Re: [Qemu-devel] [PATCH 06/10] drive-backup: added support for data compression

[Eric Blake]

On 05/14/2016 06:45 AM, Denis V. Lunev wrote:
> From: Pavel Butsykin <address@hidden>
> 
> The idea is simple - backup is "written-once" data. It is written block
> by block and it is large enough. It would be nice to save storage
> space and compress it.
> 
> The patch adds a flag to the qmp/hmp drive-backup command which enables
> block compression. Compression should be implemented in the format driver
> to enable this feature.
> 
> There are some limitations of the format driver to allow compressed writes.
> We can write data only once. Though for backup this is perfectly fine.
> These limitations are maintained by the driver and the error will be
> reported if we are doing something wrong.
> 

> +++ b/qapi/block-core.json
> @@ -905,7 +905,7 @@
>  { 'struct': 'DriveBackup',
>    'data': { 'device': 'str', 'target': 'str', '*format': 'str',
>              'sync': 'MirrorSyncMode', '*mode': 'NewImageMode',
> -            '*speed': 'int', '*bitmap': 'str',
> +            '*speed': 'int', '*bitmap': 'str', '*compress': 'bool',

Missing documentation of the new option.

>              '*on-source-error': 'BlockdevOnError',
>              '*on-target-error': 'BlockdevOnError' } }
>  
> diff --git a/qmp-commands.hx b/qmp-commands.hx
> index 94847e5..8915a0b 100644
> --- a/qmp-commands.hx
> +++ b/qmp-commands.hx
> @@ -1186,7 +1186,8 @@ EQMP
>      {
>          .name       = "drive-backup",
>          .args_type  = "sync:s,device:B,target:s,speed:i?,mode:s?,format:s?,"
> -                      "bitmap:s?,on-source-error:s?,on-target-error:s?",
> +                      "bitmap:s?,compress:b?,"
> +                      "on-source-error:s?,on-target-error:s?",
>          .mhandler.cmd_new = qmp_marshal_drive_backup,
>      },
>  
> @@ -1220,6 +1221,7 @@ Arguments:
>  - "mode": whether and how QEMU should create a new image
>            (NewImageMode, optional, default 'absolute-paths')
>  - "speed": the maximum speed, in bytes per second (json-int, optional)
> +- "compress": compress data blocks (if the target format supports it).

Missing mention that it is optional, default false.

>  - "on-source-error": the action to take on an error on the source, default
>                       'report'.  'stop' and 'enospc' can only be used
>                       if the block device supports io-status.
> 

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

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