Re: [Qemu-devel] [PATCH v5 00/11] block: drive-backup live backup command

[Wenchao Xia]

于 2013-5-30 20:34, Stefan Hajnoczi 写道:
> Note: These patches apply to kevin/block.  You can also grab the code from git
> here:
> git://github.com/stefanha/qemu.git block-backup-core
> 
> This series adds a new QMP command, drive-backup, which takes a point-in-time
> snapshot of a block device.  The snapshot is copied out to a target block
> device.  A simple example is:
> 
>    drive-backup device=virtio0 format=qcow2 target=backup-20130401.qcow2
> 
> The original drive-backup blockjob was written by Dietmar Maurer
> <address@hidden>.  He is currently busy but I feel the feature is worth
> pushing into QEMU since there has been interest.  This is my version of his
> patch, plus the QMP command and qemu-iotests test case.
> 
> QMP 'transaction' support is included since v3.  It adds support for atomic
> snapshots of multiple block devices.  I also added an 'abort' transaction to
> allow testing of the .abort()/.cleanup() code path.  Thanks to Wenchao for
> making qmp_transaction() extensible.
> 
> How is this different from block-stream and drive-mirror?
> ---------------------------------------------------------
> Both block-stream and drive-mirror do not provide immediate point-in-time
> snapshots.  Instead they copy data into a new file and then switch to it.  In
> other words, the point at which the "snapshot" is taken cannot be controlled
> directly.
> 
> drive-backup intercepts guest writes and saves data into the target block
> device before it is overwritten.  The target block device can be a raw image
> file, backing files are not used to implement this feature.
> 
> How can drive-backup be used?
> -----------------------------
> The simplest use-case is to copy a point-in-time snapshot to a local file.
> 
> More advanced users may wish to make the target an NBD URL.  The NBD server
> listening on the other side can process the backup writes any way it wishes.  
> I
> previously posted an RFC series with a backup server that streamed Dietmar's
> VMA backup archive format.
> 
> What's next for drive-backup?
> -----------------------------
> 1. Sync modes like drive-mirror (top, full, none).  This makes it possible to
>     preserve the backing file chain.
> 
> v5:
>   * Use bdrv_co_write_zeroes(job->target) [kwolf]
> 
>     This change means that we write zeroes over NBD again.  The optimization 
> can
>     be reintroduced by skipping zeroes when bdrv_has_zero_init() is true and 
> the
>     sectors are allocated.  Leave that for a future series, if we decide to do
>     this optimization again because it may require extra block driver
>     configuration to indicate that an image has zero init.
> 
>   * iostatus error handling [kwolf/pbonzini]
> 
>     Add configurable on-source-error and on-target-error actions just like
>     drive-mirror.  These are used when the block job coroutine hits an error.
>     If we are in guest write request context, return the errno and let the 
> usual
>     guest error handling take over.
> 
>   * Allow BdrvActionOps->commit() to be NULL [eblake]
>   * Use bdrv_getlength() in qmp_drive_mirror() [kwolf]
>   * Drop redundant proto_drv check [kwolf]
>   * Fix outdated DPRINTF() function names
>   * Drop comment about non-existent bitmap coroutine race [kwolf]
>   * Rename BACKUP_SECTORS_PER_CLUSTER [kwolf]
>   * Fix completion when image is not multiple of backup cluster size [fam]
> 
> v4:
>   * Use notifier lists and BdrvTrackedRequest instead of custom callbacks 
> [bonzini]
>   * Add drive-backup QMP example JSON [eblake]
>   * Add "Since: 1.6" to QMP schema changes [eblake]
> 
> v3:
>   * Rename to drive-backup for consistency with drive-mirror [kwolf]
>   * Add QMP transaction support [kwolf]
>   * Introduce bdrv_add_before_write_cb() to hook writes
>   * Mention 'query-block-jobs' lists job of type 'backup' [eblake]
>   * Rename rwlock to flush_rwlock [kwolf]
>   * Fix space in block/backup.c comment [kwolf]
> 
> v2:
>   * s/block_backup/block-backup/ in commit message [eblake]
>   * Avoid funny spacing in QMP docs [eblake]
>   * Document query-block-jobs and block-job-cancel usage [eblake]
> 
> Dietmar Maurer (1):
>    block: add basic backup support to block driver
> 
> Stefan Hajnoczi (10):
>    notify: add NotiferWithReturn so notifier list can abort
>    block: add bdrv_add_before_write_notifier()
>    blockdev: drop redundant proto_drv check
>    blockdev: use bdrv_getlength() in qmp_drive_mirror()
>    block: add drive-backup QMP command
>    blockdev: rename BlkTransactionStates to singular
>    blockdev: allow BdrvActionOps->commit() to be NULL
>    blockdev: add DriveBackup transaction
>    blockdev: add Abort transaction
>    qemu-iotests: add 055 drive-backup test case
> 
>   block.c                    |  23 +--
>   block/Makefile.objs        |   1 +
>   block/backup.c             | 355 
> +++++++++++++++++++++++++++++++++++++++++++++
>   blockdev.c                 | 288 +++++++++++++++++++++++++++---------
>   include/block/block_int.h  |  42 +++++-
>   include/qemu/notify.h      |  25 ++++
>   qapi-schema.json           |  97 ++++++++++++-
>   qmp-commands.hx            |  46 ++++++
>   tests/qemu-iotests/055     | 256 ++++++++++++++++++++++++++++++++
>   tests/qemu-iotests/055.out |   5 +
>   tests/qemu-iotests/group   |   1 +
>   util/notify.c              |  30 ++++
>   12 files changed, 1088 insertions(+), 81 deletions(-)
>   create mode 100644 block/backup.c
>   create mode 100755 tests/qemu-iotests/055
>   create mode 100644 tests/qemu-iotests/055.out
> 
  Reviewed patch 4, 7, 8 and they seems good, will use them in my
following work.

-- 
Best Regards

Wenchao Xia