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

[Eric Blake <eblake@redhat.com>]

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On 08/16/2017 07:11 AM, Manos Pitsidianakis wrote:

>>
>> 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?
> 
> The parent in this case is the storage device (disk / cdrom), whose name
> is specified as the parent. The first example in the
> qapi/block-core.json is such a case. In code I check blk_by_name(parent)
> and if that doesn't exist, I try with bdrv_find_node(parent).  Perhaps I
> should reword the documentation or did I misunderstand what you wrote?

Ah, so you are including both BB and BDS in your set of names for parent
objects.  Yes, clarifying the documentation that the parent can be
either a device name (for the top of the chain) or a node name (for the
middle of the chain) would help; the child name is always a node name
(since we are filtering how the child will be used when accessed from
the parent).

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


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