Re: [Qemu-devel] [PATCH RFC] block: add block-insert-node QMP command

[Eric Blake]

On 08/16/2017 04:41 AM, Manos Pitsidianakis wrote:

>>> +##
>>> +# @block-insert-node:
>>> +#
>>> +# Insert a filter node between a specific edge in the block driver
>>> state graph.
>>> +# @parent:  the name of the parent node or device
>>> +# @node:    the name of the node to insert under parent
>>> +# @child:   the name of the child of both node and parent
>>
>> Is this always going to be between two existing nodes, or can this
>> command also be used to insert at the end of the chain (for example, if
>> parent or child is omitted)?
> 
> If this is used for filter nodes, I suppose only between would make
> sense (for now). Is there a use case for the latter?

Perhaps.

Given a qcow2 image backing chain:

base <- active

there are four BDS (2 format, 2 protocol).  Ideally, I could add
filtering to any one of those four nodes (a filter on the base protocol
level restricts how much guest data can be used from the backing image,
but with no limits on the qcow2 metadata; a filter on the base format
level restricts metadata reads as well; similarly for filters on the
active protocol and format layers).

But adding a filter on 'active' at the format level has no pre-existing
parent (I'm adding the filter as the new top-level).  Or am I missing
something?

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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