Re: [Qemu-devel] [PATCH v3 6/8] blockdev: add DriveBackup transaction

[Eric Blake]

On 05/15/2013 08:34 AM, Stefan Hajnoczi wrote:
> This patch adds a transactional version of the drive-backup QMP command.
> It allows atomic snapshots of multiple drives along with automatic
> cleanup if there is a failure to start one of the backup jobs.
> 
> Note that QMP events are emitted for block job completion/cancellation
> and the block job will be listed by query-block-jobs.
> 

> +
> +static void drive_backup_abort(BlkTransactionState *common)
> +{
> +    DriveBackupState *state = DO_UPCAST(DriveBackupState, common, common);
> +    BlockDriverState *bs = state->bs;
> +
> +    /* Only cancel if it's the job we started */
> +    if (bs && bs->job && bs->job == state->job) {
> +        block_job_cancel_sync(bs->job);
> +    }

Question - if starting the job created the target file, should aborting
the job unlink() that file so that we aren't polluting the file system?

> +++ b/qapi-schema.json
> @@ -1609,6 +1609,27 @@
>              '*mode': 'NewImageMode' } }
>  
>  ##
> +# @DriveBackup
> +#
> +# @device: the name of the device whose writes should be mirrored.
> +#
> +# @target: the target of the new image. If the file exists, or if it
> +#          is a device, the existing file/device will be used as the new
> +#          destination.  If it does not exist, a new file will be created.
> +#
> +# @format: #optional the format of the new destination, default is to
> +#          probe if @mode is 'existing', else the format of the source
> +#
> +# @mode: #optional whether and how QEMU should create a new image, default is
> +#        'absolute-paths'.
> +#
> +# @speed: #optional the maximum speed, in bytes per second
> +##

Mention "Since: 1.6"

> +{ 'type': 'DriveBackup',
> +  'data': { 'device': 'str', 'target': 'str', '*format': 'str',
> +            '*mode': 'NewImageMode', '*speed': 'int' } }
> +
> +##
>  # @TransactionAction
>  #
>  # A discriminated record of operations that can be performed with
> @@ -1616,7 +1637,8 @@
>  ##
>  { 'union': 'TransactionAction',
>    'data': {
> -       'blockdev-snapshot-sync': 'BlockdevSnapshot'
> +       'blockdev-snapshot-sync': 'BlockdevSnapshot',
> +       'drive-backup': 'DriveBackup'
>     } }
>  
>  ##
> 

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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