Re: [Qemu-devel] RFC: libyajl for JSON

[Luiz Capitulino <lcapitulino@redhat.com>]

On Tue, 3 Nov 2015 06:40:32 -0700
Eric Blake <eblake@redhat.com> wrote:

> On 11/03/2015 06:19 AM, Luiz Capitulino wrote:
> > On Tue, 03 Nov 2015 08:17:58 +0100
> > Markus Armbruster <armbru@redhat.com> wrote:
> > 
> >>> So at this point, I want to see if lloyd makes any progress towards an
> >>> actual yajl release and/or adding a co-maintainer, before even trying to
> >>> get formal upstream support for single quoting.  We could always create
> >>> a git submodule with our own choice of fork (since there are already
> >>> forks that do single-quote parsing) - but the mantra of 'upstream first'
> >>> has a lot of merit (I'm reluctant to fork without good reason).
> >>
> >> The value proposition of replacing our flawed JSON parser isn't in
> >> saving big on maintenance, it's in not having to find and fix its flaws.
> >>
> >> If the replacement needs a lot of work to fit our needs, the value
> >> proposition becomes negative.
> >>
> >> A JSON parser shouldn't require much maintenance, as JSON is simple,
> >> doesn't change, and parsing has few system dependencies.
> > 
> > Let me suggest this crazy idea: have you guys considered breaking
> > compatibility?
> 
> As in, requiring QMP clients to send "quotes" rather than 'quotes'?

Yes.

> It's worth considering (we already guarantee that our output is strict
> JSON, and that the 'quotes' on input is merely for convenience).  If we
> want to go that route, than 2.5 should document loudly that we are
> deprecating 'quotes' in QMP, so that 2.6 can actually remove it when
> switching to yajl.  

I'd go for more craziness: disable the feature for the next release
and watch. If we suddenly found out that there are some big users of
the feature, we back off and re-enable it on a -stable release.

> And as single quotes appears to be the only JSON
> extension we have been relying on, I think that would indeed free us
> from having to wait for a yajl release or carry our own yajl fork.
> 
> Interesting idea; I'm still thinking whether it would help us more than
> it would hurt lazy clients that were depending on the extension.

The point is, apart from libvirt, I've never heard of any serious QMP
client that's not a simple automation script. And I'd bet those are
sending in "quotes" to talk to QMP.