Re: [Qemu-devel] [PATCH 0/3] block: block-backup live backup command

[Wenchao Xia]

于 2013-4-24 0:25, Stefan Hajnoczi 写道:
> This series adds a new QMP command, block-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:
> 
>    block-backup device=virtio0 format=qcow2 target=backup-20130401.qcow2
> 
> The original block-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.
> 
> 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.
> 
> block-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.
> 
  Besides, compared to snapshot-blkdev, it mainly brings better
performance by avoid merging later, however, other tool may
be needed to form an incremental backup, which may be not related to
this patch.
  No objection to this patch, but perhaps a better way is using
internal snapshot by adding base/delta data export support.


> How can block-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 block-backup?
> -----------------------------
> The following enhancements are left for future patches:
> 
> 1. QMP 'transaction' support.  It is handy to atomically snapshot multiple
>     block devices.  We need qmp_transaction() support for this.  Wenchao Xia 
> is
>     currently making qmp_transaction() extensible so new action types, like
>     block-backup, can be added.
> 
> 2. Sync modes like drive-mirror (top, full, none).  This makes it possible to
>     preserve the backing file chain.
> 
> Dietmar Maurer (1):
>    block: add basic backup support to block driver
> 
> Stefan Hajnoczi (2):
>    block: add block_backup QMP command
>    qemu-iotests: add 054 block-backup test case
> 
>   block.c                    |  69 ++++++++++++-
>   block/Makefile.objs        |   1 +
>   block/backup.c             | 252 
> +++++++++++++++++++++++++++++++++++++++++++++
>   blockdev.c                 |  92 +++++++++++++++++
>   include/block/block.h      |   2 +
>   include/block/block_int.h  |  16 +++
>   include/block/blockjob.h   |  10 ++
>   qapi-schema.json           |  28 +++++
>   qmp-commands.hx            |   6 ++
>   tests/qemu-iotests/054     | 230 +++++++++++++++++++++++++++++++++++++++++
>   tests/qemu-iotests/054.out |   5 +
>   tests/qemu-iotests/group   |   1 +
>   12 files changed, 707 insertions(+), 5 deletions(-)
>   create mode 100644 block/backup.c
>   create mode 100755 tests/qemu-iotests/054
>   create mode 100644 tests/qemu-iotests/054.out
> 


-- 
Best Regards

Wenchao Xia