16:[0011] [FC] 'block/dirty-bitmap: Add bdrv_dirty_iter_next_area' 012/16:[0017] [FC] 'block/mirror: Distinguish active from passive ops' 013/16:[down] 'block/mirror: Add MirrorBDSOpaque' 014/16:[0112] [FC] 'block/mirror: Add active mirroring' 015/16:[0011] [FC] 'block/mirror: Add copy mode QAPI interface' 016/16:[0023] [FC] 'iotests: Add test for active mirroring' Max Reitz (16): block: BDS deletion during bdrv_drain_recurse block: BDS deletion in bdrv_do_drained_begin() tests: Add bdrv-drain test for node deletion block/mirror: Pull out mirror_perform() block/mirror: Convert to coroutines block/mirror: Use CoQueue to wait on in-flight ops block/mirror: Wait for in-flight op conflicts block/mirror: Use source as a BdrvChild block: Generalize should_update_child() rule hbitmap: Add @advance param to hbitmap_iter_next() block/dirty-bitmap: Add bdrv_dirty_iter_next_area block/mirror: Distinguish active from passive ops block/mirror: Add MirrorBDSOpaque block/mirror: Add active mirroring block/mirror: Add copy mode QAPI interface iotests: Add test for active mirroring qapi/block-core.json | 29 ++- include/block/block_int.h | 6 +- include/block/dirty-bitmap.h | 2 + include/qemu/hbitmap.h | 5 +- block.c | 44 +++- block/backup.c | 2 +- block/dirty-bitmap.c | 53 ++++- block/io.c | 59 ++++- block/mirror.c | 540 +++++++++++++++++++++++++++++++++---------- blockdev.c | 9 +- tests/test-bdrv-drain.c | 165 +++++++++++++ tests/test-hbitmap.c | 26 +-- util/hbitmap.c | 10 +- tests/qemu-iotests/151 | 114 +++++++++ tests/qemu-iotests/151.out | 5 + tests/qemu-iotests/group | 1 + 16 files changed, 910 insertions(+), 160 deletions(-) create mode 100755 tests/qemu-iotests/151 create mode 100644 tests/qemu-iotests/151.out -- 2.14.3