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Re: [Qemu-devel] [PATCH v2 6/6] qapi: Promote blockdev-change-medium arg

From: Eric Blake
Subject: Re: [Qemu-devel] [PATCH v2 6/6] qapi: Promote blockdev-change-medium arguments to QAPI type
Date: Fri, 20 Jan 2017 08:38:49 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.6.0

On 01/20/2017 01:15 AM, Markus Armbruster wrote:

>>> Isn't Since: 2.5 misleading?  The anonymous type goes back to 2.5, but
>>> the name doesn't.
>> It matches what we've done elsewhere - when refactoring .json files to
>> create a new type, but where the new type doesn't represent anything
>> different over the wire than what was previously sent, we've documented
>> the new struct name as of the older release where the wire format was
>> introduced.  But as long as the command says 'since 2.5', I'm okay if we
>> want to mark the struct as 'since 2.9', if that's easier to think about.
> Sticking to established practice is better than inconsistent practice.
> That said, I wonder why we bother to track "since" for types.  "Since"
> is important information for external interfaces.  Why is it useful for
> purely internal ones?
> External visible are commands, events, and members of types used by
> commands or events.

I guess what we can do is treat a type-wide 'Since: 2.5' as the default
for all its members that don't supply any other '(since 2.6)' note.
You're right that types themselves (even when used in a command) are NOT
the API, and that we can refactor type names without breaking wire
compatibility, but having a default for when each member of the type was
first made available makes sense since we DO care when members were

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

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