Re: [Qemu-devel] RFC: making QMP query-block more useful

[Daniel P. Berrange]

On Fri, Oct 05, 2012 at 05:52:35PM -0600, Eric Blake wrote:
> Right now, 'query-block' has no way to filter to a single device, but
> conversely, for each device, it shows only the first backing file,
> rather than the entire backing chain.  Jeff and I were lamenting this
> fact on IRC while debugging his block-commit stuff.
> 
> Would it be worth enhancing the QMP to be:
> 
> ##
> # @query-block:
> #
> # Get a list of BlockInfo for various virtual block devices.
> #
> # @devices: #optional If provided, limit the output to the given
> #           device names (since 1.3)
> #
> # @recurse: #optional Provide recursive information on any backing
> #           chains (since 1.3, default false)
> #
> # Returns: a list of @BlockInfo describing each virtual block device
> #
> # Since: 0.14.0
> ##
> { 'command': 'query-block',
>   'arguments': { '*names': ['str'], 'recurse': 'bool' },
>   'returns': ['BlockInfo'] }
> 
> as well as enhancing BlockDeviceInfo to be self-recursive, by adding
> backing_chain as in:
> 
> # @backing_chain: #optional, only present if @backing_file is present
> and 'query-block' requested recursion (since 1.3)
> 
> { 'type': 'BlockDeviceInfo',
>   'data': { 'file': 'str', 'ro': 'bool', 'drv': 'str',
>             '*backing_file': 'str', 'backing_file_depth': 'int',
>             '*backing_chain' : 'BlockDeviceInfo',
>             'encrypted': 'bool', 'encryption_key_missing': 'bool',
>             'bps': 'int', 'bps_rd': 'int', 'bps_wr': 'int',
>             'iops': 'int', 'iops_rd': 'int', 'iops_wr': 'int'} }
> 
> Or would such modifications require the creation of a new QMP command,
> instead of altering 'query-block'?

I think I'd probably go for creating a new command myself. I agree that
both the changes you describe would be useful for libvirt needs.

> Likewise, can 'qemu-img info' be enhanced to add a recursion flag?

Sounds like a good idea.


Daniel
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