Re: [Qemu-devel] [PATCH v12 10/19] block: Add QMP support for streaming to an intermediate layer

[Eric Blake]

On 10/27/2016 03:58 AM, Kevin Wolf wrote:
>>>> -# @backing-file: #optional The backing file string to write into the 
>>>> active
>>>> -#                          layer. This filename is not validated.
>>>> +# @backing-file: #optional The backing file string to write into the top
>>>> +#                          image. This filename is not validated.
>>>>  #
>>>>  #                          If a pathname string is such that it cannot be
>>>>  #                          resolved by QEMU, that means that subsequent 
>>>> QMP or
>>>
>>> As we discussed in v10, this is not discoverable through
>>> introspection.  You added patch 18 which introduces a base-node option
>>> and can serve as a witness for the changed semantics, which is
>>> good. Should this be documented here?
>>
>> In the commit message I don't see why not, but in the JSON file?
>>
>> "This feature was added together with the base-node parameter" ?
> 
> Eric may have a better suggestion for the wording, but maybe something
> like this:
> 
> "Presence of this feature can't directly be tested with introspection;
> check for the presence of base-node instead as a witness for it."

The sentence on checking for the feature should go earlier, with this
paragraph.  Maybe as follows:

# The node that receives the data is called the top image, and can be
# located in any part of the chain (but always above the base image;
# see below) and can be specified using its device or node name.
# Earlier qemu versions only allowed 'device' to name the top level
# node; presence of the 'base-node' parameter during introspection can
# be used as a witness of the enhanced semantics of 'device'.

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

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